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ExVCR

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Record and replay HTTP interactions library for Elixir. It's inspired by Ruby's VCR (https://github.com/vcr/vcr), and trying to provide similar functionalities.

Basics

The following HTTP libraries can be applied.

  • ibrowse-based libraries.
  • hackney-based libraries.
    • HTTPoison
    • support is very limited, and tested only with sync request of HTTPoison yet.
  • httpc-based libraries.
    • erlang-oauth
    • tirexs
    • support is very limited, and tested only with :httpc.request/1 and :httpc.request/4.
  • Finch
    • the deprecated Finch.request/6 functions is not supported

HTTP interactions are recorded as JSON file. The JSON file can be recorded automatically (vcr_cassettes) or manually updated (custom_cassettes).

Notes

  • ExVCR.Config functions must be called from setup or test. Calls outside of test process, such as in setup_all will not work.

Install

Add :exvcr to deps section of mix.exs.

def deps do
  [ {:exvcr, "~> 0.11", only: :test} ]
end

Optionally, preferred_cli_env: [vcr: :test] can be specified for running mix vcr in :test env by default.

def project do
  [ ...
    preferred_cli_env: [
      vcr: :test, "vcr.delete": :test, "vcr.check": :test, "vcr.show": :test
    ],
    ...
end

Usage

Add use ExVCR.Mock to the test module. This mocks ibrowse by default. For using hackney, specify adapter: ExVCR.Adapter.Hackney options as follows.

Example with ibrowse
defmodule ExVCR.Adapter.IBrowseTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock

  setup do
    ExVCR.Config.cassette_library_dir("fixture/vcr_cassettes")
    :ok
  end

  test "example single request" do
    use_cassette "example_ibrowse" do
      :ibrowse.start
      {:ok, status_code, _headers, body} = :ibrowse.send_req('http://example.com', [], :get)
      assert status_code == '200'
      assert to_string(body) =~ ~r/Example Domain/
    end
  end

  test "httpotion" do
    use_cassette "example_httpotion" do
      HTTPotion.start
      assert HTTPotion.get("http://example.com", []).body =~ ~r/Example Domain/
    end
  end
end
Example with hackney
defmodule ExVCR.Adapter.HackneyTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock, adapter: ExVCR.Adapter.Hackney

  setup_all do
    HTTPoison.start
    :ok
  end

  test "get request" do
    use_cassette "httpoison_get" do
      assert HTTPoison.get!("http://example.com").body =~ ~r/Example Domain/
    end
  end
end
Example with httpc
defmodule ExVCR.Adapter.HttpcTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock, adapter: ExVCR.Adapter.Httpc

  setup_all do
    :inets.start
    :ok
  end

  test "get request" do
    use_cassette "example_httpc_request" do
      {:ok, result} = :httpc.request('http://example.com')
      {{_http_version, _status_code = 200, _reason_phrase}, _headers, body} = result
      assert to_string(body) =~ ~r/Example Domain/
    end
  end
end
Example with Finch
defmodule ExVCR.Adapter.FinchTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock, adapter: ExVCR.Adapter.Finch

  setup_all do
    Finch.start_link(name: MyFinch)
    :ok
  end

  test "get request" do
    use_cassette "example_finch_request" do
      {:ok, response} = Finch.build(:get, "http://example.com/") |> Finch.request(MyFinch)
      assert response.status == 200
      assert Map.new(response.headers)["content-type"] == "text/html; charset=UTF-8"
      assert response.body =~ ~r/Example Domain/
    end
  end
end

Custom Cassettes

You can manually define custom cassette JSON file for more flexible response control rather than just recoding the actual server response.

  • Optional 2nd parameter of ExVCR.Config.cassette_library_dir method specifies the custom cassette directory. The directory is separated from vcr cassette one for avoiding mistakenly overwriting.

  • Adding custom: true option to use_cassette macro indicates to use the custom cassette, and it just returns the pre-defined JSON response, instead of requesting to server.

defmodule ExVCR.MockTest do
  use ExUnit.Case, async: true
  import ExVCR.Mock

  setup do
    ExVCR.Config.cassette_library_dir("fixture/vcr_cassettes", "fixture/custom_cassettes")
    :ok
  end

  test "custom with valid response" do
    use_cassette "response_mocking", custom: true do
      assert HTTPotion.get("http://example.com", []).body =~ ~r/Custom Response/
    end
  end

The custom JSON file format is the same as vcr cassettes.

fixture/custom_cassettes/response_mocking.json

[
  {
    "request": {
      "url": "http://example.com"
    },
    "response": {
      "status_code": 200,
      "headers": {
        "Content-Type": "text/html"
      },
      "body": "<h1>Custom Response</h1>"
    }
  }
]

Recording VCR Cassettes

Matching

ExVCR uses URL parameter to match request and cassettes. The url parameter in the JSON file is taken as regexp string.

