This was created to validate that on MACOS fixed source port makes it impossible to immediately restart the client due to the socket going into TIME_WAIT state for 30 seconds or so.

client.c

#include <assert.h>
#include <ctype.h>
#include <ifaddrs.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/time.h>

int main(void) {
    int ret, fd;
    struct sockaddr_in sa_dst;
    struct sockaddr_in sa_loc;
    const char buffer[] = "GET / HTTP/1.1\r\nHost: www.example.com\r\n\r\n";
    char resp_buffer[16384];

    fd = socket(AF_INET, SOCK_STREAM, 0);
    assert(fd != -1);

    // Client-side configuration
    memset(&sa_loc, 0, sizeof(sa_dst));
    sa_loc.sin_family = AF_INET;
    sa_loc.sin_port = htons(10456); /* pinned port */
    sa_loc.sin_addr.s_addr = inet_addr("0.0.0.0");

    struct timeval tv;
    tv.tv_sec = 2;
    tv.tv_usec = 0;
    setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, (const char*)&tv, sizeof(tv));

    // This does not do anything on a client socket, which means that if a 
    // service were to crash it could not restart until the connection left 
    // TIME_WAIT state.
    int optval = 1;
    ret = setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &optval, sizeof(optval));
    assert(ret != -1);

    ret = bind(fd, (struct sockaddr *)&sa_loc, sizeof(struct sockaddr));
    assert(ret != -1);

    // Remote end
    memset(&sa_dst, 0, sizeof(struct sockaddr_in));
    sa_dst.sin_family = AF_INET;
    sa_dst.sin_port = htons(80);
    sa_dst.sin_addr.s_addr = inet_addr("93.184.216.34"); // example.com

    ret = connect(fd, (struct sockaddr *)&sa_dst, sizeof(struct sockaddr));
    assert(ret != -1);

    send(fd, buffer, strlen(buffer), 0);
    ssize_t recv_ret;
    int newline = 0;
    int size_nchars = 0;
    long body_length = -1;
    ssize_t total_recvd = 0;
    char body_length_s[12];
    while (1) {
        if (body_length > 0 && total_recvd >= body_length) {
            close(fd);
            exit(EXIT_SUCCESS);
        }
        recv_ret = recv(fd, resp_buffer, sizeof(resp_buffer), 0);
        if (recv_ret < 0) {
            perror("Failed to recv");
            exit(EXIT_FAILURE);
        }

        total_recvd += recv_ret;
        printf("%s", resp_buffer);

        if (body_length < 0) {
            for (size_t i = 0 ; i < recv_ret; i++) {
                if (newline) {
                    newline = 0;
                    int diff = strncasecmp(&resp_buffer[i], "Content-Length:", strlen("Content-Length:"));
                    if (!diff) {
                        char *start =  &resp_buffer[i] + strlen("Content-Length: ");
                        char *p = start;
                        while (isdigit(*p)) {
                            size_nchars++;
                            p++;
                        }
                        strncpy(body_length_s, start, p - start);
                        body_length = strtol(body_length_s, NULL, 10);
                        break;
                    }
                }
                if (resp_buffer[i] == '\n') {
                    newline = 1;
                    continue;
                }
            }
        }
        resp_buffer[0] = '\0';
    }
}