Question

我尝试使用HTTPoison编写Web抓取工具。作为第一步，我按照下面显示的步骤编写了一个简短的HTTP访问代码;

通过mix
创建项目
$ mix new httptest1

在lib / httptest1.ex上写一个简短的代码。

defmodule Httptest1 do
  require HTTPoison

  def test1 do
    ret = HTTPoison.get! "http://www.yahoo.com"
    %HTTPoison.Response{status_code: 200, body: body} = ret
    IO.inspect body
  end
end

Httptest1.test1()

修改HTTP.ison的mix.exs。

defmodule Httptest1.Mixfile do
  use Mix.Project

  def project do
    [app: :httptest1,
     version: "0.0.1",
     elixir: "~> 1.0",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps]
  end

  # Configuration for the OTP application
  def application do
    [applications: [:logger, :httpoison]]
  end

  # Dependencies can be Hex packages:
  #
  defp deps do
    [
     {:httpoison, "~> 0.6"}
    ]
  end
end

运行$ mix deps.get以获取相关性。

运行$ mix run，然后编译失败;

==> idna (compile)
Compiled src/idna.erl
Compiled src/idna_ucs.erl
Compiled src/punycode.erl
(... snip ...)
Generated httpoison app

== Compilation error on file lib/httptest1.ex ==
** (exit) exited in: :gen_server.call(:hackney_manager, {:new_request, #PID<0.154.0>, #Reference<0.0.1.1724>, {:client, :undefined, :hackney_dummy_metrics, :hackney_tcp_transport, 'www.yahoo.com', 80, "www.yahoo.com", [connect_timeout: 5000, recv_timeout: :infinity], nil, nil, nil, true, :hackney_pool, :infinity, false, 5, false, 5, nil, nil, nil, :undefined, :start, nil, :normal, false, false, false, false, nil, :waiting, nil, 4096, "", [], :undefined, nil, nil, nil, nil, :undefined, nil}}, :infinity)
    ** (EXIT) no process
    (stdlib) gen_server.erl:212: :gen_server.call/3
    src/hackney_client/hackney_manager.erl:66: :hackney_manager.init_request/1
    src/hackney_client/hackney_manager.erl:56: :hackney_manager.new_request/1
    src/hackney_connect/hackney_connect.erl:181: :hackney_connect.socket_from_pool/4
    src/hackney_connect/hackney_connect.erl:36: :hackney_connect.connect/5
    src/hackney_client/hackney.erl:319: :hackney.request/5
    lib/httpoison.ex:60: HTTPoison.request/5
    lib/httpoison.ex:60: HTTPoison.request!/5

当我使用$ iex -S mix时，结果是相同的。

但是，如果我将httptest1.ex移动到放置了mix.exs的同一目录，例如$ mv lib/httptest1.ex .，并尝试明确指定源文件; $ mix run httptest1，它运作正常。

问题： 我怀疑我的mix.exs设置有问题，那是什么？

Answer 1

.ex中的所有lib/都已编译完毕。由于Elixir是编译文件时的元编程语言，因此实际上是在运行代码。这意味着在编译项目时会执行Httptest1.test1()。

需要启动HTTPoison才能正常工作。它是在您的应用程序启动时启动的，当您执行mix run ...时。但是当您的项目正在编译项目或者您的依赖项未启动时，对依赖项的调用可能会失败。

在入门指南中查看本章Supervisor and Application，了解如何在应用程序启动时运行代码。

Answer 2

改进！现在我知道如何创建可执行的调用命令行。

方案;

defmodule Httptest1 do
  use Application
  require HTTPoison

  def start(_type, _args) do
    import Supervisor.Spec, warn: false
    children = []
    opts = [strategy: :one_for_one, name: Httptest1.Supervisor]
    Supervisor.start_link(children, opts)
  end

  def main(args) do # entry point
    ret = HTTPoison.get! "http://www.yahoo.com"
    %HTTPoison.Response{status_code: _, body: body} = ret # no status code matching now
    IO.inspect body
  end

end

和mix.exs（均由$ mix new httptest1 --sup主管选项创建）;

defmodule Httptest1.Mixfile do
  use Mix.Project

  def project do
    [app: :httptest1,
     version: "0.0.1",
     elixir: "~> 1.0",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     escript: escript,  # <<<< Added 
     deps: deps]
  end

  def escript do # define escript 
    [main_module: Httptest1]
  end

  def application do
    [applications: [:logger, :httpoison],
     mod: {Httptest1, []}] # 
  end

  defp deps do
    [
      {:httpoison, "~> 0.6"}
    ]
  end
end

然后在$ iex -S mix类型Httptest.test1调用的iex中，预期的结果出现了！感谢。

另外，要创建命令行可执行文件，

   $ mix escript.build

然后生成./httptest1。完成。

Elixir：如何正确描述mix.exs设置？

2 个答案: