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pdfObjStream

AGPL-3.0-onlyRelease 2L4

Object-stream parser /Type /ObjStm — ISO 32000-2 §7.5.7.

Module pdfObjStream | Source packages/front/office/pdf/src/syntax/objStream.js | Deps pdfErrors, pdfParserObj, pdfTokenizer, pdfParser | Worker-safe yes

An object stream is a compressed container holding several non-stream indirect objects. Its dictionary carries /N (object count), /First (offset of the first body inside the decoded payload) and, optionally, /Extends. The payload starts with N pairs <num> <byteOffset> (offsets relative to /First), followed by the bodies concatenated without obj/endobj. The generation is always 0 by spec §7.5.8.4 (compressed objects). The payload must already be decoded: pdfDocument composes this module and runs the container through pdfFilterDispatch — once per container per document — so doc._raw.resolve(ref) returns a compressed object like any other indirect. Callers driving the parser on its own apply /Filter (typically Flate) themselves.

Resolve

const objStm = runtime.resolve('pdfObjStream');
// Returns: { parseObjectStream }

API

Method Signature Returns
parseObjectStream (decoded: Uint8Array, dict: PdfDict) => Array<{num, gen:0, value}> Every member object.

parseObjectStream

  1. Validates /Type /ObjStm when present.
  2. Reads /N and /First (required, integers ≥ 0).
  3. Tokenises [0, First[ to recover the (num, offset) pairs.
  4. Slices each body [First+off[i], First+off[i+1][ (or to the end for the last one) and feeds it to the standard parseObject.

Out-of-order or out-of-payload offsets raise pdf/objstm/bad-offset.

Examples

Parse a freshly inflated ObjStm

const objStm = runtime.resolve('pdfObjStream');
const dict = streamObj.dict;             // { type: 'dict', entries: { Type, N, First, … } }
const decoded = filterDispatch.decode(streamObj);
const members = objStm.parseObjectStream(decoded, dict);
// → [{ num: 5, gen: 0, value: { type: 'dict', entries: { Type: …, Count: … } } }, …]

Feed the members back into a resolver

for (const { num, value } of members) {
    indirects.set(`${num}:0`, { value, offset: -1 });   // -1 → "compressed"
}

Errors

Code Class When
pdf/objstm/bad-input ParseError decoded is not a Uint8Array.
pdf/objstm/bad-dict ParseError dict is not a typed dictionary.
pdf/objstm/wrong-type ParseError /Type present but not /ObjStm.
pdf/objstm/missing-int ParseError /N or /First missing or not an int.
pdf/objstm/bad-N ParseError /N negative.
pdf/objstm/bad-First ParseError /First outside the payload range.
pdf/objstm/bad-pair ParseError Malformed (num, off) header pair.
pdf/objstm/bad-offset ParseError Member offset out of range.

See also