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Configure SOCKS5 UDP replies for framing tests #88

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afaf598
Read SOCKS5 UDP hostname lengths as unsigned
M-Hassan-Raza Sep 27, 2026
29e5205
Configure SOCKS5 UDP response headers
M-Hassan-Raza Sep 27, 2026
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14 changes: 12 additions & 2 deletions include/simulator/socks_server.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -54,10 +54,18 @@ enum socks_flag
udp_associate_respond_empty_hostname = 2
};

// Override UDP response fields to simulate malformed proxy replies.
struct socks_udp_header
{
std::uint16_t reserved = 0;
// A negative value preserves the address type of the forwarded packet.
int address_type = -1;
};

struct SIMULATOR_DECL socks_connection : std::enable_shared_from_this<socks_connection>
{
socks_connection(asio::io_context& ios, int version, std::array<int, 3>& cmd_counts
, std::uint32_t flags, int& bind_port);
, std::uint32_t flags, int& bind_port, socks_udp_header header);

asio::ip::tcp::socket& socket() { return m_client_connection; }

Expand Down Expand Up @@ -149,14 +157,15 @@ struct SIMULATOR_DECL socks_connection : std::enable_shared_from_this<socks_conn
std::array<int, 3>& m_cmd_counts;

std::uint32_t const m_flags;
socks_udp_header const m_udp_header;
};

// This is a very simple socks4 and 5 server that only supports a single
// concurrent connection
struct SIMULATOR_DECL socks_server
{
socks_server(asio::io_context& ios, unsigned short listen_port
, int version = 5, std::uint32_t flags = 0);
, int version = 5, std::uint32_t flags = 0, socks_udp_header header = {});

void stop();

Expand Down Expand Up @@ -190,6 +199,7 @@ struct SIMULATOR_DECL socks_server
std::array<int, 3> m_cmd_counts;

std::uint32_t const m_flags;
socks_udp_header const m_udp_header;
};

}
Expand Down
29 changes: 18 additions & 11 deletions src/socks_server.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -34,12 +34,14 @@ namespace sim
using namespace aux;

socks_server::socks_server(io_context& ios, unsigned short listen_port, int version
, std::uint32_t const flags)
, std::uint32_t const flags, socks_udp_header const header)
: m_ios(ios)
, m_listen_socket(ios)
, m_conn(std::make_shared<socks_connection>(m_ios, version, m_cmd_counts, flags, m_bind_port))
, m_conn(std::make_shared<socks_connection>(
m_ios, version, m_cmd_counts, flags, m_bind_port, header))
, m_version(version)
, m_flags(flags)
, m_udp_header(header)
{
m_cmd_counts.fill(0);
address local_ip = ios.get_ips().front();
Expand Down Expand Up @@ -77,7 +79,8 @@ namespace sim
m_conn->start();

// create a new connection to accept into
m_conn = std::make_shared<socks_connection>(m_ios, m_version, m_cmd_counts, m_flags, m_bind_port);
m_conn = std::make_shared<socks_connection>(
m_ios, m_version, m_cmd_counts, m_flags, m_bind_port, m_udp_header);

// now we can accept another connection
m_listen_socket.async_accept(m_conn->socket(), m_ep
Expand All @@ -91,7 +94,8 @@ namespace sim
}

socks_connection::socks_connection(asio::io_context& ios
, int version, std::array<int, 3>& cmd_counts, std::uint32_t const flags, int& bind_port)
, int version, std::array<int, 3>& cmd_counts, std::uint32_t const flags
, int& bind_port, socks_udp_header const header)
: m_bind_port(bind_port)
, m_ios(ios)
, m_udp_resolver(ios)
Expand All @@ -106,6 +110,7 @@ namespace sim
, m_command(0)
, m_cmd_counts(cmd_counts)
, m_flags(flags)
, m_udp_header(header)
{
}

Expand Down Expand Up @@ -620,7 +625,7 @@ namespace sim
if (atyp == 3)
{
// hostname
int const len = buf[4];
int const len = static_cast<unsigned char>(buf[4]);

buf += 5;
bytes_transferred -= 5;
Expand Down Expand Up @@ -708,10 +713,11 @@ namespace sim
if (it != m_name_mapping.left.end())
{
std::vector<char> header(7 + it->second.size());
header[0] = 0; // RSV
header[1] = 0;
header[0] = static_cast<char>(m_udp_header.reserved >> 8); // RSV
header[1] = static_cast<char>(m_udp_header.reserved & 0xff);
header[2] = 0; // fragment
header[3] = 3; // ATYP
header[3] = static_cast<char>(
m_udp_header.address_type < 0 ? 3 : m_udp_header.address_type); // ATYP
header[4] = static_cast<char>(it->second.size());
int idx = 5;
std::copy(it->second.begin(), it->second.end(), header.data() + idx);
Expand All @@ -732,10 +738,11 @@ namespace sim
// add UDP ASSOCIATE header and forward to client
std::uint32_t const from_addr = m_udp_from.address().to_v4().to_uint();
std::array<char, 10> header;
header[0] = 0; // RSV
header[1] = 0;
header[0] = static_cast<char>(m_udp_header.reserved >> 8); // RSV
header[1] = static_cast<char>(m_udp_header.reserved & 0xff);
header[2] = 0; // fragment
header[3] = 1; // ATYP
header[3] = static_cast<char>(
m_udp_header.address_type < 0 ? 1 : m_udp_header.address_type); // ATYP
header[4] = (from_addr >> 24) & 0xff; // Address
header[5] = (from_addr >> 16) & 0xff;
header[6] = (from_addr >> 8) & 0xff;
Expand Down