Method copyStream

src/document/object-copier.ts:365–424

* Copy a stream, handling encryption state. * * If source wasn't encrypted, copies raw encoded bytes (fastest). * If source was encrypted, decodes and re-encodes with same filters.

(stream: PdfStream)

   * If source was encrypted, decodes and re-encodes with same filters.
   */
  private copyStream(stream: PdfStream): PdfStream {
    const sourceWasEncrypted = this.source.isEncrypted;

    // Clone the stream's dictionary
    const clonedDict = stream.clone();

    // Copy dict values (remapping refs, but not stream data yet)
    this.copyDictValues(clonedDict);

    if (!sourceWasEncrypted) {
      // Source wasn't encrypted - copy raw encoded bytes directly
      // This preserves exact encoding and is fastest
      return new PdfStream(clonedDict, stream.data);
    }

    // Source was encrypted - we have decrypted data in memory
    // Must decode and re-encode. Wrap in try/catch for robustness.
    try {
      const decodedData = stream.getDecodedData();
      const filterEntry = stream.get("Filter");

      if (filterEntry) {
        // Re-encode with same filters
        try {
          const filterSpecs = this.buildFilterSpecs(stream);
          const encodedData = FilterPipeline.encode(decodedData, filterSpecs);

          // Update length
          clonedDict.set("Length", PdfNumber.of(encodedData.length));

          return new PdfStream(clonedDict, encodedData);
        } catch (error) {
          console.warn(`Could not re-encode stream, will use uncompressed data`);
          console.warn(error);

          // If re-encoding fails, store uncompressed
          clonedDict.delete("Filter");
          clonedDict.delete("DecodeParms");
          clonedDict.set("Length", PdfNumber.of(decodedData.length));

          return new PdfStream(clonedDict, decodedData);
        }
      }

      // No filters - store uncompressed
      clonedDict.set("Length", PdfNumber.of(decodedData.length));

      return new PdfStream(clonedDict, decodedData);
    } catch (error) {
      console.warn(`Could not decode stream, will use raw data`);
      console.warn(error);

      // If decoding fails entirely, copy raw bytes as fallback
      clonedDict.delete("Filter");
      clonedDict.delete("DecodeParms");
      clonedDict.set("Length", PdfNumber.of(stream.data.length));

      return new PdfStream(clonedDict, stream.data);