Function probeFormFields

examples/pdf-server/server.ts:1029–1073

* Open `url` via PdfCacheRangeTransport and return form metadata. * Uses `disableAutoFetch` so PDFs without an AcroForm are probed with only * the trailer/xref/catalog (~5-25% of bytes); PDFs with forms still walk * every page via extractFormFieldInfo but those are typically small

(
  url: string,
  totalBytes: number,
  readPdfRange: PdfCache["readPdfRange"],
)

 * {@link PdfCacheRangeTransport.failed}) resolve to empty results.
 */
async function probeFormFields(
  url: string,
  totalBytes: number,
  readPdfRange: PdfCache["readPdfRange"],
): Promise<{
  formSchema: Awaited<ReturnType<typeof extractFormSchema>>;
  fieldInfo: FormFieldInfo[];
}> {
  // Assigned sequentially below so a throw in extractFormFieldInfo (no per-page
  // guard, unlike extractFormSchema) doesn't discard an already-computed schema.
  let formSchema: Awaited<ReturnType<typeof extractFormSchema>> = null;
  let fieldInfo: FormFieldInfo[] = [];
  try {
    const transport = new PdfCacheRangeTransport(url, totalBytes, readPdfRange);
    const orFail = <T>(p: Promise<T>): Promise<T> =>
      Promise.race([p, transport.failed]);
    const pdfDoc = await orFail(
      getDocument({
        range: transport,
        length: totalBytes,
        disableAutoFetch: true,
        disableStream: true,
        rangeChunkSize: 64 * 1024,
        standardFontDataUrl: STANDARD_FONT_DATA_URL,
        StandardFontDataFactory: FetchStandardFontDataFactory,
        verbosity: VerbosityLevel.ERRORS,
      }).promise,
    );
    try {
      const fieldObjects = (await orFail(pdfDoc.getFieldObjects())) as Record<
        string,
        PdfJsFieldObject[]
      > | null;
      if (fieldObjects && Object.keys(fieldObjects).length > 0) {
        formSchema = await orFail(extractFormSchema(pdfDoc, fieldObjects));
        fieldInfo = await orFail(extractFormFieldInfo(pdfDoc));
      }
    } finally {
      pdfDoc.destroy();
    }
  } catch {
    // Non-fatal — return whatever was assigned before the throw.
  }
  return { formSchema, fieldInfo };
}

/**
 * Extract detailed form field info (name, type, page, bounding box, label)