See dmtcp.md for the design rationale behind this API.
| Type |
Description |
dmtcp_conn_t |
Opaque handle to one TCP connection (a TCB) - see "Handle lifetime" in include/dmtcp.h |
dmtcp_state_t |
RFC 793 §3.2 connection state (dmtcp_state_established, _fin_wait_1, _time_wait, ...) |
dmtcp_header_t |
Parsed TCP header fields: src_port, dst_port, seq_num, ack_num, flags, window, checksum (parse output only), urgent_pointer |
dmtcp_accept_handler_t |
Callback registered via dmtcp_listen()/_listen_any(), fires once per completed incoming handshake |
dmtcp_established_handler_t |
Fires once a dmtcp_connect()'d connection completes its handshake |
dmtcp_data_handler_t |
Fires for new in-order payload, and once more (data == NULL) on peer FIN (EOF) |
dmtcp_writable_handler_t |
Edge-triggered: fires once after an ACK frees outbound buffer space, but only if an earlier dmtcp_send() came up short |
dmtcp_closed_handler_t |
TERMINAL - graceful close completed |
dmtcp_reset_handler_t |
TERMINAL - RST (peer's or dmtcp_abort()'s own) |
dmtcp_error_handler_t |
TERMINAL - dmtcp gave up (currently: retransmission retry limit, -ETIMEDOUT) |
dmtcp_conn_callbacks_t |
Bundle of the six callbacks above, passed to dmtcp_connect()/dmtcp_conn_set_callbacks() |
| Constant |
Value |
Description |
DMTCP_HEADER_LEN |
20 |
Length of a TCP header with no options |
DMTCP_FLAG_FIN/_SYN/_RST/_PSH/_ACK/_URG |
- |
TCP header control bits |
DMTCP_PORT_EPHEMERAL_FIRST |
49152 |
First port dmtcp_listen_any() will consider (RFC 6335) |
DMTCP_PORT_EPHEMERAL_LAST |
65535 |
Last port dmtcp_listen_any() will consider |
Header build/parse
| Function |
Description |
dmtcp_build_header() |
Build a 20-byte TCP header (no options) into a buffer (checksum field left 0) |
dmtcp_parse_header() |
Parse a TCP header, reporting its real length (Data Offset * 4) so options can be skipped |
| Function |
Description |
dmtcp_v4_checksum_valid() |
Verify a TCP-over-IPv4 segment's checksum (mandatory, unlike UDP's "0 means none") |
dmtcp_v6_checksum_valid() |
Verify a TCP-over-IPv6 segment's checksum (mandatory, RFC 8200 8.1) |
| Function |
Description |
dmtcp_listen() |
Reserve a specific port and register an accept handler for it |
dmtcp_listen_any() |
Reserve the first free port in the ephemeral range and register a handler for it |
dmtcp_unlisten() |
Stop accepting new connections on a port - safe no-op if never listened |
| Function |
Description |
dmtcp_connect() |
Actively open a connection - non-blocking, callback-driven; the outcome arrives via on_established/on_reset/on_error |
| Function |
Description |
dmtcp_conn_set_callbacks() |
Replace a connection's callbacks/user_data |
dmtcp_conn_get_user_data() |
Read back the stored user_data |
dmtcp_conn_get_state() |
Current RFC 793 state |
dmtcp_conn_get_local_endpoint() |
Local address/port |
dmtcp_conn_get_peer_endpoint() |
Remote peer's address/port |
dmtcp_send() |
Queue bytes for delivery - byte-stream semantics, may return a partial count |
dmtcp_send_space() |
Free room in the outbound buffer - the largest dmtcp_send() guaranteed to be taken in full |
dmtcp_close() |
Graceful close (sends FIN) - idempotent |
dmtcp_abort() |
Abortive close (sends RST, tears the connection down immediately) |
- No congestion control (fixed window only), no TCP options (MSS/SACK/window
scaling/timestamps are neither sent nor interpreted), no out-of-order
reassembly buffer, no zero-window probe/persist timer.
- No
dmtcp_connect() success over IPv6 (-ENOSYS) - blocked on
dmip_v6_send() not existing yet (no NDP module). Inbound IPv6 SYNs/
segments are still parsed and checksum-validated correctly; a v6 SYN just
never gets a reply (logged and dropped).
- Simultaneous active open (a bare SYN arriving in SYN_SENT) is unhandled.
DMTCP_TIME_WAIT_MS is 4 seconds, not RFC 793's real 2×MSL.- ISS is
dmosi_get_tick_count()-derived, not randomized.
See dmtcp.md's "Known limitations" section for the complete,
explained list.