# net-io - Edge cases and their tests
> Every case in [`PLAN.md`](./PLAN.md) appendix A has a test by the version that ships the feature it concerns. This file maps each case to its tests, or to the version that ships it with the reason. Updated with every version.
Test locations: `tests/<file>.rs::<name>`, unit tests as `src/<file>.rs::<name>`. `shim` tests need `--cfg net_io_shim`; `loom_` tests need `--cfg loom`.
## Reads
| 1. EOF in Idle: `PeerClosed` | `edge::edge_01_eof_in_idle_is_peer_closed`, `close_reasons::reason_peer_closed` |
| 2. EOF in Receiving reaches the session | `edge::edge_02_37_eof_mid_request_reaches_the_session_which_may_still_write` |
| 3. Partial reads at every split | `edge::edge_03_partial_reads_at_every_split` |
| 4. Full buffer, nothing consumed: `Limit(ReadBuffer)`, no spin | `edge::edge_04_full_buffer_with_nothing_consumed_is_a_limit_not_a_spin`, `close_reasons::reason_limit_read_buffer` |
| 5. `EINTR` retried | `shim::test_interrupted_receives_are_retried`, `src/sys/mod.rs::test_retry_interrupted_retries_then_returns` |
| 6. Spurious `EAGAIN` retried | `shim::test_spurious_would_block_is_retried` |
| 7. `ECONNRESET`: `PeerReset` | `edge::edge_07_33_peer_reset_is_peer_reset`, `close_reasons::reason_peer_reset`, `shim::test_receive_error_closes_only_that_connection` |
| 8. Keepalive `ETIMEDOUT`: `Io(TimedOut)` | `shim::test_keepalive_timeout_is_an_io_error_not_a_deadline` (D-080) |
| 9. Data after our `shutdown(Read)` never delivered | `server::test_kill_ends_a_blocked_handler`, `src/tcp.rs::test_kill_wakes_blocked_recv` |
| 10. Data while parked read after the wake | `edge::edge_10_bytes_sent_while_parked_are_read_after_the_wake` |
| 11. Buffer budget exhausted: reading pauses | `reactor::test_buffer_budget_pauses_reading`, `reactor::test_paused_connection_closes_cleanly` (the reactor; the blocking pool takes its buffers at warm-up and validates the budget at build, so it never runs dry mid-connection) |
| 12. Zero-length `recv` | `edge::edge_12_zero_length_receive_returns_at_once` |
| 13. 107 bytes without CRLF: `V1TooLong` | `src/proxy_parse.rs::test_v1_too_long` (0.4) |
| 14. v2 signature split across 12 segments | `src/proxy_parse.rs::test_v2_split_into_segments_waits_then_succeeds`, `src/proxy_parse.rs::prop_every_split_point_agrees` (0.4) |
| 15. Header and data in one segment: `consumed` leaves the rest | `src/proxy_parse.rs::test_v1_tcp4_and_rest_is_data`, `proxy::test_v1_header_gives_the_real_client_and_keeps_the_rest`, `tls::test_proxy_then_tls_in_one_segment` (0.4) |
| 16. A second header is application data | `src/proxy_parse.rs::test_second_header_is_data` (0.4) |
| 17. First byte of a header, then silence: handshake deadline | `proxy::test_missing_invalid_and_slow_headers` (0.4) |
## Writes
| 18. Partial writes from the exact offset | `shim::test_partial_writes_at_many_splits`, `shim::test_short_writes_still_deliver_everything`, `src/session.rs::prop_output_stream_matches_accepted_pushes` |
| 19. `send` returns 0: full once, then an error | `shim::test_zero_byte_send_once_then_error` (D-074) |
| 20. `EAGAIN`: wait within the write deadline | `server::test_sessions_echo_large_message`, `edge::edge_25_32_large_response_after_peer_fin_uses_several_checked_sends` |
| 21. `EPIPE` without a signal | `edge::edge_21_22_peer_gone_mid_write_is_peer_reset_without_a_signal` |
| 22. `ECONNRESET` mid-write: `PeerReset`, output released | `edge::edge_21_22_peer_gone_mid_write_is_peer_reset_without_a_signal` |
| 23. Write deadline: `WriteTimeout` | `server::test_peer_that_never_reads_hits_the_write_timeout`, `close_reasons::reason_write_timeout` |
| 24. Vectored write partly into a later slice | `src/session.rs::prop_output_stream_matches_accepted_pushes`, `src/session.rs::test_output_advance_releases_chunks` |
| 25. Several system calls, each after a gate check | `edge::edge_25_32_large_response_after_peer_fin_uses_several_checked_sends` |
| 26. Denial between two chunks of a response: RST, no denial | `edge::edge_26_denial_inside_a_response_resets_without_a_denial` |
| 27, 28. Denial before the first byte: written once, not checked again | `edge::edge_27_28_denial_before_the_first_byte_is_written_once`, `close_reasons::reason_egress_denied` |
| 29. Output budget full: `OutputFull`, `Step::Write` | `server::test_sessions_echo_large_message`, `src/session.rs::test_output_push_all_or_nothing_and_partial` |
