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# Tesla
[![Build Status](https://travis-ci.org/teamon/tesla.svg?branch=master)](https://travis-ci.org/teamon/tesla)
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Tesla is an HTTP client loosely based on [Faraday](https://github.com/lostisland/faraday).
It embraces the concept of middleware when processing the request/response cycle.
> Note that this README refers to the `master` branch of Tesla, not the latest
released version on Hex. See [the documentation](http://hexdocs.pm/tesla) for
the documentation of the version you're using.
## HTTP Client example
Define module with `use Tesla` and choose from a variety of middleware.
```elixir
defmodule GitHub do
use Tesla
plug Tesla.Middleware.BaseUrl, "https://api.github.com"
plug Tesla.Middleware.Headers, %{"Authorization" => "token xyz"}
plug Tesla.Middleware.JSON
def user_repos(login) do
get("/user/" <> login <> "/repos")
end
end
```
Then use it like this:
```elixir
response = GitHub.user_repos("teamon")
response.status # => 200
response.body # => [%{…}, …]
response.headers # => %{'content-type' => 'application/json'}
```
See below for documentation.
## Installation
Add `tesla` as dependency in `mix.exs`
```elixir
defp deps do
[{:tesla, "~> 0.10.0"},
{:poison, ">= 1.0.0"}] # optional, required by JSON middleware
end
```
Also, unless using Elixir `>= 1.4`, add `:tesla` to the `applications` list:
```ex
def application do
[applications: [:tesla, ...], ...]
end
```
## Documentation
- [Middleware](#middleware)
- [Runtime middleware](#runtime-middleware)
- [Adapters](#adapters)
- [Streaming](#streaming)
- [Multipart](#multipart)
- [Testing](#testing)
- [Writing middleware](#writing-middleware)
- [Direct usage](#direct-usage)
- [Cheatsheet](#cheatsheet)
- [Changelog](https://github.com/teamon/tesla/releases)
## Middleware
Tesla is built around the concept of composable middlewares.
This is very similar to how [Plug Router](https://github.com/elixir-plug/plug#the-plug-router) works.
#### Basic
- [`Tesla.Middleware.BaseUrl`](https://hexdocs.pm/tesla/Tesla.Middleware.BaseUrl.html) - set base url
- [`Tesla.Middleware.Headers`](https://hexdocs.pm/tesla/Tesla.Middleware.Headers.html) - set request headers
- [`Tesla.Middleware.Query`](https://hexdocs.pm/tesla/Tesla.Middleware.Query.html) - set query parameters
- [`Tesla.Middleware.Opts`](https://hexdocs.pm/tesla/Tesla.Middleware.Opts.html) - set request options
- [`Tesla.Middleware.FollowRedirects`](https://hexdocs.pm/tesla/Tesla.Middleware.FollowRedirects.html) - follow 3xx redirects
- [`Tesla.Middleware.MethodOverride`](https://hexdocs.pm/tesla/Tesla.Middleware.MethodOverride.html) - set X-Http-Method-Override
- [`Tesla.Middleware.Logger`](https://hexdocs.pm/tesla/Tesla.Middleware.Logger.html) - log requests (method, url, status, time)
- [`Tesla.Middleware.DebugLogger`](https://hexdocs.pm/tesla/Tesla.Middleware.DebugLogger.html) - log full requests & responses
#### Formats
- [`Tesla.Middleware.FormUrlencoded`](https://hexdocs.pm/tesla/Tesla.Middleware.FormUrlencoded.html) - urlencode POST body parameter, useful for POSTing a map/keyword list
- [`Tesla.Middleware.JSON`](https://hexdocs.pm/tesla/Tesla.Middleware.JSON.html) - JSON request/response body
- [`Tesla.Middleware.Compression`](https://hexdocs.pm/tesla/Tesla.Middleware.Compression.html) - gzip & deflate
- [`Tesla.Middleware.DecodeRels`](https://hexdocs.pm/tesla/Tesla.Middleware.DecodeRels.html) - decode `Link` header into `opts[:rels]` field in response
#### Auth
- [`Tesla.Middleware.BasicAuth`](https://hexdocs.pm/tesla/Tesla.Middleware.BasicAuth.html) - HTTP Basic Auth
- [`Tesla.Middleware.DigestAuth`](https://hexdocs.pm/tesla/Tesla.Middleware.DigestAuth.html) - Digest access authentication
#### Error handling
- [`Tesla.Middleware.Timeout`](https://hexdocs.pm/tesla/Tesla.Middleware.Timeout.html) - timeout request after X milliseconds despite of server response
- [`Tesla.Middleware.Retry`](https://hexdocs.pm/tesla/Tesla.Middleware.Retry.html) - retry few times in case of connection refused
- [`Tesla.Middleware.Fuse`](https://hexdocs.pm/tesla/Tesla.Middleware.Fuse.html) - fuse circuit breaker integration
- [`Tesla.Middleware.Tuples`](https://hexdocs.pm/tesla/Tesla.Middleware.Tuples.html) - return `{:ok, env} | {:error, reason}` instead of raising exception
## Runtime middleware
All HTTP functions (`get`, `post`, etc.) can take a dynamic client function as the first parameter.
