View Source Pdf.Reader.XRef.Stream (ExPDF v1.0.1)

Parses a PDF 1.5+ compressed cross-reference stream (/Type /XRef).

Per PDF 1.7 ISO 32000-1 § 7.5.8 "Cross-Reference Streams":

  • The stream object dictionary must have /Type /XRef.
  • Required fields: /Size (total object count), /W [w1 w2 w3] (byte widths).
  • Optional /Index [first count ...] — subsection ranges; default [0 /Size].
  • Optional /Prev — byte offset of previous xref section (chain support).
  • The stream body (after decoding all filters) contains exactly w1 + w2 + w3 bytes per entry:
    • Field 1 (w1 bytes): entry type. If w1 = 0, type is implicitly 1.
    • Field 2 (w2 bytes): meaning depends on type.
    • Field 3 (w3 bytes): meaning depends on type.

Entry types (§ 7.5.8 Table 18):

  • Type 0 (free): f2 = next free object number, f3 = generation when reused.
  • Type 1 (in-use, classic): f2 = byte offset, f3 = generation number.
  • Type 2 (compressed): f2 = object number of containing ObjStm, f3 = index within it.

This module decodes the stream body using Pdf.Reader.Filter.apply_chain/3, which handles FlateDecode and PNG predictors transparently (batch 1 impl).

Summary

Functions

parse(arg)

Parses a /Type /XRef stream object tuple into an xref entries map.

Functions

Link to this function

parse(arg)

View Source 
@spec parse({:stream, map(), binary()}) ::
  {:ok,
   %{required(Pdf.Reader.Document.ref()) => Pdf.Reader.Document.xref_entry()}}
  | {:error, term()}

Parses a /Type /XRef stream object tuple into an xref entries map.

Accepts {:stream, dict, raw_bytes} where raw_bytes is the still-encoded (FlateDecode-compressed) stream body.

Returns:

  • {:ok, entries_map} — map of {obj_num, gen_num} => entry
  • {:error, :not_an_xref_stream} — dict does not have /Type /XRef
  • {:error, reason} — filter/decoding error propagated from the filter chain