gemserve/server/server.go

package server

import (
	"bytes"
	"context"
	"crypto/tls"
	"errors"
	"fmt"
	"io"
	"net"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

	"gemserve/lib/apperrors"
	"gemserve/lib/logging"

	"gemserve/config"
	"gemserve/gemini"

	"github.com/gabriel-vasile/mimetype"
)

type contextKey string

const CtxConnIdKey contextKey = "connId"

type ServerConfig interface {
	DirIndexingEnabled() bool
	RootPath() string
}

func CloseConnection(conn *tls.Conn) error {
	err := conn.CloseWrite()
	if err != nil {
		return apperrors.NewNetworkError(fmt.Errorf("failed to close TLS connection: %w", err))
	}
	err = conn.Close()
	if err != nil {
		return apperrors.NewNetworkError(fmt.Errorf("failed to close connection: %w", err))
	}
	return nil
}

func checkRequestURL(url *gemini.URL) error {
	if !utf8.ValidString(url.String()) {
		return apperrors.NewGeminiError(fmt.Errorf("invalid URL"), gemini.StatusBadRequest)
	}

	if url.Protocol != "gemini" {
		return apperrors.NewGeminiError(fmt.Errorf("invalid URL"), gemini.StatusProxyRequestRefused)
	}

	_, portStr, err := net.SplitHostPort(config.CONFIG.ListenAddr)
	if err != nil {
		return apperrors.NewGeminiError(fmt.Errorf("failed to parse server listen address: %w", err), gemini.StatusBadRequest)
	}
	listenPort, err := strconv.Atoi(portStr)
	if err != nil {
		return apperrors.NewGeminiError(fmt.Errorf("invalid server listen port: %w", err), gemini.StatusBadRequest)
	}
	if url.Port != listenPort {
		return apperrors.NewGeminiError(fmt.Errorf("port mismatch"), gemini.StatusProxyRequestRefused)
	}
	return nil
}

func GenerateResponse(ctx context.Context, conn *tls.Conn, input string) ([]byte, error) {
	logger := logging.FromContext(ctx)
	connId := ctx.Value(CtxConnIdKey).(string)

	if err := ctx.Err(); err != nil {
		return nil, err
	}

	trimmedInput := strings.TrimSpace(input)
	// url will have a cleaned and normalized path after this
	url, err := gemini.ParseURL(trimmedInput, "", true)
	if err != nil {
		return nil, apperrors.NewGeminiError(fmt.Errorf("failed to parse URL: %w", err), gemini.StatusBadRequest)
	}
	logger.Debug("normalized URL path", "id", connId, "remoteAddr", conn.RemoteAddr(), "path", url.Path)

	err = checkRequestURL(url)
	if err != nil {
		return nil, err
	}

	serverRootPath := config.CONFIG.RootPath
	localPath, err := calculateLocalPath(url.Path, serverRootPath)
	if err != nil {
		return nil, apperrors.NewGeminiError(err, gemini.StatusBadRequest)
	}
	logger.Debug("request path", "id", connId, "remoteAddr", conn.RemoteAddr(), "local path", localPath)

	// Get file/directory information
	info, err := os.Stat(localPath)
	if err != nil {
		return nil, apperrors.NewGeminiError(fmt.Errorf("failed to access path: %w", err), gemini.StatusNotFound)
	}

	// Handle directory.
	if info.IsDir() {
		return generateResponseDir(ctx, localPath)
	}
	return generateResponseFile(ctx, localPath)
}

func generateResponseFile(ctx context.Context, localPath string) ([]byte, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	data, err := os.ReadFile(localPath)
	if err != nil {
		return nil, apperrors.NewGeminiError(fmt.Errorf("failed to access path: %w", err), gemini.StatusNotFound)
	}

	var mimeType string
	if path.Ext(localPath) == ".gmi" {
		mimeType = "text/gemini"
	} else {
		mimeType = mimetype.Detect(data).String()
	}
	headerBytes := []byte(fmt.Sprintf("%d %s; lang=en\r\n", gemini.StatusSuccess, mimeType))
	response := append(headerBytes, data...)
	return response, nil
}

func generateResponseDir(ctx context.Context, localPath string) (output []byte, err error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	entries, err := os.ReadDir(localPath)
	if err != nil {
		return nil, apperrors.NewGeminiError(fmt.Errorf("failed to access path: %w", err), gemini.StatusNotFound)
	}

	if config.CONFIG.DirIndexingEnabled {
		var contents []string
		contents = append(contents, "Directory index:\n\n")
		contents = append(contents, "=> ../\n")
		for _, entry := range entries {
			// URL-encode entry names for safety
			safeName := url.PathEscape(entry.Name())
			if entry.IsDir() {
				contents = append(contents, fmt.Sprintf("=> %s/\n", safeName))
			} else {
				contents = append(contents, fmt.Sprintf("=> %s\n", safeName))
			}
		}
		data := []byte(strings.Join(contents, ""))
		headerBytes := []byte(fmt.Sprintf("%d text/gemini; lang=en\r\n", gemini.StatusSuccess))
		response := append(headerBytes, data...)
		return response, nil
	}
	filePath := filepath.Join(localPath, "index.gmi")
	return generateResponseFile(ctx, filePath)
}

func calculateLocalPath(input string, basePath string) (string, error) {
	// Check for invalid characters early
	if strings.ContainsAny(input, "\\") {
		return "", apperrors.NewGeminiError(fmt.Errorf("invalid characters in path: %s", input), gemini.StatusBadRequest)
	}

