fix(edf): use offset instead of stale slice for MarshalEDF length prefix#257
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halturin merged 2 commits intoergo-services:masterfrom Apr 20, 2026
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When MarshalEDF writes enough data to trigger lib.Buffer reallocation (via append), the slice returned by Extend(4) points to freed memory. The 4-byte length prefix is then written to the old backing array, leaving zeros in the new buffer. The decoder reads length=0 and fails with "malformed EDF: end of data". Fix by recording the buffer offset before Extend and indexing into b.B[] after MarshalEDF returns, which always references the current (potentially reallocated) backing array.
Verifies that Encode/Decode roundtrip works correctly when MarshalEDF writes enough data to trigger lib.Buffer reallocation. Uses a small initial buffer capacity (64 bytes) to guarantee reallocation occurs. Without the offset-based fix in register.go, the length prefix is written to a stale slice and the decoder returns zero-length data.
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Such a great catch 👍. Will take a look closer in a week (on a vacation now), but so far looks good |
halturin
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…fix (#257) * fix(edf): use offset instead of stale slice for MarshalEDF length prefix When MarshalEDF writes enough data to trigger lib.Buffer reallocation (via append), the slice returned by Extend(4) points to freed memory. The 4-byte length prefix is then written to the old backing array, leaving zeros in the new buffer. The decoder reads length=0 and fails with "malformed EDF: end of data". Fix by recording the buffer offset before Extend and indexing into b.B[] after MarshalEDF returns, which always references the current (potentially reallocated) backing array. * test(edf): regression test for MarshalEDF buffer reallocation Verifies that Encode/Decode roundtrip works correctly when MarshalEDF writes enough data to trigger lib.Buffer reallocation. Uses a small initial buffer capacity (64 bytes) to guarantee reallocation occurs. Without the offset-based fix in register.go, the length prefix is written to a stale slice and the decoder returns zero-length data.
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When a type registered via
RegisterTypeOfimplementsMarshaler, the encoder reserves a 4-byte length prefix viaExtend(4)before callingMarshalEDF. IfMarshalEDFwrites enough data to triggerlib.Bufferreallocation (via append), the slice returned byExtendpoints to the old backing array. The length prefix is then written to freed memory, leaving zeros in the actual buffer. The decoder reads length=0 and fails withmalformed EDF: end of data.The fix records the buffer offset before
Extendand indexes intob.B[]afterMarshalEDFreturns, which always references the current backing array regardless of reallocation.