Add first version of gemini-grc.

2024-12-27 12:09:55 +02:00
parent 93822b239e
commit b52df073e9
30 changed files with 2754 additions and 0 deletions
--- a/bin/normalizeSnapshot/main.go
+++ b/bin/normalizeSnapshot/main.go
@@ -0,0 +1,116 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"gemini-grc/gemini"
+	_ "github.com/jackc/pgx/v5/stdlib" // PGX driver for PostgreSQL
+	"github.com/jmoiron/sqlx"
+)
+
+// Populates the `host` field
+func main() {
+	db := connectToDB()
+	count := 0
+
+	for {
+		tx := db.MustBegin()
+		query := `
+        SELECT * FROM snapshots
+        ORDER BY id
+        LIMIT 10000 OFFSET $1
+    `
+		var snapshots []gemini.Snapshot
+		err := tx.Select(&snapshots, query, count)
+		if err != nil {
+			printErrorAndExit(tx, err)
+		}
+		if len(snapshots) == 0 {
+			fmt.Println("Done!")
+			return
+		}
+		for _, s := range snapshots {
+			count++
+			escaped := gemini.EscapeURL(s.URL.String())
+			normalizedGeminiURL, err := gemini.ParseURL(escaped, "")
+			if err != nil {
+				fmt.Println(s.URL.String())
+				fmt.Println(escaped)
+				printErrorAndExit(tx, err)
+			}
+			normalizedURLString := normalizedGeminiURL.String()
+			// If URL is already normalized, skip snapshot
+			if normalizedURLString == s.URL.String() {
+				// fmt.Printf("[%5d] Skipping %d %s\n", count, s.ID, s.URL.String())
+				continue
+			}
+			// If a snapshot already exists with the normalized
+			// URL, delete the current snapshot and leave the other.
+			var ss []gemini.Snapshot
+			err = tx.Select(&ss, "SELECT * FROM snapshots WHERE URL=$1", normalizedURLString)
+			if err != nil {
+				printErrorAndExit(tx, err)
+			}
+			if len(ss) > 0 {
+				tx.MustExec("DELETE FROM snapshots WHERE id=$1", s.ID)
+				fmt.Printf("%d Deleting %d %s\n", count, s.ID, s.URL.String())
+				//err = tx.Commit()
+				//if err != nil {
+				//	printErrorAndExit(tx, err)
+				//}
+				//return
+				continue
+			}
+			// fmt.Printf("%s =>\n%s\n", s.URL.String(), normalizedURLString)
+			// At this point we just update the snapshot,
+			// and the normalized URL will be saved.
+			fmt.Printf("%d Updating %d %s => %s\n", count, s.ID, s.URL.String(), normalizedURLString)
+			// Saves the snapshot with the normalized URL
+			tx.MustExec("DELETE FROM snapshots WHERE id=$1", s.ID)
+			s.URL = *normalizedGeminiURL
+			err = gemini.UpsertSnapshot(0, tx, &s)
+			if err != nil {
+				printErrorAndExit(tx, err)
+			}
+			//err = tx.Commit()
+			//if err != nil {
+			//	printErrorAndExit(tx, err)
+			//}
+			//return
+		}
+		err = tx.Commit()
+		if err != nil {
+			printErrorAndExit(tx, err)
+		}
+	}
+}
+
+func printErrorAndExit(tx *sqlx.Tx, err error) {
+	_ = tx.Rollback()
+	panic(err)
+}
+
+func connectToDB() *sqlx.DB {
+	connStr := fmt.Sprintf("postgres://%s:%s@%s:%s/%s",
+		os.Getenv("PG_USER"),
+		os.Getenv("PG_PASSWORD"),
+		os.Getenv("PG_HOST"),
+		os.Getenv("PG_PORT"),
+		os.Getenv("PG_DATABASE"),
+	)
+
+	// Create a connection pool
+	db, err := sqlx.Open("pgx", connStr)
+	if err != nil {
+		panic(fmt.Sprintf("Unable to connect to database with URL %s: %v\n", connStr, err))
+	}
+	db.SetMaxOpenConns(20)
+	err = db.Ping()
+	if err != nil {
+		panic(fmt.Sprintf("Unable to ping database: %v\n", err))
+	}
+
+	fmt.Println("Connected to database")
+	return db
+}
--- a/config/config.go
+++ b/config/config.go
@@ -0,0 +1,156 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+
+	"github.com/rs/zerolog"
+)
+
+// Environment variable names.
+const (
+	EnvLogLevel               = "LOG_LEVEL"
+	EnvNumWorkers             = "NUM_OF_WORKERS"
+	EnvWorkerBatchSize        = "WORKER_BATCH_SIZE"
+	EnvMaxResponseSize        = "MAX_RESPONSE_SIZE"
+	EnvResponseTimeout        = "RESPONSE_TIMEOUT"
+	EnvPanicOnUnexpectedError = "PANIC_ON_UNEXPECTED_ERROR"
+	EnvBlacklistPath          = "BLACKLIST_PATH"
+	EnvDryRun                 = "DRY_RUN"
+)
+
+// Config holds the application configuration loaded from environment variables.
+type Config struct {
+	LogLevel               zerolog.Level // Logging level (debug, info, warn, error)
+	MaxResponseSize        int           // Maximum size of response in bytes
+	NumOfWorkers           int           // Number of concurrent workers
+	ResponseTimeout        int           // Timeout for responses in seconds
+	WorkerBatchSize        int           // Batch size for worker processing
+	PanicOnUnexpectedError bool          // Panic on unexpected errors when visiting a URL
+	BlacklistPath          string        // File that has blacklisted strings of "host:port"
+	DryRun                 bool          // If false, don't write to disk
+}
+
+var CONFIG Config //nolint:gochecknoglobals
+
+// parsePositiveInt parses and validates positive integer values.
+func parsePositiveInt(param, value string) (int, error) {
+	val, err := strconv.Atoi(value)
+	if err != nil {
+		return 0, ValidationError{
+			Param:  param,
+			Value:  value,
+			Reason: "must be a valid integer",
+		}
+	}
+	if val <= 0 {
+		return 0, ValidationError{
+			Param:  param,
+			Value:  value,
+			Reason: "must be positive",
+		}
+	}
+	return val, nil
+}
+
+func parseBool(param, value string) (bool, error) {
+	val, err := strconv.ParseBool(value)
+	if err != nil {
+		return false, ValidationError{
+			Param:  param,
+			Value:  value,
+			Reason: "cannot be converted to boolean",
+		}
+	}
+	return val, nil
+}
+
+// GetConfig loads and validates configuration from environment variables
+func GetConfig() *Config {
+	config := &Config{}
+
+	// Map of environment variables to their parsing functions
+	parsers := map[string]func(string) error{
+		EnvLogLevel: func(v string) error {
+			level, err := zerolog.ParseLevel(v)
+			if err != nil {
+				return ValidationError{
+					Param:  EnvLogLevel,
+					Value:  v,
+					Reason: "must be one of: debug, info, warn, error",
+				}
+			}
+			config.LogLevel = level
+			return nil
+		},
+		EnvNumWorkers: func(v string) error {
+			val, err := parsePositiveInt(EnvNumWorkers, v)
+			if err != nil {
+				return err
+			}
+			config.NumOfWorkers = val
+			return nil
+		},
+		EnvWorkerBatchSize: func(v string) error {
+			val, err := parsePositiveInt(EnvWorkerBatchSize, v)
+			if err != nil {
+				return err
+			}
+			config.WorkerBatchSize = val
+			return nil
+		},
+		EnvMaxResponseSize: func(v string) error {
+			val, err := parsePositiveInt(EnvMaxResponseSize, v)
+			if err != nil {
+				return err
+			}
+			config.MaxResponseSize = val
+			return nil
+		},
+		EnvResponseTimeout: func(v string) error {
+			val, err := parsePositiveInt(EnvResponseTimeout, v)
+			if err != nil {
+				return err
+			}
+			config.ResponseTimeout = val
+			return nil
+		},
+		EnvPanicOnUnexpectedError: func(v string) error {
+			val, err := parseBool(EnvPanicOnUnexpectedError, v)
+			if err != nil {
+				return err
+			}
+			config.PanicOnUnexpectedError = val
+			return nil
+		},
+		EnvBlacklistPath: func(v string) error {
+			config.BlacklistPath = v
+			return nil
+		},
+		EnvDryRun: func(v string) error {
+			val, err := parseBool(EnvDryRun, v)
+			if err != nil {
+				return err
+			}
+			config.DryRun = val
+			return nil
+		},
+	}
+
+	// Process each environment variable
+	for envVar, parser := range parsers {
+		value, ok := os.LookupEnv(envVar)
+		if !ok {
+			fmt.Fprintf(os.Stderr, "Missing required environment variable: %s\n", envVar)
+			os.Exit(1)
+		}
+
+		if err := parser(value); err != nil {
+			fmt.Fprintf(os.Stderr, "Configuration error: %v\n", err)
+			os.Exit(1)
+		}
+	}
+
+	return config
+}
--- a/config/errors.go
+++ b/config/errors.go
@@ -0,0 +1,14 @@
+package config
+
+import "fmt"
+
+// ValidationError represents a config validation error
+type ValidationError struct {
+	Param  string
+	Value  string
+	Reason string
+}
+
+func (e ValidationError) Error() string {
+	return fmt.Sprintf("invalid value '%s' for %s: %s", e.Value, e.Param, e.Reason)
+}
--- a/gemini/blacklist.go
+++ b/gemini/blacklist.go
@@ -0,0 +1,50 @@
+package gemini
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"gemini-grc/config"
+	"gemini-grc/logging"
+)
+
+var Blacklist *[]string //nolint:gochecknoglobals
+
+func LoadBlacklist() {
+	if Blacklist == nil {
+		data, err := os.ReadFile(config.CONFIG.BlacklistPath)
+		if err != nil {
+			Blacklist = &[]string{}
+			logging.LogWarn("Could not load Blacklist file: %v", err)
+			return
+		}
+		lines := strings.Split(string(data), "\n")
+
+		// Ignore lines starting with '#' (comments)
+		filteredLines := func() []string {
+			out := make([]string, 0, len(lines))
+			for _, line := range lines {
+				if !strings.HasPrefix(line, "#") {
+					out = append(out, line)
+				}
+			}
+			return out
+		}()
+
+		if len(lines) > 0 {
+			Blacklist = &filteredLines
+			logging.LogInfo("Blacklist has %d entries", len(*Blacklist))
+		}
+	}
+}
+
+func IsBlacklisted(url URL) bool {
+	hostWithPort := fmt.Sprintf("%s:%d", url.Hostname, url.Port)
+	for _, v := range *Blacklist {
+		if v == url.Hostname || v == hostWithPort {
+			return true
+		}
+	}
+	return false
+}
--- a/gemini/connectionPool.go
+++ b/gemini/connectionPool.go
@@ -0,0 +1,28 @@
+package gemini
+
+import (
+	"gemini-grc/logging"
+)
+
+var IPPool = IpAddressPool{IPs: make(map[string]int)}
+
+func AddIPsToPool(ips []string) {
+	IPPool.Lock.Lock()
+	for _, ip := range ips {
+		logging.LogDebug("Adding %s to pool", ip)
+		IPPool.IPs[ip] = 1
+	}
+	IPPool.Lock.Unlock()
+}
+
+func RemoveIPsFromPool(IPs []string) {
+	IPPool.Lock.Lock()
+	for _, ip := range IPs {
