feat(c-api): the experimental zstd.h and zdict.h surface by polaz · Pull Request #601 · structured-world/structured-zstd

polaz · 2026-10-18T14:53:04Z

Summary

The C ABI now exports every symbol upstream libzstd 1.5.7 exports, the ZSTD_STATIC_LINKING_ONLY / ZDICT_STATIC_LINKING_ONLY sections included, so a binary linked against upstream's full surface links against this library.
Every behaviour lives in the codec; c-api/ only translates. Where upstream refuses and this library can work, it works: a sequence producer next to long-distance matching keeps the long matches, ZSTD_compressSequencesAndLiterals takes a checksum or a parse without block delimiters, and an external parse is always validated, in shape and against the input it is given, so no parse yields a frame that does not decode to that input.

Replaces #599, squashed onto main as one commit.

Changes

Frame and buffer queries: ZSTD_isFrame, skippable frames, ZSTD_decompressionMargin, ZSTD_decodingBufferSize_min, the CDict/DDict/DStream estimates, ZSTD_getCParams / getParams / adjustCParams / checkCParams, ZSTD_DCtx_setFormat / setMaxWindowSize
ZSTD_CCtx_params objects with the experimental ZSTD_c_* parameters, ZSTD_CCtx_setCParams / setFParams / setParams, ZSTD_compress_advanced, ZSTD_createCDict_advanced2, the *_usingCCtxParams estimates. A CDict's explicit window is raised toward a source of known size as upstream raises it, through the codec's CompressionParameters::for_dictionary_frame
The memory estimates budget what a context actually keeps, each part sized by the function its allocation uses; context sizes count every dictionary the context alone keeps, once
Stream init variants, ZSTD_resetCStream / resetDStream, the *_simpleArgs calls, ZSTD_getFrameProgression, ZSTD_toFlushNow, the *_advanced constructors (default allocator only). ZSTD_compressStream2 takes input only while its output fits the caller's buffer; ZSTD_decompressStream takes headers, blocks, checksums and skippable frames in pieces of any size
Buffer-less compression and decompression (ZSTD_compressBegin* / Continue / End, ZSTD_decompressBegin* / Continue), the block API, ZSTD_copyCCtx / copyDCtx
One-shot decompression takes the in-place layout ZSTD_decompressionMargin describes; a ZSTD_DDict is parsed when it is created and shared by the contexts that use it; a single-use prefix is spent when its frame starts, as upstream spends it
Sequences: encoding::sequences in the codec (parse capture, SequenceReplay, SequenceProducer, RebuiltSource), and ZSTD_generateSequences, ZSTD_compressSequences, ZSTD_compressSequencesAndLiterals (rebuilding the input one window at a time), ZSTD_sequenceBound, ZSTD_mergeBlockDelimiters, ZSTD_registerSequenceProducer on top. A FrameCompressor can borrow a prepared dictionary (DictionaryHold, new_with_matcher_and_dictionary), so a frame built from a parse references it as upstream references a CDict
The worker-pool parameters and thread pools are accepted and read back as upstream's multi-threaded build takes them, and frames are built on the calling thread; ZSTD_initStatic* answer NULL, a context cannot live in a caller's workspace
ZDICT_addEntropyTablesFromBuffer, ZDICT_trainFromBuffer_legacy
CI builds upstream libzstd at the pinned tag and requires each of its exports to be exported here, in place of a hand-kept list

Testing

Formatting, clippy across the feature sets, the codec, C ABI and ffi-bench suites, doctests and rustdoc pass; expected values in the C ABI tests were read from upstream libzstd 1.5.7.

Closes #127

Summary by CodeRabbit

New Features
- Expanded the C API with buffer-less and block-level compression and decompression, configurable compression parameters, sequence capture and replay, and streaming progress and input-size reporting.
- Added sequence-producer callbacks, frame inspection and buffer-sizing utilities, dictionary memory estimates, and skippable-frame parsing and writing.
- Made the typed skippable-frame API available in all builds and added a minimum block-size constant.
Bug Fixes
- Improved handling of partial frame headers, dictionary inputs, overlapping buffers, and incremental streaming.
Documentation
- Added examples for capturing, validating, and replaying compression sequences.

The C ABI exports every symbol upstream libzstd 1.5.7 exports, the ZSTD_STATIC_LINKING_ONLY and ZDICT_STATIC_LINKING_ONLY sections included, so a binary linked against upstream's full surface links against this library. Every behaviour lives in the codec; c-api/ only translates. - Frame and buffer queries, skippable frames, ZSTD_decompressionMargin, ZSTD_decodingBufferSize_min, the CDict/DDict/DStream estimates, ZSTD_getCParams/getParams/adjustCParams/checkCParams, the DCtx format and window setters - ZSTD_CCtx_params with the experimental ZSTD_c_* parameters, the setCParams/setFParams/setParams setters, ZSTD_compress_advanced, ZSTD_createCDict_advanced2, the *_usingCCtxParams estimates; a CDict's explicit window is raised toward a source of known size as upstream raises it (CompressionParameters::for_dictionary_frame) - Memory estimates budget what a context keeps, each part sized by the function its allocation uses; context sizes count every dictionary the context alone keeps, once - Stream init variants, resets, the *_simpleArgs calls, frame progression, ZSTD_toFlushNow, the *_advanced constructors (default allocator only); ZSTD_compressStream answers the input that completes the block being filled - Buffer-less compression and decompression, the block API, ZSTD_copyCCtx/copyDCtx; one-shot decompression takes the in-place layout; a DDict is parsed when it is created and shared by the contexts that use it; a single-use prefix is spent when its frame starts, as upstream spends it - Sequences: encoding::sequences in the codec (capture, replay, producers, rebuilt sources) and ZSTD_generateSequences, ZSTD_compressSequences, ZSTD_compressSequencesAndLiterals, ZSTD_sequenceBound, ZSTD_mergeBlockDelimiters, ZSTD_registerSequenceProducer on top; an external parse is checked to be well formed and to copy the bytes of the input it is given; a FrameCompressor can borrow a prepared dictionary (DictionaryHold) - Worker-pool parameters and thread pools are accepted and read back as upstream's multi-threaded build takes them, frames are built on the calling thread; ZSTD_initStatic* answer NULL - ZDICT_addEntropyTablesFromBuffer, ZDICT_trainFromBuffer_legacy - CI builds upstream libzstd at the pinned tag and requires each of its exports to be exported here Closes #127

chatgpt-codex-connector · 2026-10-18T14:53:18Z

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coderabbitai · 2026-10-18T14:53:41Z

📝 Walkthrough

The change expands the Rust codec and C API with sequence, bufferless, parameter, streaming, dictionary, and frame operations. It also adds tests, updates documentation, and changes CI test and export checks.

Changes: C API and codec functionality

Layer / File(s)	Summary
Sequence capture, production, and replay `zstd/src/encoding/sequences.rs`, `zstd/src/encoding/frame_compressor.rs`, `zstd/src/encoding/match_generator/*`, `c-api/src/sequences.rs`, `c-api/src/tests/sequences.rs`, `README.md`	The codec adds sequence validation, reconstruction, replay, capture, and producer support. C entry points expose sequence generation and sequence-based compression.
Frame inspection and block decoding `zstd/src/decoding/*`, `c-api/src/frame.rs`, `c-api/src/ffi.rs`, `c-api/src/simple.rs`	The decoder adds block-level operations, frame inspection, header sizing, buffer calculations, and overlap-aware input handling. C frame functions expose inspection and skippable-frame utilities.
C context parameters and streaming `c-api/src/cctx_params.rs`, `c-api/src/params.rs`, `c-api/src/context.rs`, `c-api/src/streaming.rs`, `c-api/src/tests/{cctx_params,streams}.rs`	The C API adds parameter sets, context configuration, frame progress reporting, and streaming initialization and processing. Streaming compression consumes input incrementally, and streaming decompression stages partial input.
Bufferless frame and block APIs `c-api/src/bufferless.rs`, `c-api/src/tests/bufferless.rs`	The C API adds incremental frame and raw-block compression and decompression, including dictionary setup, checksums, skippable frames, and context copying.
Dictionary handling and memory estimates `c-api/src/{attach,cdict,dict,estimate,provided}.rs`, `zstd/src/{decoding/dictionary.rs,encoding/frame_compressor.rs,encoding/levels/config.rs,encoding/parameters.rs}`, `c-api/src/tests/{provided,experimental}.rs`	Dictionary recognition, ownership, prefix selection, and size accounting change across codec and C API paths. The change adds dictionary training entry points, parameter adjustment, workspace estimates, and thread-pool and static-workspace APIs.
Skippable frames and integration `zstd/src/skippable.rs`, `zstd/src/lib.rs`, `c-api/src/lib.rs`, `.github/workflows/ci.yml`, `docs/SKIPPABLE_MAGIC_ALLOCATIONS.md`	The typed skippable-frame API becomes available in all builds and gains slice parsing. Crate exports and documentation change. CI uses nextest and compares project exports with upstream symbols.

Priority: ⬇️ Low

Estimated code review effort: 5 (Critical) | ~120 minutes

Merge Risk: ⚪ Minimal · up to 73ad1

No merge-blocking issue is established; the remaining test-coverage improvement does not prevent merging.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Linked Issues check		Issue `#127` requires a warning when `nbWorkers > 0` falls back to single-threaded compression. `c-api/src/provided.rs` documents and implements a no-op thread pool, but emits no warning. Issue `#127` als…	Emit the required warning for nonzero `nbWorkers` while keeping the single-threaded fallback. Extend `c-api/tests/c_consumer.c` to exercise every wrapper listed in issue `#127` and test the required 16 MiB corpus variants.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the main change: adding the experimental zstd.h and zdict.h C API surface.
Out of Scope Changes check		The codec, C ABI wrappers, tests, export validation, dictionary training, sequence support, frame support, and documentation implement the stated upstream v1.5.7 compatibility goal. The issue also tar…
Docstring Coverage		Docstring coverage is 88.42% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 622 functions across 57 files.

Full details: Out of Scope Changes check

Explanation

The codec, C ABI wrappers, tests, export validation, dictionary training, sequence support, frame support, and documentation implement the stated upstream v1.5.7 compatibility goal. The issue also targets a symbol-complete v1.5.7 surface, excluding only multi-threaded compression, the CLI, and legacy frames. No unrelated change is demonstrated.

Full details: Linked Issues check

Explanation

Issue #127 requires a warning when nbWorkers > 0 falls back to single-threaded compression. c-api/src/provided.rs documents and implements a no-op thread pool, but emits no warning. Issue #127 also requires every listed wrapper to run in a C consumer test. c-api/tests/c_consumer.c covers selected advanced, streaming, dictionary, and training calls only. Its streaming corpus is 1 MiB and does not cover the required 16 MiB random, low-entropy, and high-entropy cases.

Resolution

Emit the required warning for nonzero nbWorkers while keeping the single-threaded fallback. Extend c-api/tests/c_consumer.c to exercise every wrapper listed in issue #127 and test the required 16 MiB corpus variants.

Fix all pre-merge checks with AI

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Inline comments:
Review comments at @c-api/src/bufferless.rs:
- Around line 560-567: Update the `begin_blocks` setup in `begin_decode` to use
`dctx.max_window_size` when setting the decoder’s maximum window, so block
history respects the configured context limit rather than
`MAX_DECODER_WINDOW_SIZE`.

Review comments at @c-api/src/tests/experimental.rs:
- Around line 514-524: Update stream_decode to record inb.pos and outb.pos
before each ZSTD_decompressStream call, then assert that at least one position
advances when decoding continues; preserve the existing error and completion
handling.

Review comments at @c-api/src/tests/streams.rs:
- Around line 56-82: Add a progress check to decode_simple that records src_pos
before each decompression call and verifies afterward that either src_pos
advanced or dst_pos is nonzero. Fail with a clear message if neither changed,
while preserving the existing success and decompression-error paths.

Review comments at @zstd/src/encoding/sequences.rs:
- Around line 106-108: Update the literal-length merge in merge_block_delimiters
to use wrapping addition for next.lit_len and sequence.lit_len, ensuring
overflow matches upstream C behavior without panicking.

