fastapi - Auto-generated OpenAPI documentation

Want to have your API documented with OpenAPI? But don't want to be bothered with manual YAML or JSON tweaking? Would like it to be so easy that it would almost be utopic? Don't worry: fastapi is here to fill this gap. It aims to do, if not all, then most of the heavy lifting for you, enabling you to focus on writing the actual API logic instead of documentation. It aims to be minimal, simple and fast. It uses simple proc macros which you can use to annotate your code to have items documented.

The fastapi crate provides auto-generated OpenAPI documentation for Rust REST APIs. It treats code-first approach as a first class citizen and simplifies API documentation by providing simple macros for generating the documentation from your code.

It also contains Rust types of the OpenAPI spec, allowing you to write the OpenAPI spec only using Rust if auto generation is not your flavor or does not fit your purpose.

Long term goal of the library is to be the place to go when OpenAPI documentation is needed in any Rust codebase.

Fastapi is framework-agnostic, and could be used together with any web framework, or even without one. While being portable and standalone, one of its key aspects is simple integration with web frameworks.

Choose your flavor and document your API with ice-cold IPA

Others* = For example warp but could be anything.

Refer to the existing examples to find out more.

Features

• OpenAPI 3.1
• Pluggable, easy setup and integration with frameworks.
• No bloat, enable what you need.
• Support for generic types
  • Note!
    Tuples, arrays and slices cannot be used as generic arguments on types. Types implementing ToSchema manually should not have generic arguments, as they are not composeable and will result compile error.
• Automatic schema collection from usages recursively.
  • Request body from either handler function arguments (if supported by framework) or from request_body attribute.
  • Response body from response body attribute or response content attribute.
• Various OpenAPI visualization tools supported out of the box.
• Rust type aliases via fastapi-config.

Crate Features

• macros Enable fastapi-gen macros. This is enabled by default.
• yaml: Enables serde_yaml serialization of OpenAPI objects.
• actix_extras: Enhances actix-web integration with being able to parse path, path and query parameters from actix web path attribute macros. See docs or examples for more details.
• rocket_extras: Enhances rocket framework integration with being able to parse path, path and query parameters from rocket path attribute macros. See docs or examples for more details.
• axum_extras: Enhances axum framework integration allowing users to use IntoParams without defining the parameter_in attribute. See docs or examples for more details.
• debug: Add extra traits such as debug traits to openapi definitions and elsewhere.
• chrono: Add support for chrono DateTime, Date, NaiveDate, NaiveDateTime, NaiveTime and Duration types. By default these types are parsed to string types with additional format information. format: date-time for DateTime and NaiveDateTime and format: date for Date and NaiveDate according RFC3339 as ISO-8601. To override default string representation users have to use value_type attribute to override the type. See docs for more details.
• time: Add support for time OffsetDateTime, PrimitiveDateTime, Date, and Duration types. By default these types are parsed as string. OffsetDateTime and PrimitiveDateTime will use date-time format. Date will use date format and Duration will not have any format. To override default string representation users have to use value_type attribute to override the type. See docs for more details.
• decimal: Add support for rust_decimal Decimal type. By default it is interpreted as String. If you wish to change the format you need to override the type. See the value_type in component derive docs.
• decimal_float: Add support for rust_decimal Decimal type. By default it is interpreted as Number. This feature is mutually exclusive with decimal and allow to change the default type used in your documentation for Decimal much like serde_with_float feature exposed by rust_decimal.
• uuid: Add support for uuid. Uuid type will be presented as String with format uuid in OpenAPI spec.
• ulid: Add support for ulid. Ulid type will be presented as String with format ulid in OpenAPI spec.
• url: Add support for url. Url type will be presented as String with format uri in OpenAPI spec.
• smallvec: Add support for smallvec. SmallVec will be treated as Vec.
• openapi_extensions: Adds traits and functions that provide extra convenience functions. See the request_body docs for an example.
• repr: Add support for repr_serde's repr(u*) and repr(i*) attributes to unit type enums for C-like enum representation. See docs for more details.
• preserve_order: Preserve order of properties when serializing the schema for a component. When enabled, the properties are listed in order of fields in the corresponding struct definition. When disabled, the properties are listed in alphabetical order.
• preserve_path_order: Preserve order of OpenAPI Paths according to order they have been introduced to the #[openapi(paths(...))] macro attribute. If disabled the paths will be ordered in alphabetical order. However the operations order under the path will be always constant according to specification
• indexmap: Add support for indexmap. When enabled IndexMap will be rendered as a map similar to BTreeMap and HashMap.
• non_strict_integers: Add support for non-standard integer formats int8, int16, uint8, uint16, uint32, and uint64.
• rc_schema: Add ToSchema support for Arc<T> and Rc<T> types. Note! serde rc feature flag must be enabled separately to allow serialization and deserialization of Arc<T> and Rc<T> types. See more about serde feature flags.
• config Enables fastapi-config for the project which allows defining global configuration options for fastapi.

