fix(pdu): keep the packed byte of RLEX segments when the palette has a single entry by AdrienAvalon · Pull Request #1903 · Devolutions/IronRDP

Adrien CROS (AdrienAvalon) · 2026-09-04T16:28:11Z

Closes #1902.

decode_rlex special-cased a one-entry palette (stop_index_bits = 0, bare run lengths). Per MS-RDPEGFX 2.2.4.6.2.2 and FreeRDP's clear_decompress_subcode_rlex (CLEAR_LOG2_FLOOR[0] == 0), stopIndex still takes one bit in that case and every segment keeps its packed byte. The shortcut read every run length one byte off and rejected the one-colour regions Windows Server uses for the solid corners of its taskbar (14×64, 64×46) with "suite exceeds region pixel count".

This PR gives stopIndex one bit for a single entry, removes the special path, and adds a test decoding such a 14×64 region (a run of 895 on a 16-bit length plus a suite of one). No encoder emitted the old form. cargo test -p ironrdp-pdu rlex: 8 passed.

Shipped in avash's vendored ironrdp-pdu since 0.7.1, verified against Windows Server 2025 with the recorded session that exposed it.

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The full test suite fails because an existing one-entry RLEX fixture was not updated.

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Pull request overview

Fixes single-entry RLEX palette decoding by preserving the mandatory packed segment byte.

Changes:

Uses one stopIndex bit for single-entry palettes.
Removes the obsolete bare-run decoder path.
Adds a Windows Server regression test.

File summaries

File	Review
`crates/ironrdp-pdu/src/codecs/clearcodec/rlex.rs`	Corrects RLEX parsing. The existing subcodec fixture must include the packed byte and updated bitmap length. Renaming the helper to `decode_segments` is a non-blocking nit.

Review details

Suppressed comments (1)

crates/ironrdp-pdu/src/codecs/clearcodec/rlex.rs:87

Now that this path also handles one-entry palettes, decode_multi_palette_segments no longer describes the helper's responsibility. Rename it to decode_segments so future changes do not mistakenly assume the helper is only valid for multi-entry palettes.

    decode_multi_palette_segments(

Files reviewed: 1/1 changed files
Comments generated: 1
Review effort level: Balanced

Adrien CROS (AdrienAvalon) · 2026-09-04T20:41:13Z

-            &mut segments,
-        )?;
-    }
+    decode_multi_palette_segments(


Thanks for looking. On this branch cargo test -p ironrdp-pdu passes (423 tests, and the CI checks are green): decode_subcodec_layer only records each region with its codec id and never runs the RLEX decoder on it, so this fixture was not parsed. It did still describe the old encoding, so 399ea8c makes it a valid one-entry RLEX stream (bitmap length 6, a zero packed byte before the run length), as you suggested.

Benoît Cortier (CBenoit)

Thank you!

github-actions · 2026-09-11T16:42:47Z

Automated review will not run because this contributor is not yet eligible under the automation policy.

Contributors become eligible after one qualifying IronRDP pull request is merged into master. Maintainer review is required.

Benoît Cortier (CBenoit) · 2026-10-01T08:12:27Z

Adrien CROS (@AdrienAvalon) I think this just needs the formatter to run, can you look into that, please?

Adrien CROS (AdrienAvalon) · 2026-10-06T17:18:03Z

Thanks Benoît Cortier (@CBenoit), done: rebased on master and ran the formatter (07ed330), whose newer config orders the ironrdp_core imports in subcodec.rs differently. cargo xtask check fmt passes, and cargo test -p ironrdp-pdu (426 tests) and clippy on the crate are green locally.

Adrien CROS (AdrienAvalon) · 2026-10-06T17:32:05Z

Note on the one red check, Check public API compatibility: it fails before comparing any API, while building rustdoc for ironrdp with freshly resolved dependencies. sspi 0.21.3 does not compile against picky-krb 0.12.5 (GssApiMessageError::InvalidMechanismOid not covered, E0004), which looks like what #2080 addresses. This PR only touches ironrdp-pdu's RLEX decoder and its tests.

