Fix go vet: non-constant format string in robots.go

[Copilot]

go vet was failing because fmt.Fprintf(ctx, paths.String()) passes a variable as the format string, which is both a vet warning and a latent correctness issue if the string ever contains % characters.

Changes

• internal/http/robots.go: Replace fmt.Fprintf with ctx.WriteString — no formatting is happening here, so writing directly is both correct and more efficient. Removed the now-unused fmt import.

// before
if _, err := fmt.Fprintf(ctx, paths.String()); err != nil {

// after
if _, err := ctx.WriteString(paths.String()); err != nil {

Original prompt

Fix go vet Warning: Non-Constant Format String

Problem

The build is failing with a go vet error:

# github.com/bdk38/HellPot/internal/http
internal/http/robots.go:30:32: non-constant format string in call to fmt.Fprintf
make: *** [Makefile:5: check] Error 1

Root Cause

In internal/http/robots.go line 30, we're using fmt.Fprintf with a variable string:

if _, err := fmt.Fprintf(ctx, paths.String()); err != nil {
    slog.Error().Err(err).Msg("SERVE_ROBOTS_ERROR")
}

go vet correctly identifies this as a potential security issue because paths.String() is not a constant format string. If the string contains format specifiers like %s or %d, it could cause unexpected behavior or security vulnerabilities.

Solution

Since we're not actually doing any formatting (just writing a plain string), we should use ctx.WriteString() directly instead of fmt.Fprintf.

Change Required

In file internal/http/robots.go, line 30:

OLD CODE:

if _, err := fmt.Fprintf(ctx, paths.String()); err != nil {
    slog.Error().Err(err).Msg("SERVE_ROBOTS_ERROR")
}

NEW CODE:

if _, err := ctx.WriteString(paths.String()); err != nil {
    slog.Error().Err(err).Msg("SERVE_ROBOTS_ERROR")
}

Why This Fix is Better

1. ✅ Fixes the go vet warning - No more non-constant format string issue
2. ✅ More efficient - Direct write without format parsing overhead
3. ✅ More correct - We're not formatting, just writing a string
4. ✅ Same behavior - ctx.WriteString() returns the same (int, error) signature

Alternative Fix (if needed)

If for some reason ctx.WriteString() doesn't work, we could use fmt.Fprint() (without the f):

if _, err := fmt.Fprint(ctx, paths.String()); err != nil {

But ctx.WriteString() is the preferred approach since we're working with fasthttp's RequestCtx.

Testing

After the fix:

1. Run make - should pass without errors
2. Run go vet ./... - should pass without warnings
3. Test robots.txt endpoint - should work as before

Impact

• ✅ Low risk - Simple function replacement
• ✅ Same behavior - Just changes how we write the string
• ✅ Allows build to succeed

This pull request was created from Copilot chat.

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