golang/go · error

invalid format: invalid header line

Error message

invalid format: invalid header line

What it means

Raised inside parseUserAuth for each header line. A header line must (1) contain a `: ` separator (strings.Cut succeeds), (2) have a name passing validHeaderFieldName, and (3) have a value (after TrimSpace) passing validHeaderFieldValue. Failure of any check aborts parsing.

Source

Thrown at src/cmd/go/internal/auth/userauth.go:87

			if err != nil {
				return nil, fmt.Errorf("could not parse URL %s: %v", line, err)
			}
			urls = append(urls, u.String())
		}
		// Parse Headers second.
		header := make(http.Header)
		for {
			line, data, ok = strings.Cut(data, "\n")
			if !ok {
				return nil, fmt.Errorf("invalid format: missing empty line after headers")
			}
			if line == "" {
				break
			}
			name, value, ok := strings.Cut(line, ": ")
			value = strings.TrimSpace(value)
			if !ok || !validHeaderFieldName(name) || !validHeaderFieldValue(value) {
				return nil, fmt.Errorf("invalid format: invalid header line")
			}
			header.Add(name, value)
		}
		maps.Copy(credentials, mapHeadersToPrefixes(urls, header))
	}
	return credentials, nil
}

// mapHeadersToPrefixes returns a mapping of prefix → http.Header without
// the leading "https://".
func mapHeadersToPrefixes(prefixes []string, header http.Header) map[string]http.Header {
	prefixToHeaders := make(map[string]http.Header, len(prefixes))
	for _, p := range prefixes {
		p = strings.TrimPrefix(p, "https://")
		prefixToHeaders[p] = header.Clone() // Clone the header to avoid sharing
	}
	return prefixToHeaders
}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Format headers as `Name: value` (a colon followed by exactly one space).
2. Use only RFC 7230 token characters for header names.
3. Keep header values on a single line with no control characters.
4. Strip any trailing carriage return from CRLF input before emitting.

Example fix

// before
Authorization:Bearer x
// after
Authorization: Bearer x

// Validate a header line matches the expected shape.
func validHeaderLine(line string) error {
    name, value, ok := strings.Cut(line, ": ")
    if !ok || !validHeaderFieldName(name) || !validHeaderFieldValue(strings.TrimSpace(value)) {
        return errors.New("invalid header line: expected 'Name: value'")
    }
    return nil
}

When it happens

Trigger: A header line without `: ` (e.g. `Authorization:Bearer x` with no space, or a bare token), a name with invalid token characters or whitespace, or a value containing control characters/newlines.

Common situations: Using a colon without the required space; header names containing spaces or non-token characters; header values with embedded newlines; CRLF endings leaving a stray CR.

Related errors

• cannot parse output of GOAUTH command %s: %v
• invalid format: missing empty line after URLs
• could not parse URL %s: %v
• invalid format: missing empty line after headers
• 'git credential fill' failed for url=%s, could not parse url

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/612f4c8ca75a8dbe. Report an issue: GitHub.