+		_, ok := IPPool.IPs[ip]
+		if ok {
+			logging.LogDebug("Removing %s from pool", ip)
+			delete(IPPool.IPs, ip)
+		}
+	}
+	IPPool.Lock.Unlock()
+}
--- a/gemini/db.go
+++ b/gemini/db.go
@@ -0,0 +1,176 @@
+package gemini
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+
+	"gemini-grc/config"
+	"gemini-grc/logging"
+	_ "github.com/jackc/pgx/v5/stdlib" // PGX driver for PostgreSQL
+	"github.com/jmoiron/sqlx"
+	"github.com/lib/pq"
+)
+
+func ConnectToDB() *sqlx.DB {
+	connStr := fmt.Sprintf("postgres://%s:%s@%s:%s/%s", //nolint:nosprintfhostport
+		os.Getenv("PG_USER"),
+		os.Getenv("PG_PASSWORD"),
+		os.Getenv("PG_HOST"),
+		os.Getenv("PG_PORT"),
+		os.Getenv("PG_DATABASE"),
+	)
+
+	// Create a connection pool
+	db, err := sqlx.Open("pgx", connStr)
+	if err != nil {
+		panic(fmt.Sprintf("Unable to connect to database with URL %s: %v\n", connStr, err))
+	}
+	// TODO move PG_MAX_OPEN_CONNECTIONS to config env variables
+	maxConnections, err := strconv.Atoi(os.Getenv("PG_MAX_OPEN_CONNECTIONS"))
+	if err != nil {
+		panic(fmt.Sprintf("Unable to set max DB connections: %s\n", err))
+	}
+	db.SetMaxOpenConns(maxConnections)
+	err = db.Ping()
+	if err != nil {
+		panic(fmt.Sprintf("Unable to ping database: %v\n", err))
+	}
+
+	logging.LogDebug("Connected to database")
+	return db
+}
+
+// isDeadlockError checks if the error is a PostgreSQL deadlock error
+func isDeadlockError(err error) bool {
+	var pqErr *pq.Error
+	if errors.As(err, &pqErr) {
+		return pqErr.Code == "40P01" // PostgreSQL deadlock error code
+	}
+	return false
+}
+
+func GetSnapshotsToVisit(tx *sqlx.Tx) ([]Snapshot, error) {
+	var snapshots []Snapshot
+	err := tx.Select(&snapshots, SQL_SELECT_UNVISITED_SNAPSHOTS_UNIQUE_HOSTS, config.CONFIG.WorkerBatchSize)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrDatabase, err)
+	}
+	return snapshots, nil
+}
+
+func SaveSnapshotIfNew(tx *sqlx.Tx, s *Snapshot) error {
+	if config.CONFIG.DryRun {
+		marshalled, err := json.MarshalIndent(s, "", "  ")
+		if err != nil {
+			panic(fmt.Sprintf("JSON serialization error for %v", s))
+		}
+		logging.LogDebug("Would insert (if new) snapshot %s", marshalled)
+		return nil
+	}
+	query := SQL_INSERT_SNAPSHOT_IF_NEW
+	_, err := tx.NamedExec(query, s)
+	if err != nil {
+		return fmt.Errorf("[%s] GeminiError inserting snapshot: %w", s.URL, err)
+	}
+	return nil
+}
+
+func UpsertSnapshot(workedID int, tx *sqlx.Tx, s *Snapshot) (err error) {
+	//	if config.CONFIG.DryRun {
+	//marshalled, err := json.MarshalIndent(s, "", "  ")
+	//if err != nil {
+	//	panic(fmt.Sprintf("JSON serialization error for %v", s))
+	//}
+	//logging.LogDebug("[%d] Would upsert snapshot %s", workedID, marshalled)
+	//		return nil
+	//	}
+	query := SQL_UPSERT_SNAPSHOT
+	rows, err := tx.NamedQuery(query, s)
+	if err != nil {
+		return fmt.Errorf("[%d] %w while upserting snapshot: %w", workedID, ErrDatabase, err)
+	}
+	defer func() {
+		_err := rows.Close()
+		if _err != nil {
+			err = fmt.Errorf("[%d] %w error closing rows: %w", workedID, ErrDatabase, _err)
+		}
+	}()
+	if rows.Next() {
+		var returnedID int
+		err = rows.Scan(&returnedID)
+		if err != nil {
+			return fmt.Errorf("[%d] %w error scanning returned id: %w", workedID, ErrDatabase, err)
+		}
+		s.ID = returnedID
+		// logging.LogDebug("[%d] Upserted snapshot with ID %d", workedID, returnedID)
+	}
+	return nil
+}
+
+func UpdateSnapshot(workedID int, tx *sqlx.Tx, s *Snapshot) (err error) {
+	//	if config.CONFIG.DryRun {
+	//marshalled, err := json.MarshalIndent(s, "", "  ")
+	//if err != nil {
+	//	panic(fmt.Sprintf("JSON serialization error for %v", s))
+	//}
+	//logging.LogDebug("[%d] Would upsert snapshot %s", workedID, marshalled)
+	//		return nil
+	//	}
+	query := SQL_UPDATE_SNAPSHOT
+	rows, err := tx.NamedQuery(query, s)
+	if err != nil {
+		return fmt.Errorf("[%d] %w while updating snapshot: %w", workedID, ErrDatabase, err)
+	}
+	defer func() {
+		_err := rows.Close()
+		if _err != nil {
+			err = fmt.Errorf("[%d] %w error closing rows: %w", workedID, ErrDatabase, _err)
+		}
+	}()
+	if rows.Next() {
+		var returnedID int
+		err = rows.Scan(&returnedID)
+		if err != nil {
+			return fmt.Errorf("[%d] %w error scanning returned id: %w", workedID, ErrDatabase, err)
+		}
+		s.ID = returnedID
+		// logging.LogDebug("[%d] Updated snapshot with ID %d", workedID, returnedID)
+	}
+	return nil
+}
+
+func SaveLinksToDBinBatches(tx *sqlx.Tx, snapshots []*Snapshot) error {
+	if config.CONFIG.DryRun {
+		return nil
+	}
+	const batchSize = 5000
+	query := SQL_INSERT_SNAPSHOT_IF_NEW
+	for i := 0; i < len(snapshots); i += batchSize {
+		end := i + batchSize
+		if end > len(snapshots) {
+			end = len(snapshots)
+		}
+		batch := snapshots[i:end]
+		_, err := tx.NamedExec(query, batch)
+		if err != nil {
+			return fmt.Errorf("%w: While saving links in batches: %w", ErrDatabase, err)
+		}
+	}
+	return nil
+}
+
+func SaveLinksToDB(tx *sqlx.Tx, snapshots []*Snapshot) error {
+	if config.CONFIG.DryRun {
+		return nil
+	}
+	query := SQL_INSERT_SNAPSHOT_IF_NEW
+	_, err := tx.NamedExec(query, snapshots)
+	if err != nil {
+		logging.LogError("GeminiError batch inserting snapshots: %w", err)
+		return fmt.Errorf("DB error: %w", err)
+	}
+	return nil
+}
--- a/gemini/db_queries.go
+++ b/gemini/db_queries.go
@@ -0,0 +1,78 @@
+package gemini
+
+const (
+	SQL_SELECT_RANDOM_UNVISITED_SNAPSHOTS = `
+SELECT *
+FROM snapshots
+WHERE response_code IS NULL
+  AND error IS NULL
+ORDER BY RANDOM()
+FOR UPDATE SKIP LOCKED
+LIMIT $1
+	`
+	SQL_SELECT_RANDOM_UNVISITED_SNAPSHOTS_UNIQUE_HOSTS = `
+SELECT *
+FROM snapshots s
+WHERE response_code IS NULL
+  AND error IS NULL
+  AND s.id IN (
+      SELECT MIN(id)
+      FROM snapshots
+      WHERE response_code IS NULL 
+        AND error IS NULL
+      GROUP BY host
+  )
+ORDER BY RANDOM()
+FOR UPDATE SKIP LOCKED
+LIMIT $1
+`
+	SQL_SELECT_UNVISITED_SNAPSHOTS_UNIQUE_HOSTS = `
+SELECT *
+FROM snapshots s
+WHERE response_code IS NULL
+  AND error IS NULL
+  AND s.id IN (
+      SELECT MIN(id)
+      FROM snapshots
+      WHERE response_code IS NULL
+        AND error IS NULL
+      GROUP BY host
+  )
+FOR UPDATE SKIP LOCKED
+LIMIT $1
+`
+	SQL_INSERT_SNAPSHOT_IF_NEW = `
+        INSERT INTO snapshots (url, host, timestamp, mimetype, data, gemtext, links, lang, response_code, error)
+        VALUES (:url, :host, :timestamp, :mimetype, :data, :gemtext, :links, :lang, :response_code, :error)
+        ON CONFLICT (url) DO NOTHING
+    `
+	SQL_UPSERT_SNAPSHOT = `INSERT INTO snapshots (url, host, timestamp, mimetype, data, gemtext, links, lang, response_code, error)
+        VALUES (:url, :host, :timestamp, :mimetype, :data, :gemtext, :links, :lang, :response_code, :error)
+        ON CONFLICT (url) DO UPDATE SET
+            url = EXCLUDED.url,
+            host = EXCLUDED.host,
+            timestamp = EXCLUDED.timestamp,
+            mimetype = EXCLUDED.mimetype,
+            data = EXCLUDED.data,
+            gemtext = EXCLUDED.gemtext,
+            links = EXCLUDED.links,
+            lang = EXCLUDED.lang,
+            response_code = EXCLUDED.response_code,
+            error = EXCLUDED.error
+        RETURNING id
+`
+	SQL_UPDATE_SNAPSHOT = `UPDATE snapshots
+SET url = :url,
+host = :host,
+timestamp = :timestamp,
+mimetype = :mimetype,
+data = :data,
+gemtext = :gemtext,
+links = :links,
+lang = :lang,
+response_code = :response_code,
+error = :error
+WHERE id = :id
+RETURNING id
+`
+)
--- a/gemini/errors.go
+++ b/gemini/errors.go
@@ -0,0 +1,100 @@
+package gemini
+
+import (
+	"errors"
+	"fmt"
+)
+
+type GeminiError struct {
+	Msg    string
+	Code   int
+	Header string
+}
+
+func (e *GeminiError) Error() string {
+	return fmt.Sprintf("%s: %s", e.Msg, e.Header)
+}
+
+func NewErrGeminiStatusCode(code int, header string) error {
+	var msg string
+	switch {
+	case code >= 10 && code < 20:
+		msg = "needs input"
+	case code >= 30 && code < 40:
+		msg = "redirect"
+	case code >= 40 && code < 50:
+		msg = "bad request"
+	case code >= 50 && code < 60:
+		msg = "server error"
+	case code >= 60 && code < 70:
+		msg = "TLS error"
+	default:
+		msg = "unexpected status code"
+	}
+	return &GeminiError{
+		Msg:    msg,
+		Code:   code,
+		Header: header,
+	}
+}
+
+var (
+	ErrGeminiRobotsParse      = errors.New("gemini robots.txt parse error")
+	ErrGeminiRobotsDisallowed = errors.New("gemini robots.txt disallowed")
+	ErrGeminiResponseHeader   = errors.New("gemini response header error")
+	ErrGeminiRedirect         = errors.New("gemini redirection error")
+	ErrGeminiLinkLineParse    = errors.New("gemini link line parse error")
+
+	ErrURLParse     = errors.New("URL parse error")
+	ErrURLNotGemini = errors.New("not a Gemini URL")
+	ErrURLDecode    = errors.New("URL decode error")
+	ErrUTF8Parse    = errors.New("UTF-8 parse error")
+	ErrTextParse    = errors.New("text parse error")
+
+	ErrNetwork                        = errors.New("network error")
+	ErrNetworkDNS                     = errors.New("network DNS error")
+	ErrNetworkTLS                     = errors.New("network TLS error")
+	ErrNetworkSetConnectionDeadline   = errors.New("network error - cannot set connection deadline")
+	ErrNetworkCannotWrite             = errors.New("network error - cannot write")
+	ErrNetworkResponseSizeExceededMax = errors.New("network error - response size exceeded maximum size")
+
+	ErrDatabase = errors.New("database error")
+)
+
+// We could have used a map for speed, but
+// we would lose ability to check wrapped
+// errors via errors.Is().
