What causes "environment variable name '%s' exceeds maximum length" in Tencent/WeKnora?

Shorten the variable name to a conventional short identifier (<=256 chars, typically <64)

environment variable name '%s' exceeds maximum length

Error message

environment variable name '%s' exceeds maximum length

What it means

ValidateStdioEnvVars limits environment-variable NAME length to 256 characters. Overly long names are rejected to prevent abuse and platform limitations. Note the message logs only the first 50 characters (SanitizeForLog(key[:50])).

Source

Thrown at internal/utils/security.go:604

// ValidateStdioEnvVars validates environment variables for MCP stdio transport
// Returns an error if any env var name or value is dangerous
func ValidateStdioEnvVars(envVars map[string]string) error {
	if len(envVars) == 0 {
		return nil
	}

	for key, value := range envVars {
		// Check key against dangerous patterns
		for _, pattern := range DangerousEnvVarPatterns {
			if pattern.MatchString(key) {
				return fmt.Errorf("environment variable '%s' is not allowed for security reasons", key)
			}
		}

		// Check key length
		if len(key) > 256 {
			return fmt.Errorf("environment variable name '%s' exceeds maximum length", SanitizeForLog(key[:50]))
		}

		// Check value length
		if len(value) > 4096 {
			return fmt.Errorf("environment variable '%s' value exceeds maximum length", key)
		}

		// Check for null bytes in value
		if strings.Contains(value, "\x00") {
			return fmt.Errorf("environment variable '%s' value contains null bytes", key)
		}

		// Check value for shell injection patterns
		for _, pattern := range DangerousArgPatterns {
			if pattern.MatchString(value) {
				return fmt.Errorf("environment variable '%s' value contains potentially dangerous pattern", key)
			}
		}

View on GitHub (pinned to 988cbb0330)

Solutions

Shorten the variable name to a conventional short identifier (<=256 chars, typically <64)
Check whether a value was accidentally placed as a key (key containing '=' or very long text) and restructure the map
Validate env keys against ^[A-Za-z_][A-Za-z0-9_]*$ before building the config

Example fix

// before
"env": {"MY_VERY_LONGGenerated_KEY_NAME_that_goes_on_and_on_for_300_chars...": "v"}
// after
"env": {"MY_KEY": "v"}

Defensive patterns

Strategy: validation

Validate before calling

for k := range cfg.Env {
    if len(k) > 256 {
        return fmt.Errorf("env key too long (%d > 256): %.50q", len(k), k)
    }
    if !regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`).MatchString(k) {
        return fmt.Errorf("env key %q is not a valid identifier", k)
    }
}

Try / catch

if err := ValidateStdioConfig(cfg); err != nil {
    if strings.Contains(err.Error(), "exceeds maximum length") {
        return fmt.Errorf("fix env map — a value was likely placed in the key position: %w", err)
    }
    return err
}

Prevention

Use conventional short env var names
Check for paste errors where 'KEY=value' was inserted as a whole key
Validate keys with an identifier regex before building the config

When it happens

Trigger: ValidateStdioConfig called with an env map containing a key longer than 256 bytes — usually from malformed configs or generated keys.

Common situations: Copy-paste errors where a value was accidentally placed in the key position ("API_KEY=secret" pasted as a whole line); programmatically generated env keys embedding long identifiers; corrupted config files.

Related errors

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/b29aa1bf7d034eb0. Report an issue: GitHub.