gofiber/fiber · error

failed to read

Error message

failed to read: %w

What it means

Returned by readContent when rf.ReadFrom fails after the file was successfully opened. Wraps the underlying read error: 'failed to read: <err>'. Used by Ctx.Render's raw-template path (res.go:938). Distinct from the open failure: here the open succeeded but reading bytes errored.

Solutions

1. Log the wrapped underlying error to identify whether it is a transient I/O or a media failure.
2. Embed templates (go:embed) so reads come from the binary, eliminating filesystem I/O errors entirely.
3. If reading from a network mount, add retry-on-read-error logic or fall back to a cached copy.
4. Validate file integrity (size, checksum) after deploy so truncated templates are caught before serving.

Example fix

// before: templates read from disk at request time
return c.Render("templates/home.tmpl", bind)

// after: templates embedded into the binary; no runtime read
//go:embed templates/*
var tmplFS embed.FS

null

null

if err := c.Render(name, bind); err != nil {
    if strings.Contains(err.Error(), "failed to read") {
        log.Errorf("template read error for %s: %v", name, err)
        return fiber.NewError(fiber.StatusInternalServerError)
    }
    return err
}

When it happens

Trigger: An I/O error occurs while reading the template file: the file is truncated mid-read, the storage is interrupted, the file is a special device that errors on read, or (rarely) the filesystem fails after open.

Common situations: Corrupted template file on disk, network filesystem hiccup after open, concurrent truncation of the file mid-read, or a path that resolves to a non-regular file.

Related errors

• failed to open
• favicon: read limited
• %w: %q: %w
• cannot chmod %#o for
• ErrUnknownTag

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/1bdfd334862e8958. Report an issue: GitHub.

Appendix: source

Thrown at helpers.go:167

	return cfg
}

// readContent opens a named file and read content from it
func readContent(rf io.ReaderFrom, name string) (int64, error) {
	// Read file
	f, err := os.Open(filepath.Clean(name))
	if err != nil {
		return 0, fmt.Errorf("failed to open: %w", err)
	}
	defer func() {
		if err = f.Close(); err != nil {
			log.Errorf("Error closing file: %s", err)
		}
	}()
	n, readErr := rf.ReadFrom(f)
	if readErr != nil {
		return n, fmt.Errorf("failed to read: %w", readErr)
	}
	return n, nil
}

// quoteEscapeMask marks the lanes of w holding bytes quoteRawString must
// escape: '\\', '"', any C0 control (including HTAB), or DEL. Lanes >= 0x80
// are never marked; non-ASCII bytes pass through verbatim. This is
// utils.IndexNonQuotable's RFC 9110 set widened by HTAB, which the RFC
// permits as qdtext but this function has always percent-encoded.
func quoteEscapeMask(w uint64) uint64 {
	return swar.MatchByteMask(w, '\\') | swar.MatchByteMask(w, '"') |
		swar.MatchRangeMask(w, 0x00, 0x1f) | swar.MatchByteMask(w, 0x7f)
}

// indexQuoteEscape returns the index of the first byte quoteEscapeMask
// matches, or -1 if raw needs no escaping. It scans eight bytes at a time,
// finishing inputs of 8+ bytes with one overlapping word; shorter inputs
// are checked byte-wise.

View on GitHub (pinned to a105acad6c)