Billionmail/BillionMail · error

error unmarshalling prompt config: %v

Error message

error unmarshalling prompt config: %v

What it means

GetPrompt reads PRODUCT_CONFIG_PATH/<Domain>/prompt_config.json into a PromptConfig struct. This error is wrapped when json.Unmarshal fails, meaning the file exists but its bytes are not valid JSON or do not match the PromptConfig shape (e.g. a JSON string where an object is expected). It is thrown so callers like ModifyPrompt fail fast instead of silently operating on a zero-value config.

Source

Thrown at core/internal/service/askai/project.go:807

		if err != nil {
			return PromptConfig{}, fmt.Errorf("error marshalling default prompt config: %v", err)
		}
		err = os.WriteFile(filename, defaultPromptJson, 0644)
		if err != nil {
			return PromptConfig{}, fmt.Errorf("error saving default prompt config file: %v", err)
		}
		return defaultPromptConfig, nil
	}
	data, err := os.ReadFile(filename)
	if err != nil {
		return PromptConfig{}, fmt.Errorf("error reading prompt config file: %v", err)
	}

	var config PromptConfig
	err = json.Unmarshal(data, &config)
	if err != nil {
		return PromptConfig{}, fmt.Errorf("error unmarshalling prompt config: %v", err)
	}
	return config, nil
}

// ModifyPrompt updates the prompt configuration for a given domain.
// It reads the existing prompt configuration, modifies the specified fields, and saves the updated configuration back to the file.
// If the prompt is empty, it will not be updated.
func ModifyPrompt(Domain string, Prompt string) error {
	config, err := GetPrompt(Domain)
	if err != nil {
		return fmt.Errorf("error getting prompt config: %v", err)
	}

	// Update the prompt configuration
	if Prompt != "" {
		config.Prompt = Prompt
	}

View on GitHub (pinned to fc36c76c05)

Solutions

1. Open PRODUCT_CONFIG_PATH/<Domain>/prompt_config.json and validate it with `jq .` or `python -m json.tool` to find the syntax error
2. Fix the JSON manually or delete the file — GetPrompt recreates it from the default config on next call
3. Ensure writes are atomic (write to temp file then os.Rename) to prevent truncated/partial configs
4. Check the file has no UTF-8 BOM and is not empty

Example fix

// before
$ cat prompt_config.json
{"prompt": "Hello"  // trailing comment breaks JSON

// after
$ cat prompt_config.json
{"prompt": "Hello", "update_time": 1725500000}

// validate the config file before calling GetPrompt
func validatePromptConfig(domain string) error {
	data, err := os.ReadFile(fmt.Sprintf("%s/%s/prompt_config.json", PRODUCT_CONFIG_PATH, domain))
	if err != nil {
		return err // file missing: GetPrompt will create a default
	}
	if len(bytes.TrimPrefix(data, []byte{0xEF, 0xBB, 0xBF})) == 0 {
		return errors.New("config file is empty")
	}
	var cfg map[string]any
	return json.Unmarshal(data, &cfg) // syntax/shape check
}

func isValidPromptConfigJSON(data []byte) bool {
	var cfg map[string]any
	if err := json.Unmarshal(data, &cfg); err != nil {
		return false
	}
	_, ok := cfg["prompt"]
	return ok
}

cfg, err := GetPrompt(domain)
if err != nil {
	if strings.Contains(err.Error(), "unmarshalling") {
		// corrupt file: reset to default
		os.Remove(filepath.Join(PRODUCT_CONFIG_PATH, domain, "prompt_config.json"))
		cfg, err = GetPrompt(domain)
	}
	if err != nil {
		return err
	}
}

When it happens

Trigger: Calling GetPrompt(domain) when prompt_config.json contains malformed JSON — truncated writes, manual edits with syntax errors, BOM bytes, or the file holding a JSON array/string instead of an object with a 'prompt' field.

Common situations: Someone hand-edited prompt_config.json and broke the syntax; a concurrent write was interrupted leaving a partial file; an upgrade changed the config schema; the file was overwritten with HTML/error output by another tool.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• error unmarshalling project configuration: %v
• error marshalling project configuration: %v
• error unmarshalling footer config: %v
• error marshalling footer config: %v
• error marshalling default prompt config: %v

AI-assisted analysis of Billionmail/BillionMail@fc36c76c05 (2026-09-05). Data as JSON: /api/errors/e5b3fb333562266d. Report an issue: GitHub.