Elixir：如何正确描述mix.exs设置？

Question

我试图用HTTPoison编写一个网页抓取工具。作为第一步，我沿着下面的步骤写了一个简短的HTTP访问代码;

1. 通过混合

   创建一个项目$混用新httptest1

2. 撰写的lib/httptest1.ex短代码。

   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() 
   

3. 修改mix.exs为HTTPoison。

   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 
   

4. 运行$ mix deps.get的依赖关系。

5. 运行$ mix run，则编译失败;

   ==> 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代替，其结果是一样的。

但是，如果我将httptest1.ex移动到放置mix.exs的相同目录中，如$ mv lib/httptest1.ex .，并试图明确指定源文件;它工作正常。

问题： 我怀疑我的mix.exs设置出了问题，那是什么？

Answer 1

全部.ex在lib/被编译。由于Elixir是编译文件时的元编程语言，因此您实际上正在运行代码。这意味着编译项目时会执行Httptest1.test1()。

HTTPoison需要启动才能正常工作。它是在您的应用程序启动时启动的，当您执行mix run ...时。但是当你的项目正在编译你的项目，或者你的依赖没有启动，因此对你的依赖关系的调用可能会失败。

查看本章Supervisor and Application的入门指南，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一个可执行的调用命令行。

程序;

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 supervisor选项创建）;

由 Httptest.test1 $ iex -S mix类型调用IEX

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，预期的结果登场！谢谢。

此外，为了创建命令行可执行，

$ mix escript.build 

则产生./httptest1。完成。