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fix(envd): malformed error message %!w(<nil>) when watch path is not a directory

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
86/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
go
Domain
backend, testing-qa

Research direction

Start in packages/envd/internal/services/filesystem/watch.go and watch_sync.go, focusing on the non-directory checks described in the issue. Add or update the TestCreateWatcher_NotADirectory test in watch_test.go, then run the filesystem service tests. Done means both watcher paths return a clean invalid-argument message without %!w when given a non-directory.

Written by the indexing model from the issue text.

Description

Problem

In packages/envd/internal/services/filesystem/watch.go and watch_sync.go, the guest agent's filesystem service checks whether a path targeted for watching is a valid directory:

info, err := os.Stat(watchPath)
if err != nil {
    if os.IsNotExist(err) {
        return connect.NewError(connect.CodeNotFound, fmt.Errorf("path %s not found: %w", watchPath, err))
    }
    return connect.NewError(connect.CodeInternal, fmt.Errorf("error statting path %s: %w", watchPath, err))
}

if !info.IsDir() {
    return connect.NewError(connect.CodeInvalidArgument, fmt.Errorf("path %s not a directory: %w", watchPath, err))
}

When os.Stat(watchPath) succeeds for a non-directory (e.g. a regular file, FIFO, or socket), err is nil. Because err is nil, Go's fmt.Errorf %w verb produces the malformed string %!w(<nil>).

Clients and Connect-RPC error logs receive corrupted messages such as:

path /home/user/file.txt not a directory: %!w(<nil>)

Root Cause

fmt.Errorf was invoked with the error-wrapping format verb %w against a nil error reference instead of formatting a clean static error message:

Location Current Formatting Output for regular file /tmp/test.txt Expected Formatting
watch.go:L44 fmt.Errorf("path %s not a directory: %w", watchPath, err) "path /tmp/test.txt not a directory: %!w(<nil>)" "path /tmp/test.txt is not a directory"
watch_sync.go:L171 fmt.Errorf("path %s not a directory: %w", watchPath, err) "path /tmp/test.txt not a directory: %!w(<nil>)" "path /tmp/test.txt is not a directory"

This formatting also aligns with other filesystem endpoints in packages/envd/internal/services/filesystem/dir.go:L131 ("path is not a directory: %s").

Reproduction Steps

  1. Start envd.
  2. Create a normal file /home/user/test.txt.
  3. Call CreateWatcher on /home/user/test.txt.
  4. Observed Error: connect.CodeInvalidArgument with message "path /home/user/test.txt not a directory: %!w(<nil>)".
  5. Expected Error: connect.CodeInvalidArgument with message "path /home/user/test.txt is not a directory".

Technical Context

  • Files affected: packages/envd/internal/services/filesystem/watch.go, packages/envd/internal/services/filesystem/watch_sync.go
  • Subsystem: Guest Agent (envd) / Filesystem Service
  • Impact: Low (Error cleanliness, log readability, and API response quality)

Proposed Changes

# Change File(s) Affected Complexity
1 Replace fmt.Errorf("path %s not a directory: %w", watchPath, err) with fmt.Errorf("path %s is not a directory", watchPath) watch.go, watch_sync.go Trivial
2 Add unit test TestCreateWatcher_NotADirectory asserting clean message without %!w watch_test.go Low
Dominant language
Go
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