pretend

pretend is a modular, Feign-inspired HTTP, client based on macros. It's goal is to decouple the definition of a REST API from it's implementation.

Some features:

• Declarative
• Asynchronous-first implementations
• HTTP client agnostic
• JSON support thanks to serde

Getting started

A REST API is described by annotating a trait:

use pretend::{pretend, request, Result};

#[pretend]
trait HttpBin {
    #[request(method = "POST", path = "/anything")]
    async fn post_anything(&self, body: &'static str) -> Result<String>;
}

Under the hood, pretend will implement this trait for Pretend. An instance of this struct can be constructed by passing a client implementation, and the REST API's base url. In the following example, we are using the reqwest based client.

use pretend::{Pretend, Url};
use pretend_reqwest::Client;

#[tokio::main]
async fn main() {
    let client = Client::default();
    let url = Url::parse("https://httpbin.org").unwrap();
    let pretend = Pretend::for_client(client).with_url(url);
    let response = pretend.post_anything("hello").await.unwrap();
    assert!(response.contains("hello"));
}

Sending headers, query parameters and bodies

Headers are provided as attributes using header.

use pretend::{header, pretend, request, Result};

#[pretend]
trait HttpBin {
    #[request(method = "GET", path = "/get")]
    #[header(name = "X-Test-Header-1", value = "abc")]
    #[header(name = "X-Test-Header-2", value = "other")]
    async fn get_with_headers(&self, value: i32, custom: &str) -> Result<()>;
}

Query parameters and bodies are provided as method parameters. Body type is guessed based on the parameter name:

• Parameter body will be sent as raw bytes. This requires the body to have 'static lifetime.
• Parameter form will be serialized as form-encoded using serde.
• Parameter json will be serialized as JSON using serde.

Query parameter is passed with the query parameter. It is also serialized using serde.

use pretend::{pretend, request, Json, Result, Serialize};

#[derive(Serialize)]
struct Data {
    value: i32,
}

#[pretend]
trait HttpBin {
    #[request(method = "POST", path = "/anything")]
    async fn post_bytes(&self, body: &'static [u8]) -> Result<()>;

    #[request(method = "POST", path = "/anything")]
    async fn post_string(&self, body: &'static str) -> Result<()>;

    #[request(method = "POST", path = "/anything")]
    async fn post_with_query_params(&self, query: &Data) -> Result<()>;

    #[request(method = "POST", path = "/anything")]
    async fn post_json(&self, json: &Data) -> Result<()>;
}

Handling responses

pretend support a wide range of response types, based on the return type of the method. The body can be returned as a Vec<u8>, a string or as JSON by using the Json wrapper type. The unit type () can also be used if the body should be discarded.

JsonResult is also offered as a convenience type. It will deserialize into a value type or an error type depending on the HTTP status code.

When retrieving body alone, an HTTP error will cause the method to return an error. It is possible to prevent the method to fail and access the HTTP status code by wrapping these types inside a Response. This also allows accessing response headers.

use pretend::{pretend, request, Deserialize, Json, JsonResult, Response, Result};

#[derive(Deserialize)]
struct Data {
    value: i32,
}

#[derive(Deserialize)]
struct Error {
    error: String,
}

#[pretend]
trait HttpBin {
    #[request(method = "POST", path = "/anything")]
    async fn read_bytes(&self) -> Result<Vec<u8>>;

    #[request(method = "POST", path = "/anything")]
    async fn read_string(&self) -> Result<String>;

    #[request(method = "POST", path = "/anything")]
    async fn read_json(&self) -> Result<Json<Data>>;

    #[request(method = "POST", path = "/anything")]
    async fn read_json_result(&self) -> Result<JsonResult<Data, Error>>;

    #[request(method = "POST", path = "/anything")]
    async fn read_status(&self) -> Result<Response<()>>;
}

Templating

Request paths and headers support templating. A value between braces will be replaced by a parameter with the same name. The replacement is done with format!, meaning that any type that implement Display is supported.

use pretend::{header, pretend, request, Deserialize, Json, Pretend, Result};
use pretend_reqwest::Client;
use std::collections::HashMap;

#[derive(Deserialize)]
struct Data {
    url: String,
    headers: HashMap<String, String>,
}

#[pretend]
trait HttpBin {
    #[request(method = "POST", path = "/{path}")]
    #[header(name = "X-{header}", value = "{value}$")]
    async fn read(&self, path: &str, header: &str, value: i32) -> Result<Json<Data>>;
}

#[tokio::main]
async fn main() {
    let client = Client::default();
    let url = Url::parse("https://httpbin.org").unwrap();
    let pretend = Pretend::for_client(client).with_url(url);
    let response = pretend.read("anything", "My-Header", 123).await.unwrap();
    let data = response.value();
    assert_eq!(data.url, "https://httpbin.org/anything");
    assert_eq!(*data.headers.get("X-My-Header").unwrap(), "123$".to_string());
}

Documentation

For more information, please refer to the API reference.