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[modbus] Build single-value register writes on a right-sized stack buffer (#18844)

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Co-authored-by: J. Nick Koston <nick@koston.org>
This commit is contained in:
Bonne Eggleston
2026-08-28 18:36:24 +00:00
committed by GitHub
co-authored by J. Nick Koston
parent 768ab5b672
commit 59397b4e28
6 changed files with 61 additions and 3 deletions
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tests/components/modbus/modbus_helpers_test.cpp
+22
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@@ -489,6 +489,28 @@ TEST(ModbusTypedBuilders, WriteRegistersPduRejectsOverLimit) {
EXPECT_FALSE(create_write_registers_pdu(0x0000, values).empty());
}
TEST(ModbusTypedBuilders, WriteFewRegistersPduMatchesFullSizeBuilder) {
static_assert(sizeof(WriteFewRegistersPdu) < sizeof(PduBuffer) / 4,
"WriteFewRegistersPdu must be meaningfully smaller");
const uint16_t values[] = {0x000B, 0x0016, 0xABCD, 0xFF00};
for (size_t count = 1; count <= MAX_FEW_REGISTERS; count++) {
auto small = create_write_few_registers_pdu(0x0102, std::span<const uint16_t>(values, count));
auto full = create_write_registers_pdu(0x0102, std::span<const uint16_t>(values, count));
EXPECT_EQ(std::vector<uint8_t>(small.begin(), small.end()), std::vector<uint8_t>(full.begin(), full.end()))
<< count << " registers";
EXPECT_EQ(small.size(), 6u + 2 * count);
EXPECT_TRUE(is_client_pdu_standard(small.data(), small.size()));
}
}
TEST(ModbusTypedBuilders, WriteFewRegistersPduRejectsInvalidInput) {
const uint16_t values[MAX_FEW_REGISTERS + 1] = {0xAAAA, 0xAAAA, 0xAAAA, 0xAAAA, 0xAAAA};
EXPECT_TRUE(create_write_few_registers_pdu(0x0000, values).empty());
EXPECT_FALSE(create_write_few_registers_pdu(0x0000, std::span<const uint16_t>(values, MAX_FEW_REGISTERS)).empty());
EXPECT_TRUE(create_write_few_registers_pdu(0x0000, std::span<const uint16_t>()).empty());
EXPECT_TRUE(create_write_few_registers_pdu(0xFFFF, std::span<const uint16_t>(values, 2)).empty());
}
TEST(ModbusTypedBuilders, ReadWriteMultipleRegistersPduWireBytes) {
const uint16_t write_values[] = {0x000B, 0x0016};
// Read 2 registers at 0x0010, write 2 registers at 0x0020.