View Source Pdf.Reader.ObjectStream (ExPDF v1.0.1)

Decodes objects embedded in a PDF Object Stream (/Type /ObjStm).

Per PDF 1.7 ISO 32000-1 § 7.5.7 "Object Streams":

An Object Stream is a stream whose decoded body has two parts:

  1. Header: N whitespace-separated pairs obj_num offset, where offset is the byte offset of that object's value relative to /First.
  2. Object values: starting at byte /First, the N object bodies concatenated. Each body is a PDF value (integer, name, dictionary, array, etc.) but never a stream object — embedded streams are forbidden.

Caller contract

The caller (object resolver) is responsible for:

  1. Resolving the ObjStm indirect object itself.
  2. Decoding its filter chain (FlateDecode etc.) to get the raw body binary.
  3. Calling fetch/3 with the decoded body, the /First offset, and the desired object's 0-based index within the stream.

This design avoids a circular dependency between the resolver and ObjStm: the resolver is stateful (cache), ObjStm is pure (binary in, value out).

Error reasons

  • {:error, :objstm_index_out_of_range} — index ≥ N (the object count).
  • {:error, :malformed} — header cannot be parsed.

Summary

Functions

fetch(first, body, index)

Fetch the PDF value at 0-based index from a decoded ObjStm body.

Functions

Link to this function

fetch(first, body, index)

View Source 
@spec fetch(non_neg_integer(), binary(), non_neg_integer()) ::
  {:ok, term()} | {:error, term()}

Fetch the PDF value at 0-based index from a decoded ObjStm body.

first is the /First value from the stream dictionary — the byte offset within body where object data starts.

body is the decoded (filtered) stream body binary.

Returns {:ok, value} or {:error, reason}.