Elixir：如何正確描述mix.exs設置？

Question

我試圖用HTTPoison編寫一個網頁抓取工具。作爲第一步，我沿着下面的步驟寫了一個簡短的HTTP訪問代碼;

1. 通過混合

   創建一個項目$混用新httptest1

2. 撰寫的lib/httptest1.ex短代碼。

   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爲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. 運行$ mix deps.get的依賴關係。

5. 運行$ mix run，則編譯失敗;

   ==> 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 
   

當我使用$ iex -S mix代替，其結果是一樣的。

但是，如果我將httptest1.ex移動到放置mix.exs的相同目錄中，如$ mv lib/httptest1.ex .，並試圖明確指定源文件;它工作正常。

問題： 我懷疑我的mix.exs設置出了問題，那是什麼？

Answer 1

全部.ex在lib/被編譯。由於Elixir是編譯文件時的元編程語言，因此您實際上正在運行代碼。這意味着編譯項目時會執行Httptest1.test1()。

HTTPoison需要啓動才能正常工作。它是在您的應用程序啓動時啓動的，當您執行mix run ...時。但是當你的項目正在編譯你的項目，或者你的依賴沒有啓動，因此對你的依賴關係的調用可能會失敗。

查看本章Supervisor and Application的入門指南，瞭解如何在應用程序啓動時運行代碼。

Answer 2

改進！現在我知道如何創建一個可執行的調用命令行。

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選項創建）;

由 Httptest.test1 $ iex -S mix類型調用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 

然後，預期的結果登場！謝謝。

此外，爲了創建命令行可執行，

$ mix escript.build 

則產生./httptest1。完成。