gofiber/fiber · error

failed to read: %w

Error message

failed to read: %w

What it means

Returned by the internal readContent helper when rf.ReadFrom(f) fails after the file was successfully opened. readContent streams the file into an io.ReaderFrom (e.g. a bytes.Buffer for template rendering). The error wraps the underlying read error such as an I/O failure mid-read.

Source

Thrown at helpers.go:164

	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 9a4c7e57fe)

Solutions

1. Inspect the wrapped error for the specific I/O cause.
2. Ensure template files are not being hot-swapped while the server reads them.
3. For network filesystems, add retry logic or cache templates in memory at startup.
4. Preload and validate templates at boot rather than reading them per-request.

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

When it happens

Trigger: Calling c.Render() whose underlying readContent opens the template file successfully but the ReadFrom call errors — e.g. the file is truncated on disk, a concurrent process truncates it mid-read, or a disk I/O error occurs.

Common situations: File truncated or replaced atomically during read, disk sector errors, NFS/network filesystem hiccups, or the file being a special device that errors on read.

Related errors

• failed to open: %w
• fiber: failed to reload views: %w
• file: failed to open file: %q: %w
• failed to render: %w
• logtemplate: unknown tag

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/1bdfd334862e8958.json. Report an issue: GitHub.