defmodule Req.Request do
@moduledoc ~S"""
The low-level API and the request struct.
Req is composed of three main pieces:
* `Req` - the high-level API
* `Req.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"](#module-writing-plugins) section for more information.
## 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
* `: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"](#module-options) section below
for more information.
* `:halted` - whether the request pipeline is halted. See `halt/1`
* `:adapter` - a request step that makes the actual HTTP request. Defaults to
`Req.Steps.run_finch/1`. See ["Adapter"](#module-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 accepts `t:atom/0` keys.
## 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
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
A 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
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}
end
### 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
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 struct
* The 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 call `merge_options/2`. Remember to first register
options before merging!
## Adapter
As noted in the ["Request steps"](#module-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."
"""
@type t() :: %Req.Request{
method: atom(),
url: URI.t(),
headers: [{binary(), binary()}],
body: iodata() | nil,
options: map(),
registered_options: MapSet.t(),
halted: boolean(),
adapter: request_step(),
request_steps: [{name :: atom(), request_step()}],
response_steps: [{name :: atom(), response_step()}],
error_steps: [{name :: atom(), error_step()}],
private: map()
}
@typep request_step() :: fun()
@typep response_step() :: fun()
@typep error_step() :: fun()
defstruct method: :get,
url: URI.parse(""),
headers: [],
body: nil,
options: %{},
halted: false,
adapter: &Req.Steps.run_finch/1,
request_steps: [],
response_steps: [],
error_steps: [],
private: %{},
registered_options: MapSet.new(),
current_request_steps: []
@doc """
Gets the value for a specific private `key`.
"""
def get_private(request, key, default \\ nil) when is_atom(key) do
Map.get(request.private, key, default)
end
@doc """
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
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}
"""
def update_private(request, key, default, fun) when is_atom(key) and is_function(fun, 1) do
update_in(request.private, &Map.update(&1, key, default, fun))
end
@doc """
Assigns a private `key` to `value`.
"""
def put_private(request, key, value) when is_atom(key) do
put_in(request.private[key], value)
end
@doc """
Halts the request pipeline preventing any further steps from executing.
"""
def halt(request) do
%{request | halted: true}
end
@doc """
Appends request steps.
## Examples
Req.Request.append_request_steps(request,
noop: fn request -> request end,
inspect: &IO.inspect/1
)
"""
def append_request_steps(request, steps) do
%{
request
| request_steps: request.request_steps ++ steps,
current_request_steps: request.current_request_steps ++ Keyword.keys(steps)
}
end
@doc """
Prepends request steps.
## Examples
Req.Request.prepend_request_steps(request,
noop: fn request -> request end,
inspect: &IO.inspect/1
)
"""
def prepend_request_steps(request, steps) do
%{
request
| request_steps: steps ++ request.request_steps,
current_request_steps: Keyword.keys(steps) ++ request.current_request_steps
}
end
@doc """
Appends response steps.
## Examples
Req.Request.append_response_steps(request,
noop: fn {request, response} -> {request, response} end,
inspect: &IO.inspect/1
)
"""
def append_response_steps(request, steps) do
%{
request
| response_steps: request.response_steps ++ steps
}
end
@doc """
Prepends response steps.
## Examples
Req.Request.prepend_response_steps(request,
noop: fn {request, response} -> {request, response} end,
inspect: &IO.inspect/1
)
"""
def prepend_response_steps(request, steps) do
%{
request
| response_steps: steps ++ request.response_steps
}
end
@doc """
Appends error steps.
## Examples
Req.Request.append_error_steps(request,
noop: fn {request, exception} -> {request, exception} end,
inspect: &IO.inspect/1
)
"""
def append_error_steps(request, steps) do
%{
request
| error_steps: request.error_steps ++ steps
}
end
@doc """
Prepends error steps.
## Examples
Req.Request.prepend_error_steps(request,
noop: fn {request, exception} -> {request, exception} end,
inspect: &IO.inspect/1
)
"""
def prepend_error_steps(request, steps) do
%{
request
| error_steps: steps ++ request.error_steps
}
end
@doc false
def prepare(%{request_steps: [step | steps]} = request) do
case run_step(step, request) do
%Req.Request{} = request ->
request = %{request | request_steps: steps}
prepare(request)
{_request, %{__exception__: true} = exception} ->
raise exception
end
end
def prepare(%Req.Request{request_steps: []} = request) do
request
end
@doc """
Merges given options into the request.
## 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}
"""
@spec merge_options(t(), keyword()) :: t()
def merge_options(%Req.Request{} = request, options) when is_list(options) do
# TODO: remove on v0.5
deprecated = [:method, :url, :headers, :body, :adapter]
options =
case deprecated -- deprecated -- Keyword.keys(options) do
[] ->
options
deprecated ->
IO.warn(
"Passing " <>
Enum.map_join(deprecated, "/", &inspect/1) <>
" is deprecated, use Req.update/2 instead."
)
Keyword.drop(options, deprecated)
end
validate_options(request, options)
update_in(request.options, &Map.merge(&1, Map.new(options)))
end
@doc """
Returns the values of the header specified by `key`.
## Examples
iex> req = Req.new(headers: [{"accept", "application/json"}])
iex> Req.Request.get_header(req, "accept")
["application/json"]
"""
@spec get_header(t(), binary()) :: [binary()]
def get_header(%Req.Request{} = request, key) when is_binary(key) do
for {^key, value} <- request.headers, do: value
end
@doc """
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
iex> req = Req.new()
iex> req = Req.Request.put_header(req, "accept", "application/json")
iex> req.headers
[{"accept", "application/json"}]
"""
@spec put_header(t(), binary(), binary()) :: t()
def put_header(%Req.Request{} = request, key, value)
when is_binary(key) and is_binary(value) do
%{request | headers: List.keystore(request.headers, key, 0, {key, value})}
end
@doc """
Adds (or replaces) multiple request headers.