Default Library Support

• Implicit partial support for serde attributes. See docs for more details.
• Support for http StatusCode in responses.

Install

Add dependency declaration to Cargo.toml.

[dependencies]
fastapi = "0.1.1"

Examples

Create type with ToSchema and use it in #[fastapi::path(...)] that is registered to the OpenApi.

use fastapi::{OpenApi, ToSchema};

#[derive(ToSchema)]
struct Pet {
   id: u64,
   name: String,
   age: Option<i32>,
}

mod pet_api {
    /// Get pet by id
    ///
    /// Get pet from database by pet id
    #[fastapi::path(
        get,
        path = "/pets/{id}",
        responses(
            (status = 200, description = "Pet found successfully", body = Pet),
            (status = NOT_FOUND, description = "Pet was not found")
        ),
        params(
            ("id" = u64, Path, description = "Pet database id to get Pet for"),
        )
    )]
    async fn get_pet_by_id(pet_id: u64) -> Result<Pet, NotFound> {
        Ok(Pet {
            id: pet_id,
            age: None,
            name: "lightning".to_string(),
        })
    }
}

#[derive(OpenApi)]
#[openapi(paths(pet_api::get_pet_by_id))]
struct ApiDoc;

println!("{}", ApiDoc::openapi().to_pretty_json().unwrap());

{
  "openapi": "3.1.0",
  "info": {
    "title": "application name from Cargo.toml",
    "description": "description from Cargo.toml",
    "contact": {
      "name": "author name from Cargo.toml",
      "email": "author email from Cargo.toml"
    },
    "license": {
      "name": "license from Cargo.toml"
    },
    "version": "version from Cargo.toml"
  },
  "paths": {
    "/pets/{id}": {
      "get": {
        "tags": [
          "pet_api"
        ],
        "summary": "Get pet by id",
        "description": "Get pet from database by pet id",
        "operationId": "get_pet_by_id",
        "parameters": [
          {
            "name": "id",
            "in": "path",
            "description": "Pet database id to get Pet for",
            "required": true,
            "schema": {
              "type": "integer",
              "format": "int64",
              "minimum": 0
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Pet found successfully",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Pet"
                }
              }
            }
          },
          "404": {
            "description": "Pet was not found"
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "Pet": {
        "type": "object",
        "required": [
          "id",
          "name"
        ],
        "properties": {
          "age": {
            "type": [
              "integer",
              "null"
            ],
            "format": "int32"
          },
          "id": {
            "type": "integer",
            "format": "int64",
            "minimum": 0
          },
          "name": {
            "type": "string"
          }
        }
      }
    }
  }
}

Modify OpenAPI at runtime

You can modify generated OpenAPI at runtime either via generated types directly or using Modify trait.

Modify generated OpenAPI via types directly.

#[derive(OpenApi)]
#[openapi(
    info(description = "My Api description"),
)]
struct ApiDoc;

let mut doc = ApiDoc::openapi();
doc.info.title = String::from("My Api");

You can even convert the generated OpenApi to OpenApiBuilder.

let builder: OpenApiBuilder = ApiDoc::openapi().into();

See Modify trait for examples on how to modify generated OpenAPI via it.

Go beyond the surface

• See how to serve OpenAPI doc via Swagger UI check fastapi-swagger-ui crate for more details.
• Browse to examples for more comprehensive examples.
• Check IntoResponses and ToResponse for examples on deriving responses.
• More about OpenAPI security in security documentation.
• Dump generated API doc to file at build time. See issue 214 comment.

FAQ

Swagger UI returns 404 NotFound from built binary

This is highly probably due to RustEmbed not embedding the Swagger UI to the executable. This is natural since the RustEmbed library does not by default embed files on debug builds. To get around this you can do one of the following.

1. Build your executable in --release mode

Find fastapi-swagger-ui feature flags here.

License

Licensed under either of Apache 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, shall be dual licensed, without any additional terms or conditions.