empty string is not a valid method binary logging config

Error message

empty string is not a valid method binary logging config

What it means

Returned by fillMethodLoggerWithConfigString when a single comma-separated segment of the binary-log config string is empty. NewLoggerFromConfigString splits the config by commas and processes each part; an empty part (e.g., from a trailing comma or double comma) is not a valid method pattern. The empty config string itself ("") returns a nil logger and does not reach this function, so this error specifically fires for empty segments within a non-empty config.

Source

Thrown at internal/binarylog/env_config.go:65

		return nil
	}
	l := newEmptyLogger()
	methods := strings.Split(s, ",")
	for _, method := range methods {
		if err := l.fillMethodLoggerWithConfigString(method); err != nil {
			grpclogLogger.Warningf("failed to parse binary log config: %v", err)
			return nil
		}
	}
	return l
}

// fillMethodLoggerWithConfigString parses config, creates TruncatingMethodLogger and adds
// it to the right map in the logger.
func (l *logger) fillMethodLoggerWithConfigString(config string) error {
	// "" is invalid.
	if config == "" {
		return errors.New("empty string is not a valid method binary logging config")
	}

	// "-service/method", blacklist, no * or {} allowed.
	if config[0] == '-' {
		s, m, suffix, err := parseMethodConfigAndSuffix(config[1:])
		if err != nil {
			return fmt.Errorf("invalid config: %q, %v", config, err)
		}
		if m == "*" {
			return fmt.Errorf("invalid config: %q, %v", config, "* not allowed in blacklist config")
		}
		if suffix != "" {
			return fmt.Errorf("invalid config: %q, %v", config, "header/message limit not allowed in blacklist config")
		}
		if err := l.setBlacklist(s + "/" + m); err != nil {
			return fmt.Errorf("invalid config: %v", err)
		}
		return nil

View on GitHub (pinned to 0c51461d27)

Solutions

Remove trailing or duplicate commas from the binary log filter string.
Validate the config string before applying it: split by comma and ensure no empty segments.
Check gRPC warning logs ('failed to parse binary log config') if binary logging appears inactive.

Example fix

# before
GRPC_BINARY_LOG_FILTER="Foo/*," # trailing comma → error, logging disabled
# after
GRPC_BINARY_LOG_FILTER="Foo/*" # valid

Defensive patterns

Strategy: validation

Validate before calling

// Validate the binary log filter string before applying:
for _, part := range strings.Split(filter, ",") {
    if part == "" {
        return fmt.Errorf("binary log filter has an empty segment (check trailing/double commas): %q", filter)
    }
}

Prevention

Avoid trailing and double commas in GRPC_BINARY_LOG_FILTER.
Validate filter strings before setting the env var.
Check gRPC warning logs ('failed to parse binary log config') if logging is unexpectedly disabled.

When it happens

Trigger: Setting GRPC_BINARY_LOG_FILTER to a value with a trailing comma (e.g., Foo/*,) or double comma (e.g., Foo/*,,Foo/Bar), or calling NewLoggerFromConfigString with such a string. Each empty segment triggers the error, which causes the entire logger to be discarded (returns nil).

Common situations: Operators edit the GRPC_BINARY_LOG_FILTER env var and accidentally introduce stray commas. Config-management tooling concatenates filter segments with commas and produces a trailing comma. The resulting nil logger silently disables binary logging, which is hard to notice without checking logs for the warning.

Related errors

AI-assisted analysis of grpc/grpc-go@0c51461d27 (2026-08-11). Data as JSON: /api/errors/6af754fb70d50473. Report an issue: GitHub.