| 30. `sendfile` short or file shrinks | `send_file::test_file_that_ends_early_is_an_error_with_the_count`, `send_file::test_push_file_that_ends_early_resets_on_both_drivers` |
| 31. TLS ciphertext over the budget | 0.4 (the TLS seam is wired then) |
## Close
| 32. Peer FIN with output pending: finish, then close | `edge::edge_25_32_large_response_after_peer_fin_uses_several_checked_sends` |
| 33. Peer RST while we write | `edge::edge_07_33_peer_reset_is_peer_reset`, `edge::edge_21_22_peer_gone_mid_write_is_peer_reset_without_a_signal` |
| 34. Graceful close with unread input lingers | `edge::edge_34_close_with_unread_input_lingers_so_the_reply_arrives` |
| 35. Abort sends RST | `edge::edge_35_abort_sends_a_reset` |
| 36. Kill during the linger | `edge::edge_36_kill_during_the_linger_closes_at_once` |
| 37. Half-closed peer keeps reading | `edge::edge_02_37_eof_mid_request_reaches_the_session_which_may_still_write`, `edge::edge_25_32_large_response_after_peer_fin_uses_several_checked_sends` |
| 38, 39. `shutdown(Write)` twice; close after the peer closed | `edge::edge_38_39_shutdown_twice_and_close_after_the_peer_closed` |
## Accept
| 40, 41. `EMFILE` with the reserve; reserve not reopened | `src/accept.rs::test_emfile_sheds_and_retries_the_reserve`, `shim::test_accept_out_of_descriptors_recovers` |
| 42, 45. `ENFILE`, `ENOBUFS`, `ENOMEM`: pause, resume | `shim::test_accept_resource_errors_pause_then_resume` |
| 43, 44. `ECONNABORTED`, `EPERM`: counted, continue | `shim::test_accept_per_connection_errors_continue` |
| 46. `EBADF` / `EINVAL`: listener failed, no spin | `shim::test_accept_listener_failure_stops_without_spinning` |
| 47. Unspecified peer address | `src/accept.rs::test_unspecified_or_portless_peer_is_not_usable` (D-070; loopback cannot produce one) |
| 48. A burst in the backlog does not stall IO | `edge::edge_48_burst_in_the_backlog_does_not_stall_open_connections` |
| 49. Door closed with a backlog: kept, or reset by `shutdown` | `server::test_closed_door_leaves_connections_in_the_backlog`, `edge::edge_49_backlog_is_reset_by_shutdown` |
| 50. Handed-off listener's backlog unknown | 0.4 (hand-off ships then) |
| 51. IPv4-mapped peer normalized before caps and the gate | `edge::edge_51_mapped_peer_is_normalized_before_the_gate`, `src/addr.rs::test_normalize_mapped_v6_becomes_v4` |
| 52. Scope id kept; the prefix key ignores it | `src/addr.rs::test_normalize_socket_keeps_port_and_scope` (`PrefixKey::of` takes an `IpAddr`, which has no scope id) |
## Timers
| 53 to 60. Wheel cases | `src/wheel.rs`: `test_fires_at_its_tick_and_never_before`, `test_deadline_at_the_current_tick`, `test_deadline_in_the_past`, `test_overflow_fires_across_the_wrap`, `test_many_timers_in_one_slot_are_bounded_by_the_caller`, `test_extended_a_million_times_fires_once`, `test_clock_jump_fires_everything_in_order`, `test_frozen_clock_fires_nothing`, `prop_matches_a_sorted_model` |
| 61. Tick coarser than a deadline: rejected at build | `src/limits.rs::test_timeout_below_tick_rejected` |
## IOCP, io_uring, Unix sockets, named pipes, UDP, hand-off (62 to 105)
io_uring (cases of its own, 71 to 75) after 1.0 (D-015). IOCP, named pipes, and the Windows hand-off shipped in 0.5; Unix sockets, UDP, and the Unix hand-off in 0.4:
| 62. `CancelIoEx` returns `ERROR_NOT_FOUND`: success | `src/driver/iocp.rs::test_cancel_completes_once_with_the_buffer` |
| 63. The operation succeeds after the cancel: its result stands | `src/driver/iocp.rs::test_cancel_after_success_keeps_the_result` |
| 64. A completion for a reused slot: dropped with its buffer | `src/driver/iocp.rs::test_stale_packet_is_dropped` |
| 65. A packet with a null `OVERLAPPED`: the wake, nothing else | `src/driver/iocp.rs::test_waker_ends_a_wait` |
| 66. A client resets before the worker's association: closed quietly, counted | `close_reasons::reason_peer_reset`, on the reactor by default |
| 67. A socket on exactly one port, never a listener | `src/driver/iocp.rs::test_listener_is_refused` |
| 68. Zero-byte receive, then the peer had closed: the next receive returns 0 | `src/driver/iocp.rs::test_zero_byte_receive_then_end_of_stream` |
| 69. Skip mode on and off | every test in `src/driver/iocp.rs` runs both through `both()` |
| 86. All instances busy: waits within the timeout | `src/pipe.rs::test_instance_cap_makes_a_client_wait` |
