HttpURLConnection 的套接字泄漏

Question

我在 Linux 上使用 OpenJDK 11，我需要确保使用 HttpURLConnection 完成的所有 Web 请求都正确关闭，并且不要让任何文件描述符保持打开状态。

Oracle's manual tells to use close on the InputStream and Android's manual 告诉在 HttpURLConnection 对象上使用 disconnect。

我还将 Connection: close 和 http.keepAlive 设置为 false 以避免连接池。

这似乎适用于纯 http 请求，但未加密 https 请求，其响应是 non-分块编码。似乎只有 GC 会清理已关闭的连接。

此示例代码：

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.stream.Stream;

public class Test {
    private static int printFds() throws IOException {
        int cnt = 0;
        try (Stream<Path> paths = Files.list(new File("/proc/self/fd").toPath())) {
            for (Path path : (Iterable<Path>)paths::iterator) {
                System.out.println(path);
                ++cnt;
            }
        }
        System.out.println();
        return cnt;
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        System.setProperty("http.keepAlive", "false");
        for (int i = 0; i < 10; i++) {
            // Must be a https endpoint returning non-chunked response
            HttpURLConnection conn = (HttpURLConnection) new URL("https://www.google.com/").openConnection();
            conn.setRequestProperty("Connection", "close");
            BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            while (in.readLine() != null) {
            }
            in.close();
            conn.disconnect();
            conn = null;
            in = null;
        }

        Thread.sleep(1000);
        int numBeforeGc = printFds();

        System.gc();
        Thread.sleep(1000);
        int numAfterGc = printFds();
        System.out.println(numBeforeGc == numAfterGc ? "No socket leaks" : "Sockets were leaked");
    }
}

打印此输出：

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/9
/proc/self/fd/6
/proc/self/fd/7
/proc/self/fd/8
/proc/self/fd/10
/proc/self/fd/11
/proc/self/fd/12
/proc/self/fd/13
/proc/self/fd/14
/proc/self/fd/15
/proc/self/fd/16
/proc/self/fd/17
/proc/self/fd/18
/proc/self/fd/19

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/9
/proc/self/fd/6
/proc/self/fd/7
/proc/self/fd/8

Sockets were leaked

更改为 http URL 可以在没有 GC 的情况下按预期正确关闭套接字：

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/6

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/6

No socket leak

同时使用 OpenJDK 11 和 12 进行了测试。我是否遗漏了什么或者这是一个错误？

Answer 1

原来是个bug：https://bugs.openjdk.java.net/browse/JDK-8216326

shutdownInput 现在在 JDK 11 和 13（但不是 12）的最新版本中被 close 取代。

HttpURLConnection 的套接字泄漏

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