What causes "failed to write output [%s]: %s\n" in nodejs/node?

Check free space on the output filesystem: `df -h `.

failed to write output [%s]: %s\n

Error message

failed to write output [%s]: %s\n

What it means

After `fwrite` of the output buffer, `ferror(context->fout)` is set, meaning the write failed. The message shows the output path and errno string. This aborts the operation; the output file is likely incomplete or corrupt.

Source

Thrown at deps/brotli/c/tools/brotli.c:1109

  context->next_in = context->input;
  if (ferror(context->fin)) {
    fprintf(stderr, "failed to read input [%s]: %s\n",
            PrintablePath(context->current_input_path), strerror(errno));
    return BROTLI_FALSE;
  }
  return BROTLI_TRUE;
}

/* Internal: should be used only in Provide-/Flush-Output. */
static BROTLI_BOOL WriteOutput(Context* context) {
  size_t out_size = (size_t)(context->next_out - context->output);
  context->total_out += out_size;
  if (out_size == 0) return BROTLI_TRUE;
  if (context->test_integrity) return BROTLI_TRUE;

  fwrite(context->output, 1, out_size, context->fout);
  if (ferror(context->fout)) {
    fprintf(stderr, "failed to write output [%s]: %s\n",
            PrintablePath(context->current_output_path), strerror(errno));
    return BROTLI_FALSE;
  }
  return BROTLI_TRUE;
}

static BROTLI_BOOL ProvideOutput(Context* context) {
  if (!WriteOutput(context)) return BROTLI_FALSE;
  context->available_out = kFileBufferSize;
  context->next_out = context->output;
  return BROTLI_TRUE;
}

static BROTLI_BOOL FlushOutput(Context* context) {
  if (!WriteOutput(context)) return BROTLI_FALSE;
  context->available_out = 0;
  context->next_out = context->output;
  return BROTLI_TRUE;

View on GitHub (pinned to 1b2de5e052)

Solutions

Check free space on the output filesystem: `df -h <output_dir>`.
If piping to another process, ensure it reads all data before exiting (avoid `| head`).
Verify the output filesystem is mounted read-write: `mount | grep <dir>`.
Check user quota: `quota -s`.
Clean up partial output and re-run after resolving the underlying issue.

Defensive patterns

Strategy: validation

Validate before calling

#include <sys/statvfs.h>
#include <stdbool.h>

bool output_writable_with_space(const char *dir, unsigned long long min_bytes) {
    struct statvfs vfs;
    if (statvfs(dir, &vfs) != 0) return false;
    unsigned long long avail = (unsigned long long)vfs.f_bavail * vfs.f_bsize;
    return avail > min_bytes;
}

Prevention

Pre-check free disk space and quota before writing large outputs.
Never pipe brotli output to `head`, `tail`, or any command that may exit early.
Monitor write errors in CI logs and fail the job if the output is truncated.

When it happens

Trigger: Disk full (ENOSPC); write to a full quota; broken pipe (EPIPE) when outputting to stdout/another process that exited; read-only filesystem (EROFS); I/O error on the output device.

Common situations: Output disk filled during compression of a large/incompressible file; piping brotli output to a consumer that exits before reading everything; writing to a mounted-but-read-only filesystem; network share write timeout.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/6076d331d067f251. Report an issue: GitHub.