closed TG-1; git was inited;

tests/test_ais_assembler.py

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+"""Multi-fragment AIS assembler: strict-order and strengthened-key tests.
+
+These tests exercise the assembler logic only up to fragment validation.
+Actual decoding with pyais is covered by a separate integration check
+if pyais is importable.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from ais_hub.core.stats import Stats
+from ais_hub.parser.ais import AisAssembler
+
+
+SRC_A = "ais_udp:10.0.0.1:5000"
+SRC_B = "ais_udp:10.0.0.2:5000"
+
+
+def _frag(total: int, n: int, seq: str, channel: str = "A", payload: str = "abcd", fill: str = "0") -> str:
+    # Compute checksum so parse_sentence accepts the line.
+    body = f"AIVDM,{total},{n},{seq},{channel},{payload},{fill}"
+    cs = 0
+    for ch in body.encode("ascii"):
+        cs ^= ch
+    return f"!{body}*{cs:02X}"
+
+
+def test_single_fragment_fast_path_attempts_decode():
+    """A single-fragment sentence is passed to pyais; decode may fail, but
+    the assembler must not keep any buffers for it."""
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    line = _frag(1, 1, "")
+    a.feed(SRC_A, line)
+    # No multi-fragment buffers.
+    assert len(a._buffers) == 0
+
+
+def test_multi_fragment_happy_path_clears_buffer():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 1, "3"))
+    assert len(a._buffers) == 1
+    a.feed(SRC_A, _frag(2, 2, "3"))
+    # After the final fragment arrives, the buffer is removed (regardless
+    # of whether pyais decodes successfully).
+    assert len(a._buffers) == 0
+
+
+def test_out_of_order_fragment_triggers_error_and_reset():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(3, 1, "7"))
+    a.feed(SRC_A, _frag(3, 3, "7"))  # skipped fragment 2
+    assert stats.counters["ais_fragment_errors"] >= 1
+
+
+def test_duplicate_fragment_is_error():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 1, "9"))
+    a.feed(SRC_A, _frag(2, 1, "9"))  # duplicate
+    assert stats.counters["ais_fragment_errors"] >= 1
+
+
+def test_mid_stream_fragment_without_leading_is_error():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 2, "4"))
+    assert stats.counters["ais_fragment_errors"] >= 1
+    assert len(a._buffers) == 0
+
+
+def test_strengthened_key_isolates_sources():
+    """Two sources reusing the same seq_id must not cross-contaminate."""
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 1, "5"))
+    a.feed(SRC_B, _frag(2, 1, "5"))
+    assert len(a._buffers) == 2  # two independent buffers
+    assert stats.counters.get("ais_fragment_errors", 0) == 0
+
+
+def test_multi_fragment_without_seq_id_is_error():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 1, ""))  # empty seq_id on a multi-fragment
+    assert stats.counters["ais_fragment_errors"] >= 1
+
+
+def test_total_mismatch_on_followup_is_error():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, _frag(2, 1, "2"))
+    # Fragment claims total=3 now; must be treated as a fresh start or error.
+    a.feed(SRC_A, _frag(3, 2, "2"))
+    assert stats.counters["ais_fragment_errors"] >= 1
+
+
+def test_ttl_gc_evicts_stale_buffers():
+    stats = Stats()
+    a = AisAssembler(stats=stats, ttl_sec=1.0)
+    a.feed(SRC_A, _frag(2, 1, "8"), ts=1000.0)
+    assert len(a._buffers) == 1
+    a.gc(now=1002.0)
+    assert len(a._buffers) == 0
+    assert stats.counters["ais_fragment_timeouts"] >= 1
+
+
+def test_bad_checksum_ignored_with_counter():
+    stats = Stats()
+    a = AisAssembler(stats=stats)
+    a.feed(SRC_A, "!AIVDM,1,1,,A,x,0*00")  # deliberately wrong checksum
+    assert stats.counters["parser_checksum_errors"] >= 1