Review comments at @zstd/src/skippable/tests.rs:
- Around line 3-35: Add assertions in parse_skippable_frame_borrows_or_refuses
for an empty slice returning the expected truncated error, a frame with a
zero-length payload parsing successfully, and the maximum valid skippable magic
0x184D2A5F being accepted. Reuse the existing frame-writing and parsing helpers.

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📒 Files selected for processing: 66

.github/workflows/ci.yml
README.md
c-api/src/attach.rs
c-api/src/bufferless.rs
c-api/src/cctx_params.rs
c-api/src/cdict.rs
c-api/src/context.rs
c-api/src/dict.rs
c-api/src/estimate.rs
c-api/src/ffi.rs
c-api/src/frame.rs
c-api/src/lib.rs
c-api/src/params.rs
c-api/src/provided.rs
c-api/src/sequences.rs
c-api/src/simple.rs
c-api/src/streaming.rs
c-api/src/tests.rs
c-api/src/tests/bufferless.rs
c-api/src/tests/cctx_params.rs
c-api/src/tests/experimental.rs
c-api/src/tests/provided.rs
c-api/src/tests/sequences.rs
c-api/src/tests/streams.rs
docs/SKIPPABLE_MAGIC_ALLOCATIONS.md
zstd/Cargo.toml
zstd/src/common/mod.rs
zstd/src/decoding/block_api_tests.rs
zstd/src/decoding/decode_buffer.rs
zstd/src/decoding/dictionary.rs
zstd/src/decoding/dictionary/tests.rs
zstd/src/decoding/frame.rs
zstd/src/decoding/frame_decoder.rs
zstd/src/decoding/mod.rs
zstd/src/decoding/scratch.rs
zstd/src/dictionary/legacy.rs
zstd/src/dictionary/mod.rs
zstd/src/dictionary/tests.rs
zstd/src/encoding/block_input.rs
zstd/src/encoding/blocks/compressed.rs
zstd/src/encoding/blocks/compressed/tests.rs
zstd/src/encoding/cparams.rs
zstd/src/encoding/frame_compressor.rs
zstd/src/encoding/frame_compressor/tests.rs
zstd/src/encoding/levels/config.rs
zstd/src/encoding/levels/config/tests.rs
zstd/src/encoding/levels/fastest.rs
zstd/src/encoding/levels/fastest/tests.rs
zstd/src/encoding/match_generator/long_distance.rs
zstd/src/encoding/match_generator/mod.rs
zstd/src/encoding/match_generator/tests.rs
zstd/src/encoding/match_table/storage.rs
zstd/src/encoding/mod.rs
zstd/src/encoding/parameters.rs
zstd/src/encoding/parameters/tests.rs
zstd/src/encoding/sequences.rs
zstd/src/encoding/sequences/tests.rs
zstd/src/encoding/streaming_encoder.rs
zstd/src/encoding/streaming_encoder/tests.rs
zstd/src/fse/fse_decoder.rs
zstd/src/huff0/huff0_decoder.rs
zstd/src/huff0/huff0_encoder.rs
zstd/src/huff0/huff0_encoder/tests.rs
zstd/src/lib.rs
zstd/src/skippable.rs
zstd/src/skippable/tests.rs

💤 Files with no reviewable changes: 1

zstd/Cargo.toml

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codecov · 2026-10-18T15:23:05Z

Codecov Report

❌ Patch coverage is 99.70588% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
zstd/src/encoding/frame_compressor.rs	98.06%	3 Missing ⚠️
zstd/src/encoding/match_generator/mod.rs	99.18%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

- Every one-shot (ZSTD_compress2, generateSequences, the compressSequences pair) starts from a fresh session as upstream does: a streamed frame left open is abandoned and a pledge that disagrees with the input in hand is dropped, rather than refused. - ZSTD_compressEnd keeps room for one block of output after the frame, as the streaming path does, not the frame's peak. - A parameter reset leaves a begun buffer-less run as it was begun: the run keeps the format it started in, and the decoder is not replaced. - merge_block_delimiters wraps a literal sum past u32::MAX, as upstream, instead of panicking inside the C entry point. - exclusive_heap_size counts holders, not references: one handle listed twice is one holder (both dictionary kinds). - ZSTD_decompressBegin documents that the block history grows with the output, up to the largest window plus a block. - Codec unit tests for the new accounting, header-in-pieces, parse checks, replay with a dictionary, dictionary windows, read hints and the block API; progress guards in two C ABI test helpers. Regression tests: compress2_abandons_a_stream_in_flight, compress2_roundtrips_with_sticky_parameters, a_finished_frame_leaves_no_frame_sized_output_behind, a_parameter_reset_leaves_a_begun_run_alone, merging_delimiters_past_u32_max_wraps, a_handle_accounts_for_what_it_keeps, exclusive_heap_size_counts_what_only_the_set_holds.