This allow to use convenient syntax for modifying the behaviour in runtime.
Consider the following case: GitHub API can be accessed using OAuth token authorization.
We can't use `plug Tesla.Middleware.Headers, %{"Authorization" => "token here"}`
since this would be compiled only once and there is no way to insert dynamic user token.
Instead, we can use `Tesla.build_client` to create a dynamic middleware function:
```elixir
defmodule GitHub do
# same as above with a slightly change to `user_repos/1`
def user_repos(client, login) do
# pass `client` argument to `get` function
get(client, "/user/" <> login <> "/repos")
end
def issues(client \\ %Tesla.Client{}) do
# default to empty client that will not include runtime token
get(client, "/issues")
end
# build dynamic client based on runtime arguments
def client(token) do
Tesla.build_client [
{Tesla.Middleware.Headers, %{"Authorization" => "token: " <> token }}
]
end
end
```
and then:
```elixir
client = GitHub.client(user_token)
client |> GitHub.user_repos("teamon")
client |> GitHub.get("/me")
GitHub.issues()
client |> GitHub.issues()
```
The `Tesla.build_client` function can take two arguments: `pre` and `post` middleware.
The first list (`pre`) will be included before any other middleware. In case there is a need
to inject middleware at the end you can pass a second list (`post`). It will be put just
before adapter. In fact, one can even dynamically override the adapter.
For example, a private (per user) cache could be implemented as:
```elixir
def new(user) do
Tesla.build_client [], [
fn env, next ->
case my_private_cache.fetch(user, env) do
{:ok, env} -> env # return cached response
:error -> Tesla.run(env, next) # make real request
end
end
end
end
```
## Adapters
Tesla supports multiple HTTP adapter that do the actual HTTP request processing.
- [`Tesla.Adapter.Httpc`](https://hexdocs.pm/tesla/Tesla.Adapter.Httpc.html) - the default, built-in erlang [httpc](http://erlang.org/doc/man/httpc.html) adapter
- [`Tesla.Adapter.Hackney`](https://hexdocs.pm/tesla/Tesla.Adapter.Hackney.html) - [hackney](https://github.com/benoitc/hackney), "simple HTTP client in Erlang"
- [`Tesla.Adapter.Ibrowse`](https://hexdocs.pm/tesla/Tesla.Adapter.Ibrowse.html) - [ibrowse](https://github.com/cmullaparthi/ibrowse), "Erlang HTTP client"
When using ibrowse or hackney adapters remember to alter applications list in `mix.exs` (for Elixir < 1.4)
```elixir
def application do
[applications: [:tesla, :ibrowse, ...], ...] # or :hackney
end
```
and add it to the dependency list
```elixir
defp deps do
[{:tesla, "~> 0.7.0"},
{:ibrowse, "~> 4.2"}, # or :hackney
{:poison, ">= 1.0.0"}] # for JSON middleware
end
```
## Streaming
If adapter supports it, you can pass a [Stream](http://elixir-lang.org/docs/stable/elixir/Stream.html) as body, e.g.:
```elixir
defmodule ElasticSearch do
use Tesla
plug Tesla.Middleware.BaseUrl, "http://localhost:9200"
plug Tesla.Middleware.JSON
def index(records_stream) do
stream = records_stream |> Stream.map(fn record -> %{index: [some, data]})
post("/_bulk", stream)
end
end
```
Each piece of stream will be encoded as JSON and sent as a new line (conforming to JSON stream format)
## Multipart
You can pass a `Tesla.Multipart` struct as the body.
```elixir
alias Tesla.Multipart
mp =
Multipart.new
|> Multipart.add_content_type_param("charset=utf-8")
|> Multipart.add_field("field1", "foo")
|> Multipart.add_field("field2", "bar", headers: [{:"Content-Id", 1}, {:"Content-Type", "text/plain"}])
|> Multipart.add_file("test/tesla/multipart_test_file.sh")
|> Multipart.add_file("test/tesla/multipart_test_file.sh", name: "foobar")
|> Multipart.add_file_content("sample file content", "sample.txt")
response = MyApiClient.post("http://httpbin.org/post", mp)
```
## Testing
-You can set the adapter to `:mock` in tests.
+You can set the adapter to `Tesla.Mock` in tests.
