third_party/ulib/musl/src/stdio/popen.c

#include "libc.h"
#include "stdio_impl.h"
#include <errno.h>
#include <fcntl.h>
#include <spawn.h>
#include <string.h>
#include <unistd.h>

FILE* popen(const char* cmd, const char* mode) {
    int p[2], op, e;
    pid_t pid;
    FILE* f;
    posix_spawn_file_actions_t fa;

    if (*mode == 'r') {
        op = 0;
    } else if (*mode == 'w') {
        op = 1;
    } else {
        errno = EINVAL;
        return 0;
    }

    if (pipe2(p, O_CLOEXEC))
        return NULL;
    f = fdopen(p[op], mode);
    if (!f) {
        close(p[0]);
        close(p[1]);
        return NULL;
    }
    FLOCK(f);

    /* If the child's end of the pipe happens to already be on the final
     * fd number to which it will be assigned (either 0 or 1), it must
     * be moved to a different fd. Otherwise, there is no safe way to
     * remove the close-on-exec flag in the child without also creating
     * a file descriptor leak race condition in the parent. */
    if (p[1 - op] == 1 - op) {
        int tmp = fcntl(1 - op, F_DUPFD_CLOEXEC, 0);
        if (tmp < 0) {
            e = errno;
            goto fail;
        }
        close(p[1 - op]);
        p[1 - op] = tmp;
    }

    e = ENOMEM;
    if (!posix_spawn_file_actions_init(&fa)) {
        if (!posix_spawn_file_actions_adddup2(&fa, p[1 - op], 1 - op)) {
            if (!(e = posix_spawn(&pid, "/bin/sh", &fa, 0, (char* []){(char*)"sh", (char*)"-c", (char*)cmd, 0},
                                  __environ))) {
                posix_spawn_file_actions_destroy(&fa);
                f->pipe_pid = pid;
                if (!strchr(mode, 'e'))
                    fcntl(p[op], F_SETFD, 0);
                close(p[1 - op]);
                FUNLOCK(f);
                return f;
            }
        }
        posix_spawn_file_actions_destroy(&fa);
    }
fail:
    fclose(f);
    close(p[1 - op]);

    errno = e;
    return 0;
}