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Inline comments:
Review comments at @zstd/src/encoding/sequences/tests.rs:
- Around line 943-944: Update the final-delimiter test around replay_frame to
use a block limit smaller than its suffix and enough suffix data to require
multiple blocks; assert block_count(&frame) while preserving the decoded-output
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c-api/src/attach.rs
c-api/src/bufferless.rs
c-api/src/cdict.rs
c-api/src/context.rs
c-api/src/sequences.rs
c-api/src/streaming.rs
c-api/src/tests.rs
c-api/src/tests/bufferless.rs
c-api/src/tests/experimental.rs
c-api/src/tests/streams.rs
zstd/src/decoding/block_api_tests.rs
zstd/src/decoding/dictionary.rs
zstd/src/decoding/dictionary/tests.rs
zstd/src/decoding/frame_inspection_tests.rs
zstd/src/encoding/cparams/tests.rs
zstd/src/encoding/frame_compressor.rs
zstd/src/encoding/frame_compressor/tests.rs
zstd/src/encoding/parameters/tests.rs
zstd/src/encoding/sequences.rs
zstd/src/encoding/sequences/tests.rs
zstd/src/encoding/streaming_encoder/tests.rs
zstd/src/skippable/tests.rs

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structured-zstd/c-api/src/streaming.rs

Line 462 in 73ad1a9

match stream.context.finish_frame(&mut stream.pending) {

Honor single-call end's pledge override

When a caller pledges 10 bytes and immediately supplies and consumes 5 bytes in a single ZSTD_compressStream2(..., ZSTD_e_end) call, this finishes the frame with the original pledge, causing finish_frame to return InvalidInput, which is mapped to srcSize_wrong. The vendored API contract in c-api/include/zstd.h lines 582-585 explicitly requires this one-round call to override the pledge with the actual input size; upstream therefore succeeds and emits a frame for 5 bytes. The remaining fresh case after fixing the one-shot helpers is this streaming end path, so it must apply the same override instead of enforcing the stale pledge.

