当有两个背靠背的连接时，基于libuv的服务器崩溃

Question

为了测试的目的，对高性能的TCP服务器(不一定是HTTP)进行了一些研究。遵循一些示例代码并创建了一个基于libuv的TCP服务器，但是以下示例代码将崩溃，并在uv_write(req, stream, buffer, 1, on_write);行上显示错误SIGPIPE。以下是控制台输出：

client=0x562529924700
1writing to 0x562529924700
2writing to 0x562529924700
wrote.
1writing to 0x562529924700

请注意，tcp客户端通过tcp重置关闭第一个TCP连接。Wireshark显示TCP客户端已经建立了第二个tcp连接并发送了请求，但是tcp服务器不知何故没有打印类似于行client=0x562529924700的内容来指示它已经接受了第二个连接。

任何想法都将不胜感激。

以下是服务器代码

//from https://gist.github.com/Jxck/4305806
//     https://nikhilm.github.io/uvbook/networking.html
//api guide http://docs.libuv.org/en/v1.x/
#include <stdio.h>
#include <stdlib.h>
#include <uv.h>
#include <string.h>
#include <unistd.h>
#define DEFAULT_PORT 8080
#define DEFAULT_BACKLOG 1000

uv_loop_t *loop;
int cnt = 0;
char *str = "HTTP/1.1 200 Ok\r\nContent-Length: 7\r\n\r\n%07d\n";

void on_write(uv_write_t* req, int status)
{
    if (status) {
        perror( "uv_write error ");
        return;
    }
    printf("wrote.\n");
    free(req);
    //uv_close((uv_handle_t*)req->handle, on_close);
}

void write2(uv_stream_t* stream, char *data, int len2) {
    uv_buf_t buffer[] = {
            {.base = data, .len = len2}
    };
    uv_write_t *req = malloc(sizeof(uv_write_t));
    printf("1writing to %p\n", stream);
    uv_write(req, stream, buffer, 1, on_write);
    printf("2writing to %p\n", stream);
}
void on_close(uv_handle_t* handle)
{
    //printf("closed.");
}
void echo_read(uv_stream_t *sock, ssize_t nread, const uv_buf_t *buf) {
    if (nread == -1) {
        fprintf(stderr, "error echo_read");
        return;
    } else if (nread == 0) {
        uv_close((uv_handle_t*)sock, on_close);
        return;
    }
    char respMsg[52];
    sprintf(respMsg, str, cnt++);
    //snprintf(&respMsg[41],  6,"%6d", cnt++);
    write2(sock, respMsg, strlen(respMsg));
    //printf("result: %s\n", buf->base);
}
static void my_alloc_cb(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf) {
    buf->base = malloc(suggested_size);
    buf->len = suggested_size;
}

void on_new_connection(uv_stream_t *server, int status) {
    if (status < 0) {
        fprintf(stderr, "New connection error %s\n", uv_strerror(status));
        // error!
        return;
    }

    uv_tcp_t *client = (uv_tcp_t*) malloc(sizeof(uv_tcp_t));
    printf("client=%p\n", client);
    uv_tcp_init(loop, client);
    if (uv_accept(server, (uv_stream_t*) client) == 0) {
        uv_read_start((uv_stream_t*) client, my_alloc_cb, echo_read);
    }
    else {
        printf("failed to accept\n");
        uv_close((uv_handle_t*) client, NULL);
    }
}

int main() {
    loop = uv_default_loop();

    uv_tcp_t server;
    uv_tcp_init(loop, &server);

    struct sockaddr_in addr;
    uv_ip4_addr("0.0.0.0", DEFAULT_PORT, &addr);
    int r;
    r = uv_tcp_bind(&server, (const struct sockaddr*)&addr, 0);

    r = uv_listen((uv_stream_t*) &server, DEFAULT_BACKLOG, on_new_connection);

    if (r) {
        fprintf(stderr, "Listen error %s\n", uv_strerror(r));
        return 1;
    }
    return uv_run(loop, UV_RUN_DEFAULT);
}

Answer 1

原来问题出在echo_read()上。当TCP连接通过tcp重置终止时，nread不是-1，而是某个负数(在我的例子中是-4095)。能够使用nread < 0而不是nread == -1来处理它。

void echo_read(uv_stream_t *sock, ssize_t nread, const uv_buf_t *buf) {
    if (nread == -1) {
        fprintf(stderr, "error echo_read");
        return;
    } else if (nread == 0) {
        uv_close((uv_handle_t*)sock, on_close);
        return;
    }