Removing Sensitive Data

ExVCR.Config.filter_sensitive_data(pattern, placeholder) method can be used to remove sensitive data. It searches for string matches with pattern, which is a string representing a regular expression, and replaces with placeholder. Replacements happen both in URLs and request and response bodies.

test "replace sensitive data" do
  ExVCR.Config.filter_sensitive_data("<PASSWORD>.+</PASSWORD>", "PLACEHOLDER")
  use_cassette "sensitive_data" do
    assert HTTPotion.get("http://something.example.com", []).body =~ ~r/PLACEHOLDER/
  end
end

ExVCR.Config.filter_request_headers(header) and ExVCR.Config.filter_request_options(option) can be used to remove sensitive data in the request headers. It checks if the header is found in the request headers and blanks out it's value with ***.

test "replace sensitive data in request header" do
  ExVCR.Config.filter_request_headers("X-My-Secret-Token")
  use_cassette "sensitive_data_in_request_header" do
    body = HTTPoison.get!("http://localhost:34000/server?", ["X-My-Secret-Token": "my-secret-token"]).body
    assert body == "test_response"
  end

  # The recorded cassette should contain replaced data.
  cassette = File.read!("#{@dummy_cassette_dir}/sensitive_data_in_request_header.json")
  assert cassette =~ "\"X-My-Secret-Token\": \"***\""
  refute cassette =~  "\"X-My-Secret-Token\": \"my-secret-token\""

  ExVCR.Config.filter_request_headers(nil)
end
test "replace sensitive data in request options" do
  ExVCR.Config.filter_request_options("basic_auth")
  use_cassette "sensitive_data_in_request_options" do
    body = HTTPoison.get!(@url, [], [hackney: [basic_auth: {"username", "password"}]]).body
    assert body == "test_response"
  end

  # The recorded cassette should contain replaced data.
  cassette = File.read!("#{@dummy_cassette_dir}/sensitive_data_in_request_options.json")
  assert cassette =~ "\"basic_auth\": \"***\""
  refute cassette =~  "\"basic_auth\": {\"username\", \"password\"}"

  ExVCR.Config.filter_request_options(nil)
end

Ignoring query params in URL

If ExVCR.Config.filter_url_params(true) is specified, query params in URL will be ignored when recording cassettes.

test "filter url param flag removes url params when recording cassettes" do
  ExVCR.Config.filter_url_params(true)
  use_cassette "example_ignore_url_params" do
    assert HTTPotion.get(
      "http://localhost:34000/server?should_not_be_contained", []).body =~ ~r/test_response/
  end
  json = File.read!("#{__DIR__}/../#{@dummy_cassette_dir}/example_ignore_url_params.json")
  refute String.contains?(json, "should_not_be_contained")

Removing headers from response

If ExVCR.Config.response_headers_blacklist(headers_blacklist) is specified, the headers in the list will be removed from the response.

test "remove blacklisted headers" do
  use_cassette "original_headers" do
    assert Map.has_key?(HTTPoison.get!(@url, []).headers, "connection") == true
  end

  ExVCR.Config.response_headers_blacklist(["Connection"])
  use_cassette "remove_blacklisted_headers" do
    assert Map.has_key?(HTTPoison.get!(@url, []).headers, "connection") == false
  end

  ExVCR.Config.response_headers_blacklist([])
end

Matching Options

Matching against query params

By default, query params are not used for matching. In order to include query params, specify match_requests_on: [:query] for use_cassette call.

test "matching query params with match_requests_on params" do
  use_cassette "different_query_params", match_requests_on: [:query] do
    assert HTTPotion.get("http://localhost/server?p=3", []).body =~ ~r/test_response3/
    assert HTTPotion.get("http://localhost/server?p=4", []).body =~ ~r/test_response4/
  end
end
Matching against request body

By default, request body is not used for matching. In order to include request body, specify match_requests_on: [:request_body] for use_cassette call.

test "matching request body with match_requests_on params" do
  use_cassette "different_request_body_params", match_requests_on: [:request_body] do
    assert HTTPotion.post("http://localhost/server", [body: "p=3"]).body =~ ~r/test_response3/
    assert HTTPotion.post("http://localhost/server", [body: "p=4"]).body =~ ~r/test_response4/
  end
end
Matching against custom parameters

You can define and use your own matchers for cases not covered by the build-in matchers. To do this you can specify custom_matchers: [func_one, func_two, ...] for use_cassette call.

