actix-json-validator

A user-friendly JSON extractor for Actix Web that automatically runs serde_valid validations on incoming JSON requests and returns friendly and consistent error messages in a style inspired by Django REST Framework (DRF).

Top-level validation errors appear under "non_field_errors", and nested field errors appear under their respective fields—making it straightforward to parse and display errors on forms or any client interface.

actix-json-validator is a lightweight extractor built around Actix’s FromRequest trait. It integrates serde_valid to validate your request structs, reducing boilerplate and ensuring consistent nested error structures reminiscent of the well-known DRF format.

Features

Automatic Validation
Let serde_valid handle your validation rules (e.g., #[validate(min_length = 3)], #[validate(range(min = 10))]), and have your handlers receive pre-validated data.
Friendly, Nested Error Messages (DRF-Inspired)
Any fields that fail validation are shown in an organized, nested structure akin to DRF. Top-level errors go under "non_field_errors" so that client code (and form handlers) can easily distinguish between global and field-specific issues.
Consistent JSON Format
Provides a uniform and intuitive JSON response for errors, such as:
```
{
  "username": ["This field may not be blank."],
  "non_field_errors": ["Some global issue"]
}
```
This structure is reminiscent of Django REST Framework, popular for its clarity and ease of parsing by front-end frameworks or form validation libraries.
Built on Actix Web 4
Uses actix_web::FromRequest for an idiomatic Rust approach.
Minimal Overhead
One extractor, a small bit of error-handling logic, and you’re set!

Installation

Add the following to your Cargo.toml:

[dependencies]
actix-json-validator = "0.1.0"
actix-web = "4"
serde = "1"
serde_valid = "1"
serde_json = "1"
futures-util = "0.3"
thiserror = "2"
mime = "0.3"

Then run:

cargo build

You’ll be all set.

Motivation

Simplify Request Validation
Writing validation logic for every request and building structured error responses can be repetitive. With actix-json-validator, you simply annotate your structs using serde_valid’s rich validation attributes, and the extractor automatically returns an error response if validation fails.
DRF-Inspired, Easy-to-Parse Error Format
Inspired by the popular Django REST Framework style, the library returns a uniform JSON structure with top-level errors grouped under "non_field_errors" and nested field errors under their respective field names. This consistency makes it much easier for client-side code or form libraries to handle and display error messages.
Reduced Boilerplate
No more building custom error handlers or manually scanning validation errors. This crate provides a quick integration that “just works,” so you can focus on implementing features rather than repeating error-handling patterns.

Usage

1. Define Your Request Struct

Annotate your request structs with serde_valid validation attributes:

use serde::Deserialize;
use serde_valid::Validate;

#[derive(Debug, Deserialize, Validate)]
struct CreateUser {
    #[validate(min_length = 3)]
    username: String,

    #[validate(range(min = 1, max = 120))]
    age: u8,
}

2. Use `AppJson<T>` in Your Actix Handler

use actix_web::{post, HttpResponse, Responder};
use actix_json_validator::AppJson; // from this crate

#[post("/user")]
async fn create_user(body: AppJson<CreateUser>) -> impl Responder {
    // body has already been validated!
    let user_data = body.into_inner();
    // ... do something with user_data ...

    HttpResponse::Ok().json({ "status": "success" })
}

3. Enjoy Clear Error Responses

If the user sends invalid data, the response will automatically be an HTTP 400 with a JSON body like:

{
  "username": ["The length of the value must be `>= 3`."]
}

Or, for a top-level error:

{
  "non_field_errors": ["Some global issue"]
}

All structured with familiar DRF-inspired field/key groupings.

Advanced Customization

JsonConfig: Tweak the maximum payload size or restrict content types via a predicate:

JsonConfig::default()
    .limit(65536) // max payload 64 KB
    .content_type(|mime| mime.subtype() == mime::JSON)

Nested Objects & Arrays: The crate’s internal process_errors method builds a nested map structure for complex fields (e.g., {"profile": {"address": ["Cannot be empty"]}}).
Customizing the Format: Feel free to fork or copy process_errors if you want a different structure or to localize messages differently.

Example

Example usage of the crate can be found in the docs/examples/good-foods directory. To run the example, build the application with cargo build and run it with cargo run:

good-foods$ cargo build
   Compiling good-foods v0.1.0 (/actix-json-validator/docs/examples/good-foods)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.42s

good-foods$ cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s
     Running `target/debug/good-foods`
Starting good-foods server on http://localhost:8080

Test the application by sending a POST request to http://localhost:8080/food with a JSON body:

good-foods$ curl -X POST -H "Content-Type: application/json" \
  -d '{"name": "Ice Cream", "rating": 9}' \
  http://localhost:8080/foods

You should see a response like so:

{"name":"Ice Cream","rating":9}

To test validation errors, send a POST request with invalid data:

good-foods$ curl -X POST -H "Content-Type: application/json" \
  -d '{"name": "Ice Cream", "rating": 12}' \
  http://localhost:8080/foods

You should see a response like:

{"rating":["The number must be `<= 10`."]}

Limitations

Actix Web 4: This crate is designed for Actix Web 4.
JSON only: Non-JSON or incorrectly typed payloads lead to a 400 response, with an error key of "error" containing the error text.
serde_valid: All validations rely on serde_valid attributes; any custom logic must integrate at the struct level or via custom validators.

Contributing

Want to improve error formatting or add features? Pull requests and issues are welcome:

Fork the repository.
Create a feature branch.
Write tests for your changes.
Submit a PR with a clear description of your improvement or fix.

License

[Your License Text Here]

actix-json-validator is distributed under the terms of the MIT license. See LICENSE for details.

Thank you for checking out actix-json-validator! If you have any questions, suggestions, or issues, please open an issue on the repository. Enjoy concise, easy-to-parse validation error messages for your Actix apps!

actix-json-validator 0.1.0