+
+var errGemini *GeminiError
+
+var knownErrors = []error{ //nolint:gochecknoglobals
+	errGemini,
+	ErrGeminiLinkLineParse,
+	ErrGeminiRobotsParse,
+	ErrGeminiRobotsDisallowed,
+	ErrGeminiResponseHeader,
+	ErrGeminiRedirect,
+
+	ErrURLParse,
+	ErrURLDecode,
+	ErrUTF8Parse,
+	ErrTextParse,
+
+	ErrNetwork,
+	ErrNetworkDNS,
+	ErrNetworkTLS,
+	ErrNetworkSetConnectionDeadline,
+	ErrNetworkCannotWrite,
+	ErrNetworkResponseSizeExceededMax,
+
+	ErrDatabase,
+}
+
+func IsKnownError(err error) bool {
+	for _, known := range knownErrors {
+		if errors.Is(err, known) {
+			return true
+		}
+	}
+	return errors.As(err, new(*GeminiError))
+}
--- a/gemini/errors_test.go
+++ b/gemini/errors_test.go
@@ -0,0 +1,24 @@
+package gemini
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestErrGemini(t *testing.T) {
+	t.Parallel()
+	err := NewErrGeminiStatusCode(50, "50 server error")
+	if !errors.As(err, new(*GeminiError)) {
+		t.Errorf("TestErrGemini fail")
+	}
+}
+
+func TestErrGeminiWrapped(t *testing.T) {
+	t.Parallel()
+	err := NewErrGeminiStatusCode(50, "50 server error")
+	errWrapped := fmt.Errorf("%w wrapped", err)
+	if !errors.As(errWrapped, new(*GeminiError)) {
+		t.Errorf("TestErrGeminiWrapped fail")
+	}
+}
--- a/gemini/files.go
+++ b/gemini/files.go
@@ -0,0 +1,113 @@
+package gemini
+
+import (
+	"fmt"
+	"net/url"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"gemini-grc/logging"
+)
+
+// sanitizePath encodes invalid filesystem characters using URL encoding.
+// Example:
+// /example/path/to/page?query=param&another=value
+// would become
+// example/path/to/page%3Fquery%3Dparam%26another%3Dvalue
+func sanitizePath(p string) string {
+	// Split the path into its components
+	components := strings.Split(p, "/")
+
+	// Encode each component separately
+	for i, component := range components {
+		// Decode any existing percent-encoded characters
+		decodedComponent, err := url.PathUnescape(component)
+		if err != nil {
+			decodedComponent = component // Fallback to original if unescape fails
+		}
+
+		// Encode the component to escape invalid filesystem characters
+		encodedComponent := url.QueryEscape(decodedComponent)
+
+		// Replace '+' (from QueryEscape) with '%20' to handle spaces correctly
+		encodedComponent = strings.ReplaceAll(encodedComponent, "+", "%20")
+
+		components[i] = encodedComponent
+	}
+
+	// Rejoin the components into a sanitized path
+	safe := filepath.Join(components...)
+
+	return safe
+}
+
+// getFilePath constructs a safe file path from the root path and URL path.
+// It URL-encodes invalid filesystem characters to ensure the path is valid.
+func calcFilePath(rootPath, urlPath string) (string, error) {
+	// Normalize the URL path
+	cleanPath := filepath.Clean(urlPath)
+
+	// Safe check to prevent directory traversal
+	if strings.Contains(cleanPath, "..") {
+		return "", fmt.Errorf("Invalid URL path: contains directory traversal")
+	}
+
+	// Sanitize the path by encoding invalid characters
+	safePath := sanitizePath(cleanPath)
+
+	// Join the root path and the sanitized URL path
+	finalPath := filepath.Join(rootPath, safePath)
+
+	return finalPath, nil
+}
+
+func SaveToFile(rootPath string, s *Snapshot, done chan struct{}) {
+	parentPath := path.Join(rootPath, s.URL.Hostname)
+	urlPath := s.URL.Path
+	// If path is empty, add `index.gmi` as the file to save
+	if urlPath == "" || urlPath == "." {
+		urlPath = "index.gmi"
+	}
+	// If path ends with '/' then add index.gmi for the
+	// directory to be created.
+	if strings.HasSuffix(urlPath, "/") {
+		urlPath = strings.Join([]string{urlPath, "index.gmi"}, "")
+	}
+
+	finalPath, err := calcFilePath(parentPath, urlPath)
+	if err != nil {
+		logging.LogError("GeminiError saving %s: %w", s.URL, err)
+		return
+	}
+	// Ensure the directory exists
+	dir := filepath.Dir(finalPath)
+	if err := os.MkdirAll(dir, os.ModePerm); err != nil {
+		logging.LogError("Failed to create directory: %w", err)
+		return
+	}
+	if s.MimeType.Valid && s.MimeType.String == "text/gemini" {
+		err = os.WriteFile(finalPath, (*s).Data.V, 0o666)
+	} else {
+		err = os.WriteFile(finalPath, []byte((*s).GemText.String), 0o666)
+	}
+	if err != nil {
+		logging.LogError("GeminiError saving %s: %w", s.URL.Full, err)
+	}
+	close(done)
+}
+
+func ReadLines(path string) []string {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		panic(fmt.Sprintf("Failed to read file: %s", err))
+	}
+	lines := strings.Split(string(data), "\n")
+	// Remove last line if empty
+	// (happens when file ends with '\n')
+	if lines[len(lines)-1] == "" {
+		lines = lines[:len(lines)-1]
+	}
+	return lines
+}
--- a/gemini/gemini.go
+++ b/gemini/gemini.go
@@ -0,0 +1,139 @@
+package gemini
+
+import (
+	"fmt"
+	"net/url"
+	"regexp"
+	"strconv"
+
+	"gemini-grc/logging"
+)
+
+func GetPageLinks(currentURL URL, gemtext string) LinkList {
+	// Grab link lines
+	linkLines := ExtractLinkLines(gemtext)
+	if len(linkLines) == 0 {
+		return nil
+	}
+	var linkURLs LinkList
+	// Normalize URLs in links, and store them in snapshot
+	for _, line := range linkLines {
+		linkURL, err := NormalizeLink(line, currentURL.String())
+		if err != nil {
+			logging.LogDebug("%s: %s", ErrGeminiLinkLineParse, err)
+			continue
+		}
+		linkURLs = append(linkURLs, *linkURL)
+	}
+	return linkURLs
+}
+
+// ExtractLinkLines takes a Gemtext document as a string and returns all lines that are link lines
+func ExtractLinkLines(gemtext string) []string {
+	// Define the regular expression pattern to match link lines
+	re := regexp.MustCompile(`(?m)^=>[ \t]+.*`)
+
+	// Find all matches using the regular expression
+	matches := re.FindAllString(gemtext, -1)
+
+	return matches
+}
+
+// NormalizeLink takes a single link line and the current URL,
+// return the URL converted to an absolute URL
+// and its description.
+func NormalizeLink(linkLine string, currentURL string) (*URL, error) {
+	// Parse the current URL
+	baseURL, err := url.Parse(currentURL)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrURLParse, err)
+	}
+
+	// Regular expression to extract the URL part from a link line
+	re := regexp.MustCompile(`^=>[ \t]+(\S+)([ \t]+.*)?`)
+
+	// Use regex to extract the URL and the rest of the line
+	matches := re.FindStringSubmatch(linkLine)
+	if len(matches) == 0 {
+		// If the line doesn't match the expected format, return it unchanged
+		return nil, fmt.Errorf("%w for link line %s", ErrGeminiLinkLineParse, linkLine)
+	}
+
+	originalURLStr := matches[1]
+	_, err = url.QueryUnescape(originalURLStr)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrURLDecode, err)
+	}
+
+	restOfLine := ""
+	if len(matches) > 2 {
+		restOfLine = matches[2]
+	}
+
+	// Parse the URL from the link line
+	parsedURL, err := url.Parse(originalURLStr)
+	if err != nil {
+		// If URL parsing fails, return an error
+		return nil, fmt.Errorf("%w: %w", ErrURLParse, err)
+	}
+
+	// Resolve relative URLs against the base URL
+	if !parsedURL.IsAbs() {
+		parsedURL = baseURL.ResolveReference(parsedURL)
+	}
+
+	// Remove usual first space from URL description:
+	// => URL description
+	//       ^^^^^^^^^^^^
+	if len(restOfLine) > 0 && restOfLine[0] == ' ' {
+		restOfLine = restOfLine[1:]
+	}
+
+	finalURL, err := ParseURL(parsedURL.String(), restOfLine)
+	if err != nil {
+		// If URL parsing fails, return an error
+		return nil, fmt.Errorf("%w: %w", ErrURLParse, err)
+	}
+
+	return finalURL, nil
+}
+
+// ParseFirstTwoDigits takes a string and returns the first one or two digits as an int.
+// If no valid digits are found, it returns an error.
