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NOTES.md
13
NOTES.md
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# Notes
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Avoiding endless loops while crawling
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- Make sure we follow robots.txt
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- Announce our own agent so people can block us in their robots.txt
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- Put a limit on number of pages per host, and notify on limit reach.
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- Put a limit on the number of redirects (not needed?)
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Heuristics:
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- Do _not_ parse links from pages that have '/git/' or '/cgi/' or '/cgi-bin/' in their URLs.
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- Have a list of "whitelisted" hosts/urls that we visit in regular intervals.
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@@ -22,8 +22,12 @@ This crawler uses `InsecureSkipVerify: true` in TLS configuration to accept all
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## How to run
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## How to run
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Spin up a PostgreSQL, check `misc/sql/initdb.sql` to create the tables and start the crawler.
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```shell
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All configuration is done via command-line flags.
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make build
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./dist/crawler --help
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```
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Check `misc/sql/initdb.sql` to create the PostgreSQL tables.
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## Configuration
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## Configuration
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38
TODO.md
38
TODO.md
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# TODO
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## Outstanding Issues
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### 1. Ctrl+C Signal Handling Issue
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**Problem**: The crawler sometimes doesn't exit properly when Ctrl+C is pressed.
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**Root Cause**: The main thread gets stuck in blocking operations before it can check for signals:
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- Database operations in the polling loop (`cmd/crawler/crawler.go:239-250`)
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- Job queueing when channel is full (`jobs <- url` can block if workers are slow)
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- Long-running database transactions
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**Location**: `cmd/crawler/crawler.go` - main polling loop starting at line 233
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**Solution**: Add signal/context checking to blocking operations:
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- Use cancellable context instead of `context.Background()` for database operations
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- Make job queueing non-blocking or context-aware
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- Add timeout/cancellation to database operations
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### 2. fetchSnapshotsFromHistory() Doesn't Work with --skip-identical-content=true
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**Problem**: When `--skip-identical-content=true` (default), URLs with unchanged content get continuously re-queued.
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**Root Cause**: The function tracks when content last changed, not when URLs were last crawled:
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- Identical content → no new snapshot created
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- Query finds old snapshot timestamp → re-queues URL
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- Creates infinite loop of re-crawling unchanged content
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**Location**: `cmd/crawler/crawler.go:388-470` - `fetchSnapshotsFromHistory()` function
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**Solution Options**:
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1. Add `last_crawled` timestamp to URLs table
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2. Create separate `crawl_attempts` table
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3. Always create snapshot entries (even for duplicates) but mark them as such
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4. Modify logic to work with existing schema constraints
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**Current Status**: Function assumes `SkipIdenticalContent=false` per original comment at line 391.
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