使用 Java 套接字的 HTTP 1.1 持久连接

HTTP 1.1 Persistent Connections using Sockets in Java

提问by Zxaos

Let's say I have a java program that makes an HTTP request on a server using HTTP 1.1 and doesn't close the connection. I make one request, and read all data returned from the input stream I have bound to the socket. However, upon making a second request, I get no response from the server (or there's a problem with the stream - it doesn't provide any more input). If I make the requests in order (Request, request, read) it works fine, but (request, read, request, read) doesn't.

假设我有一个 Java 程序，它使用 HTTP 1.1 在服务器上发出 HTTP 请求并且不关闭连接。我发出一个请求，并读取从绑定到套接字的输入流返回的所有数据。但是，在发出第二个请求时，我没有得到服务器的响应（或者流存在问题 - 它不再提供任何输入）。如果我按顺序发出请求 (Request, request, read) 它工作正常，但 (request, read, request, read) 没有。

Could someone shed some insight onto why this might be happening? (Code snippets follow). No matter what I do, the second read loop's isr_reader.read() only ever returns -1.

有人可以深入了解为什么会发生这种情况吗？（代码片段如下）。无论我做什么，第二个读取循环的 isr_reader.read() 都只会返回 -1。

try{
        connection = new Socket("SomeServer", port);
        con_out = connection.getOutputStream();
        con_in  = connection.getInputStream();
        PrintWriter out_writer = new PrintWriter(con_out, false);
        out_writer.print("GET http://somesite HTTP/1.1\r\n");
        out_writer.print("Host: thehost\r\n");
        //out_writer.print("Content-Length: 0\r\n");
        out_writer.print("\r\n");
        out_writer.flush();

        // If we were not interpreting this data as a character stream, we might need to adjust byte ordering here.
        InputStreamReader isr_reader = new InputStreamReader(con_in);
        char[] streamBuf = new char[8192];
        int amountRead;
        StringBuilder receivedData = new StringBuilder();
        while((amountRead = isr_reader.read(streamBuf)) > 0){
            receivedData.append(streamBuf, 0, amountRead);
        }

// Response is processed here.

        if(connection != null && !connection.isClosed()){
            //System.out.println("Connection Still Open...");

        out_writer.print("GET http://someSite2\r\n");
        out_writer.print("Host: somehost\r\n");
        out_writer.print("Connection: close\r\n");
        out_writer.print("\r\n");
        out_writer.flush();

        streamBuf = new char[8192];
        amountRead = 0;
        receivedData.setLength(0);
        while((amountRead = isr_reader.read(streamBuf)) > 0 || amountRead < 1){
            if (amountRead > 0)
                receivedData.append(streamBuf, 0, amountRead);
        }
}
        // Process response here
    }

Responses to questions: Yes, I'm receiving chunked responses from the server. I'm using raw sockets because of an outside restriction.

对问题的回答：是的，我正在从服务器接收分块响应。由于外部限制，我正在使用原始套接字。

Apologies for the mess of code - I was rewriting it from memory and seem to have introduced a few bugs.

为混乱的代码道歉 - 我是从记忆中重写它的，似乎引入了一些错误。

So the consensus is I have to either do (request, request, read) and let the server close the stream once I hit the end, or, if I do (request, read, request, read) stop before I hit the end of the stream so that the stream isn'tclosed.

所以共识是我必须要么做（请求，请求，读取）并让服务器在我结束时关闭流，或者，如果我这样做（请求，读取，请求，读取）在我结束之前停止流，以便流不会关闭。

采纳答案by Alexander

According to your code, the only time you'll even reach the statements dealing with sending the second request is when the server closes the output stream (your input stream) after receiving/responding to the first request.

根据您的代码，您甚至可以到达处理发送第二个请求的语句的唯一时间是服务器在接收/响应第一个请求后关闭输出流（您的输入流）。

The reason for that is that your code that is supposed to read only the first response

原因是您的代码应该只读取第一个响应

while((amountRead = isr_reader.read(streamBuf)) > 0) {
  receivedData.append(streamBuf, 0, amountRead);
}

will block until the server closes the output stream (i.e., when readreturns -1) or until the read timeout on the socket elapses. In the case of the read timeout, an exception will be thrown and you won't even get to sending the second request.

将阻塞直到服务器关闭输出流（即，当read返回时-1）或直到套接字上的读取超时过去。在读取超时的情况下，将抛出异常，您甚至无法发送第二个请求。

The problem with HTTP responses is that they don't tell you how many bytes to read from the stream until the end of the response. This is not a big deal for HTTP 1.0 responses, because the server simply closes the connection after the response thus enabling you to obtain the response (status line + headers + body) by simply reading everything until the end of the stream.

HTTP 响应的问题在于它们不会告诉您在响应结束之前要从流中读取多少字节。这对于 HTTP 1.0 响应来说不是什么大问题，因为服务器只是在响应之后关闭连接，从而使您能够通过简单地读取所有内容直到流结束来获取响应（状态行 + 标头 + 正文）。

With HTTP 1.1 persistent connections you can no longer simply read everything until the end of the stream. You first need to read the status line and the headers, line by line, and then, based on the status code and the headers (such as Content-Length) decide how many bytes to read to obtain the response body (if it's present at all). If you do the above properly, your read operations will complete before the connection is closed or a timeout happens, and you will have read exactly the response the server sent. This will enable you to send the next request and then read the second response in exactly the same manner as the first one.

