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[udp] Drop datagrams longer than the receive buffer

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A read cuts a datagram longer than the buffer to fit, so a 600 byte
datagram arrived as a valid looking 508 byte packet. The buffer is now one
byte longer, and a read that fills it is dropped. The split packet test
also checks the bytes joined in the copy buffer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
clydebarrow
2026-10-19 14:40:33 +11:00
co-authored by Claude Opus 5.5
parent f128049f99
commit ef6bb95608
2 changed files with 9 additions and 1 deletions
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esphome/components/udp/udp_component.cpp
+6 -1
View File
@@ -209,7 +209,8 @@ void UDPComponent::loop() {
this->disable_loop();
return;
}
std::array<uint8_t, MAX_PACKET_SIZE> buf;
// One byte more than the largest packet, as a read cuts a longer datagram to fit and so cannot report it
std::array<uint8_t, MAX_PACKET_SIZE + 1> buf;
for (;;) {
if (!this->listen_socket_->ready())
break;
@@ -217,6 +218,10 @@ void UDPComponent::loop() {
if (len <= 0)
break;
size_t packet_len = static_cast<size_t>(len);
if (packet_len > MAX_PACKET_SIZE) {
ESP_LOGV(TAG, "Packet longer than %zu bytes dropped", MAX_PACKET_SIZE);
continue;
}
ESP_LOGV(TAG, "Received packet of length %zu", packet_len);
this->packet_listeners_.call(std::span<const uint8_t>(buf.data(), packet_len));
}
tests/components/udp/udp_packet_interface.cpp
+3
View File
@@ -56,6 +56,9 @@ TEST_F(UdpPacketInterfaceTest, SendsContiguousAndSplitPackets) {
uint8_t header = 0;
PacketBuffer body(packet);
EXPECT_TRUE(this->link_.send_to_interface(PacketBuffer(&header, 1, &body, nullptr, 0), {}));
// A packet split across buffers is joined in the copy buffer before it is sent
const auto *storage = this->link_.tx_buffer_storage;
EXPECT_EQ(Packet(storage, storage + 5), (Packet{0, 1, 2, 3, 4}));
}
TEST_F(UdpPacketInterfaceTest, OversizedPacketNotSent) {