+func ParseFirstTwoDigits(input string) (int, error) {
+	// Define the regular expression pattern to match one or two leading digits
+	re := regexp.MustCompile(`^(\d{1,2})`)
+
+	// Find the first match in the string
+	matches := re.FindStringSubmatch(input)
+	if len(matches) == 0 {
+		return 0, fmt.Errorf("%w", ErrGeminiResponseHeader)
+	}
+
+	// Parse the captured match as an integer
+	snapshot, err := strconv.Atoi(matches[1])
+	if err != nil {
+		return 0, fmt.Errorf("%w: %w", ErrTextParse, err)
+	}
+
+	return snapshot, nil
+}
+
+// extractRedirectTarget returns the redirection
+// URL by parsing the header (or error message)
+func extractRedirectTarget(currentURL URL, input string) (*URL, error) {
+	// \d+ - matches one or more digits
+	// \s+ - matches one or more whitespace
+	// ([^\r]+) - captures everything until it hits a \r (or end of string)
+	pattern := `\d+\s+([^\r]+)`
+	re := regexp.MustCompile(pattern)
+	matches := re.FindStringSubmatch(input)
+	if len(matches) < 2 {
+		return nil, fmt.Errorf("%w: %s", ErrGeminiRedirect, input)
+	}
+	newURL, err := DeriveAbsoluteURL(currentURL, matches[1])
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w: %s", ErrGeminiRedirect, err, input)
+	}
+	return newURL, nil
+}
--- a/gemini/gemini_test.go
+++ b/gemini/gemini_test.go
@@ -0,0 +1,65 @@
+package gemini
+
+import "testing"
+
+func TestExtractRedirectTargetFullURL(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://smol.gr", "")
+	input := "redirect: 31 gemini://target.gr"
+	result, err := extractRedirectTarget(*currentURL, input)
+	expected := "gemini://target.gr:1965"
+	if err != nil || (result.String() != expected) {
+		t.Errorf("fail: Expected %s got %s", expected, result)
+	}
+}
+
+func TestExtractRedirectTargetFullURLSlash(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://smol.gr", "")
+	input := "redirect: 31 gemini://target.gr/"
+	result, err := extractRedirectTarget(*currentURL, input)
+	expected := "gemini://target.gr:1965/"
+	if err != nil || (result.String() != expected) {
+		t.Errorf("fail: Expected %s got %s", expected, result)
+	}
+}
+
+func TestExtractRedirectTargetRelativeURL(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://smol.gr", "")
+	input := "redirect: 31 /a/b"
+	result, err := extractRedirectTarget(*currentURL, input)
+	if err != nil || (result.String() != "gemini://smol.gr:1965/a/b") {
+		t.Errorf("fail: %s", result)
+	}
+}
+
+func TestExtractRedirectTargetRelativeURL2(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://nox.im:1965", "")
+	input := "redirect: 31 ./"
+	result, err := extractRedirectTarget(*currentURL, input)
+	if err != nil || (result.String() != "gemini://nox.im:1965/") {
+		t.Errorf("fail: %s", result)
+	}
+}
+
+func TestExtractRedirectTargetRelativeURL3(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://status.zvava.org:1965", "")
+	input := "redirect: 31 index.gmi"
+	result, err := extractRedirectTarget(*currentURL, input)
+	if err != nil || (result.String() != "gemini://status.zvava.org:1965/index.gmi") {
+		t.Errorf("fail: %s", result)
+	}
+}
+
+func TestExtractRedirectTargetWrong(t *testing.T) {
+	t.Parallel()
+	currentURL, _ := ParseURL("gemini://smol.gr", "")
+	input := "redirect: 31"
+	result, err := extractRedirectTarget(*currentURL, input)
+	if result != nil || err == nil {
+		t.Errorf("fail: result should be nil, err is %s", err)
+	}
+}
--- a/gemini/gemini_url.go
+++ b/gemini/gemini_url.go
@@ -0,0 +1,229 @@
+package gemini
+
+import (
+	"database/sql/driver"
+	"fmt"
+	"net/url"
+	"path"
+	"strconv"
+	"strings"
+)
+
+type URL struct {
+	Protocol string `json:"protocol,omitempty"`
+	Hostname string `json:"hostname,omitempty"`
+	Port     int    `json:"port,omitempty"`
+	Path     string `json:"path,omitempty"`
+	Descr    string `json:"descr,omitempty"`
+	Full     string `json:"full,omitempty"`
+}
+
+func (u *URL) Scan(value interface{}) error {
+	if value == nil {
+		// Clear the fields in the current GeminiUrl object (not the pointer itself)
+		*u = URL{}
+		return nil
+	}
+	b, ok := value.(string)
+	if !ok {
+		return fmt.Errorf("failed to scan GeminiUrl: expected string, got %T", value)
+	}
+	parsedURL, err := ParseURLNoNormalize(b, "")
+	if err != nil {
+		err = fmt.Errorf("failed to scan GeminiUrl %s: %v", b, err)
+		return err
+	}
+	*u = *parsedURL
+	return nil
+}
+
+func (u URL) String() string {
+	return u.Full
+}
+
+func (u URL) StringNoDefaultPort() string {
+	if u.Port == 1965 {
+		return fmt.Sprintf("%s://%s%s", u.Protocol, u.Hostname, u.Path)
+	}
+	return u.Full
+}
+
+func (u URL) Value() (driver.Value, error) {
+	if u.Full == "" {
+		return nil, nil
+	}
+	return u.Full, nil
+}
+
+func ParseURLNoNormalize(input string, descr string) (*URL, error) {
+	u, err := url.Parse(input)
+	if err != nil {
+		return nil, fmt.Errorf("%w: Input %s URL Parse Error: %w", ErrURLParse, input, err)
+	}
+	if u.Scheme != "gemini" {
+		return nil, fmt.Errorf("%w: URL scheme '%s' is not supported", ErrURLNotGemini, u.Scheme)
+	}
+	protocol := u.Scheme
+	hostname := u.Hostname()
+	strPort := u.Port()
+	urlPath := u.Path
+	if strPort == "" {
+		strPort = "1965"
+	}
+	port, err := strconv.Atoi(strPort)
+	if err != nil {
+		return nil, fmt.Errorf("%w: Input %s GeminiError %w", ErrURLParse, input, err)
+	}
+	full := fmt.Sprintf("%s://%s:%d%s", protocol, hostname, port, urlPath)
+	return &URL{Protocol: protocol, Hostname: hostname, Port: port, Path: urlPath, Descr: descr, Full: full}, nil
+}
+
+func ParseURL(input string, descr string) (*URL, error) {
+	u, err := NormalizeURL(input)
+	if err != nil {
+		return nil, fmt.Errorf("%w: Input %s URL Parse Error: %w", ErrURLParse, input, err)
+	}
+	if u.Scheme != "gemini" {
+		return nil, fmt.Errorf("%w: URL scheme '%s' is not supported", ErrURLNotGemini, u.Scheme)
+	}
+	protocol := u.Scheme
+	hostname := u.Hostname()
+	strPort := u.Port()
+	urlPath := u.Path
+	if strPort == "" {
+		strPort = "1965"
+	}
+	port, err := strconv.Atoi(strPort)
+	if err != nil {
+		return nil, fmt.Errorf("%w: Input %s GeminiError %w", ErrURLParse, input, err)
+	}
+	full := fmt.Sprintf("%s://%s:%d%s", protocol, hostname, port, urlPath)
+	return &URL{Protocol: protocol, Hostname: hostname, Port: port, Path: urlPath, Descr: descr, Full: full}, nil
+}
+
+// DeriveAbsoluteURL converts a (possibly) relative
+// URL to an absolute one. Used primarily to calculate
+// the full redirection URL target from a response header.
+func DeriveAbsoluteURL(currentURL URL, input string) (*URL, error) {
+	// If target URL is absolute, return just it
+	if strings.Contains(input, "://") {
+		return ParseURL(input, "")
+	}
+	// input is a relative path. Clean it and construct absolute.
+	var newPath string
+	// Handle weird cases found in the wild
+	if strings.HasPrefix(input, "/") {
+		newPath = path.Clean(input)
+	} else if input == "./" || input == "." {
+		newPath = path.Join(currentURL.Path, "/")
+	} else {
+		newPath = path.Join(currentURL.Path, "/", path.Clean(input))
+	}
+	strURL := fmt.Sprintf("%s://%s:%d%s", currentURL.Protocol, currentURL.Hostname, currentURL.Port, newPath)
+	return ParseURL(strURL, "")
+}
+
+// NormalizeURL takes a URL string and returns a normalized version.
+// Normalized meaning:
+// - Path normalization (removing redundant slashes, . and .. segments)
+// - Proper escaping of special characters
+// - Lowercase scheme and host
+// - Removal of default ports
+// - Empty path becomes "/"
+func NormalizeURL(rawURL string) (*url.URL, error) {
+	// Parse the URL
+	u, err := url.Parse(rawURL)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrURLParse, err)
+	}
+
+	// Convert scheme to lowercase
+	u.Scheme = strings.ToLower(u.Scheme)
+
+	// Convert hostname to lowercase
+	if u.Host != "" {
+		u.Host = strings.ToLower(u.Host)
+	}
+
+	// Remove default ports
+	if u.Port() != "" {
+		switch {
+		case u.Scheme == "http" && u.Port() == "80":
+			u.Host = u.Hostname()
+		case u.Scheme == "https" && u.Port() == "443":
+			u.Host = u.Hostname()
+		case u.Scheme == "gemini" && u.Port() == "1965":
+			u.Host = u.Hostname()
+		}
+	}
+
+	// Handle path normalization while preserving trailing slash
+	if u.Path != "" {
+		// Check if there was a trailing slash before cleaning
+		hadTrailingSlash := strings.HasSuffix(u.Path, "/")
+
+		u.Path = path.Clean(u.Path)
+		// If path was "/", path.Clean() will return "."
