v4.0e — embedding library / DLL / .so API + decompression guard

Library / embedding release for the v4.0 LTS line. On-disk .pjg format is unchanged from v4.0b/c/d — output is byte-exact, full backward compatibility: v4.0e decodes every v4.0-line file (v4.0, v4.0a, v4.0b, v4.0c, v4.0d). Not a format break, no v4.1.

What's new

1. Embedding library API — a C-linkage API to use packJPG inside other programs (archivers, image tools, web services). Available as a self-contained Windows DLL (packJPG.dll, no external runtime DLLs), a Unix shared object (libpackJPG.so), and a static lib (packJPGlib.a). Same .pjg format as the CLI.

2. Multithreading on by default in the library: each single-file convert uses up to 3 cores (Y/Cb/Cr) when the host has ≥3 logical cores. New pjglib_convert_batch() converts N files in parallel over a worker pool, plus thread controls (pjglib_set_intra/inter_file_threads, pjglib_suggest_batch_threads). No code change required in existing FFI consumers.

3. Decompression-bomb guard — a malformed .pjg can reconstruct into a much larger JPEG (a tiny low-entropy trailing blob expands on decode; this is inherent to lossless compression and is present in upstream packJPG too). New optional cap makes the decoder fail cleanly instead of producing oversized output, for hosts decoding untrusted .pjg:

   • CLI: -maxout<MB> (e.g. packjpg x -maxout64 file.pjg).
   • Library: pjglib_set_max_output_size(bytes).
   • Default off (0 = unlimited) — no behavior change for trusted workflows.

4. Bug fixes (found in a QA pass over a 153-file real-world JPEG corpus + ASan/UBSan/TSan):

   • Windows DLL crashed at process exit after the first convert under the MinGW win32 thread model — now built with the posix model (the dll target refuses the broken model).
   • pjglib_convert_batch file→file with out_dest=NULL wrote the wrong extension on decompress, clobbering the source .pjg — now picks the extension from the input's magic.
   • Per-worker-thread memory leak of the filename buffers.

5. Legacy build (XP/Vista/7/8) bumped to v4.0e with the same decompression guard (-maxout<MB>). The library MT API is source/-only (it relies on thread_local, which the XP toolchain lacks).

Compatibility

.pjg from	Decoded by v4.0e
v4.0 / v4.0a	✅ (transparent)
v4.0b / v4.0c / v4.0d	✅ (byte-exact)
v3.x / v2.x	❌ — use the v3.1d build

Verified on Linux, Windows 10 (x64), and Windows 7 (x64 + x86): round-trip byte-exact; library round-trip byte-exact across the inter×intra thread grid; guard aborts oversized decodes cleanly.

Embedding

See the README › Library / DLL API for the function reference and a worked example. Ready-to-link SDK archives are attached — each contains the library, headers, and (Windows) an MSVC .def:

Asset	Contents
packJPG-4.0e-win64-lib.zip	packJPG.dll (x64, self-contained) + libpackJPG.a + packJPG.def + headers
packJPG-4.0e-win32-lib.zip	same, 32-bit (XP+)
packJPG-4.0e-linux-x64-lib.tar.gz	libpackJPG.so + packJPGlib.a (static) + header