Function cbm_tail_log

src/foundation/subprocess.c:117–211

Tail one bounded batch from the child log. While the owned tree can still * write, a partial final line remains buffered. Once the tree is quiescent, * final=true delivers that last fragment exactly once. */

 * write, a partial final line remains buffered. Once the tree is quiescent,
 * final=true delivers that last fragment exactly once. */
static cbm_tail_result_t cbm_tail_log(const char *log_file, long *tail_pos, cbm_proc_log_cb cb,
                                      void *ud, bool final) {
    cbm_tail_result_t result = {.status = CBM_TAIL_ERROR, .progressed = false};
    if (!log_file || !tail_pos) {
        return result;
    }
#ifdef _WIN32
    FILE *lf = cbm_fopen(log_file, "r");
#else
    int open_flags = O_RDONLY | O_NONBLOCK;
#ifdef O_CLOEXEC
    open_flags |= O_CLOEXEC;
#endif
#ifdef O_NOFOLLOW
    open_flags |= O_NOFOLLOW;
#endif
    int log_fd = open(log_file, open_flags);
    if (log_fd < 0) {
        return result;
    }
    struct stat log_status;
    if (fstat(log_fd, &log_status) != 0 || !S_ISREG(log_status.st_mode)) {
        (void)close(log_fd);
        return result;
    }
    FILE *lf = fdopen(log_fd, "r");
#endif
    if (!lf) {
#ifndef _WIN32
        (void)close(log_fd);
#endif
        return result;
    }
    if (fseek(lf, *tail_pos, SEEK_SET) == 0) {
        char line[1024];
        size_t delivered_lines = 0;
        size_t delivered_bytes = 0;
        enum {
            CBM_TAIL_MAX_LINES_PER_POLL = 64,
            CBM_TAIL_MAX_BYTES_PER_POLL = 64 * 1024,
        };
        while (delivered_lines < CBM_TAIL_MAX_LINES_PER_POLL &&
               delivered_bytes < CBM_TAIL_MAX_BYTES_PER_POLL) {
            long before = ftell(lf);
            if (!fgets(line, sizeof(line), lf)) {
                result.status = ferror(lf) ? CBM_TAIL_ERROR : CBM_TAIL_CAUGHT_UP;
                break;
            }
            size_t l = strlen(line);
            delivered_bytes += l;
            bool complete = (l > 0 && line[l - 1] == '\n');
            if (complete) {
                line[l - 1] = '\0';
                *tail_pos = ftell(lf);
                result.progressed = true;
                delivered_lines++;
                if (line[0] && cb) {
                    cb(line, ud);