+		if u.Path == "." {
+			u.Path = "/"
+		} else if hadTrailingSlash && u.Path != "/" {
+			// Restore trailing slash if it existed and path isn't just "/"
+			u.Path += "/"
+		}
+	}
+
+	// Properly escape the path
+	// First split on '/' to avoid escaping them
+	parts := strings.Split(u.Path, "/")
+	for i, part := range parts {
+		parts[i] = url.PathEscape(part)
+	}
+	u.Path = strings.Join(parts, "/")
+
+	// Remove trailing fragment if empty
+	if u.Fragment == "" {
+		u.Fragment = ""
+	}
+
+	// Remove trailing query if empty
+	if u.RawQuery == "" {
+		u.RawQuery = ""
+	}
+
+	return u, nil
+}
+
+func EscapeURL(input string) string {
+	// Only escape if not already escaped
+	if strings.Contains(input, "%") && !strings.Contains(input, "% ") {
+		return input
+	}
+	// Split URL into parts (protocol, host, path)
+	parts := strings.SplitN(input, "://", 2)
+	if len(parts) != 2 {
+		return input
+	}
+
+	protocol := parts[0]
+	remainder := parts[1]
+
+	// If URL ends with just a slash, return as is
+	if strings.HasSuffix(remainder, "/") && !strings.Contains(remainder[:len(remainder)-1], "/") {
+		return input
+	}
+
+	// Split host and path
+	parts = strings.SplitN(remainder, "/", 2)
+	host := parts[0]
+	if len(parts) == 1 {
+		return protocol + "://" + host
+	}
+
+	path := parts[1]
+
+	// Escape the path portion
+	escapedPath := url.PathEscape(path)
+
+	// Reconstruct the URL
+	return protocol + "://" + host + "/" + escapedPath
+}
--- a/gemini/gemini_url_test.go
+++ b/gemini/gemini_url_test.go
@@ -0,0 +1,223 @@
+package gemini
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseURL(t *testing.T) {
+	t.Parallel()
+	input := "gemini://caolan.uk/cgi-bin/weather.py/wxfcs/3162"
+	parsed, err := ParseURL(input, "")
+	value, _ := parsed.Value()
+	if err != nil || !(value == "gemini://caolan.uk:1965/cgi-bin/weather.py/wxfcs/3162") {
+		t.Errorf("fail: %s", parsed)
+	}
+}
+
+func TestDeriveAbsoluteURL_abs_url_input(t *testing.T) {
+	t.Parallel()
+	currentURL := URL{
+		Protocol: "gemini",
+		Hostname: "smol.gr",
+		Port:     1965,
+		Path:     "/a/b",
+		Descr:    "Nothing",
+		Full:     "gemini://smol.gr:1965/a/b",
+	}
+	input := "gemini://a.b/c"
+	output, err := DeriveAbsoluteURL(currentURL, input)
+	if err != nil {
+		t.Errorf("fail: %v", err)
+	}
+	expected := &URL{
+		Protocol: "gemini",
+		Hostname: "a.b",
+		Port:     1965,
+		Path:     "/c",
+		Descr:    "",
+		Full:     "gemini://a.b:1965/c",
+	}
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestDeriveAbsoluteURL_abs_path_input(t *testing.T) {
+	t.Parallel()
+	currentURL := URL{
+		Protocol: "gemini",
+		Hostname: "smol.gr",
+		Port:     1965,
+		Path:     "/a/b",
+		Descr:    "Nothing",
+		Full:     "gemini://smol.gr:1965/a/b",
+	}
+	input := "/c"
+	output, err := DeriveAbsoluteURL(currentURL, input)
+	if err != nil {
+		t.Errorf("fail: %v", err)
+	}
+	expected := &URL{
+		Protocol: "gemini",
+		Hostname: "smol.gr",
+		Port:     1965,
+		Path:     "/c",
+		Descr:    "",
+		Full:     "gemini://smol.gr:1965/c",
+	}
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestDeriveAbsoluteURL_rel_path_input(t *testing.T) {
+	t.Parallel()
+	currentURL := URL{
+		Protocol: "gemini",
+		Hostname: "smol.gr",
+		Port:     1965,
+		Path:     "/a/b",
+		Descr:    "Nothing",
+		Full:     "gemini://smol.gr:1965/a/b",
+	}
+	input := "c/d"
+	output, err := DeriveAbsoluteURL(currentURL, input)
+	if err != nil {
+		t.Errorf("fail: %v", err)
+	}
+	expected := &URL{
+		Protocol: "gemini",
+		Hostname: "smol.gr",
+		Port:     1965,
+		Path:     "/a/b/c/d",
+		Descr:    "",
+		Full:     "gemini://smol.gr:1965/a/b/c/d",
+	}
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeURLSlash(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/retro-computing/magazines/"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := input
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeURLNoSlash(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/retro-computing/magazines"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := input
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeMultiSlash(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/retro-computing/////////a///magazines"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/retro-computing/a/magazines"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeTrailingSlash(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeNoTrailingSlash(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeTrailingSlashPath(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/a/"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/a/"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeNoTrailingSlashPath(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/a"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/a"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeDot(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net/retro-computing/./././////a///magazines"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/retro-computing/a/magazines"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizePort(t *testing.T) {
+	t.Parallel()
+	input := "gemini://uscoffings.net:1965/a"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://uscoffings.net/a"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
+
+func TestNormalizeURL(t *testing.T) {
+	t.Parallel()
+	input := "gemini://chat.gemini.lehmann.cx:11965/"
+	normalized, _ := NormalizeURL(input)
+	output := normalized.String()
+	expected := "gemini://chat.gemini.lehmann.cx:11965/"
+	pass := reflect.DeepEqual(output, expected)
+	if !pass {
+		t.Errorf("fail: %#v != %#v", output, expected)
+	}
+}
--- a/gemini/ip-address-pool.go
+++ b/gemini/ip-address-pool.go
@@ -0,0 +1,54 @@
+package gemini
+
+import "sync"
+
+// Used to limit requests per
+// IP address. Maps IP address
+// to number of active connections.
+type IpAddressPool struct {
+	IPs  map[string]int
+	Lock sync.RWMutex
+}
+
+func (p *IpAddressPool) Set(key string, value int) {
+	p.Lock.Lock()         // Lock for writing
+	defer p.Lock.Unlock() // Ensure mutex is unlocked after the write
+	p.IPs[key] = value
+}
+
+func (p *IpAddressPool) Get(key string) int {
+	p.Lock.RLock()         // Lock for reading
+	defer p.Lock.RUnlock() // Ensure mutex is unlocked after reading
+	if value, ok := p.IPs[key]; !ok {
+		return 0
+	} else {
+		return value
+	}
+}
+
+func (p *IpAddressPool) Delete(key string) {
+	p.Lock.Lock()
+	defer p.Lock.Unlock()
+	delete(p.IPs, key)
+}
+
+func (p *IpAddressPool) Incr(key string) {
+	p.Lock.Lock()
+	defer p.Lock.Unlock()
+	if _, ok := p.IPs[key]; !ok {
+		p.IPs[key] = 1
+	} else {
+		p.IPs[key] = p.IPs[key] + 1
+	}
+}
+
+func (p *IpAddressPool) Decr(key string) {
+	p.Lock.Lock()
+	defer p.Lock.Unlock()
+	if val, ok := p.IPs[key]; ok {
+		p.IPs[key] = val - 1
+		if p.IPs[key] == 0 {
+			delete(p.IPs, key)
+		}
+	}
+}
--- a/gemini/network.go
+++ b/gemini/network.go
@@ -0,0 +1,244 @@
+package gemini
+
+import (
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	gourl "net/url"
+	"regexp"
+	"slices"
+	"strconv"
+	"strings"
+	"time"
+
+	"gemini-grc/config"
+	"gemini-grc/logging"
+	"github.com/guregu/null/v5"
+)
+
+type PageData struct {
+	ResponseCode   int
+	ResponseHeader string
+	MimeType       string
+	Lang           string
+	GemText        string
+	Data           []byte
+}
+
+// Resolve the URL hostname and
+// check if we already have an open
+// connection to this host.
+// If we can connect, return a list
+// of the resolved IPs.
+func getHostIPAddresses(hostname string) ([]string, error) {
+	addrs, err := net.LookupHost(hostname)
+	if err != nil {
+		return nil, fmt.Errorf("%w:%w", ErrNetworkDNS, err)
+	}
+	IPPool.Lock.RLock()
+	defer func() {
+		IPPool.Lock.RUnlock()
+	}()
+	return addrs, nil
+}
+
+func ConnectAndGetData(url string) ([]byte, error) {
+	parsedURL, err := gourl.Parse(url)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrURLParse, err)
+	}
+	hostname := parsedURL.Hostname()
+	port := parsedURL.Port()
+	if port == "" {
+		port = "1965"
+	}
+	host := fmt.Sprintf("%s:%s", hostname, port)
+	// Establish the underlying TCP connection.
+	dialer := &net.Dialer{
+		Timeout: time.Duration(config.CONFIG.ResponseTimeout) * time.Second,
+	}
+	conn, err := dialer.Dial("tcp", host)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrNetwork, err)
+	}
+	// Make sure we always close the connection.
+	defer func() {
+		// No need to handle error:
+		// Connection will time out eventually if still open somehow.
+		_ = conn.Close()
+	}()
+
+	// Set read and write timeouts on the TCP connection.
+	err = conn.SetReadDeadline(time.Now().Add(time.Duration(config.CONFIG.ResponseTimeout) * time.Second))
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrNetworkSetConnectionDeadline, err)
+	}
+	err = conn.SetWriteDeadline(time.Now().Add(time.Duration(config.CONFIG.ResponseTimeout) * time.Second))
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrNetworkSetConnectionDeadline, err)
+	}
+
+	// Perform the TLS handshake
+	tlsConfig := &tls.Config{
+		InsecureSkipVerify: true,                 //nolint:gosec    // Accept all TLS certs, even if insecure.
+		ServerName:         parsedURL.Hostname(), // SNI says we should not include port in hostname
+		// MinVersion:         tls.VersionTLS12, // Use a minimum TLS version. Warning breaks a lot of sites.
+	}
+	tlsConn := tls.Client(conn, tlsConfig)
+	if err := tlsConn.Handshake(); err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrNetworkTLS, err)
+	}
+
+	// We read `buf`-sized chunks and add data to `data`.
+	buf := make([]byte, 4096)
+	var data []byte
+
+	// Send Gemini request to trigger server response.
+	// Fix for stupid server bug:
+	// Some servers return 'Header: 53 No proxying to other hosts or ports!'
+	// when the port is 1965 and is still specified explicitly in the URL.
+	_url, _ := ParseURL(url, "")
+	_, err = tlsConn.Write([]byte(fmt.Sprintf("%s\r\n", _url.StringNoDefaultPort())))
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrNetworkCannotWrite, err)
+	}
+	// Read response bytes in len(buf) byte chunks
+	for {
+		n, err := tlsConn.Read(buf)
+		if n > 0 {
+			data = append(data, buf[:n]...)
+		}
+		if len(data) > config.CONFIG.MaxResponseSize {
+			return nil, fmt.Errorf("%w: %v", ErrNetworkResponseSizeExceededMax, config.CONFIG.MaxResponseSize)
+		}
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return nil, fmt.Errorf("%w: %w", ErrNetwork, err)
+		}
+	}
+	return data, nil
+}
+
+// Visit given URL, using the Gemini protocol.
+// Mutates given Snapshot with the data.
+// In case of error, we store the error string
+// inside snapshot and return the error.
+func Visit(s *Snapshot) (err error) {
+	// Don't forget to also store error
+	// response code (if we have one)
+	// and header
+	defer func() {
+		if err != nil {
+			s.Error = null.StringFrom(err.Error())
+			if errors.As(err, new(*GeminiError)) {
+				s.Header = null.StringFrom(err.(*GeminiError).Header)
+				s.ResponseCode = null.IntFrom(int64(err.(*GeminiError).Code))
+			}
+		}
+	}()
+	s.Timestamp = null.TimeFrom(time.Now())
+	data, err := ConnectAndGetData(s.URL.String())
+	if err != nil {
+		return err
+	}
+	pageData, err := processData(data)
+	if err != nil {
+		return err
+	}
+	s.Header = null.StringFrom(pageData.ResponseHeader)
+	s.ResponseCode = null.IntFrom(int64(pageData.ResponseCode))
+	s.MimeType = null.StringFrom(pageData.MimeType)
+	s.Lang = null.StringFrom(pageData.Lang)
+	if pageData.GemText != "" {
+		s.GemText = null.StringFrom(pageData.GemText)
+	}
+	if pageData.Data != nil {
+		s.Data = null.ValueFrom(pageData.Data)
+	}
+	return nil
+}
+
+// processData returne results from
+// parsing Gemini header data:
+// Code, mime type and lang (optional)
+// Returns error if header was invalid
+func processData(data []byte) (*PageData, error) {
+	header, body, err := getHeadersAndData(data)
+	if err != nil {
+		return nil, err
+	}
+	code, mimeType, lang := getMimeTypeAndLang(header)
+	logging.LogDebug("Header: %s", strings.TrimSpace(header))
+	if code != 20 {
+		return nil, NewErrGeminiStatusCode(code, header)
+	}
+
+	pageData := PageData{
+		ResponseCode:   code,
+		ResponseHeader: header,
+		MimeType:       mimeType,
+		Lang:           lang,
+	}
+	// If we've got a Gemini document, populate
+	// `GemText` field, otherwise raw data goes to `Data`.
