pdf_cos

The COS (Carousel Object System) layer of the dart-pdf suite: everything a PDF file is made of, before any notion of pages or rendering.

Pure Dart with no dart:io or Flutter dependency, so it runs on the VM, in CLIs and servers, and on the web.

Features

• Object model: dictionaries, arrays, names, strings, numbers, streams, and indirect references, with lazy object loading through the cross-reference machinery.
• Lenient parsing. Real-world PDFs are broken (wrong /Length, missing endobj, junk before the header); the parser tolerates them on input and stays strict on output, including full xref recovery by scanning for object headers when the chain is broken.
• Filters: Flate, LZW, RunLength, ASCIIHex, ASCII85, CCITT G3/G4, JBIG2 (embedded profile), JPEG 2000, plus predictors. The image codecs are validated against reference implementations (libtiff, jbig2dec, OpenJPEG).
• Encryption: RC4, AES-128, and AES-256 decryption, and encrypt-on-write for incremental saves.
• Crypto primitives (ASN.1, RSA, ECDSA, CMS, X.509 chain verification) used by the document layer for digital signatures.
• Writing: incremental updates that append to the original bytes, and a from-scratch document builder.

Usage

import 'dart:typed_data';
import 'package:pdf_cos/pdf_cos.dart';

final doc = CosDocument.open(bytes);
final catalog = doc.catalog; // the /Root dictionary
final info = doc.trailer['Info'];

The suite