Benoît Cortier (CBenoit) · 2026-10-07T13:22:03Z

PR automation is failing because of a picky-krb 0.12.5 incompatibility, fixed on master by #2074. Please rebase on master to fix it.

…a single entry MS-RDPEGFX 2.2.4.6.2.2 gives stopIndex floor(log2(paletteCount - 1)) + 1 bits; with a single palette entry FreeRDP's CLEAR_LOG2_FLOOR table yields 0, so stopIndex still takes one bit and every segment keeps its packed byte. The single-entry shortcut read bare run lengths instead, one byte off, and failed with "suite exceeds region pixel count" on the solid taskbar corners Windows Server encodes this way (14x64, 64x46). Closes Devolutions#1902

The subcodec layer only records the region and its codec id, so this fixture is never parsed by the RLEX decoder and the test kept passing. It still documented the old, incorrect encoding (no packed byte when the palette has a single entry); make it match what the decoder now expects so the fixture stays a valid RLEX stream.

Rebased on master, whose rustfmt configuration orders the ironrdp_core imports differently; cargo xtask check fmt now passes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01BPFSPcmEWGpgTDP24ADEkZ

Adrien CROS (AdrienAvalon) · 2026-10-07T13:25:33Z

Rebased on master with #2074 (b523188). cargo xtask check fmt passes, cargo test -p ironrdp-pdu (426 tests) and clippy on the crate are green locally. Thanks for the pointer!

Adrien CROS (AdrienAvalon) · 2026-10-07T13:29:17Z

After the rebase, Check public API compatibility now fails differently (run): cargo-semver-checks stops on unsupported rustdoc format v61 while reading target/doc/ironrdp.json, before comparing anything with the baseline 4132836. It looks like the semver-checks binary in the automation predates the rustdoc JSON format of the toolchain it runs with; the branch itself only changes ironrdp-pdu's RLEX decoder and tests, and its rust-toolchain.toml is master's.

Adrien CROS (AdrienAvalon) temporarily deployed to llm-providers September 4, 2026 16:28 — with GitHub Actions Inactive

Benoît Cortier (CBenoit) requested a balanced review from Copilot September 4, 2026 20:31

Copilot started reviewing on behalf of Benoît Cortier (CBenoit) September 4, 2026 20:32 View session

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Comment thread crates/ironrdp-pdu/src/codecs/clearcodec/subcodec.rs Outdated

Benoît Cortier (CBenoit) temporarily deployed to llm-providers September 9, 2026 00:22 — with GitHub Actions Inactive

Benoît Cortier (CBenoit) enabled auto-merge (squash) September 9, 2026 00:23

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Benoît Cortier (CBenoit) added needs-author-action The pull request author is the current next actor and removed needs-review A human reviewer is the current next actor labels Oct 1, 2026

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Adrien CROS (AdrienAvalon) force-pushed the fix/rlex-single-palette-packed-byte branch from 9421798 to 07ed330 Compare October 6, 2026 17:18

Adrien CROS (AdrienAvalon) deployed to llm-providers October 6, 2026 17:18 — with GitHub Actions Active

Adrien CROS (AdrienAvalon) and others added 2 commits October 7, 2026 15:25

Benoît Cortier (CBenoit) and others added 2 commits October 7, 2026 15:25

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Adrien CROS (AdrienAvalon) force-pushed the fix/rlex-single-palette-packed-byte branch from 07ed330 to b523188 Compare October 7, 2026 13:25

Adrien CROS (AdrienAvalon) deployed to llm-providers October 7, 2026 13:26 — with GitHub Actions Active

Benoît Cortier (CBenoit) enabled auto-merge (squash) October 8, 2026 04:29

Benoît Cortier (CBenoit) merged commit 8e76c31 into Devolutions:master Oct 8, 2026
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fix(pdu): keep the packed byte of RLEX segments when the palette has a single entry - #1903

fix(pdu): keep the packed byte of RLEX segments when the palette has a single entry#1903
Benoît Cortier (CBenoit) merged 4 commits into
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AdrienAvalon:fix/rlex-single-palette-packed-byte

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