+	if mimeType == "text/gemini" {
+		validBody, err := BytesToValidUTF8(body)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %w", ErrUTF8Parse, err)
+		}
+		pageData.GemText = validBody
+	} else {
+		pageData.Data = body
+	}
+	return &pageData, nil
+}
+
+// Checks for a Gemini header, which is
+// basically the first line of the response
+// and should contain the response code,
+// mimeType and language.
+func getHeadersAndData(data []byte) (string, []byte, error) {
+	firstLineEnds := slices.Index(data, '\n')
+	if firstLineEnds == -1 {
+		return "", nil, ErrGeminiResponseHeader
+	}
+	firstLine := string(data[:firstLineEnds])
+	rest := data[firstLineEnds+1:]
+	return firstLine, rest, nil
+}
+
+// Parses code, mime type and language
+// from a Gemini header.
+// Examples:
+// `20 text/gemini lang=en` (code, mimetype, lang)
+// `20 text/gemini` (code, mimetype)
+// `31 gemini://redirected.to/other/site` (code)
+func getMimeTypeAndLang(headers string) (int, string, string) {
+	// Regex that parses code, mimetype & optional charset/lang parameters
+	re := regexp.MustCompile(`^(\d+)\s+([a-zA-Z0-9/\-+]+)(?:[;\s]+(?:(?:charset|lang)=([a-zA-Z0-9-]+)))?\s*$`)
+	matches := re.FindStringSubmatch(headers)
+	if matches == nil || len(matches) <= 1 {
+		// Try to get code at least
+		re := regexp.MustCompile(`^(\d+)\s+`)
+		matches := re.FindStringSubmatch(headers)
+		if matches == nil || len(matches) <= 1 {
+			return 0, "", ""
+		}
+		code, err := strconv.Atoi(matches[1])
+		if err != nil {
+			return 0, "", ""
+		}
+		return code, "", ""
+	}
+	code, err := strconv.Atoi(matches[1])
+	if err != nil {
+		return 0, "", ""
+	}
+	mimeType := matches[2]
+	param := matches[3] // This will capture either charset or lang value
+	return code, mimeType, param
+}
--- a/gemini/network_test.go
+++ b/gemini/network_test.go
@@ -0,0 +1,78 @@
+package gemini
+
+import (
+	"testing"
+)
+
+// Test for input: `20 text/gemini`
+func TestGetMimeTypeAndLang1(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/gemini")
+	if code != 20 || mimeType != "text/gemini" || lang != "" {
+		t.Errorf("Expected (20, 'text/gemini', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang11(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/gemini\n")
+	if code != 20 || mimeType != "text/gemini" || lang != "" {
+		t.Errorf("Expected (20, 'text/gemini', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang12(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/plain; charset=utf-8")
+	if code != 20 || mimeType != "text/plain" || lang != "utf-8" {
+		t.Errorf("Expected (20, 'text/plain', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang13(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/gemini; charset=utf-8")
+	if code != 20 || mimeType != "text/gemini" || lang != "utf-8" {
+		t.Errorf("Expected (20, 'text/plain', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetTypeAndLang2(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/gemini charset=en")
+	if code != 20 || mimeType != "text/gemini" || lang != "en" {
+		t.Errorf("Expected (20, 'text/gemini', 'en'), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetTypeAndLang21(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("20 text/gemini lang=en")
+	if code != 20 || mimeType != "text/gemini" || lang != "en" {
+		t.Errorf("Expected (20, 'text/gemini', 'en'), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang3(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("31 gemini://redirect.to/page")
+	if code != 31 || mimeType != "" || lang != "" {
+		t.Errorf("Expected (20, '', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang4(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("aaafdasdasd")
+	if code != 0 || mimeType != "" || lang != "" {
+		t.Errorf("Expected (0, '', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
+
+func TestGetMimeTypeAndLang5(t *testing.T) {
+	t.Parallel()
+	code, mimeType, lang := getMimeTypeAndLang("")
+	if code != 0 || mimeType != "" || lang != "" {
+		t.Errorf("Expected (0, '', ''), got (%d, '%s', '%s')", code, mimeType, lang)
+	}
+}
--- a/gemini/processing.go
+++ b/gemini/processing.go
@@ -0,0 +1,59 @@
+package gemini
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"unicode/utf8"
+
+	"golang.org/x/text/encoding/charmap"
+	"golang.org/x/text/encoding/japanese"
+	"golang.org/x/text/encoding/korean"
+	"golang.org/x/text/transform"
+)
+
+var (
+	ErrInputTooLarge  = errors.New("input too large")
+	ErrUTF8Conversion = errors.New("UTF-8 conversion error")
+)
+
+func BytesToValidUTF8(input []byte) (string, error) {
+	if len(input) == 0 {
+		return "", nil
+	}
+	const maxSize = 10 * 1024 * 1024 // 10MB
+	if len(input) > maxSize {
+		return "", fmt.Errorf("%w: %d bytes (max %d)", ErrInputTooLarge, len(input), maxSize)
+	}
+	// Remove NULL byte 0x00 (ReplaceAll accepts slices)
+	inputNoNull := bytes.ReplaceAll(input, []byte{byte(0)}, []byte{})
+	if utf8.Valid(inputNoNull) {
+		return string(inputNoNull), nil
+	}
+	encodings := []transform.Transformer{
+		charmap.ISO8859_1.NewDecoder(),
+		charmap.ISO8859_7.NewDecoder(),
+		charmap.Windows1250.NewDecoder(), // Central European
+		charmap.Windows1251.NewDecoder(), // Cyrillic
+		charmap.Windows1252.NewDecoder(),
+		charmap.Windows1256.NewDecoder(), // Arabic
+		japanese.EUCJP.NewDecoder(),      // Japanese
+		korean.EUCKR.NewDecoder(),        // Korean
+	}
+	// First successful conversion wins.
+	var lastErr error
+	for _, encoding := range encodings {
+		reader := transform.NewReader(bytes.NewReader(inputNoNull), encoding)
+		result, err := io.ReadAll(reader)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		if utf8.Valid(result) {
+			return string(result), nil
+		}
+	}
+
+	return "", fmt.Errorf("%w (tried %d encodings): %w", ErrUTF8Conversion, len(encodings), lastErr)
+}
--- a/gemini/processing_test.go
+++ b/gemini/processing_test.go
@@ -0,0 +1,14 @@
+package gemini
+
+import "testing"
+
+// Make sure NULL bytes are removed
+func TestEnsureValidUTF8(t *testing.T) {
+	t.Parallel()
+	// Create a string with a null byte
+	strWithNull := "Hello" + string('\x00') + "world"
+	result, _ := BytesToValidUTF8([]byte(strWithNull))
+	if result != "Helloworld" {
+		t.Errorf("Expected string without NULL byte, got %s", result)
+	}
+}
--- a/gemini/robotmatch.go
+++ b/gemini/robotmatch.go
@@ -0,0 +1,82 @@
+package gemini
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+
+	"gemini-grc/logging"
+)
+
+// RobotsCache is a map of blocked URLs
+// key: URL
+// value: []string list of disallowed URLs
+// If a key has no blocked URLs, an empty
+// list is stored for caching.
+var RobotsCache sync.Map //nolint:gochecknoglobals
+
+func populateBlacklist(key string) (entries []string) {
+	// We either store an empty list when
+	// no rules, or a list of disallowed URLs.
+	// This applies even if we have an error
+	// finding/downloading robots.txt
+	defer func() {
+		RobotsCache.Store(key, entries)
+	}()
+	url := fmt.Sprintf("gemini://%s/robots.txt", key)
+	robotsContent, err := ConnectAndGetData(url)
+	if err != nil {
+		logging.LogDebug("robots.txt error %s", err)
+		return []string{}
+	}
+	robotsData, err := processData(robotsContent)
+	if err != nil {
+		logging.LogDebug("robots.txt error %s", err)
+		return []string{}
+	}
+	if robotsData.ResponseCode != 20 {
+		logging.LogDebug("robots.txt error code %d, ignoring", robotsData.ResponseCode)
+		return []string{}
+	}
+	// Some return text/plain, others text/gemini.
+	// According to spec, the first is correct,
+	// however let's be lenient
+	var data string
+	switch {
+	case robotsData.MimeType == "text/plain":
+		data = string(robotsData.Data)
+	case robotsData.MimeType == "text/gemini":
+		data = robotsData.GemText
+	default:
+		return []string{}
+	}
+	entries = ParseRobotsTxt(data, key)
+	return entries
+}
+
+// RobotMatch checks if the snapshot URL matches
+// a robots.txt allow rule.
+func RobotMatch(url URL) bool {
+	key := strings.ToLower(fmt.Sprintf("%s:%d", url.Hostname, url.Port))
+	logging.LogDebug("Checking robots.txt cache for %s", key)
+	var disallowedURLs []string
+	cacheEntries, ok := RobotsCache.Load(key)
+	if !ok {
+		// First time check, populate robot cache
+		disallowedURLs = populateBlacklist(key)
+		logging.LogDebug("Added to robots.txt cache: %v => %v", key, disallowedURLs)
+	} else {
+		disallowedURLs, _ = cacheEntries.([]string)
+	}
+	return isURLblocked(disallowedURLs, url.Full)
+}
+
+func isURLblocked(disallowedURLs []string, input string) bool {
+	for _, url := range disallowedURLs {
+		if strings.HasPrefix(strings.ToLower(input), url) {
+			logging.LogDebug("robots.txt match: %s matches %s", input, url)
+			return true
+		}
+	}
+	return false
+}
--- a/gemini/robots.go
+++ b/gemini/robots.go
@@ -0,0 +1,31 @@
+package gemini
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ParseRobotsTxt takes robots.txt content and a host, and
+// returns a list of full URLs that shouldn't
+// be visited.
+// TODO Also take into account the user agent?
