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

Locates the startxref byte offset in a PDF binary and parses the trailer dictionary at a given xref section offset.

PDF spec references

§ 7.5.5 — File Trailer
§ 7.5.4 — Cross-Reference Table

Summary

Types

t()

Functions

locate_startxref(binary)

Scans binary in reverse for %%EOF, then reads the startxref offset on the line immediately before it.

parse(binary, offset)

Parses the xref section and trailer dictionary at offset within binary.

Types

t()

@type t() :: %Pdf.Reader.Trailer{
  dict: map(),
  encrypt: term(),
  id: [{:hex_string, binary()} | {:string, binary()} | binary()] | nil,
  info: Pdf.Reader.Document.ref() | nil,
  prev: non_neg_integer() | nil,
  root: Pdf.Reader.Document.ref() | nil,
  size: pos_integer() | nil
}

Functions

locate_startxref(binary)

@spec locate_startxref(binary()) :: {:ok, non_neg_integer()} | {:error, :malformed}

Scans binary in reverse for %%EOF, then reads the startxref offset on the line immediately before it.

Returns {:ok, offset} or {:error, :malformed}.

Per PDF spec § 7.5.5: the file ends with %%EOF. The line above that is the byte offset to the xref section. The line above that is the keyword startxref.

parse(binary, offset)

@spec parse(binary(), non_neg_integer()) :: {:ok, t()} | {:error, :malformed}

Parses the xref section and trailer dictionary at offset within binary.

Seeks forward from offset to the trailer keyword, then parses the dictionary that follows. Populates a %Pdf.Reader.Trailer{} struct.

Returns {:ok, %Pdf.Reader.Trailer{}} or {:error, :malformed}.