Erlang TCP套接字关闭 [英] Erlang TCP sockets get closed

问题描述

要学习Erlang，我正在尝试基于 gen_tcp 实现一个小型的Web服务器。不幸的是，我的代码似乎触发了一些有线的行为。为了演示这个问题，我已经附加了我的实现的最小化版本，足以重现问题。只要提供静态200 OK，无论HTTP请求是什么。

To learn Erlang I am trying to implement a tiny web server based on gen_tcp. Unfortunately, my code seems to trigger some wired behaviour. To demonstrate the problem I have attached a minimised version of my implementation which is sufficient to reproduce the problem. It is just delivering a static 200 OK, no matter what the HTTP request was.

当我尝试运行 ab （Apache HTTP服务器基准测试）对我的Web服务器（使用回送接口）。没有任何并发​​请求（ -c ）一切都正常运行。但是，如果我使用 -c 8 或 -c 16 ，则调用 gen_tcp：接受/ 1 似乎在某些套接字上失败，因为我在shell中看到一些请求：关闭行。

The problem arises when I try to run ab (Apache HTTP server benchmarking) against my web server (using loopback interface). Without any concurrent requests (-c) everything is running just fine. However, if I use -c 8 or -c 16, the call to gen_tcp:accept/1 seems to fail on some sockets as I see a number of request: closed lines in the shell.

什么使得整个故事甚至是weirder是，我看到不同的行为在不同的操作系统：

What makes the whole story even weirder is, that I see different behaviours on different operating systems:

• 操作系统X + Erlang / OTP 18： ab 报告启动后几乎立即重新启动连接。


• Debian + Erlang R15B01：全部但是有两个HTTP请求似乎正在运行。但是，然后， ab 挂起几秒钟，并报告指定的超时已过期，总共4998个请求完成，当我运行 ab 与 -n 5000 。同样地，当我运行15000次测试时，报告了14998。

• OS X+Erlang/OTP 18: ab reports "Connection reset by peer" almost immediately after starting.
• Debian+Erlang R15B01: All but two of the HTTP requests seem to run through. But then, ab hangs for a few seconds and reports "The timeout specified has expired, Total of 4998 requests completed", when i run ab with -n 5000. Similarly, 14998 is reported when I run 15000 tests.

这个似乎不是问题。我真的很失落，因此感谢任何帮助！ :)谢谢！

This one does not seem to be the problem. I am honestly quite lost and therefore appreciate any help! :) Thanks!

server(Port) ->
    Opt = [list, {active, false}, {reuseaddr, true}],
    case gen_tcp:listen(Port, Opt) of
        {ok, Listen} ->
            handler(Listen),
            gen_tcp:close(Listen),
            ok;
        {error, Error} ->
            io:format("init: ~w~n", [Error])
    end.

handler(Listen) ->
    case gen_tcp:accept(Listen) of
        {ok, Client} ->
            request(Client),
            handler(Listen);
        {error, Error} ->
            io:format("request: ~w~n", [Error])
    end.

request(Client) ->
    Recv = gen_tcp:recv(Client, 0),
    case Recv of
        {ok, _} ->
            Response = reply(),
            gen_tcp:send(Client, Response);
        {error, Error} ->
            io:format("request: ~w~n", [Error])
    end,
    gen_tcp:close(Client).


reply() ->
    "HTTP/1.0 200 OK\r\n" ++
    "Content-Length: 7\r\n\r\n"
    "static\n".

推荐答案

当您增加与 ab -c N 它将立即打开多个TCP套接字到服务器。

When you increase the number of concurrent requests sent with ab -c N it will immediately open multiple TCP sockets to the server.

默认情况下，使用gen_tcp打开的套接字： listen / 2将仅支持五个未完成的连接请求。使用{backlog，N}选项来增加未完成的连接请求数量到gen_tcp：listen / 2。

By default a socket opened with gen_tcp:listen/2 will support only five outstanding connection requests. Increase the number of connection requests outstanding with the {backlog, N} option to gen_tcp:listen/2.

我用ab测试了在OS X上的代码，看到这个解决具有由对等体重新连接的文件。

I tested your code on OS X with ab and saw this resolve the prolem with "Connection reset by peer".

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