View Source Req.Request (req v0.3.10)
The low-level API and the request struct.
Req is composed of three main pieces:
Req
- the high-level APIReq.Request
- the low-level API and the request struct (you're here!)Req.Steps
- the collection of built-in steps
The low-level API and the request struct is the foundation of Req's extensibility. Virtually all of the functionality is broken down into individual pieces - steps. Req works by running the request struct through these steps. You can easily reuse or rearrange built-in steps or write new ones.
To make using custom steps by others even easier, they can be packaged up into plugins. See "Writing Plugins" section for more information.
the-low-level-api
The Low-level API
Most Req users would use it like this:
Req.get!("https://api.github.com/repos/wojtekmach/req").body["description"]
#=> "Req is a batteries-included HTTP client for Elixir."
Here is the equivalent using the low-level API:
url = "https://api.github.com/repos/wojtekmach/req"
req =
%Req.Request{method: :get, url: url}
|> Req.Request.append_request_steps(
put_user_agent: &Req.Steps.put_user_agent/1,
# ...
)
|> Req.Request.append_response_steps(
# ...
decompress_body: &Req.Steps.decompress_body/1,
decode_body: &Req.Steps.decode_body/1,
# ...
)
|> Req.Request.append_error_steps(
retry: &Req.Steps.retry/1,
# ...
)
{req, resp} = Req.Request.run_request(req)
resp.body["description"]
#=> "Req is a batteries-included HTTP client for Elixir."
By putting the request pipeline yourself you have precise control of exactly what is running and in what order.
the-request-struct
The Request Struct
:method
- the HTTP request method:url
- the HTTP request URL:headers
- the HTTP request headers:body
- the HTTP request body:options
- the options to be used by steps. See "Options" section below for more information.:halted
- whether the request pipeline is halted. Seehalt/1
:adapter
- a request step that makes the actual HTTP request. Defaults toReq.Steps.run_finch/1
. See "Adapter" section below for more information.:request_steps
- the list of request steps:response_steps
- the list of response steps:error_steps
- the list of error steps:private
- a map reserved for libraries and frameworks to use. Prefix the keys with the name of your project to avoid any future conflicts. Only acceptsatom/0
keys.
steps
Steps
Req has three types of steps: request, response, and error.
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.Request.run_request/1
.
request-steps
Request steps
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
end
response-and-error-steps
Response and error steps
A response step is a function that accepts a {request, response}
tuple and returns one of the
following:
A
{request, response}
tupleA
{request, exception}
tuple. In that case, no further response steps are executed but the 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}
tupleA
{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}
end
halting
Halting
Any step can call 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
end
writing-plugins
Writing Plugins
Custom steps can be packaged into plugins so that they are even easier to use by others.
Here's an example plugin:
defmodule PrintHeaders do
@doc """
Prints request and response headers.
## Request Options
* `:print_headers` - if `true`, prints the headers. Defaults to `false`.
"""
def attach(%Req.Request{} = request, options \\ []) do
request
|> Req.Request.register_options([:print_headers])
|> Req.Request.merge_options(options)
|> Req.Request.append_request_steps(print_headers: &print_request_headers/1)
|> Req.Request.prepend_response_steps(print_headers: &print_response_headers/1)
end
defp print_request_headers(request) do
if request.options[:print_headers] do
print_headers("> ", request.headers)
end
request
end
defp print_response_headers({request, response}) do
if request.options[:print_headers] do
print_headers("< ", response.headers)
end
{request, response}
end
defp print_headers(prefix, headers) do
for {name, value} <- headers do
IO.puts([prefix, name, ": ", value])
end
end
end
And here is how we can use it:
req = Req.new() |> PrintHeaders.attach()
Req.get!(req, url: "https://httpbin.org/json").status
200
Req.get!(req, url: "https://httpbin.org/json", print_headers: true).status
# Outputs:
# > accept-encoding: br, gzip, deflate
# > user-agent: req/0.3.0-dev
# < date: Wed, 11 May 2022 11:10:47 GMT
# < content-type: application/json
# ...
200
req = Req.new() |> PrintHeaders.attach(print_headers: true)
Req.get!(req, url: "https://httpbin.org/json").status
# Outputs:
# > accept-encoding: br, gzip, deflate
# ...
200
As you can see a plugin is simply a module. While this is not enforced, the plugin should follow these conventions:
It should export an
attach/1
function that takes and returns the request structThe attach functions mostly just adds steps and it is the steps that do the actual work
A user should be able to attach your plugin alongside other plugins. For this reason, plugin functionality should usually only happen on a specific "trigger": on a specific option, on a specific URL scheme or host, etc. This is especially important for plugins that perform authentication; you don't want to accidentally expose a token from service A when a user makes request to service B.
If your plugin supports custom options, register them with
register_options/2
Sometimes it is useful to pass options when attaching the plugin. For that, export an
attach/2
function and callmerge_options/2
. Remember to first register options before merging!
adapter
Adapter
As noted in the "Request steps" section, a request step besides returning the request,
might also return {request, response}
or {request, exception}
, thus invoking either response or error steps next.
This is exactly how Req makes the underlying HTTP call, by invoking a request step that follows this contract.
The default adapter is using Finch via the Req.Steps.run_finch/1
step.
Here is a mock adapter that always returns a successful response:
adapter = fn request ->
response = %Req.Response{status: 200, body: "it works!"}
{request, response}
end
Req.request!(url: "http://example", adapter: adapter).body
#=> "it works!"
