2021-03-17

    /**
     * 从 buf 中查找 "\r\n"，并返回这段（包括 \r\n）空间的长度。
     * 如果 buf 中没有，则返回 0 。
     */
    private static int findLineEnd(final byte[] buf, int rlen) {
        int splitbyte = 0;
        while (splitbyte + 1 < rlen) {
            if (buf[splitbyte] == '\r' && buf[splitbyte + 1] == '\n' && splitbyte + 1 < rlen) {
                return splitbyte + 2;
            }
            splitbyte++;
        }
        return 0;
    }

    /**
     * 半包、粘包问题解决：
     *      从 InputStream 中找一行数据并返回。“一行”的标志是截止到 \r\n，不包括 \r\n 。
     */
    private static String readLine(InputStream inputStream) throws IOException, RuntimeException {
        int splitbyte = 0;
        int rlen = 0;
        byte[] buf = new byte[BUFSIZE];
        int read = -1;
        inputStream.mark(BUFSIZE);
        try {
            read = inputStream.read(buf, 0, BUFSIZE);
        } catch (Exception e) {
            throw new SocketException("Could not Read");
        }

        if (read == -1) {
            throw new SocketException("Could not Read");
        }

        /* buf 中存储的数据区间为： buf[0] ... buf[read-1]，共 read 个字节。 */

        while (read > 0) {
            rlen += read;
            splitbyte = findLineEnd(buf, rlen);
            if (splitbyte > 0) {
                break;
            }

            read = inputStream.read(buf, rlen, BUFSIZE - rlen);
        }

        /* buf 中存储的数据区间为： buf[0] ... buf[splitbyte-1]，共 splitbyte 个字节。其中包含 \r\n 在内。*/

        // -2 的目的是返回的结果内容中不包含 \r\n 。
        return new String(buf, 0, splitbyte - 2);
    }

    private static void safeClose(Closeable closeable) {
        try {
            if (closeable != null) {
                closeable.close();
            }
        } catch (IOException e) {
            System.out.println("Could not close: " + e.getMessage());
        }
    }

    private static void safeClose(Socket socket) {
        try {
            if (socket != null && !socket.isClosed()) {
                socket.close();
            }
        } catch (IOException e) {
            throw new IllegalArgumentException("Cloud not close socket: " + e.getMessage());
        }
    }

    private static void safeClose(ServerSocket serverSocket) {
        try {
            if (serverSocket != null && !serverSocket.isClosed()) {
                serverSocket.close();
            }
        } catch (IOException e) {
            throw new IllegalArgumentException("Cloud not close socket: " + e.getMessage());
        }

    }

测试：

 String message = "hello world\r\ngoodbye";
 byte[] bytes = message.getBytes(StandardCharsets.UTF_8);
 //System.out.println(findLineEnd(bytes, bytes.length));

InputStream stream = new ByteArrayInputStream(bytes);

String line = readLine(stream);

System.out.println(line);