AGENTS.md reference: AGENTS.md:L247-L251

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## Summary - The C ABI now exports every symbol upstream libzstd 1.5.7 exports, the `ZSTD_STATIC_LINKING_ONLY` / `ZDICT_STATIC_LINKING_ONLY` sections included, so a binary linked against upstream's full surface links against this library. - Every behaviour lives in the codec; `c-api/` only translates. Where upstream refuses and this library can work, it works: a sequence producer next to long-distance matching keeps the long matches, `ZSTD_compressSequencesAndLiterals` takes a checksum or a parse without block delimiters, and an external parse is always validated, in shape and against the input it is given, so no parse yields a frame that does not decode to that input. Replaces #601, squashed onto `main` as one commit. ## Changes - Frame and buffer queries: `ZSTD_isFrame`, skippable frames, `ZSTD_decompressionMargin`, `ZSTD_decodingBufferSize_min`, the CDict/DDict/DStream estimates, `ZSTD_getCParams` / `getParams` / `adjustCParams` / `checkCParams` - `ZSTD_CCtx_params` objects with the experimental `ZSTD_c_*` parameters, `ZSTD_CCtx_setCParams` / `setFParams` / `setParams`, `ZSTD_compress_advanced`, `ZSTD_createCDict_advanced2`, the `*_usingCCtxParams` estimates. A CDict's explicit window is raised toward a source of known size as upstream raises it, through the codec's `CompressionParameters::for_dictionary_frame` - Every experimental `ZSTD_d_*` parameter: the frame format and window ceiling (`ZSTD_DCtx_setFormat` / `setMaxWindowSize`), `forceIgnoreChecksum` on every decode path, `refMultipleDDicts` picking a frame's DDict by its dictionary ID, `maxBlockSize` refusing bigger blocks, `stableOutBuffer` and `disableHuffmanAssembly` stored and read back. The rules are the codec's: `FrameDecoder::set_max_block_size`, `reset_with_dict_handles`, `decode_all_with_dict_handles` - The memory estimates budget what a context actually keeps, each part sized by the function its allocation uses; context sizes count every dictionary the context alone keeps, once - Stream init variants, `ZSTD_resetCStream` / `resetDStream`, the `*_simpleArgs` calls, `ZSTD_getFrameProgression`, `ZSTD_toFlushNow`, the `*_advanced` constructors (default allocator only). `ZSTD_compressStream2` takes input only while its output fits the caller's buffer, and a frame one end call begins takes the input's size over a pledge; `ZSTD_decompressStream` takes headers, blocks, checksums and skippable frames in pieces of any size, and stops a caller that makes no progress inside a frame with upstream's `noForwardProgress` errors - One-shots (`ZSTD_compress2`, `generateSequences`, the `compressSequences` pair) start from a fresh session, as upstream's do - Buffer-less compression and decompression (`ZSTD_compressBegin*` / `Continue` / `End`, `ZSTD_decompressBegin*` / `Continue`), the block API, `ZSTD_copyCCtx` / `copyDCtx` - One-shot decompression takes the in-place layout `ZSTD_decompressionMargin` describes; a `ZSTD_DDict` is parsed when it is created and shared by the contexts that use it; a single-use prefix is spent when its frame starts, as upstream spends it - Sequences: `encoding::sequences` in the codec (parse capture, `SequenceReplay`, `SequenceProducer`, `RebuiltSource`), and `ZSTD_generateSequences`, `ZSTD_compressSequences`, `ZSTD_compressSequencesAndLiterals` (rebuilding the input one window at a time), `ZSTD_sequenceBound`, `ZSTD_mergeBlockDelimiters`, `ZSTD_registerSequenceProducer` on top. A `FrameCompressor` can borrow a prepared dictionary (`DictionaryHold`, `new_with_matcher_and_dictionary`), so a frame built from a parse references it as upstream references a CDict - The worker-pool parameters and thread pools are accepted and read back as upstream's multi-threaded build takes them, and frames are built on the calling thread; `ZSTD_initStatic*` answer `NULL`, a context cannot live in a caller's workspace - `ZDICT_addEntropyTablesFromBuffer`, `ZDICT_trainFromBuffer_legacy` - CI builds upstream libzstd at the pinned tag and requires each of its exports to be exported here, in place of a hand-kept list ## Testing Formatting, clippy across the feature sets, the codec, C ABI and ffi-bench suites, doctests and rustdoc pass; expected values in the C ABI tests were read from upstream libzstd 1.5.7. Closes #127  ## Summary by CodeRabbit - **New Features** - Expanded the C API with incremental and block-level compression and decompression, sequence-based compression, configurable parameters, dictionary tools, and frame inspection and sizing utilities. - Added Rust APIs for sequence capture and replay, custom sequence producers, block-size limits, multi-dictionary decoding, block-by-block frame decoding, and skippable-frame parsing. - Made typed skippable-frame support available in every build. - **Bug Fixes** - Improved streaming input handling, frame-header size hints, dictionary selection, and decoding of overlapping input and output. - Corrected compression parameter, memory-estimate, and dictionary-training error handling. - **Documentation** - Documented sequence capture, replay, validation, and custom producers.

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Comment thread zstd/src/encoding/sequences.rs

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Comment thread zstd/src/encoding/sequences/tests.rs

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Comment thread c-api/src/streaming.rs

Comment thread c-api/src/params.rs

polaz closed this Oct 18, 2026

polaz mentioned this pull request Oct 18, 2026

feat(c-api): the experimental zstd.h and zdict.h surface #602

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feat(c-api): the experimental zstd.h and zdict.h surface - #601

feat(c-api): the experimental zstd.h and zdict.h surface#601
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feat/#127-experimental-api

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polaz commented Oct 18, 2026 •

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