Here is another one that uses the Req.Response.json/2
function to conveniently
return a JSON response:
adapter = fn request ->
response = Req.Response.json(%{hello: 42})
{request, response}
end
resp = Req.request!(url: "http://example", adapter: adapter)
resp.headers
#=> [{"content-type", "application/json"}]
resp.body
#=> %{"hello" => 42}
And here is a naive Hackney-based adapter:
hackney = fn request ->
case :hackney.request(
request.method,
URI.to_string(request.url),
request.headers,
request.body,
[:with_body]
) do
{:ok, status, headers, body} ->
headers = for {name, value} <- headers, do: {String.downcase(name), value}
response = %Req.Response{status: status, headers: headers, body: body}
{request, response}
{:error, reason} ->
{request, RuntimeError.exception(inspect(reason))}
end
end
Req.get!("https://api.github.com/repos/wojtekmach/req", adapter: hackney).body["description"]
#=> "Req is a batteries-included HTTP client for Elixir."
Link to this section Summary
Functions
Appends error steps.
Appends request steps.
Appends response steps.
Returns the values of the header specified by key
.
Gets the value for a specific private key
.
Halts the request pipeline preventing any further steps from executing.
Merges given options into the request.
Prepends error steps.
Prepends request steps.
Prepends response steps.
Adds a new request header (key
) if not present, otherwise replaces the
previous value of that header with value
.
Adds (or replaces) multiple request headers.
Adds a request header (key
) unless already present.
Assigns a private key
to value
.
Registers options to be used by a custom steps.
Runs the request pipeline.
Updates private key
with the given function.
Link to this section Types
@type t() :: %Req.Request{ adapter: request_step(), body: iodata() | nil, current_request_steps: term(), error_steps: [{name :: atom(), error_step()}], halted: boolean(), headers: [{binary(), binary()}], method: atom(), options: map(), private: map(), registered_options: MapSet.t(), request_steps: [{name :: atom(), request_step()}], response_steps: [{name :: atom(), response_step()}], url: URI.t() }
Link to this section Functions
Appends error steps.
examples
Examples
Req.Request.append_error_steps(request,
noop: fn {request, exception} -> {request, exception} end,
inspect: &IO.inspect/1
)
Appends request steps.
examples
Examples
Req.Request.append_request_steps(request,
noop: fn request -> request end,
inspect: &IO.inspect/1
)
Appends response steps.
examples
Examples
Req.Request.append_response_steps(request,
noop: fn {request, response} -> {request, response} end,
inspect: &IO.inspect/1
)
Returns the values of the header specified by key
.
examples
Examples
iex> req = Req.new(headers: [{"accept", "application/json"}])
iex> Req.Request.get_header(req, "accept")
["application/json"]
Gets the value for a specific private key
.
Halts the request pipeline preventing any further steps from executing.
Merges given options into the request.
examples
Examples
iex> req = Req.new(auth: {"alice", "secret"}, http_errors: :raise)
iex> req = Req.Request.merge_options(req, auth: {:bearer, "abcd"}, base_url: "https://example.com")
iex> req.options
%{auth: {:bearer, "abcd"}, base_url: "https://example.com", http_errors: :raise}
Prepends error steps.
examples
Examples
Req.Request.prepend_error_steps(request,
noop: fn {request, exception} -> {request, exception} end,
inspect: &IO.inspect/1
)
Prepends request steps.
examples
Examples
Req.Request.prepend_request_steps(request,
noop: fn request -> request end,
inspect: &IO.inspect/1
)
Prepends response steps.
examples
Examples
Req.Request.prepend_response_steps(request,
noop: fn {request, response} -> {request, response} end,
inspect: &IO.inspect/1
)
Adds a new request header (key
) if not present, otherwise replaces the
previous value of that header with value
.
Because header keys are case-insensitive in both HTTP/1.1 and HTTP/2, it is recommended for header keys to be in lowercase, to avoid sending duplicate keys in a request.
Additionally, requests with mixed-case headers served over HTTP/2 are not considered valid by common clients, resulting in dropped requests.
examples
Examples
iex> req = Req.new()
iex> req = Req.Request.put_header(req, "accept", "application/json")
iex> req.headers
[{"accept", "application/json"}]
Adds (or replaces) multiple request headers.
See put_header/3
for more information.
examples
Examples
iex> req = Req.new()
iex> req = Req.Request.put_headers(req, [{"accept", "text/html"}, {"accept-encoding", "gzip"}])
iex> req.headers
[{"accept", "text/html"}, {"accept-encoding", "gzip"}]
Adds a request header (key
) unless already present.
See put_header/3
for more information.
examples
Examples
iex> req =
...> Req.new()
...> |> Req.Request.put_new_header("accept", "application/json")
...> |> Req.Request.put_new_header("accept", "application/html")
iex> req.headers
[{"accept", "application/json"}]
Assigns a private key
to value
.
Registers options to be used by a custom steps.
Req ensures that all used options were previously registered which helps finding accidentally mistyped option names. If you're adding custom steps that are accepting options, call this function to register them.
examples
Examples
iex> Req.request!(urll: "https://httpbin.org")
** (ArgumentError) unknown option :urll. Did you mean :url?
iex> Req.new(bas_url: "https://httpbin.org")
** (ArgumentError) unknown option :bas_url. Did you mean :base_url?
req =
Req.new(base_url: "https://httpbin.org")
|> Req.Request.register_options([:foo])
Req.get!(req, url: "/status/201", foo: :bar).status
#=> 201
Runs the request pipeline.
Returns {request, response}
or {request, exception}
.
Updates private key
with the given function.
If key
is present in request private map then the existing value is passed to fun
and its
result is used as the updated value of key
. If key
is not present, default
is inserted
as the value of key
. The default value will not be passed through the update function.
examples
Examples
iex> req = %Req.Request{private: %{a: 1}}
iex> Req.Request.update_private(req, :a, 11, & &1 + 1).private
%{a: 2}
iex> Req.Request.update_private(req, :b, 11, & &1 + 1).private
%{a: 1, b: 11}