| 87. Next instance made before hand-over | `src/pipe.rs::test_name_in_use_and_next_instance` |
| 88. Client gone before `ConnectNamedPipe`; `ERROR_PIPE_CONNECTED` is success | `src/pipe.rs::test_client_gone_before_accept`, `test_client_pid_and_credentials` |
| 89. A backslash in the name: refused before any call | `src/pipe.rs::test_names_are_checked_before_any_call` |
| 104. Windows blob used twice: refused before `WSASocketW` | `src/handoff.rs::test_a_hand_off_works_once` |
| 105. A received listener never joins a port | `src/driver/iocp.rs::test_listener_is_refused`, `windows_handoff::handoff_between_processes_refuses_nothing_under_load` |
| 76. Path exactly at the maximum; one more byte: `PathTooLong` | `src/local.rs::test_longest_path_binds_and_non_sockets_stay`, `src/local.rs::test_path_checks` |
| 77. NUL in the path: rejected | `src/local.rs::test_path_checks` (`InvalidConfig { reason: Malformed }`, D-095) |
| 78. Stale socket file: removed, bind succeeds | `src/local.rs::test_stale_socket_removed_live_one_refused` |
| 79. Live listener on the path: `StaleSocketInUse`, file untouched | `src/local.rs::test_stale_socket_removed_live_one_refused`, `unix::unix_listener_on_a_live_path_fails_build` |
| 80. Regular file, directory, symlink: not removed, error | `src/local.rs::test_stale_socket_removed_live_one_refused` (file), `src/local.rs::test_longest_path_binds_and_non_sockets_stay` (directory, symlink) |
| 81. `MSG_CTRUNC`: every descriptor closed, `Truncated` | `src/sys/unix.rs::test_truncated_control_message_closes_every_descriptor` (Linux; macOS runs the same receive code, without this test) |
| 82. Truncated or bad-checksum body: all closed | `src/handoff.rs::test_manifest_rejects_damage`, `src/handoff.rs::test_count_mismatch_truncation_timeout_and_peer`; fuzz target `manifest` |
| 83. More (or fewer) descriptors than declared: `CountMismatch` | `src/handoff.rs::test_count_mismatch_truncation_timeout_and_peer` |
| 84. Credentials unavailable: `None`, and `require_uid` refuses | `src/local.rs::test_unknown_credentials_fail_require_uid` |
| 85. Our path replaced by someone else's socket: `Drop` leaves it | `src/local.rs::test_drop_leaves_a_replacement_alone` |
| 90. Datagram larger than the buffer: `truncated` | `src/udp.rs::test_echo_truncation_and_zero_length`, `src/sys/unix.rs::test_udp_recv_reports_truncation_and_source`, `src/sys/windows.rs::test_udp_recv_reports_truncation_and_source` |
| 91. Zero-length datagram: valid | `src/udp.rs::test_echo_truncation_and_zero_length` |
| 92. ICMP port unreachable never fatal; Windows `SIO_UDP_CONNRESET` off | `src/udp.rs::test_icmp_reports_never_end_the_socket`; the constant is checked in `src/sys/windows.rs::test_layout_udp_matches_windows_sys` |
| 93. Source table full: strangers share the overflow budget; verified peers keep entries | `src/udp.rs::test_full_table_evicts_strangers_and_keeps_verified` |
| 94. Factor 1, 1-byte request: 2-byte reply refused until verified | `src/udp.rs::test_amplification_factor_one_until_verified` |
| 95. `LISTEN_FDS=0`: empty list | `src/inherit.rs::test_systemd_protocol` |
| 96. `LISTEN_FDS` non-numeric, negative, above 64 | `src/inherit.rs::test_systemd_protocol` |
| 97. No `LISTEN_PID`: empty list | `src/inherit.rs::test_systemd_protocol` |
| 98. Names count differs: `NamesMismatch` | `src/inherit.rs::test_systemd_protocol` |
| 99. Descriptor closed or a regular file: `NotASocket` | `src/inherit.rs::test_systemd_protocol` |
| 100. A connected socket: `NotListening` | `src/inherit.rs::test_systemd_takes_verified_listeners_with_names` |
| 101. FastCGI descriptor 0 not a listener: `None` | `src/inherit.rs::test_fastcgi_descriptor_checks`, `cross_process::fastcgi_listener_is_none_for_a_pipe_or_terminal` |
| 102. Receiver timeout: `Timeout`, nothing adopted | `src/handoff.rs::test_count_mismatch_truncation_timeout_and_peer` |
| 103. Sender dies mid-send: nothing adopted | `src/handoff.rs::test_count_mismatch_truncation_timeout_and_peer` |
End to end: `handoff::listeners_move_to_a_new_server_without_closing`, `cross_process::handoff_between_processes_refuses_nothing_under_load` (two processes, about 1,000 connections per second, zero refused), `cross_process::systemd_socket_activation_with_the_real_tool`, `cross_process::fastcgi_listener_on_descriptor_zero`.
