fix(trace-utils): fix forward compatibility for string streaming - #2295
fix(trace-utils): fix forward compatibility for string streaming#2295anais-raison wants to merge 2 commits into
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…1 decoder + add tests
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Reviewed commit: ac8e79eff6
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| match value { | ||
| rmpv::ValueRef::String(s) => { | ||
| if let Some(s) = (*s).into_str() { | ||
| table.record(&T::Text::from_static_str(s)); |
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When decoding owned bytes, this records a string borrowed from the just-skipped buffer as from_static_str, so if a future/unknown field contains the first occurrence of a string and a later known field references that ID, the decoded payload can contain a BytesString that does not retain the original Bytes allocation. In the common from_bytes(Bytes::from(Vec<_>)) path, a payload like unknown key "ghost" followed by span service ref 1 leaves service pointing at memory owned only by the decoder buffer after it is dropped; this should record skipped strings via a path that preserves the backing Bytes ownership (or copies) rather than treating them as static.
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This needs to be addressed. The 'static lifetime is actually a lie since the string you're getting is actually a reference to the Bytes buffer, to make sure the Bytes refcount is correctly updated you need to create a ByteString from the slice with from_bytes_slice
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By the way, how it's possible in safe code? I haven't looked at record or from_static_str, but should one of the two be marked as unsafe if there are additional pre-conditions to hold? As this PR shows, this seems to be actually possible to hit.
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Ok, I just looked and the culprit is as_mut_slice from the decoding buffer. Why does this method return a &'static?? It's obviously not, if T::Bytes is owning memory... Honestly we're very lucky Codex spotted this. I would have written the same code as @anais-raison here without giving it a second thought and would probably have never find that at review time either. Something went really wrong with the as_mut_slice design/implementation
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Code lgtm but the tests are hard to read, and it might be over-tested. (I don't think we need 1 test per field) |
(This is my fault lol as I originally provided these tests for this ticket after a quick claude generation and didn't clean them up to be PR ready before sharing them :P Sorry!) |
| match value { | ||
| rmpv::ValueRef::String(s) => { | ||
| if let Some(s) = (*s).into_str() { | ||
| table.record(&T::Text::from_static_str(s)); |
There was a problem hiding this comment.
This needs to be addressed. The 'static lifetime is actually a lie since the string you're getting is actually a reference to the Bytes buffer, to make sure the Bytes refcount is correctly updated you need to create a ByteString from the slice with from_bytes_slice
BenchmarksComparisonBenchmark execution time: 2026-08-06 13:32:56 Comparing candidate commit 7970c7d in PR branch Found 13 performance improvements and 17 performance regressions! Performance is the same for 107 metrics, 2 unstable metrics.
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What does this PR do?
Fixes a forward-compatibility bug in the v1 msgpack decoder: when skipping an unknown key (e.g. a field added by a newer tracer version), inline strings inside the skipped value were not interned into the shared
StringTable. This desynced the table's indices, so any later reference to a previously-interned string by ID would resolve to the wrong value.Motivation
APMSP-3836