What causes "%s%serror%s " in oven-sh/bun?

Re-run with --help and correct the flagged argument; the message after the 'error' prefix names the exact problem

%s%serror%s

Error message

%s%serror%s

What it means

die() is h3blast's fatal-error exit path: it prints '<red><bold>error<rst> <message>' to stderr and exits with status 1. It is used for unrecoverable setup failures — bad CLI arguments, invalid target URLs/schemes, TLS certificate or keylog-file problems, worker/histogram allocation failures — so seeing this prefix means the run never started or aborted hard.

Source

Thrown at packages/h3blast/src/h3blast.c:180

    _Atomic uint64_t req_other;
    _Atomic uint64_t req_err;
    _Atomic uint64_t bytes_rx;       // HTTP body bytes
    _Atomic uint64_t bytes_rx_wire;  // UDP payload bytes (incl. headers, QUIC framing)
    _Atomic uint64_t bytes_tx;
    _Atomic uint64_t conns_open;
    _Atomic uint64_t handshake_fail;
};

static volatile sig_atomic_t g_stop;
static volatile sig_atomic_t g_intr;   // SIGINT/SIGTERM — abort remaining targets
static volatile sig_atomic_t g_warm;   // set once warmup window has passed

// ───────────────────────── util ─────────────────────────

static void die(const char *fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    fprintf(stderr, "%s%serror%s ", RED, BLD, RST);
    vfprintf(stderr, fmt, ap);
    fputc('\n', stderr);
    va_end(ap);
    exit(1);
}

static uint64_t now_ns(void) {
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return (uint64_t)ts.tv_sec * 1000000000ull + (uint64_t)ts.tv_nsec;
}

static void on_sigint(int sig) {
    (void)sig;
    if (g_intr) {
        static const char restore[] = "\x1b[?7h\x1b[?25h";
        if (g_isatty) write(STDERR_FILENO, restore, sizeof(restore) - 1);
        _exit(130);

View on GitHub (pinned to 8c5296ac45)

Solutions

Re-run with --help and correct the flagged argument; the message after the 'error' prefix names the exact problem
Verify each target URL parses and uses a scheme the tool supports
Check the keylog/cert paths given on the command line exist and are writable/readable
Raise ulimits (threads) if the failure is resource-related

Defensive patterns

Strategy: validation

Validate before calling

import { spawnSync } from 'node:child_process';
const r = spawnSync(h3blastPath, ['--help']);
if (r.status !== 0) throw new Error(`h3blast unusable (exit ${r.status}): ${r.stderr}`);
// validate targets up front:
for (const t of targets) new URL(t); // throws on malformed URLs

Prevention

Validate every target URL and flag before launching the benchmark
Check the process exit code; die() always exits 1 with the reason on stderr
Smoke-test with one connection and a short duration before full runs

When it happens

Trigger: Invoking h3blast with a malformed or non-HTTP(S) URL, a negative/zero worker or duration argument, an unreadable --keylog file, unsupported ALPN/scheme, or environments where pthread/hdr_init fail.

Common situations: Typos in target URLs; passing http:// targets to an HTTP/3-only mode; CI machines with low ulimits starving thread creation; flag mistakes after upgrading CLI argument formats.

Related errors

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/1b7ad11ed76fcd00. Report an issue: GitHub.