+// Check gemini://geminiprotocol.net/docs/companion/robots.gmi
+func ParseRobotsTxt(content string, host string) []string {
+	var disallowedPaths []string
+	for _, line := range strings.Split(content, "\n") {
+		line = strings.TrimSpace(line)
+		line = strings.ToLower(line)
+		if strings.HasPrefix(line, "disallow:") {
+			parts := strings.SplitN(line, ":", 2)
+			if len(parts) == 2 {
+				path := strings.TrimSpace(parts[1])
+				if path != "" {
+					// Construct full Gemini URL
+					disallowedPaths = append(disallowedPaths,
+						fmt.Sprintf("gemini://%s%s", host, path))
+				}
+			}
+		}
+	}
+	return disallowedPaths
+}
--- a/gemini/robots_test.go
+++ b/gemini/robots_test.go
@@ -0,0 +1,55 @@
+package gemini
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseRobotsTxt(t *testing.T) {
+	t.Parallel()
+	input := `User-agent: *
+Disallow: /cgi-bin/wp.cgi/view
+Disallow: /cgi-bin/wp.cgi/media
+User-agent: googlebot
+Disallow: /admin/`
+
+	expected := []string{
+		"gemini://example.com/cgi-bin/wp.cgi/view",
+		"gemini://example.com/cgi-bin/wp.cgi/media",
+		"gemini://example.com/admin/",
+	}
+
+	result := ParseRobotsTxt(input, "example.com")
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("ParseRobotsTxt() = %v, want %v", result, expected)
+	}
+}
+
+func TestParseRobotsTxtEmpty(t *testing.T) {
+	t.Parallel()
+	input := ``
+
+	result := ParseRobotsTxt(input, "example.com")
+
+	if len(result) != 0 {
+		t.Errorf("ParseRobotsTxt() = %v, want empty []string", result)
+	}
+}
+
+func TestIsURLblocked(t *testing.T) {
+	t.Parallel()
+	disallowedURLs := []string{
+		"gemini://example.com/cgi-bin/wp.cgi/view",
+		"gemini://example.com/cgi-bin/wp.cgi/media",
+		"gemini://example.com/admin/",
+	}
+	url := "gemini://example.com/admin/index.html"
+	if !isURLblocked(disallowedURLs, url) {
+		t.Errorf("Expected %s to be blocked", url)
+	}
+	url = "gemini://example1.com/admin/index.html"
+	if isURLblocked(disallowedURLs, url) {
+		t.Errorf("expected %s to not be blocked", url)
+	}
+}
--- a/gemini/snapshot.go
+++ b/gemini/snapshot.go
@@ -0,0 +1,42 @@
+package gemini
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+
+	"github.com/guregu/null/v5"
+)
+
+type LinkList []URL
+
+func (l *LinkList) Value() (driver.Value, error) {
+	return json.Marshal(l)
+}
+
+func (l *LinkList) Scan(value interface{}) error {
+	if value == nil {
+		*l = nil
+		return nil
+	}
+	b, ok := value.([]byte) // Type assertion! Converts to []byte
+	if !ok {
+		return fmt.Errorf("failed to scan LinkList: expected []byte, got %T", value)
+	}
+	return json.Unmarshal(b, l)
+}
+
+type Snapshot struct {
+	ID           int                  `db:"id" json:"id,omitempty"`
+	URL          URL                  `db:"url" json:"url,omitempty"`
+	Host         string               `db:"host" json:"host,omitempty"`
+	Timestamp    null.Time            `db:"timestamp" json:"timestamp,omitempty"`
+	MimeType     null.String          `db:"mimetype" json:"mimetype,omitempty"`
+	Data         null.Value[[]byte]   `db:"data" json:"data,omitempty"`       // For non text/gemini files.
+	GemText      null.String          `db:"gemtext" json:"gemtext,omitempty"` // For text/gemini files.
+	Header       null.String          `db:"header" json:"header,omitempty"`   // Response header.
+	Links        null.Value[LinkList] `db:"links" json:"links,omitempty"`
+	Lang         null.String          `db:"lang" json:"lang,omitempty"`
+	ResponseCode null.Int             `db:"response_code" json:"code,omitempty"` // Gemini response status code.
+	Error        null.String          `db:"error" json:"error,omitempty"`        // On network errors only
+}
--- a/gemini/worker.go
+++ b/gemini/worker.go
@@ -0,0 +1,368 @@
+package gemini
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"gemini-grc/logging"
+	"gemini-grc/util"
+	"github.com/guregu/null/v5"
+	"github.com/jmoiron/sqlx"
+)
+
+type WorkerStatus struct {
+	id     int
+	status string
+}
+
+func PrintWorkerStatus(totalWorkers int, statusChan chan WorkerStatus) {
+	// Create a slice to store current status of each worker
+	statuses := make([]string, totalWorkers)
+
+	// Initialize empty statuses
+	for i := range statuses {
+		statuses[i] = ""
+	}
+
+	// Initial print
+	var output strings.Builder
+	// \033[H moves the cursor to the top left corner of the screen
+	// (ie, the first column of the first row in the screen).
+	// \033[J clears the part of the screen from the cursor to the end of the screen.
+	output.WriteString("\033[H\033[J") // Clear screen and move cursor to top
+	for i := range statuses {
+		output.WriteString(fmt.Sprintf("[%2d] \n", i))
+	}
+	fmt.Print(output.String())
+
+	// Continuously receive status updates
+	for update := range statusChan {
+		if update.id >= totalWorkers {
+			continue
+		}
+
+		// Update the status
+		statuses[update.id] = update.status
+
+		// Build the complete output string
+		output.Reset()
+		output.WriteString("\033[H\033[J") // Clear screen and move cursor to top
+		for i, status := range statuses {
+			output.WriteString(fmt.Sprintf("[%2d] %.100s\n", i, status))
+		}
+
+		// Print the entire status
+		fmt.Print(output.String())
+	}
+}
+
+var statusChan chan WorkerStatus
+
+func SpawnWorkers(numOfWorkers int, db *sqlx.DB) {
+	logging.LogInfo("Spawning %d workers", numOfWorkers)
+	statusChan = make(chan WorkerStatus, numOfWorkers)
+	go PrintWorkerStatus(numOfWorkers, statusChan)
+
+	for i := range numOfWorkers {
+		go func(i int) {
+			// Jitter to avoid starting everything at the same time
+			time.Sleep(time.Duration(util.SecureRandomInt(10)) * time.Second)
+			for {
+				RunWorkerWithTx(i, db, nil)
+			}
+		}(i)
+	}
+}
+
+func RunWorkerWithTx(workerID int, db *sqlx.DB, url *string) {
+	statusChan <- WorkerStatus{
+		id:     workerID,
+		status: "Starting up",
+	}
+	defer func() {
+		statusChan <- WorkerStatus{
+			id:     workerID,
+			status: "Done",
+		}
+	}()
+	tx, err := db.Beginx()
+	if err != nil {
+		panic(fmt.Sprintf("Failed to begin transaction: %v", err))
+	}
+	runWorker(workerID, tx, url)
+	logging.LogDebug("[%d] Committing transaction", workerID)
+	err = tx.Commit()
+	// On deadlock errors, rollback and return, otherwise panic.
+	if err != nil {
+		logging.LogError("[%d] Failed to commit transaction: %w", workerID, err)
+		if isDeadlockError(err) {
+			logging.LogError("[%d] Deadlock detected. Rolling back", workerID)
+			time.Sleep(time.Duration(10) * time.Second)
+			err := tx.Rollback()
+			if err != nil {
+				panic(fmt.Sprintf("[%d] Failed to roll back transaction: %v", workerID, err))
+			}
+			return
+		}
+		panic(fmt.Sprintf("[%d] Failed to commit transaction: %v", workerID, err))
+	}
+	logging.LogDebug("[%d] Worker done!", workerID)
+}
+
+func runWorker(workerID int, tx *sqlx.Tx, url *string) {
+	var snapshots []Snapshot
+	var err error
+
+	// If not given a specific URL,
+	// get some random ones to visit from DB.
+	if url == nil {
+		statusChan <- WorkerStatus{
+			id:     workerID,
+			status: "Getting snapshots",
+		}
+		snapshots, err = GetSnapshotsToVisit(tx)
+		if err != nil {
+			logging.LogError("[%d] GeminiError retrieving snapshot: %w", workerID, err)
+			panic("This should never happen")
+		} else if len(snapshots) == 0 {
+			logging.LogInfo("[%d] No snapshots to visit.", workerID)
+			time.Sleep(1 * time.Minute)
+			return
+		}
+	} else {
+		snapshotURL, err := ParseURL(*url, "")
+		if err != nil {
+			logging.LogError("Invalid URL given: %s", *url)
+			return
+		}
+		snapshots = []Snapshot{{
+			// UID:       uid.UID(),
+			URL:       *snapshotURL,
+			Host:      snapshotURL.Hostname,
+			Timestamp: null.TimeFrom(time.Now()),
+		}}
+	}
+
+	total := len(snapshots)
+	for i, s := range snapshots {
+		logging.LogDebug("[%d] Snapshot %d/%d: %s", workerID, i+1, total, s.URL.String())
+	}
+	// Start visiting URLs.
+	for i, s := range snapshots {
+		logging.LogDebug("[%d] Starting %d/%d %s", workerID, i+1, total, s.URL.String())
+		// We differentiate between errors:
+		// Unexpected errors are the ones returned from the following function.
+		// If an error is unexpected (which should never happen) we panic.
+		// Expected errors are stored as strings within the snapshot,
+		// so that they can also be stored in DB.
+		err := workOnSnapshot(workerID, tx, &s)
+		if err != nil {
+			logging.LogError("[%d] [%s] Unexpected GeminiError %w", workerID, s.URL.String(), err)
+			util.PrintStackAndPanic(err)
+		}
+		if s.Error.Valid {
+			logging.LogDebug("[%d] Error: %v", workerID, s.Error.String)
+		}
+		logging.LogDebug("[%d] Done %d/%d.", workerID, i+1, total)
+	}
+}
+
+// workOnSnapshot visits a URL and stores the result.
+// unexpected errors are returned.
+// expected errors are stored within the snapshot.
+func workOnSnapshot(workerID int, tx *sqlx.Tx, s *Snapshot) (err error) {
+	if IsBlacklisted(s.URL) {
+		logging.LogDebug("[%d] URL matches Blacklist, ignoring %s", workerID, s.URL.String())
+		return nil
+	}
+
+	// If URL matches a robots.txt disallow line,
+	// add it as an error so next time it won't be
+	// crawled.
+	if RobotMatch(s.URL) {
+		s.Error = null.StringFrom(ErrGeminiRobotsDisallowed.Error())
+		err = UpsertSnapshot(workerID, tx, s)
+		if err != nil {
+			return fmt.Errorf("[%d] %w", workerID, err)
+		}
+		return nil
+	}
+
+	// Resolve IP address via DNS
+	IPs, err := getHostIPAddresses(s.Host)
+	if err != nil {
+		s.Error = null.StringFrom(err.Error())
+		err = UpsertSnapshot(workerID, tx, s)
+		if err != nil {
+			return fmt.Errorf("[%d] %w", workerID, err)
+		}
+		return nil
+	}
+
+	for {
+		count := 1
+		if isAnotherWorkerVisitingHost(workerID, IPs) {
+			logging.LogDebug("[%d] Another worker is visiting this host, waiting", workerID)
+			statusChan <- WorkerStatus{
+				id:     workerID,
+				status: fmt.Sprintf("Waiting to grab lock for host %s", s.Host),
+			}
+			time.Sleep(1 * time.Second) // Avoid flood-retrying
+			count++
+			if count == 3 {
+				return
+			}
+		} else {
+			break
+		}
+	}
+
+	AddIPsToPool(IPs)
+	// After finishing, remove the host IPs from
+	// the connections pool, with a small delay
+	// to avoid potentially hitting the same IP quickly.
