What causes "lgwin parameter already set\n" in nodejs/node?

Pass `-w`/`--lgwin` exactly once.

lgwin parameter already set\n

Error message

lgwin parameter already set\n

What it means

`-w N` sets the brotli window size (`params->lgwin`); it is latched by `lgwin_set`, shared with `--lgwin` and `--large-window`-style setters. A second occurrence is rejected to avoid an ambiguous final value.

Source

Thrown at deps/brotli/c/tools/brotli.c:466

          if (output_set) {
            fprintf(stderr, "write to standard output already set (-o)\n");
            return COMMAND_INVALID;
          }
          params->output_path = argv[i];
        } else if (c == 'q') {
          if (quality_set) {
            fprintf(stderr, "quality already set\n");
            return COMMAND_INVALID;
          }
          quality_set = ParseInt(argv[i], BROTLI_MIN_QUALITY,
                                 BROTLI_MAX_QUALITY, &params->quality);
          if (!quality_set) {
            fprintf(stderr, "error parsing quality value [%s]\n", argv[i]);
            return COMMAND_INVALID;
          }
        } else if (c == 'w') {
          if (lgwin_set) {
            fprintf(stderr, "lgwin parameter already set\n");
            return COMMAND_INVALID;
          }
          lgwin_set = ParseInt(argv[i], 0,
                               BROTLI_MAX_WINDOW_BITS, &params->lgwin);
          if (!lgwin_set) {
            fprintf(stderr, "error parsing lgwin value [%s]\n", argv[i]);
            return COMMAND_INVALID;
          }
          if (params->lgwin != 0 && params->lgwin < BROTLI_MIN_WINDOW_BITS) {
            fprintf(stderr,
                    "lgwin parameter (%d) smaller than the minimum (%d)\n",
                    params->lgwin, BROTLI_MIN_WINDOW_BITS);
            return COMMAND_INVALID;
          }
        } else if (c == 'C') {
          if (comment_set) {
            fprintf(stderr, "comment already set\n");
            return COMMAND_INVALID;

View on GitHub (pinned to 1b2de5e052)

Solutions

Pass `-w`/`--lgwin` exactly once.
Centralize window-size selection in one variable before building argv.

Example fix

# before
brotli -w 22 -w 24 in
# after
brotli -w 24 in

Defensive patterns

Strategy: validation

Validate before calling

# bash: at most one window-size setter
w=$(printf '%s\n' "$@" | grep -cE '^(-w|--lgwin|--large-window.*)$')
if [ "$w" -gt 1 ]; then echo "multiple lgwin flags" >&2; exit 2; fi
brotli "$@"

Try / catch

# bash
if ! brotli "$@"; then rc=$?; echo "brotli exit $rc; dedupe lgwin flags" >&2; exit "$rc"; fi

Prevention

Select the window size from a single variable.
Avoid layering `--large-window` together with an explicit `-w`.

When it happens

Trigger: `brotli -w 22 -w 24 in`, or `-w 22 --lgwin 24 in`.

Common situations: Preset profiles merged into one command; tuning scripts that layer defaults over user input.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/f42dc5118c90ee2b. Report an issue: GitHub.