	// If IsLocal(path) returns true, then Join(base, path)
	// will always produce a path contained within base and
	// Clean(path) will always produce an unrooted path with
	// no ".." path elements.
	filePath := input
	filePath = strings.TrimPrefix(filePath, "/")
	if filePath == "" {
		filePath = "."
	}
	filePath = strings.TrimSuffix(filePath, "/")

	localPath, err := filepath.Localize(filePath)
	if err != nil || !filepath.IsLocal(localPath) {
		return "", apperrors.NewGeminiError(fmt.Errorf("could not construct local path from %s: %s", input, err), gemini.StatusBadRequest)
	}

	filePath = path.Join(basePath, localPath)
	return filePath, nil
}

func HandleConnection(ctx context.Context, conn *tls.Conn) (err error) {
	logger := logging.FromContext(ctx)
	start := time.Now()
	var outputBytes []byte

	// Set connection deadline based on context
	if deadline, ok := ctx.Deadline(); ok {
		_ = conn.SetDeadline(deadline)
	}

	defer func(conn *tls.Conn) {
		end := time.Now()
		tookMs := end.Sub(start).Milliseconds()
		var responseHeader string

		// On non-errors, just log response and close connection.
		if err == nil {
			// Log non-erroneous responses
			if i := bytes.Index(outputBytes, []byte{'\r'}); i >= 0 {
				responseHeader = string(outputBytes[:i])
			}
			logger.Debug("Response", "responseHeader", responseHeader, "ms", tookMs)
			_ = CloseConnection(conn)
			return
		}

		// Handle context cancellation/timeout
		if errors.Is(err, context.DeadlineExceeded) {
			logger.Info("Connection timeout", "ms", tookMs)
			responseHeader = fmt.Sprintf("%d Request timeout", gemini.StatusCGIError)
			_, _ = conn.Write([]byte(responseHeader + "\r\n"))
			_ = CloseConnection(conn)
			return
		}
		if errors.Is(err, context.Canceled) {
			logger.Info("Connection cancelled", "ms", tookMs)
			_ = CloseConnection(conn)
			return
		}

		var code int
		var responseMsg string
		if apperrors.IsFatal(err) {
			_ = CloseConnection(conn)
			return
		}
		if apperrors.IsGeminiError(err) {
			code = apperrors.GetStatusCode(err)
			responseMsg = "server error"
		} else {
			code = gemini.StatusPermanentFailure
			responseMsg = "server error"
		}
		responseHeader = fmt.Sprintf("%d %s", code, responseMsg)
		_, _ = conn.Write([]byte(responseHeader + "\r\n"))
		_ = CloseConnection(conn)
	}(conn)

	// Check context before starting
	if err := ctx.Err(); err != nil {
		return err
	}

	// Gemini is supposed to have a 1kb limit
	// on input requests.
	buffer := make([]byte, 1025)

	n, err := conn.Read(buffer)
	if err != nil && err != io.EOF {
		return apperrors.NewGeminiError(fmt.Errorf("failed to read connection data: %w", err), gemini.StatusBadRequest)
	}
	if n == 0 {
		return apperrors.NewGeminiError(fmt.Errorf("client did not send data"), gemini.StatusBadRequest)
	}
	if n > 1024 {
		return apperrors.NewGeminiError(fmt.Errorf("client request size %d > 1024 bytes", n), gemini.StatusBadRequest)
	}

	// Check context after read
	if err := ctx.Err(); err != nil {
		return err
	}

	dataBytes := buffer[:n]
	dataString := string(dataBytes)

	logger.Info("Request", "data", strings.TrimSpace(dataString), "size", len(dataBytes))
	outputBytes, err = GenerateResponse(ctx, conn, dataString)
	if len(outputBytes) > config.CONFIG.MaxResponseSize {
		return apperrors.NewGeminiError(fmt.Errorf("max response size reached"), gemini.StatusTemporaryFailure)
	}
	if err != nil {
		return err
	}

	// Check context before write
	if err := ctx.Err(); err != nil {
		return err
	}

	_, err = conn.Write(outputBytes)
	if err != nil {
		return err
	}
	return nil
}