api-response

A Rust library for standardized API error handling with automatic module-based error code management and message formatting.

Features

• Automatic Module Prefixing: Error messages automatically include module paths in [module] message format
• Auto Error Code Numbering: Sequential error code allocation based on module and base code
• Transparent Error Delegation: Proper error propagation through transparent variants
• HTTP Status Code Support: Attach HTTP status codes to error variants
• Web Framework Integration: Built-in support for Axum, Actix-web, and Poem
• Type-safe: Compile-time error code and module validation
• Zero Runtime Cost: All formatting logic uses efficient trait methods

Installation

Add to your Cargo.toml:

[dependencies]
api-response = "0.1"
thiserror = "1.0"  # For error definitions

For web framework integration:

[dependencies]
api-response = { version = "0.1", features = ["axum"] }  # or "actix", "poem"

Quick Start

1. Define Your Error Type

use api_response::Response;
use thiserror::Error;

#[derive(Debug, Error, Response)]
#[response(module = "auth", base = 1000)]
pub enum AuthError {
    #[error("User not found")]
    #[response(status = 404)]
    UserNotFound,

    #[error("Invalid password")]
    #[response(status = 401)]
    InvalidPassword,
}

2. Use the Error

let error = AuthError::UserNotFound;

// Automatic module prefix
println!("{}", error.message());
// Output: [auth] User not found

// Error code (auto-numbered)
println!("{}", error.error_code());
// Output: 1000

// HTTP status code
println!("{}", error.http_status_code());
// Output: 404

3. Convert to API Response

use api_response::ApiResponse;

// Method 1: From error
let response = ApiResponse::from_error(error);

// Method 2: From Result
let result: Result<String, AuthError> = Err(AuthError::UserNotFound);
let response: ApiResponse = result.into();

// Serialize to JSON
let json = serde_json::to_string(&response).unwrap();
// {
//   "code": 1000,
//   "message": "[auth] User not found",
//   "data": null
// }

Core Features

🎯 Automatic Module Prefixing

Error messages automatically include module paths:

#[derive(Debug, Error, Response)]
#[response(module = "payment.stripe", base = 2000)]
pub enum PaymentError {
    #[error("Insufficient balance")]
    InsufficientBalance,  // Error code: 2000
}

let err = PaymentError::InsufficientBalance;
err.message()      // → "[payment.stripe] Insufficient balance"
err.module_path()  // → "payment.stripe"
err.raw_message()  // → "Insufficient balance"

🔄 Transparent Error Delegation

Proper error propagation when wrapping errors:

#[derive(Debug, Error, Response)]
#[response(module = "api")]
pub enum ApiError {
    #[error(transparent)]
    #[response(transparent)]
    Auth(#[from] AuthError),  // Delegates to inner error
}

// When ApiError::Auth(AuthError::UserNotFound) occurs:
let error = ApiError::Auth(AuthError::UserNotFound);
error.message()      // → "[auth] User not found" (from AuthError)
error.module_path()  // → "auth" (from AuthError)
error.error_code()   // → 1000 (from AuthError)

🔢 Error Code Management

Automatic Numbering with base

#[derive(Debug, Error, Response)]
#[response(module = "user", base = 1000)]
pub enum UserError {
    #[error("Not found")]
    NotFound,        // Code: 1000

    #[error("Unauthorized")]
    Unauthorized,    // Code: 1001

    #[error("Forbidden")]
    Forbidden,       // Code: 1002
}

Manual Code Assignment (No base)

#[derive(Debug, Error, Response)]
#[response(module = "validation")]
pub enum ValidationError {
    #[error("Invalid email")]
    #[response(code = 4001, status = 400)]
    InvalidEmail,

    #[error("Weak password")]
    #[response(code = 4002, status = 400)]
    WeakPassword,
}

Override Auto-numbering

#[derive(Debug, Error, Response)]
#[response(module = "auth", base = 1000)]
pub enum AuthError {
    #[error("User not found")]
    NotFound,        // Code: 1000 (auto)

    #[error("Locked")]
    #[response(code = 1099)]  // Override: 1099 instead of 1001
    Locked,
}

No Module Attribute (Optional)

#[derive(Debug, Error, Response)]
#[response(base = 6000)]
pub enum SimpleError {
    #[error("Generic error")]
    GenericError,    // Code: 6000, no module prefix

