Req is an HTTP client with a focus on ease of use and composability, built on top of Finch.
-
Extensibility via request, response, and error steps
-
Automatic body decompression (via
decompress/1step) -
Automatic body encoding and decoding (via
encode_body/1anddecode_body/1steps) -
Encode params as query string (via
put_params/2step) -
Basic authentication (via
auth/2step) -
.netrcfile support (viaload_netrc/2step) -
Range requests (via
put_range/2step) -
Follows redirects (via
follow_redirects/1step) -
Retries on errors (via
retry/2step) -
Basic HTTP caching (via
put_if_modified_since/2step) -
Setting base URL (via
put_base_url/2step)
The easiest way to use Req is with Mix.install/2 (requires Elixir v1.12+):
Mix.install([
{:req, "~> 0.2.0"}
])
Req.get!("https://api.github.com/repos/elixir-lang/elixir").body["description"]
#=> "Elixir is a dynamic, functional language designed for building scalable and maintainable applications"If you want to use Req in a Mix project, you can add the above
dependency to your mix.exs.
Under the hood, Req works by passing a request through a series of steps.
The request struct, %Req.Request{}, initially contains data like HTTP method and
request headers. You can also add request, response, and error steps to it.
Request steps are used to refine the data that will be sent to the server.
After making the actual HTTP request, we'll either get a HTTP response or an error. The request, along with the response or error, will go through response or error steps, respectively.
Nothing is actually executed until we run the pipeline with Req.run/1.
The high-level API shown before:
Req.get!("https://api.github.com/repos/elixir-lang/elixir")is equivalent to this composition of lower-level API functions and steps:
Req.build(:get, "https://api.github.com/repos/elixir-lang/elixir")
|> Req.put_default_steps()
|> Req.run!()(See Req.build/3, Req.put_default_steps/2, and Req.run!/1 for more information.)
We can also build more complex flows like returning a response from a request step or an error from a response step. We will explore those next.
A request step is a function that accepts a request and returns one of the following:
-
A
request -
A
{request, response_or_error}tuple. In that case no further request steps are executed and the return value goes through response or error steps
Examples:
def put_default_headers(request) do
update_in(request.headers, &[{"user-agent", "req"} | &1])
end
def read_from_cache(request) do
case ResponseCache.fetch(request) do
{:ok, response} -> {request, response}
:error -> request
end
endA response step is a function that accepts a {request, response} tuple and returns one of the
following:
-
A
{request, response}tuple -
A
{request, exception}tuple. In that case, no further response steps are executed but the 72F7 exception goes through error steps
Similarly, an error step is a function that accepts a {request, exception} tuple and returns one
of the following:
-
A
{request, exception}tuple -
A
{request, response}tuple. In that case, no further error steps are executed but the response goes through response steps
Examples:
def decode({request, response}) do
case List.keyfind(response.headers, "content-type", 0) do
{_, "application/json" <> _} ->
{request, update_in(response.body, &Jason.decode!/1)}
_ ->
{request, response}
end
end
def log_error({request, exception}) do
Logger.error(["#{request.method} #{request.uri}: ", Exception.message(exception)])
{request, exception}
endAny step can call Req.Request.halt/1 to halt the pipeline. This will prevent any further steps
from being invoked.
Examples:
def circuit_breaker(request) do
if CircuitBreaker.open?() do
{Req.Request.halt(request), RuntimeError.exception("circuit breaker is open")}
else
request
end
endReq is built on top of Finch and is inspired by cURL, Requests, Tesla, and many other HTTP clients - thank you!
Copyright (c) 2021 Wojtek Mach
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.