feat: bound aggregate Gitea transport traffic (#246)

tests/test_gitea_transport.py

@@ -28,6 +28,198 @@ async def test_gitea_transport_is_reused_across_requests_and_closed():
     assert client.is_closed
 
 
+@pytest.mark.anyio
+async def test_gitea_transport_coalesces_identical_concurrent_gets():
+    calls = 0
+    release = asyncio.Event()
+
+    async def handler(request):
+        nonlocal calls
+        calls += 1
+        await release.wait()
+        return httpx.Response(200, json={"path": request.url.path})
+
+    gitea_proxy.start_client(
+        transport=httpx.MockTransport(handler),
+        max_concurrency=4,
+        admission_timeout=0.1,
+    )
+    try:
+        requests = [asyncio.create_task(gitea_proxy.fetch("user")) for _ in range(20)]
+        await asyncio.sleep(0)
+        release.set()
+        results = await asyncio.gather(*requests)
+    finally:
+        await gitea_proxy.stop_client()
+
+    assert calls == 1
+    assert results == [{"path": "/api/v1/user"}] * 20
+
+
+@pytest.mark.anyio
+async def test_cancelling_one_coalesced_waiter_keeps_the_shared_get_running():
+    started = asyncio.Event()
+    release = asyncio.Event()
+
+    async def handler(request):
+        started.set()
+        await release.wait()
+        return httpx.Response(200, json={"path": request.url.path})
+
+    gitea_proxy.start_client(transport=httpx.MockTransport(handler))
+    owner = asyncio.create_task(gitea_proxy.fetch("user"))
+    try:
+        await started.wait()
+        waiter = asyncio.create_task(gitea_proxy.fetch("user"))
+        await asyncio.sleep(0)
+        waiter.cancel()
+        with pytest.raises(asyncio.CancelledError):
+            await waiter
+        release.set()
+        assert await owner == {"path": "/api/v1/user"}
+    finally:
+        release.set()
+        await asyncio.gather(owner, return_exceptions=True)
+        await gitea_proxy.stop_client()
+
+
+@pytest.mark.anyio
+async def test_gitea_transport_rejects_reads_beyond_bounded_capacity():
+    active = 0
+    peak = 0
+    saturated = asyncio.Event()
+    release = asyncio.Event()
+
+    async def handler(request):
+        nonlocal active, peak
+        active += 1
+        peak = max(peak, active)
+        if active == 2:
+            saturated.set()
+        try:
+            await release.wait()
+            return httpx.Response(200, json={"path": request.url.path})
+        finally:
+            active -= 1
+
+    gitea_proxy.start_client(
+        transport=httpx.MockTransport(handler),
+        max_concurrency=3,
+        admission_timeout=0.02,
+    )
+    first = asyncio.create_task(gitea_proxy.fetch("first"))
+    second = asyncio.create_task(gitea_proxy.fetch("second"))
+    try:
+        await asyncio.wait_for(saturated.wait(), timeout=0.2)
+        with pytest.raises(gitea_proxy.GiteaOverloadedError):
+            await gitea_proxy.fetch("third")
+    finally:
+        release.set()
+        await asyncio.gather(first, second)
+        await gitea_proxy.stop_client()
+
+    assert peak == 2
+
+
+@pytest.mark.anyio
+async def test_gitea_transport_reserves_one_slot_for_mutations_and_bounds_them():
+    active = 0
+    peak = 0
+    reads_started = asyncio.Event()
+    mutation_started = asyncio.Event()
+    release = asyncio.Event()
+
+    async def handler(request):
+        nonlocal active, peak
+        active += 1
+        peak = max(peak, active)
+        if active == 2:
+            reads_started.set()
+        if request.method == "POST":
+            mutation_started.set()
+        try:
+            await release.wait()
+            return httpx.Response(200, json={"method": request.method})
+        finally:
+            active -= 1
+
+    client = gitea_proxy.start_client(
+        transport=httpx.MockTransport(handler),
+        max_concurrency=3,
+        admission_timeout=0.02,
+    )
+    reads = [
+        asyncio.create_task(gitea_proxy.fetch("first")),
+        asyncio.create_task(gitea_proxy.fetch("second")),
+    ]
+    mutation = None
+    try:
+        await asyncio.wait_for(reads_started.wait(), timeout=0.2)
+        mutation = asyncio.create_task(client.post("/api/v1/mutate", json={"value": 1}))
+        await asyncio.wait_for(mutation_started.wait(), timeout=0.2)
+        with pytest.raises(gitea_proxy.GiteaOverloadedError):
+            await asyncio.wait_for(
+                client.post("/api/v1/mutate", json={"value": 1}), timeout=0.1
+            )
+    finally:
+        release.set()
+        await asyncio.gather(*reads, *(task for task in [mutation] if task is not None))
+        await gitea_proxy.stop_client()
+
+    assert peak == 3
+
+
+@pytest.mark.anyio
+async def test_gitea_transport_reads_bulkhead_configuration_from_environment(monkeypatch):
+    monkeypatch.setenv("GITEA_MAX_CONCURRENCY", "12")
+    monkeypatch.setenv("GITEA_ADMISSION_TIMEOUT_SECONDS", "0.75")
+
+    client = gitea_proxy.start_client(
+        transport=httpx.MockTransport(lambda request: httpx.Response(200, json={}))
+    )
+    try:
+        assert client.max_concurrency == 12
+        assert client.admission_timeout == 0.75
+    finally:
+        await gitea_proxy.stop_client()
+
+
+@pytest.mark.anyio
+async def test_streaming_reads_share_the_same_bounded_read_capacity():
+    active = 0
+    saturated = asyncio.Event()
+    release = asyncio.Event()
+
+    async def handler(request):
+        nonlocal active
+        active += 1
+        if active == 2:
+            saturated.set()
+        try:
+            await release.wait()
+            return httpx.Response(200, content=b"diff")
+        finally:
+            active -= 1
+
+    gitea_proxy.start_client(
+        transport=httpx.MockTransport(handler),
+        max_concurrency=3,
+        admission_timeout=0.02,
+    )
+    streams = [
+        asyncio.create_task(gitea_proxy.fetch_text("first", 100)),
+        asyncio.create_task(gitea_proxy.fetch_text("second", 100)),
+    ]
+    try:
+        await asyncio.wait_for(saturated.wait(), timeout=0.2)
+        with pytest.raises(gitea_proxy.GiteaOverloadedError):
+            await asyncio.wait_for(gitea_proxy.fetch("third"), timeout=0.1)
+    finally:
+        release.set()
+        await asyncio.gather(*streams)
+        await gitea_proxy.stop_client()
+
+
 @pytest.mark.anyio
 async def test_application_lifespan_opens_and_closes_gitea_transport(monkeypatch):
     calls = []