```elixir
# config/test.exs
# Use mock adapter for all clients
-config :tesla, adapter: :mock
+config :tesla, adapter: Tesla.Mock
# or only for one
-config :tesla, MyClient, adapter: :mock
+config :tesla, MyClient, adapter: Tesla.Mock
```
Then, mock requests before using your client:
```elixir
defmodule MyAppTest do
use ExUnit.Case
setup do
Tesla.Mock.mock fn
%{method: :get, url: "http://example.com/hello"} ->
%Tesla.Env{status: 200, body: "hello"}
%{method: :post, url: "http://example.com/world"} ->
%Tesla.Env{status: 200, body: "hi!"}
end
:ok
end
test "list things" do
assert %Tesla.Env{} = env = MyApp.get("/hello")
assert env.status == 200
assert env.body == "hello"
end
end
```
## Writing middleware
A Tesla middleware is a module with `call/3` function, that at some point calls `Tesla.run(env, next)` to process
the rest of stack.
```elixir
defmodule MyMiddleware do
@behaviour Tesla.Middleware
def call(env, next, options) do
env
|> do_something_with_request
|> Tesla.run(next)
|> do_something_with_response
end
end
```
The arguments are:
- `env` - `Tesla.Env` instance
- `next` - middleware continuation stack; to be executed with `Tesla.run(env, next)`
- `options` - arguments passed during middleware configuration (`plug MyMiddleware, options`)
There is no distinction between request and response middleware, it's all about executing `Tesla.run/2` function at the correct time.
For example, a request logger middleware could be implemented like this:
```elixir
defmodule Tesla.Middleware.RequestLogger do
@behaviour Tesla.Middleware
def call(env, next, _) do
IO.inspect env # print request env
Tesla.run(env, next)
end
end
```
and response logger middleware like this:
```elixir
defmodule Tesla.Middleware.ResponseLogger do
@behaviour Tesla.Middleware
def call(env, next, _) do
res = Tesla.run(env, next)
IO.inspect res # print response env
res
end
end
```
See [built-in middlewares](https://github.com/teamon/tesla/tree/master/lib/tesla/middleware) for more examples.
Middleware should have documentation following this template:
````elixir
defmodule Tesla.Middleware.SomeMiddleware do
@behaviour Tesla.Middleware
@moduledoc """
Short description what it does
Longer description, including e.g. additional dependencies.
### Example usage
```
defmodule MyClient do
use Tesla
plug Tesla.Middleware.SomeMiddleware, most: :common, options: "here"
end
```
### Options
- `:list` - all possible options
- `:with` - their default values
"""
end
````
## Direct usage
You can also use Tesla directly, without creating a client module.
This however won’t include any middleware.
```elixir
# Example get request
response = Tesla.get("http://httpbin.org/ip")
response.status # => 200
response.body # => '{\n "origin": "87.205.72.203"\n}\n'
response.headers # => %{'Content-Type' => 'application/json' ...}
response = Tesla.get("http://httpbin.org/get", query: [a: 1, b: "foo"])
response.url # => "http://httpbin.org/get?a=1&b=foo"
# Example post request
response = Tesla.post("http://httpbin.org/post", "data", headers: %{"Content-Type" => "application/json"})
```
## Cheatsheet
#### Making requests 101
```elixir
# GET /path
get("/path")
# GET /path?a=hi&b[]=1&b[]=2&b[]=3
get("/path", query: [a: "hi", b: [1,2,3]])
# GET with dynamic client
get(client, "/path")
get(client, "/path", query: [page: 3])
# arguments are the same for GET, HEAD, OPTIONS & TRACE
head("/path")
options("/path")
trace("/path")
# POST, PUT, PATCH
post("/path", "some-body-i-used-to-know")
put("/path", "some-body-i-used-to-know", query: [a: "0"])
patch("/path", multipart)
```
#### Configuring HTTP functions visibility
```elixir
# generate only get and post function
use Tesla, only: ~w(get post)a
# generate only delete fuction
use Tesla, only: [:delete]
# generate all functions except delete and options
use Tesla, except: [:delete, :options]
```
#### Disable docs for HTTP functions
```elixir
use Tesla, docs: false
```
#### Decode only JSON response (do not encode request)
```elixir
plug Tesla.Middleware.DecodeJson
```
#### Use other JSON library
```elixir
# use JSX
plug Tesla.Middleware.JSON, engine: JSX, engine_opts: [strict: [:comments]]
# use custom functions
plug Tesla.Middleware.JSON, decode: &JSX.decode/1, encode: &JSX.encode/1
```
#### Custom middleware
```elixir
defmodule Tesla.Middleware.MyCustomMiddleware do
def call(env, next, options) do
env
|> do_something_with_request
|> Tesla.run(next)
|> do_something_with_response
end
end
```
## Contributing
1. Fork it (https://github.com/teamon/tesla/fork)
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new Pull Request
## License
This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details
Copyright (c) 2015-2017 [Tymon Tobolski](http://teamon.eu/about/)

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