test "matching special header with custom_matchers" do
  matches_special_header = fn response, keys, _recorder_options ->
    recorded_headers = always_map(response.request.headers)
    expected_value = recorded_headers["X-Special-Header"]
    keys[:headers]
    |> Enum.any?(&(match?({"X-Special-Header", ^expected_value}, &1)))
  end

  use_cassette "special_header_match", custom_matchers: [matches_special_header] do
    # These two requests will match with each other since our custom matcher matches (even if without matching all headers)
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "My App", "X-Special-Header": "Value One"]]).body =~ ~r/test_response_one/
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "Other App", "X-Special-Header": "Value One"]]).body =~ ~r/test_response_one/

    # This will not match since the header has a different value:
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "My App", "X-Special-Header": "Value Two"]]).body =~ ~r/test_response_two/
  end
end

Default Config

Default parameters for ExVCR.Config module can be specified in config\config.exs as follows.

use Mix.Config

config :exvcr, [
  vcr_cassette_library_dir: "fixture/vcr_cassettes",
  custom_cassette_library_dir: "fixture/custom_cassettes",
  filter_sensitive_data: [
    [pattern: "<PASSWORD>.+</PASSWORD>", placeholder: "PASSWORD_PLACEHOLDER"]
  ],
  filter_url_params: false,
  filter_request_headers: [],
  response_headers_blacklist: []
]

If exvcr is defined as test-only dependency, describe the above statement in test-only config file (ex. config\test.exs) or make it conditional (ex. wrap with if Mix.env == :test).

Global mock experimental feature

The global mock is an attempt to address a general issue with exvcr being slow, see #107

In general, every use_cassette takes around 500 ms so if you extensively use cassettes it could spend minutes doing :meck.expect/2 and :meck.unload/1. Even exvcr tests need 40 seconds versus 1 second when global mock is used.

Since feature is experimental be careful when using it. Please note the following:

  • ExVCR implements global mock, which means that all HTTP client calls outside of use_cassette go through meck.passthough/1.
  • There are some report that the feature doesn't work in some case, see the issue.
  • By default, the global mocking disabled, to enabled it set the following in config:
use Mix.Config

config :exvcr, [
  global_mock: true
]

All tests that are written for exvcr could also be running in global mocking mode:

$ GLOBAL_MOCK=true mix test

.........................................................

Finished in 1.3 seconds
141 tests, 0 failures

Randomized with seed 905427

Mix Tasks

The following tasks are added by including exvcr package.

[mix vcr] Show cassettes

$ mix vcr
Showing list of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Last Update]
  example_httpotion.json                   2013/11/07 23:24:49
  example_ibrowse.json                     2013/11/07 23:24:49
  example_ibrowse_multiple.json            2013/11/07 23:24:48
  httpotion_delete.json                    2013/11/07 23:24:47
  httpotion_patch.json                     2013/11/07 23:24:50
  httpotion_post.json                      2013/11/07 23:24:51
  httpotion_put.json                       2013/11/07 23:24:52

Showing list of cassettes in [fixture/custom_cassettes]
  [File Name]                              [Last Update]
  method_mocking.json                      2013/10/06 22:05:38
  response_mocking.json                    2013/09/29 17:23:38
  response_mocking_regex.json              2013/10/06 18:13:45

[mix vcr.delete] Delete cassettes

The mix vcr.delete task deletes the cassettes that contains the specified pattern in the file name.

$ mix vcr.delete ibrowse
Deleted example_ibrowse.json.
Deleted example_ibrowse_multiple.json.

If -i (--interactive) option is specified, it asks for confirmation before deleting each file.

$ mix vcr.delete ibrowse -i
delete example_ibrowse.json? y
Deleted example_ibrowse.json.
delete example_ibrowse_multiple.json? y
Deleted example_ibrowse_multiple.json.

If -a (--all) option is specified, all the cassettes in the specified folder becomes the target for delete.

[mix vcr.check] Check cassettes

The mix vcr.check shows how many times each cassette is applied while executing mix test tasks. It is intended for verifying the cassettes are properly used. [Cassette Counts] indicates the count that the pre-recorded JSON cassettes are applied. [Server Counts] indicates the count that server access is performed.

$ mix vcr.check
...............................
31 tests, 0 failures
Showing hit counts of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  example_httpotion.json                   1                    0
  example_ibrowse.json                     1                    0
  example_ibrowse_multiple.json            2                    0
  httpotion_delete.json                    1                    0
  httpotion_patch.json                     1                    0
  httpotion_post.json                      1                    0
  httpotion_put.json                       1                    0
  sensitive_data.json                      0                    2
  server1.json                             0                    2
  server2.json                             2                    2

Showing hit counts of cassettes in [fixture/custom_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  method_mocking.json                      1                    0
  response_mocking.json                    1                    0
  response_mocking_regex.json              1                    0

The target test file can be limited by specifying test files, as similar as mix test tasks.

