What causes "reason: extra input\n" in nodejs/node?

Use the 'extra input' diagnosis to investigate trailing bytes in the file.

reason: extra input\n

Error message

reason: extra input\n

What it means

Verbose diagnostic at brotli.c:1278, printed only when verbosity > 0, immediately after the 'corrupt input' message at line 1275. It specifies that the corruption was trailing data after a complete brotli stream (extra input) when allow_concatenated is false. This distinguishes it from truncated or comment-mismatch causes.

Source

Thrown at deps/brotli/c/tools/brotli.c:1278

          context->next_in = context->input;
          context->available_in = 1;
        }
      }
      if (has_more_input) {
        if (context->allow_concatenated) {
          if (context->verbosity > 0) {
            fprintf(stderr, "extra input\n");
          }
          if (!ProvideOutput(context)) return BROTLI_FALSE;
          BrotliDecoderDestroyInstance(context->decoder);
          context->decoder = NULL;
          if (!InitDecoder(context)) return BROTLI_FALSE;
          s = context->decoder;
        } else {
          fprintf(stderr, "corrupt input [%s]\n",
                  PrintablePath(context->current_input_path));
          if (context->verbosity > 0) {
            fprintf(stderr, "reason: extra input\n");
          }
          return BROTLI_FALSE;
        }
      } else {
        if (context->verbosity > 0) {
          context->end_time = clock();
          fprintf(stderr, "Decompressed ");
          PrintFileProcessingProgress(context);
          fprintf(stderr, "\n");
        }
        /* Final check */
        if (context->comment_state != COMMENT_OK) {
          fprintf(stderr, "corrupt input [%s]\n",
                  PrintablePath(context->current_input_path));
          if (context->verbosity > 0) {
            fprintf(stderr, "reason: comment mismatch\n");
          }
        }

View on GitHub (pinned to 1b2de5e052)

Solutions

Use the 'extra input' diagnosis to investigate trailing bytes in the file.
Enable concatenated-stream mode if the trailing data is another valid brotli stream.
Strip non-brotli trailing bytes before decompression.
Re-examine the compression pipeline to ensure no extra data is appended to the .br output.

Defensive patterns

Strategy: validation

Validate before calling

// Verbose diagnostic for error 725. Same prevention: ensure no trailing
// non-brotli data when allow_concatenated is disabled.

Prevention

Use -v to confirm the root cause is trailing data, then strip it or enable concatenated mode.
Inspect files with a hex dump (xxd) to identify unexpected trailing bytes.
Document file format boundaries when wrapping brotli streams in custom containers.

When it happens

Trigger: Same condition as error 725: extra bytes follow a successfully decoded brotli stream while allow_concatenated is disabled. This message appears only when the user ran with -v (verbosity > 0).

Common situations: A developer debugging a 'corrupt input' failure runs 'brotli -d -v file.br' and sees 'reason: extra input', revealing that the file has trailing data beyond the brotli stream boundary. The file may have been packaged with extra metadata, footers, or was accidentally concatenated.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/73bc52b577c79aad. Report an issue: GitHub.