+	defer func() {
+		go func() {
+			time.Sleep(1 * time.Second)
+			RemoveIPsFromPool(IPs)
+		}()
+	}()
+
+	statusChan <- WorkerStatus{
+		id:     workerID,
+		status: fmt.Sprintf("Visiting %s", s.URL.String()),
+	}
+
+	err = Visit(s)
+	if err != nil {
+		if !IsKnownError(err) {
+			logging.LogError("[%d] Unknown error visiting %s: %w", workerID, s.URL.String(), err)
+			return err
+		}
+		s.Error = null.StringFrom(err.Error())
+		// Check if error is redirection, and handle it
+		if errors.As(err, new(*GeminiError)) &&
+			err.(*GeminiError).Msg == "redirect" {
+			err = handleRedirection(workerID, tx, s)
+			if err != nil {
+				if IsKnownError(err) {
+					s.Error = null.StringFrom(err.Error())
+				} else {
+					return err
+				}
+			}
+		}
+	}
+	// If this is a gemini page, parse possible links inside
+	if !s.Error.Valid && s.MimeType.Valid && s.MimeType.String == "text/gemini" {
+		links := GetPageLinks(s.URL, s.GemText.String)
+		if len(links) > 0 {
+			logging.LogDebug("[%d] Found %d links", workerID, len(links))
+			s.Links = null.ValueFrom(links)
+			err = storeLinks(tx, s)
+			if err != nil {
+				return err
+			}
+		}
+	} else {
+		logging.LogDebug("[%d] Not text/gemini, so not looking for page links", workerID)
+	}
+
+	err = UpsertSnapshot(workerID, tx, s)
+	logging.LogInfo("[%3d] %2d %s", workerID, s.ResponseCode.ValueOrZero(), s.URL.String())
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func isAnotherWorkerVisitingHost(workerID int, IPs []string) bool {
+	IPPool.Lock.RLock()
+	defer func() {
+		IPPool.Lock.RUnlock()
+	}()
+	logging.LogDebug("[%d] Checking pool for IPs", workerID)
+	for _, ip := range IPs {
+		_, ok := IPPool.IPs[ip]
+		if ok {
+			return true
+		}
+	}
+	return false
+}
+
+func storeLinks(tx *sqlx.Tx, s *Snapshot) error {
+	if s.Links.Valid {
+		var batchSnapshots []*Snapshot
+		for _, link := range s.Links.ValueOrZero() {
+			if shouldPersistURL(&link) {
+				newSnapshot := &Snapshot{
+					URL:       link,
+					Host:      link.Hostname,
+					Timestamp: null.TimeFrom(time.Now()),
+				}
+				batchSnapshots = append(batchSnapshots, newSnapshot)
+			}
+		}
+
+		if len(batchSnapshots) > 0 {
+			err := SaveLinksToDBinBatches(tx, batchSnapshots)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// shouldPersistURL returns true if we
+// should save the URL in the DB.
+// Only gemini:// urls are saved.
+func shouldPersistURL(u *URL) bool {
+	return strings.HasPrefix(u.String(), "gemini://")
+}
+
+// handleRedirection saves redirect URL as new snapshot
+func handleRedirection(workerID int, tx *sqlx.Tx, s *Snapshot) error {
+	newURL, err := extractRedirectTarget(s.URL, s.Error.ValueOrZero())
+	if err != nil {
+		if errors.Is(err, ErrGeminiRedirect) {
+			logging.LogDebug("[%d] %s", workerID, err)
+		}
+		return err
+	}
+	logging.LogDebug("[%d] Page redirects to %s", workerID, newURL)
+	// Insert fresh snapshot with new URL
+	if shouldPersistURL(newURL) {
+		snapshot := &Snapshot{
+			// UID:       uid.UID(),
+			URL:       *newURL,
+			Host:      newURL.Hostname,
+			Timestamp: null.TimeFrom(time.Now()),
+		}
+		logging.LogDebug("[%d] Saving redirection URL %s", workerID, snapshot.URL.String())
+		err = SaveSnapshotIfNew(tx, snapshot)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func GetSnapshotFromURL(tx *sqlx.Tx, url string) ([]Snapshot, error) {
+	query := `
+	SELECT *
+	FROM snapshots
+	WHERE url=$1
+	LIMIT 1
+	`
+	var snapshots []Snapshot
+	err := tx.Select(&snapshots, query, url)
+	if err != nil {
+		return nil, err
+	}
+	return snapshots, nil
+}
--- a/go.mod
+++ b/go.mod
@@ -0,0 +1,24 @@
+module gemini-grc
+
+go 1.23.1
+
+require (
+	github.com/guregu/null/v5 v5.0.0
+	github.com/jackc/pgx/v5 v5.7.1
+	github.com/jmoiron/sqlx v1.4.0
+	github.com/lib/pq v1.10.9
+	github.com/matoous/go-nanoid/v2 v2.1.0
+	github.com/rs/zerolog v1.33.0
+	golang.org/x/text v0.19.0
+)
+
+require (
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	golang.org/x/crypto v0.27.0 // indirect
+	golang.org/x/sync v0.8.0 // indirect
+	golang.org/x/sys v0.25.0 // indirect
+)
--- a/go.sum
+++ b/go.sum
@@ -0,0 +1,59 @@
+filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
+filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-sql-driver/mysql v1.8.1 h1:LedoTUt/eveggdHS9qUFC1EFSa8bU2+1pZjSRpvNJ1Y=
+github.com/go-sql-driver/mysql v1.8.1/go.mod h1:wEBSXgmK//2ZFJyE+qWnIsVGmvmEKlqwuVSjsCm7DZg=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/guregu/null/v5 v5.0.0 h1:PRxjqyOekS11W+w/7Vfz6jgJE/BCwELWtgvOJzddimw=
+github.com/guregu/null/v5 v5.0.0/go.mod h1:SjupzNy+sCPtwQTKWhUCqjhVCO69hpsl2QsZrWHjlwU=
+github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
+github.com/jackc/pgpassfile v1.0.0/go.mod h1:CEx0iS5ambNFdcRtxPj5JhEz+xB6uRky5eyVu/W2HEg=
+github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 h1:iCEnooe7UlwOQYpKFhBabPMi4aNAfoODPEFNiAnClxo=
+github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761/go.mod h1:5TJZWKEWniPve33vlWYSoGYefn3gLQRzjfDlhSJ9ZKM=
+github.com/jackc/pgx/v5 v5.7.1 h1:x7SYsPBYDkHDksogeSmZZ5xzThcTgRz++I5E+ePFUcs=
+github.com/jackc/pgx/v5 v5.7.1/go.mod h1:e7O26IywZZ+naJtWWos6i6fvWK+29etgITqrqHLfoZA=
+github.com/jackc/puddle/v2 v2.2.2 h1:PR8nw+E/1w0GLuRFSmiioY6UooMp6KJv0/61nB7icHo=
+github.com/jackc/puddle/v2 v2.2.2/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/jmoiron/sqlx v1.4.0 h1:1PLqN7S1UYp5t4SrVVnt4nUVNemrDAtxlulVe+Qgm3o=
+github.com/jmoiron/sqlx v1.4.0/go.mod h1:ZrZ7UsYB/weZdl2Bxg6jCRO9c3YHl8r3ahlKmRT4JLY=
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
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--- a/logging/logging.go
+++ b/logging/logging.go
@@ -0,0 +1,23 @@
+package logging
+
+import (
+	"fmt"
+
+	zlog "github.com/rs/zerolog/log"
+)
+
+func LogDebug(format string, args ...interface{}) {
+	zlog.Debug().Msg(fmt.Sprintf(format, args...))
+}
+
+func LogInfo(format string, args ...interface{}) {
+	zlog.Info().Msg(fmt.Sprintf(format, args...))
+}
+
+func LogWarn(format string, args ...interface{}) {
+	zlog.Warn().Msg(fmt.Sprintf(format, args...))
+}
+
+func LogError(format string, args ...interface{}) {
+	zlog.Error().Err(fmt.Errorf(format, args...)).Msg("")
+}
--- a/main.go
+++ b/main.go
@@ -0,0 +1,60 @@
+package main
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+
+	"gemini-grc/config"
+	"gemini-grc/gemini"
+	"gemini-grc/logging"
+	"github.com/jmoiron/sqlx"
+	"github.com/rs/zerolog"
+	zlog "github.com/rs/zerolog/log"
+)
+
+func main() {
+	config.CONFIG = *config.GetConfig()
+	zerolog.TimeFieldFormat = zerolog.TimeFormatUnix
+	zerolog.SetGlobalLevel(config.CONFIG.LogLevel)
+	zlog.Logger = zlog.Output(zerolog.ConsoleWriter{Out: os.Stderr, TimeFormat: "[2006-01-02 15:04:05]"})
+	if err := runApp(); err != nil {
+		logging.LogError("Application error: %w", err)
+		os.Exit(1)
+	}
+}
+
+func runApp() error {
+	logging.LogInfo("Starting up. Press Ctrl+C to exit")
+	signals := make(chan os.Signal, 1)
+	signal.Notify(signals, syscall.SIGINT, syscall.SIGTERM)
+
+	db := gemini.ConnectToDB()
+
+	// !!! DANGER !!!
+	// Removes all rows and adds some seed URLs.
+	// populateDB(db)
+
+	defer func(db *sqlx.DB) {
+		err := db.Close()
+		if err != nil {
+			// TODO properly log & hangle error
+			panic(err)
+		}
+	}(db)
+
+	gemini.LoadBlacklist()
+
+	// If there's an argument, visit this
+	// URL only and don't spawn other workers
+	if len(os.Args) > 1 {
+		url := os.Args[1]
+		go gemini.RunWorkerWithTx(0, db, &url)
+	} else {
+		go gemini.SpawnWorkers(config.CONFIG.NumOfWorkers, db)
+	}
+
+	<-signals
+	logging.LogWarn("Received SIGINT or SIGTERM signal, exiting")
+	return nil
+}
--- a/uid/uid.go
+++ b/uid/uid.go
@@ -0,0 +1,14 @@
+package uid
+
+import (
+	nanoid "github.com/matoous/go-nanoid/v2"
+)
+
+func UID() string {
+	// No 'o','O' and 'l'
+	id, err := nanoid.Generate("abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ0123456789", 20)
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
--- a/util/util.go
+++ b/util/util.go
@@ -0,0 +1,36 @@
+package util
+
+import (
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"math/big"
+	"runtime/debug"
+)
+
+func PrintStackAndPanic(err error) {
+	fmt.Printf("Error %s Stack trace:\n%s", err, debug.Stack())
+	panic("PANIC")
+}
+
+// SecureRandomInt returns a cryptographically secure random integer in the range [0,max).
+// Panics if max <= 0 or if there's an error reading from the system's secure
+// random number generator.
+func SecureRandomInt(max int) int {
+	// Convert max to *big.Int for crypto/rand operations
+	maxBig := big.NewInt(int64(max))
+
+	// Generate random number
+	n, err := rand.Int(rand.Reader, maxBig)
+	if err != nil {
+		PrintStackAndPanic(fmt.Errorf("could not generate a random integer between 0 and %d", max))
+	}
+
+	// Convert back to int
+	return int(n.Int64())
+}
+
+func PrettyJson(data string) string {
+	marshalled, _ := json.MarshalIndent(data, "", "  ")
+	return fmt.Sprintf("%s\n", marshalled)
+}