使用 HTTP 1.1 持久连接，您不能再简单地读取所有内容，直到流结束。您首先需要逐行读取状态行和标题，然后根据状态代码和标题（例如 Content-Length）决定读取多少字节以获得响应正文（如果它存在于全部）。如果您正确执行上述操作，您的读取操作将在连接关闭或超时发生之前完成，并且您将准确读取服务器发送的响应。这将使您能够发送下一个请求，然后以与第一个完全相同的方式读取第二个响应。

P.S. Request, request, read might be "working" in the sense that your server supports request pipelining and thus, receives and processes both request, and you, as a result, read both responses into one buffer as your "first" response.

PS Request, request, read 可能是“工作”的，因为您的服务器支持请求流水线，因此接收和处理两个请求，因此，您将两个响应读入一个缓冲区作为“第一个”响应。

P.P.S Make sure your PrintWriteris using the US-ASCIIencoding. Otherwise, depending on your system encoding, the request line and headers of your HTTP requests might be malformed (wrong encoding).

PPS 确保您PrintWriter正在使用US-ASCII编码。否则，根据您的系统编码，您的 HTTP 请求的请求行和标头可能格式错误（错误编码）。

回答by Ates Goral

Make sure you have a Connection: keep-alivein your request. This may be a moot point though.

确保您Connection: keep-alive的请求中有一个。不过，这可能是一个有争议的问题。

What kind of response is the server returning? Are you using chunked transfer? If the server doesn't know the size of the response body, it can't provide a Content-Lengthheader and has to close the connection at the end of the response body to indicate to the client that the content has ended. In this case, the keep-alive won't work. If you're generating content on-the-fly with PHP, JSP etc., you can enable output buffering, check the size of the accumulated body, push the Content-Lengthheader and flush the output buffer.

服务器返回什么样的响应？您是否使用分块传输？如果服务器不知道响应正文的大小，则它无法提供Content-Length标头，并且必须在响应正文的末尾关闭连接以向客户端指示内容已结束。在这种情况下，keep-alive 将不起作用。如果您正在使用 PHP、JSP 等即时生成内容，则可以启用输出缓冲、检查累积正文的大小、推送Content-Length标题并刷新输出缓冲区。

回答by Ates Goral

Is there a particular reason you're using raw sockets and not Java's URL Connection or Commons HTTPClient?

您使用原始套接字而不是 Java 的 URL Connection 或Commons HTTPClient是否有特殊原因？

HTTP isn't easy to get right. I know Commons HTTP Client can re-use connections like you're trying to do.

HTTP 并不容易正确。我知道 Commons HTTP Client 可以像您尝试的那样重用连接。

If there isn't a specific reason for you using Sockets this is what I would recommend :)

如果您没有使用 Sockets 的特定原因，这就是我推荐的 :)

回答by MarkR

Writing your own correct client HTTP/1.1 implementation is nontrivial; historically most people who I've seen attempt it have got it wrong. Their implementation usually ignores the spec and just does what appears to work with one particular test server - in particular, they usually ignore the requirement to be able to handle chunked responses.

编写您自己的正确客户端 HTTP/1.1 实现非常重要；从历史上看，我见过的大多数尝试它的人都弄错了。他们的实现通常会忽略规范，只做看起来可以与一个特定测试服务器一起工作的事情——特别是，他们通常会忽略能够处理分块响应的要求。

Writing your own HTTP client is probably a bad idea, unless you have some VERY strange requirements.

编写自己的 HTTP 客户端可能是一个坏主意，除非您有一些非常奇怪的要求。

回答by Matthieu Peschaud

Writing a simple http/1.1 client respecting the RFC is not such a difficult task. To solve the problem of the blocking i/o access where reading a socket in java, you must use java.nio classes. SocketChannels give the possibility to perform a non-blocking i/o access.

编写一个简单的符合 RFC 的 http/1.1 客户端并不是一项艰巨的任务。为了解决java中读取socket时阻塞i/o访问的问题，必须使用java.nio类。SocketChannels 提供了执行非阻塞 i/o 访问的可能性。

This is necessary to send HTTP request on a persistent connection.

这是在持久连接上发送 HTTP 请求所必需的。

Furthermore, nio classes will give better performances.

此外，nio 类将提供更好的性能。

My stress test give to following results :

我的压力测试给出了以下结果：

• HTTP/1.0 (java.io) -> HTTP/1.0 (java.nio) = +20% faster

• HTTP/1.0 (java.io) -> HTTP/1.1 (java.nio with persistent connection) = +110% faster

• HTTP/1.0 (java.io) -> HTTP/1.0 (java.nio) = +20% 快

• HTTP/1.0 (java.io) -> HTTP/1.1 (带有持久连接的java.nio) = +110% 快