92 lines
3.0 KiB
C
92 lines
3.0 KiB
C
// Runs a command on a pseudo-terminal, used by scripts/orderfile/generate.ts.
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//
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// bun takes a different path on a terminal than on a pipe — isatty, TIOCGWINSZ,
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// raw mode, readline's line editor and its cursor escapes — and nothing but a
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// real pty reaches it. So one workload runs under this.
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//
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// cc -O2 -o ptyrun ptyrun.c -lutil
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// printf 'hi\n' | ./ptyrun bun cli.js
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//
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// Our stdin is typed into the terminal and the child's output is forwarded to
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// ours, so a workload looks the same to the caller either way. Exits with the
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// child's status.
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//
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// PTYRUN_PRELOAD becomes the child's LD_PRELOAD (DYLD_INSERT_LIBRARIES on
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// macOS). The tracer belongs in the binary being traced and nowhere else, and
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// it drops itself from the environment once loaded, so it is handed down here
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// rather than inherited.
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#define _GNU_SOURCE
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#include <errno.h>
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#include <poll.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/ioctl.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#if defined(__APPLE__)
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#include <util.h>
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#define PRELOAD_VAR "DYLD_INSERT_LIBRARIES"
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#else
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#include <pty.h>
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#define PRELOAD_VAR "LD_PRELOAD"
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#endif
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#define EOT 4 // ^D: how a terminal says end-of-input
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int main(int argc, char **argv)
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{
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if (argc < 2) {
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fprintf(stderr, "usage: ptyrun <command> [args...]\n");
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return 2;
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}
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struct winsize window = { .ws_row = 24, .ws_col = 80 };
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int master = -1;
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pid_t child = forkpty(&master, NULL, NULL, &window);
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if (child < 0) {
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perror("forkpty");
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return 2;
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}
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if (child == 0) {
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const char *preload = getenv("PTYRUN_PRELOAD");
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if (preload && *preload) setenv(PRELOAD_VAR, preload, 1);
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execvp(argv[1], &argv[1]);
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perror(argv[1]);
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_exit(127);
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}
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// Drain the child's output — a full pty buffer would block it — and type
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// whatever arrives on our stdin into the terminal.
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char buffer[8192];
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struct pollfd fds[2] = { { .fd = master, .events = POLLIN }, { .fd = STDIN_FILENO, .events = POLLIN } };
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for (;;) {
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if (poll(fds, 2, -1) < 0) {
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if (errno == EINTR) continue;
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break;
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}
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if (fds[0].revents) {
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ssize_t n = read(master, buffer, sizeof buffer);
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if (n <= 0) break; // EIO once the child has closed its side
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if (write(STDOUT_FILENO, buffer, (size_t)n) < 0) break;
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}
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if (fds[1].revents) {
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ssize_t n = read(STDIN_FILENO, buffer, sizeof buffer);
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if (n > 0) {
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if (write(master, buffer, (size_t)n) < 0) break;
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} else {
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// Out of input. Closing the master instead would SIGHUP the child.
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char eof = EOT;
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fds[1].fd = -1;
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if (write(master, &eof, 1) < 0) break;
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}
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}
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}
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int status = 0;
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if (waitpid(child, &status, 0) < 0) {
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perror("waitpid");
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return 2;
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}
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return WIFEXITED(status) ? WEXITSTATUS(status) : 1;
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}
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