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Fix TCP option size calculation for options with empty payload #404

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Fix TCP option size calculation for options with empty payload #404

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1 change: 1 addition & 0 deletions include/tins/tcp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,7 @@ class TINS_API TCP : public PDU {
SACK = 5,
TSOPT = 8,
ALTCHK = 14,
SCPS_CAPABILITIES = 20,
RFC_EXPERIMENT_1 = 253,
RFC_EXPERIMENT_2 = 254
};
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6 changes: 4 additions & 2 deletions src/tcp.cpp
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Expand Up @@ -385,8 +385,10 @@ uint32_t TCP::calculate_options_size() const {
for (options_type::const_iterator iter = options_.begin(); iter != options_.end(); ++iter) {
const option& opt = *iter;
options_size += sizeof(uint8_t);
// SACK_OK contains length but not data
if (opt.data_size() || opt.option() == SACK_OK) {
// Options 0 and 1 are exactly one octet which is their kind field.
// All other options have their one octet kind field,
// followed by a one octet length field (even if the option payload is empty)
if (opt.option() != 0 && opt.option() != 1) {
options_size += sizeof(uint8_t);
options_size += static_cast<uint16_t>(opt.data_size());
}
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8 changes: 8 additions & 0 deletions tests/src/tcp_test.cpp
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Expand Up @@ -277,6 +277,14 @@ TEST_F(TCPTest, SpoofedOptions) {
EXPECT_EQ(pdu.serialize().size(), pdu.size());
}

TEST_F(TCPTest, OptionWithEmptyPayload) {
TCP pdu;
// it has a payload, it's just empty (unlike EOL/NOP options which have no payload)
pdu.add_option(TCP::option(TCP::SCPS_CAPABILITIES, 2));
EXPECT_EQ(1U, pdu.options().size());
EXPECT_EQ(pdu.serialize().size(), pdu.size());
}

TEST_F(TCPTest, MalformedOptionAfterEOL) {
TCP tcp(malformed_option_after_eol_packet, sizeof(malformed_option_after_eol_packet));
EXPECT_EQ(0U, tcp.options().size());
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