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[Fix] (MG_Remote, Wire): let an encoder caller omit a tail whose own count is zero - Count == 0 is a legal record for every kVarTail row and a required placeholder entry would be a trap

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swung0x48
2026-09-11 13:59:51 -04:00
parent 1af5e31f3b
commit 91d0c6b06f
2 changed files with 32 additions and 5 deletions
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MobileGL/MG_Remote/Wire/PipeWireCodec.cpp
+11 -5
View File
@@ -672,14 +672,20 @@ namespace MobileGL::MG_Remote::Wire {
// The caller's tails are held to the layout the PAYLOAD declares, which is the same
// arithmetic the decoder will run. A Count that says 4000 while the tail holds 8 bytes
// dies here, on the producing side, rather than on a peer that can only say "corrupt".
if (tailCount != layout.TailCount) {
//
// A caller may SUPPLY FEWER TAILS THAN THE LAYOUT HAS, but only while the ones it left
// out are empty - Count == 0 is a legal record for every kVarTail row, and requiring a
// {nullptr, 0} entry for it would be a trap rather than a check. Anything else is a
// disagreement between the counts the payload declares and the bytes the caller holds.
if (tailCount > layout.TailCount) {
WireProtocolFatalAt("EncodeRecord.tailCount", tailCount, layout.TailCount);
}
for (Uint32 i = 0; i < tailCount; ++i) {
if (tails[i].Size != layout.TailBytes[i]) {
WireProtocolFatalAt("EncodeRecord.tailBytes", tails[i].Size, layout.TailBytes[i]);
for (Uint32 i = 0; i < layout.TailCount; ++i) {
const Uint64 supplied = i < tailCount ? tails[i].Size : 0;
if (supplied != layout.TailBytes[i]) {
WireProtocolFatalAt("EncodeRecord.tailBytes", supplied, layout.TailBytes[i]);
}
if (tails[i].Size != 0 && tails[i].Bytes == nullptr) {
if (supplied != 0 && tails[i].Bytes == nullptr) {
WireProtocolFatal("EncodeRecord.tail", "non-zero tail length with a null pointer");
}
}
MobileGL/MG_Test/Wire/PipeWireCodecTest.cpp
+21
View File
@@ -452,6 +452,27 @@ TEST_F(PipeWireCodecTest, KVarTailRoundTripsWithItsTailIntact) {
EXPECT_TRUE(applied);
}
TEST_F(PipeWireCodecTest, AnEmptyVarTailIsALegalRecordAndNeedsNoPlaceholderEntry) {
// Count == 0 is legal for every kVarTail row - "bind nothing at this range" - and a caller
// that had to pass a {nullptr, 0} entry for each absent tail would be walking into a trap
// rather than through a check. SetStreamOutputTargets is the sharpest case: its layout has
// TWO tails and both are empty at Count 0.
Wire2 wire;
MGPStreamOutputTargets header{};
header.Count = 0;
ASSERT_NE(wire.Encoder().EncodeRecord(MGPWireOp::SetStreamOutputTargets, &header, sizeof(header)),
kInvalidSeq);
MGPVertexBuffers buffers{};
buffers.Count = 0;
ASSERT_NE(wire.Encoder().EncodeRecord(MGPWireOp::SetVertexBuffers, &buffers, sizeof(buffers)),
kInvalidSeq);
bool applied = false;
ASSERT_TRUE(wire.PumpOne(&applied));
EXPECT_FALSE(applied); // no applier for stream output; off the reduced path
ASSERT_TRUE(wire.PumpOne(&applied));
EXPECT_TRUE(applied);
}
TEST_F(PipeWireCodecTest, KReplySlotMapPersistentIsAConstantDecline) {
// R-6 / R-2.4. DECLINED is a real answer, not a failure, and the applier is not called at
// all: the record's payload is a bare MGPHandleOnly and carries NEITHER the size NOR the