## Server lifecycle
| 106, 107. Door calls idempotent | `edge::edge_106_107_door_calls_are_idempotent` |
| 108. Drain with nothing open | `edge::edge_108_drain_with_nothing_open_returns_at_once` |
| 109. Drain deadline already passed | `edge::edge_109_drain_deadline_in_the_past_kills_at_once` |
| 110. `request_stop` from a session | `edge::edge_110_request_stop_from_a_session_is_safe`, `server::test_request_stop_ends_wait_for_stop` |
| 111. `adopt` while draining | `adopt::adopt_while_draining_is_shutting_down` (0.4) |
| 112. `release_listeners` with the door open | `handoff::listeners_move_to_a_new_server_without_closing`, `cross_process::handoff_between_processes_refuses_nothing_under_load` (0.4) |
| 113. `kill` with a foreign or closed id | `edge::edge_113_kill_with_a_foreign_or_closed_id_is_false` |
| 114. Control line changes within one iteration | `src/control.rs::test_view_sees_only_final_state` |
| 115. `Draining` without a deadline | `edge::edge_115_draining_without_a_deadline_uses_the_drain_timeout` |
| 116. More workers than CPUs | `edge::edge_116_more_workers_than_cpus` |
| 117. `post` after shutdown | `edge::edge_117_post_after_shutdown_is_server_stopped` |
| 118. Session panic contained | `server::test_session_panic_is_contained`, `close_reasons::reason_session_panicked` |
## Configuration
| 119, 120. Zero values; per-listener above global | `edge::edge_119_120_bad_caps_fail_at_build`, `src/limits.rs::test_zero_values_rejected` |
| 121. Caps above `RLIMIT_NOFILE` | `src/limits.rs::test_validate_descriptor_limit_and_budget` |
| 122, 123. PROXY configuration | 0.4 |
| 124, 125. CIDR host bits; prefix too long | `src/addr.rs::test_cidr_parse_rejects_bad_text`, `src/addr.rs::test_cidr_new_masked_clears_bits`, `src/addr.rs::prop_cidr_and_prefix_key_match_integer_masks` |
| 126. Address in use | `edge::edge_126_address_in_use`, `src/tcp.rs::test_bind_in_use_maps_to_addr_in_use` |
| 127. Low port without privileges | `edge::edge_127_low_port_without_privileges`, `src/tcp.rs::test_bind_errors_map_by_class` |
| 128. IPv6 address with IPv6 disabled | `src/tcp.rs::test_bind_errors_map_by_class` |
## Cross-thread
| 129. Kill from 64 threads | `edge::edge_129_kill_from_many_threads_closes_once`, `src/sys/kill.rs::test_kill_from_many_threads_exactly_one_wins` |
| 130. Kill racing a close | `src/sys/kill.rs::loom_kill_never_acts_after_close`, `interleave::prop_every_connection_closes_exactly_once` |
| 131. Post racing a close: never delivered elsewhere | `edge::edge_10_bytes_sent_while_parked_are_read_after_the_wake` (post after close is `WrongWorker`), `src/completer.rs::loom_ring_two_producers_one_consumer` |
| 132. `stats()` while workers run | `edge::edge_132_stats_while_workers_run` (D-069) |
## Every close reason
`tests/close_reasons.rs` produces each close reason the blocking driver has in 0.3 on a real socket and asserts exactly one `Closed` event with it; `tests/interleave.rs` checks the exactly-once rule over random interleavings of FIN, RST, kill, timeouts, and a drain. `Io` comes from `shim::test_keepalive_timeout_is_an_io_error_not_a_deadline`. `HandshakeTimeout`, `ProxyUntrusted`, `ProxyMissing`, `ProxyInvalid`, `TlsFailed`, and `HelloRefused` arrive with PROXY and TLS in 0.4.