#rest #client #http #json #async


Easy-to-use REST client with automatic serialization and deserialization

19 releases (3 stable)

1.2.0 Jan 10, 2022
1.0.0 Sep 18, 2021
0.7.0 Oct 6, 2020
0.6.0 Feb 16, 2020
0.1.1 Dec 10, 2017

#9 in HTTP client

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MIT license

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crates.io License: MIT Docs: latest

Restson Rust

Easy-to-use REST client for Rust programming language that provides automatic serialization and deserialization from Rust structs. Provides async interface and an easy wrapper for synchronous calls. The library is implemented using Hyper and Serde JSON.

Getting started

Add the following lines to your project Cargo.toml file:

restson = "^1.2"
serde = "^1.0"
serde_derive = "^1.0"

This adds dependencies for the Restson library and also for Serde which is needed to derive Serialize and Deserialize for user defined data structures.


Feature Description Default
blocking This option enables support for sync, blocking, client. When only async is used this can be disabled to remove unnecessary dependencies. Yes
lib-serde-json This option enables Serde JSON parser for GET requests. Alternative for lib-simd-json. Yes
lib-simd-json This option enables JSON parsing with simd-json for GET requests. This option can improve parsing performance if SIMD is supported on the target hardware. Alternative for lib-serde-json. No

Data structures

Next, the data structures for the REST interface should be defined. The struct fields need to match with the API JSON fields. The whole JSON does not need to be defined, the struct can also contain a subset of the fields. Structs that are used with GET should derive Deserialize and structs that are used with POST should derive Serialize.

Example JSON (subset of http://httpbin.org/anything response):

  "method": "GET", 
  "origin": "", 
  "url": "https://httpbin.org/anything"

Corresponding Rust struct:

extern crate serde_derive;

struct HttpBinAnything {
    method: String,
    url: String,

These definitions allow to automatically serialize/deserialize the data structures to/from JSON when requests are processed. For more complex scenarios, see the Serde examples.

REST paths

In Restson library the API resource paths are associated with types. That is, the URL is constructed automatically and not given as parameter to requests. This allows to easily parametrize the paths without manual URL processing and reduces URL literals in the code.

Each type that is used with REST requests needs to implement RestPath trait. The trait can be implemented multiple times with different generic parameters for the same type as shown below. The get_path can also return error to indicate that the parameters were not valid. This error is propagated directly to the client caller.

// plain API call without parameters
impl RestPath<()> for HttpBinAnything {
    fn get_path(_: ()) -> Result<String,Error> { Ok(String::from("anything")) }

// API call with one u32 parameter (e.g. "http://httpbin.org/anything/1234")
impl RestPath<u32> for HttpBinAnything {
    fn get_path(param: u32) -> Result<String,Error> { Ok(format!("anything/{}", param)) }


To run requests a client instance needs to be created first. The client can be created as asynchronous which can be used with Rust async/await system or as synchronous that will block until the HTTP request has been finished and directly returns the value. The base URL of the resource is given as parameter.

// async client
let async_client = RestClient::new("http://httpbin.org").unwrap();

// sync client
let client = RestClient::new_blocking("http://httpbin.org").unwrap();

This creates a client instance with default configuration. To configure the client, it is created with a Builder

// async client
let async_client = RestClient::builder().dns_workers(1)

// sync client
let client = RestClient::builder().dns_workers(1)


The following snippet shows an example GET request:

// Gets https://httpbin.org/anything/1234 and deserializes the JSON to data variable
// (data is struct HttpBinAnything)
let data = client.get::<_, HttpBinAnything>(1234).unwrap();

The request functions call the get_path automatically from RestPath to construct the URL from the given parameter. The type of the URL parameter (_ above, compiler infers the correct type) and returned data (HttpBinAnything) are annotated in the request.

Restson also provides get_with function which is similar to the basic get but it also accepts additional query parameters that are added to the request URL.

// Gets http://httpbin.org/anything/1234?a=2&b=abcd
let query = vec![("a","2"), ("b","abcd")];
let data = client.get_with::<_, HttpBinAnything>((), &query).unwrap();

Both GET interfaces return Result<Response<T>, Error> where T is the target type in which the returned JSON is deserialized to.


