A wrapper loaded via `LD_PRELOAD` for redirecting `STDOUT`/`STDERR` of an application to a server

procwrap.cpp

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <string.h>

void procwrap_init(int argc, char **argv, char **) {
    const char *fdStr{getenv("LOG_SOCKFD")};
    if (fdStr == nullptr)
        return;

    int fd{};
    if (sscanf(fdStr, "%d", &fd) <= 0 || fd < 0)
        return;


    int stdoutPipe[2], stderrPipe[2];
    if (pipe(stdoutPipe) != 0 || pipe(stderrPipe) != 0)
        return;

    dup2(stdoutPipe[1], STDOUT_FILENO);
    close(stdoutPipe[1]);
    dup2(stderrPipe[1], STDERR_FILENO);
    close(stderrPipe[1]);


    int pid{getpid()};
    iovec pidVec{
            .iov_base = &pid,
            .iov_len = sizeof(pid)
    };

    char *name{basename(argv[0])};
    iovec nameVec{
            .iov_base = name,
            .iov_len = strlen(name)
    };

    iovec iov[2]{pidVec, nameVec};

    char cmsgbuf[CMSG_SPACE(sizeof(int) * 2)];
    *reinterpret_cast<struct cmsghdr *>(cmsgbuf) = {
            .cmsg_len = CMSG_LEN(sizeof(int) * 2),
            .cmsg_level = SOL_SOCKET,
            .cmsg_type = SCM_RIGHTS
    };
    int *fdptr{reinterpret_cast<int *>(CMSG_DATA(cmsgbuf))};
    fdptr[0] = stdoutPipe[0];
    fdptr[1] = stderrPipe[0];

    struct msghdr msg{
            .msg_iov = iov,
            .msg_iovlen = 2,
            .msg_control = cmsgbuf,
            .msg_controllen = sizeof(cmsgbuf)
    };

    sendmsg(fd, &msg, 0);

  
    close(stdoutPipe[0]);
    close(stderrPipe[0]);
}

__attribute__((section(".init_array"))) void (*p_procwrap_init)(int, char **, char **) = &procwrap_init;