    #[error("Another error")]
    AnotherError,    // Code: 6001, no module prefix
}

// Usage
let err = SimpleError::GenericError;
err.message()      // → "Generic error" (no module prefix)
err.module_path()  // → ""

Common Usage Patterns

RESTful API Error Handling

#[derive(Debug, Error, Response)]
#[response(module = "user", base = 1000)]
pub enum UserError {
    #[error("User not found")]
    #[response(status = 404)]
    NotFound,

    #[error("Permission denied")]
    #[response(status = 403)]
    PermissionDenied,
}

// In API handler
async fn get_user(id: u64) -> Result<Json<User>, UserError> {
    let user = find_user(id).ok_or(UserError::NotFound)?;
    check_permission(&user).ok_or(UserError::PermissionDenied)?;
    Ok(Json(user))
}

Error Aggregation

#[derive(Debug, Error, Response)]
#[response(module = "app")]
pub enum AppError {
    #[error(transparent)]
    #[response(transparent)]
    User(#[from] UserError),

    #[error(transparent)]
    #[response(transparent)]
    Database(#[from] DbError),

    #[error("Internal error")]
    #[response(code = 5000, status = 500)]
    Internal,
}

Web Framework Integration

Axum

use axum::{routing::get, Router};
use api_response::ApiResponse;

async fn handler() -> ApiResponse {
    // ApiResponse automatically implements IntoResponse
    // HTTP status code is set from the status_code field
    ApiResponse::from_error(AuthError::UserNotFound)
}

let app = Router::new().route("/user", get(handler));

Actix-web

use actix_web::{get, HttpResponse};
use api_response::ApiResponse;

#[get("/user")]
async fn handler() -> ApiResponse {
    // ApiResponse implements Responder
    ApiResponse::from_error(AuthError::UserNotFound)
}

Poem

use poem::{get, handler, Route};
use api_response::ApiResponse;

#[handler]
async fn handler() -> ApiResponse {
    // ApiResponse implements IntoResponse
    ApiResponse::from_error(AuthError::UserNotFound)
}

let app = Route::new().at("/user", get(handler));

Examples

We provide comprehensive examples:

# Complete feature demonstration
cargo run --example complete_example

# Web framework integration
cargo run --example web_framework_example

API Reference

Response Trait

pub trait Response: Display {
    /// Returns the error code
    fn error_code(&self) -> u64;

    /// Returns the module path (e.g., "auth.login")
    fn module_path(&self) -> &'static str;

    /// Returns the raw error message without module prefix
    fn raw_message(&self) -> String;

    /// Returns the formatted message with module prefix: "[module] message"
    fn message(&self) -> String;

    /// Returns the HTTP status code
    fn http_status_code(&self) -> u16;
}

ApiResponse Struct

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ApiResponse {
    pub code: u64,
    pub message: String,
    pub data: serde_json::Value,
    #[serde(skip)]
    pub status_code: u16,
}

Methods:

• ApiResponse::success(data) - Create success response with data
• ApiResponse::success_with_message(data, message) - Success with custom message
• ApiResponse::ok() - Create empty success response

Attributes

Enum-level Attributes

#[response(module = "module_name", base = base_code)]
//        ^^^^^^^^^^^^^^^^^^^       ^^^^^^^^^^^^
//        Optional (default "")     Optional (if omitted, variants must specify code)

Variant-level Attributes

#[response(code = error_code, status = http_status, message = "custom_message")]
//        ^^^^^^^^^^^^^^^^^^  ^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^
//        Optional (override) Optional (default 200) Optional (override Display)

#[response(transparent)]  // Delegate to inner error

Advanced Features

Access Metadata

// Get module path
let module = error.module_path();  // "auth.login"

// Raw vs Formatted messages
error.raw_message()  // → "User not found"
error.message()      // → "[auth.login] User not found"

Multi-level Module Names

#[response(module = "api.v1.auth")]
pub enum AuthError { /* ... */ }

// Messages will be prefixed with [api.v1.auth]

Design Philosophy

• Simple by Default: Minimal boilerplate, maximum functionality
• Type Safety: Compile-time validation of error codes and modules
• Flexibility: Support both auto-numbering and manual code assignment
• Zero Cost: All abstractions compile away to efficient code
• Framework Agnostic: Core library has no web framework dependencies

Requirements

• Rust 1.70 or later
• thiserror for error definitions (recommended)
• serde and serde_json for serialization

License

MIT OR Apache-2.0

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Related Projects

• thiserror - Excellent error derive macros
• anyhow - Flexible error handling