$ mix vcr.check test/exvcr_test.exs
.............
13 tests, 0 failures
Showing hit counts of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  example_httpotion.json                   1                    0
...
...

[mix vcr.show] Show cassettes

The mix vcr.show task displays the contents of cassettes JSON file in the prettified format.

$ mix vcr.show fixture/vcr_cassettes/httpoison_get.json
[
  {
    "request": {
      "url": "http://example.com",
      "headers": [],
      "method": "get",
      "body": "",
      "options": []
    },
...

[mix vcr --help] Help

Displays helps for mix sub-tasks.

$ mix vcr --help
Usage: mix vcr [options]
  Used to display the list of cassettes

  -h (--help)         Show helps for vcr mix tasks
  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory

Usage: mix vcr.delete [options] [cassete-file-names]
  Used to delete cassettes

  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory
  -i (--interactive)  Request confirmation before attempting to delete
  -a (--all)          Delete all the files by ignoring specified [filenames]

Usage: mix vcr.check [options] [test-files]
  Used to check cassette use on test execution

  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory

Usage: mix vcr.show [cassete-file-names]
  Used to show cassette contents
Notes

If the cassette save directory is changed from the default, [-d, --dir] option (for vcr cassettes) and [-c, --custom] option (for custom cassettes) can be used to specify the directory.

IEx Helper

ExVCR.IEx module provides simple helper functions to display the HTTP request/response in JSON format, instead of recording in the cassette files.

% iex -S mix
Erlang R16B03 (erts-5.10.4) ...
Interactive Elixir (0.12.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require ExVCR.IEx
nil
iex(2)> ExVCR.IEx.print do
...(2)>   :ibrowse.send_req('http://example.com', [], :get)
...(2)> end
[
  {
    "request": {
      "url": "http://example.com",
      "headers": [],
      "method": "get",
      "body": "",
      "options": []
    },
    "response": {
      "type": "ok",
      "status_code": 200,
...

The adapter option can be specified as adapter argument of print function, as follows.

% iex -S mix
Erlang R16B03 (erts-5.10.4) ...

Interactive Elixir (0.12.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require ExVCR.IEx
nil
iex(2)> ExVCR.IEx.print(adapter: ExVCR.Adapter.Hackney) do
...(2)>   HTTPoison.get!("http://example.com").body
...(2)> end
[
  {
    "request": {
      "url": "http://example.com",
...

Stubbing Response

Specifying :stub as fixture name allows directly stubbing the response header/body information based on parameter.

test "stub request works for HTTPotion" do
  use_cassette :stub, [url: "http://example.com", body: "Stub Response", status_code: 200] do
    response = HTTPotion.get("http://example.com", [])
    assert response.body =~ ~r/Stub Response/
    assert response.headers[:"Content-Type"] == "text/html"
    assert response.status_code == 200
  end
end

test "stub request works for HTTPoison" do
  use_cassette :stub, [url: "http://www.example.com", body: "Stub Response"] do
    response = HTTPoison.get!("http://www.example.com")
    assert response.body =~ ~r/Stub Response/
    assert response.headers["Content-Type"] == "text/html"
    assert response.status_code == 200
  end
end

test "stub request works for httpc" do
  use_cassette :stub, [url: "http://www.example.com",
                       method: "get",
                       status_code: ["HTTP/1.1", 200, "OK"],
                       body: "success!"] do

  {:ok, result} = :httpc.request('http://example.com')
  {{_http_version, _status_code = 200, _reason_phrase}, _headers, body} = result
  assert to_string(body) == "success!"
end

If the specified :url parameter doesn't match requests called inside the use_cassette block, it raises ExVCR.InvalidRequestError.

The :url can be regular expression string. Please note that you should use the ~r sigil with / as delimiters.

test "match URL with regular expression" do
  use_cassette :stub, [url: "~r/(foo|bar)/", body: "Stub Response", status_code: 200] do
    # ...
  end
end

test "make sure to properly escape the /" do
  # escape /path/to/file
  use_cassette :stub, [url: "~r/\/path\/to\/file", body: "Stub Response", status_code: 200] do
    # ...
  end
end

test "the sigil delimiter cannot be anything else" do
  use_cassette :stub, [url: "~r{this-delimiter-doesn-not-work}", body: "Stub Response", status_code: 200] do
    # ...
  end
end

TODO

  • Improve performance, as it's very slow.

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HTTP request/response recording library for elixir, inspired by VCR.

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