The following snippets show an example POST request:

struct HttpBinPost {
    data: String,

impl RestPath<()> for HttpBinPost {
    fn get_path(_: ()) -> Result<String,Error> { Ok(String::from("post")) }
let data = HttpBinPost { data: String::from("test data")};
// Posts data to http://httpbin.org/post
client.post((), &data).unwrap();

In addition to the basic post interface, it is also possible to provide query parameters with post_with function. Also, post_capture and post_capture_with interfaces allow to capture and deserialize the message body returned by the server in the POST request (capture requests need type-annotation in the call).


HTTP PUT requests are also supported and the interface is similar to POST interface: put, put_with, put_capture and put_capture_with functions are available (capture requests need type-annotation in the call).


HTTP PATCH requests are also supported and the interface is similar to POST and PUT interface: patch and patch_with functions are available.


Restson supports HTTP DELETE requests to API paths. Normally DELETE request is sent to API URL without message body. However, if message body or query parameters are needed, delete_with can be used. Moreover, the response status code from server is checked, but the response body is not captured.

Similarly with other requests, the path is obtained from RestPath trait.

struct HttpBinDelete {

impl RestPath<()> for HttpBinDelete {
    fn get_path(_: ()) -> Result<String,Error> { Ok(String::from("delete")) }

The delete function does not return any data (only possible error) so the type needs to be annotated.

// DELETE request to http://httpbin.org/delete
let client = RestClient::new_blocking("http://httpbin.org").unwrap();
client.delete::<(), HttpBinDelete>(()).unwrap();

Concurrent requests

When using the async client, it is possible to run multiple requests concurrently as shown below:

let client = RestClient::new("https://httpbin.org").unwrap();

// all three GET requests are done concurrently, and then joined
let (data1, data2, data3) = tokio::try_join!(
    client.get::<_, HttpBinAnything>(1),
    client.get::<_, HttpBinAnything>(2),
    client.get::<_, HttpBinAnything>(3)

JSON with array root element

In all of the examples above the JSON structure consists of key-value pairs that can be represented with Rust structs. However, it is also possible that valid JSON has array root element without a key. For example, the following is valid JSON.


It is possible to work with APIs returning arrays in Restson. However instead of a struct, the user type needs to be a container. Vec<String> in this case. The type also needs to implement the RestPath trait as explained before, and easiest way to do so is to wrap the container in a struct.

struct Products ( pub Vec<Product> );

pub struct Product {
    pub name: String,

impl RestPath<()> for Products {
    fn get_path(_: ()) -> Result<String,Error> { Ok(String::from("/api/objects/products"))}

pub fn products(&self) -> Vec<Product> {
    let client = RestClient::new_blocking("http://localhost:8080").unwrap();
    client.get::<_, Products>(()).unwrap().0

Relative paths

It is possible to use relative paths in the base URL to avoid having to return version or other prefix from the get_path() implementation. For instance, endpoint http://localhost:8080/api/v1/ep could be handled by setting http://localhost:8080/api/v1/ as base URL and returning ep from the get_path(). Note: the trailing slash in the base URL is significant! Without it, the last element is replaced instead of appended when the elements are joined (see here for more information).

Body wash

For some APIs it is necessary to remove magic values or otherwise clean/process the returned response before it is deserialized. It is possible to provide a custom processing function with set_body_wash_fn() which is called with the raw returned body before passing it to the deserialization step.

Request headers

Custom headers can be added to requests by using set_headers(). The headers are added to all subsequent GET and POST requests until they are cleared with clear_headers() call.


The library uses the log crate to provide debug and trace logs. These logs allow to easily see both outgoing requests as well as incoming responses from the server. See the log crate documentation for details.


For more examples see tests directory.


Migration to v1.0

The version 1.0 adds new features that change the main interface of the client, most notably async support. To migrate existing code from 0.x versions, the RestClient creation needs to be updated. RestClient::new_blocking or RestClient::builder().blocking("http://httpbin.org") should be used to create synchronous client.

Migration to v1.2

The version 1.2 allows to use immutable client for requests. This has benefits such as allowing concurrent requests. However, this also changes how the server response is returned, and now all get requests (and other requests that capture data) need to be type-annotated. For example, previously let data: HttpBinAnything = client.get(1234).unwrap(); was allowed, but now it has to be written as let data = client.get::<_, HttpBinAnything>(1234).unwrap();.


The library is released under the MIT license. See LICENSE for details.


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