mozilla/pdf.js · error · FormatError

Not tracking location of ${key}

Error message

Not tracking location of ${key}

What it means

Thrown by CFFOffsetTracker.setEntryLocation when called for a key that was never registered via track(). setEntryLocation writes the final offset value into a placeholder slot that track() was supposed to reserve; calling it without a prior track means there is no slot to fill.

Source

Thrown at src/core/cff_parser.js:1461

    return key in this.offsets;
  }

  track(key, location) {
    if (key in this.offsets) {
      throw new FormatError(`Already tracking location of ${key}`);
    }
    this.offsets[key] = location;
  }

  offset(value) {
    for (const key in this.offsets) {
      this.offsets[key] += value;
    }
  }

  setEntryLocation(key, values, output) {
    if (!(key in this.offsets)) {
      throw new FormatError(`Not tracking location of ${key}`);
    }
    const data = output.data;
    const dataOffset = this.offsets[key];
    const size = 5;
    for (let i = 0, ii = values.length; i < ii; ++i) {
      const offset0 = i * size + dataOffset;
      const offset1 = offset0 + 1;
      const offset2 = offset0 + 2;
      const offset3 = offset0 + 3;
      const offset4 = offset0 + 4;
      // It's easy to screw up offsets so perform this sanity check.
      if (
        data[offset0] !== 0x1d ||
        data[offset1] !== 0 ||
        data[offset2] !== 0 ||
        data[offset3] !== 0 ||
        data[offset4] !== 0
      ) {

View on GitHub (pinned to 5903d58d58)

Solutions

1. Verify the key passed to setEntryLocation was previously tracked via track() (or isTracking returns true).
2. Report to pdf.js with the offending font — this indicates an internal compiler bug.
3. Audit track/setEntryLocation call pairs to ensure matching key names.

Example fix

// before
tracker.setEntryLocation('Private', vals, output); // throws if never tracked

// after
if (tracker.isTracking('Private')) {
  tracker.setEntryLocation('Private', vals, output);
}

// Only call setEntryLocation for keys previously tracked.
function safeSetEntryLocation(tracker, key, values, output) {
  if (!tracker.isTracking(key)) {
    throw new Error(`Refusing setEntryLocation: '${key}' not tracked`);
  }
  tracker.setEntryLocation(key, values, output);
}

function isTracked(tracker, key) {
  return tracker.isTracking(key);
}

try {
  tracker.setEntryLocation(key, values, output);
} catch (e) {
  // Key was never tracked; internal compiler state bug.
  throw new Error(`setEntryLocation for untracked key '${key}'`);
}

When it happens

Trigger: The CFF compiler calls setEntryLocation(key, values, output) for a key not in the tracker's offsets map. This is an internal invariant violation — setEntryLocation should only be called for offset names previously passed to track().

Common situations: A pdf.js internal bug where setEntryLocation references a name that compileDict never tracked; a fork that calls setEntryLocation directly; mismatched key names between track and setEntryLocation code paths after a refactor.

Related errors

• Already tracking location of ${key}
• writing to an offset that is not empty
• There must be a private dictionary.
• Unknown data type of ${type}
• Invalid dictionary name "${name}"

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/050e4b3a3d14ed66. Report an issue: GitHub.