See `put_header/3` for more information.
## 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"}]
"""
@spec put_headers(t(), [{binary(), binary()}]) :: t()
def put_headers(%Req.Request{} = request, headers) do
for {key, value} <- headers, reduce: request do
acc -> put_header(acc, key, value)
end
end
@doc """
Adds a request header (`key`) unless already present.
See `put_header/3` for more information.
## 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"}]
"""
@spec put_new_header(t(), binary(), binary()) :: t()
def put_new_header(%Req.Request{} = request, key, value)
when is_binary(key) and is_binary(value) do
case get_header(request, key) do
[] ->
put_header(request, key, value)
_ ->
request
end
end
@doc """
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
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
"""
def register_options(%Req.Request{} = request, options) when is_list(options) do
update_in(request.registered_options, &MapSet.union(&1, MapSet.new(options)))
end
@doc deprecated: "Use Req.Request.request/1 instead"
def run(request) do
case run_request(request) do
{_request, %Req.Response{} = response} ->
{:ok, response}
{_request, exception} ->
{:error, exception}
end
end
@doc deprecated: "Use Req.Request.request/1 instead"
def run!(request) do
case run_request(request) do
{_request, %Req.Response{} = response} ->
response
{_request, exception} ->
raise exception
end
end
@doc """
Runs the request pipeline.
Returns `{request, response}` or `{request, exception}`.
"""
def run_request(request)
def run_request(%{current_request_steps: [step | rest]} = request) do
step = Keyword.fetch!(request.request_steps, step)
case step.(request) do
%Req.Request{} = request ->
run_request(%{request | current_request_steps: rest})
{%Req.Request{halted: true} = request, response_or_exception} ->
{request, response_or_exception}
{request, %Req.Response{} = response} ->
run_response(request, response)
{request, %{__exception__: true} = exception} ->
run_error(request, exception)
end
end
def run_request(%{current_request_steps: []} = request) do
case request.adapter.(request) do
{request, %Req.Response{} = response} ->
run_response(request, response)
{request, %{__exception__: true} = exception} ->
run_error(request, exception)
other ->
raise "expected adapter to return {request, response} or {request, exception}, " <>
"got: #{inspect(other)}"
end
end
defp run_response(request, response) do
steps = request.response_steps
Enum.reduce_while(steps, {request, response}, fn step, {request, response} ->
case run_step(step, {request, response}) do
{%Req.Request{halted: true} = request, response_or_exception} ->
{:halt, {request, response_or_exception}}
{request, %Req.Response{} = response} ->
{:cont, {request, response}}
{request, %{__exception__: true} = exception} ->
{:halt, run_error(request, exception)}
end
end)
end
defp run_error(request, exception) do
steps = request.error_steps
Enum.reduce_while(steps, {request, exception}, fn step, {request, exception} ->
case run_step(step, {request, exception}) do
{%Req.Request{halted: true} = request, response_or_exception} ->
{:halt, {request, response_or_exception}}
{request, %{__exception__: true} = exception} ->
{:cont, {request, exception}}
{request, %Req.Response{} = response} ->
{:halt, run_response(request, response)}
end
end)
end
defp run_step({name, step}, state) when is_atom(name) and is_function(step, 1) do
step.(state)
end
@doc false
def validate_options(%Req.Request{} = request, options) do
validate_options(options, request.registered_options)
end
def validate_options([{name, _value} | rest], registered) do
if name in registered do
validate_options(rest, registered)
else
case did_you_mean(Atom.to_string(name), registered) do
{similar, score} when score > 0.8 ->
raise ArgumentError, "unknown option #{inspect(name)}. Did you mean :#{similar}?"
_ ->
raise ArgumentError, "unknown option #{inspect(name)}"
end
end
end
def validate_options([], _registered) do
:ok
end
defp did_you_mean(option, registered) do
registered
|> Enum.map(&to_string/1)
|> Enum.reduce({nil, 0}, &max_similar(&1, option, &2))
end
defp max_similar(option, registered, {_, current} = best) do
score = String.jaro_distance(option, registered)
if score < current, do: best, else: {option, score}
end
defimpl Inspect do
import Inspect.Algebra
def inspect(request, opts) do
open = color("%Req.Request{", :map, opts)
sep = color(",", :map, opts)
close = color("}", :map, opts)
{headers, options} =
if Map.get(request.options, :redact_auth, true) do
headers =
for {name, value} <- request.headers do
if name in ["authorization", "Authorization"] do
{name, "[redacted]"}
else
{name, value}
end
end
options =
case request.options do
%{auth: {:bearer, _bearer}} ->
%{request.options | auth: {:bearer, "[redacted]"}}
%{auth: {_username, _password}} ->
%{request.options | auth: {["redacted"], "[redacted]"}}
_ ->
request.options
end
{headers, options}
else
{request.headers, request.options}
end
list = [
method: request.method,
url: request.url,
headers: headers,
body: request.body,
options: options,
registered_options: request.registered_options,
halted: request.halted,
adapter: request.adapter,
request_steps: request.request_steps,
response_steps: request.response_steps,
error_steps: request.error_steps,
private: request.private
]
fun = fn
{:url, value}, opts ->
key = color("url:", :atom, opts)
doc =
concat(["URI.parse(", color("\"" <> URI.to_string(value) <> "\"", :string, opts), ")"])
concat(key, concat(" ", doc))
{key, value}, opts ->
Inspect.List.keyword({key, value}, opts)
end
container_doc(open, list, close, opts, fun, separator: sep, break: :strict)
end
end
end
