Merge branch 'main' into add-ws-transport

examples/identify/identify.py

@@ -72,13 +72,46 @@ async def run(port: int, destination: str, use_varint_format: bool = True) -> No
             client_addr = server_addr.replace("/ip4/0.0.0.0/", "/ip4/127.0.0.1/")
 
             format_name = "length-prefixed" if use_varint_format else "raw protobuf"
+            format_flag = "--raw-format" if not use_varint_format else ""
             print(
                 f"First host listening (using {format_name} format). "
                 f"Run this from another console:\n\n"
-                f"identify-demo "
-                f"-d {client_addr}\n"
+                f"identify-demo {format_flag} -d {client_addr}\n"
             )
             print("Waiting for incoming identify request...")
+
+            # Add a custom handler to show connection events
+            async def custom_identify_handler(stream):
+                peer_id = stream.muxed_conn.peer_id
+                print(f"\n🔗 Received identify request from peer: {peer_id}")
+
+                # Show remote address in multiaddr format
+                try:
+                    from libp2p.identity.identify.identify import (
+                        _remote_address_to_multiaddr,
+                    )
+
+                    remote_address = stream.get_remote_address()
+                    if remote_address:
+                        observed_multiaddr = _remote_address_to_multiaddr(
+                            remote_address
+                        )
+                        # Add the peer ID to create a complete multiaddr
+                        complete_multiaddr = f"{observed_multiaddr}/p2p/{peer_id}"
+                        print(f"   Remote address: {complete_multiaddr}")
+                    else:
+                        print(f"   Remote address: {remote_address}")
+                except Exception:
+                    print(f"   Remote address: {stream.get_remote_address()}")
+
+                # Call the original handler
+                await identify_handler(stream)
+
+                print(f"✅ Successfully processed identify request from {peer_id}")
+
+            # Replace the handler with our custom one
+            host_a.set_stream_handler(IDENTIFY_PROTOCOL_ID, custom_identify_handler)
+
             await trio.sleep_forever()
 
     else:
@@ -93,25 +126,99 @@ async def run(port: int, destination: str, use_varint_format: bool = True) -> No
             info = info_from_p2p_addr(maddr)
             print(f"Second host connecting to peer: {info.peer_id}")
 
-            await host_b.connect(info)
+            try:
+                await host_b.connect(info)
+            except Exception as e:
+                error_msg = str(e)
+                if "unable to connect" in error_msg or "SwarmException" in error_msg:
+                    print(f"\n❌ Cannot connect to peer: {info.peer_id}")
+                    print(f"   Address: {destination}")
+                    print(f"   Error: {error_msg}")
+                    print(
+                        "\n💡 Make sure the peer is running and the address is correct."
+                    )
+                    return
+                else:
+                    # Re-raise other exceptions
+                    raise
+
             stream = await host_b.new_stream(info.peer_id, (IDENTIFY_PROTOCOL_ID,))
 
             try:
                 print("Starting identify protocol...")
 
-                # Read the complete response (could be either format)
-                # Read a larger chunk to get all the data before stream closes
-                response = await stream.read(8192)  # Read enough data in one go
+                # Read the response properly based on the format
+                if use_varint_format:
+                    # For length-prefixed format, read varint length first
+                    from libp2p.utils.varint import decode_varint_from_bytes
+
+                    # Read varint length prefix
+                    length_bytes = b""
+                    while True:
+                        b = await stream.read(1)
+                        if not b:
+                            raise Exception("Stream closed while reading varint length")
+                        length_bytes += b
+                        if b[0] & 0x80 == 0:
+                            break
+
+                    msg_length = decode_varint_from_bytes(length_bytes)
+                    print(f"Expected message length: {msg_length} bytes")
+
+                    # Read the protobuf message
+                    response = await stream.read(msg_length)
+                    if len(response) != msg_length:
+                        raise Exception(
+                            f"Incomplete message: expected {msg_length} bytes, "
+                            f"got {len(response)}"
+                        )
+
+                    # Combine length prefix and message
+                    full_response = length_bytes + response
+                else:
+                    # For raw format, read all available data
+                    response = await stream.read(8192)
+                    full_response = response
 
                 await stream.close()
 
                 # Parse the response using the robust protocol-level function
                 # This handles both old and new formats automatically
-                identify_msg = parse_identify_response(response)
+                identify_msg = parse_identify_response(full_response)
                 print_identify_response(identify_msg)
 
             except Exception as e:
-                print(f"Identify protocol error: {e}")
+                error_msg = str(e)
+                print(f"Identify protocol error: {error_msg}")
+
+                # Check for specific format mismatch errors
+                if "Error parsing message" in error_msg or "DecodeError" in error_msg:
+                    print("\n" + "=" * 60)
+                    print("FORMAT MISMATCH DETECTED!")
+                    print("=" * 60)
+                    if use_varint_format:
+                        print(
+                            "You are using length-prefixed format (default) but the "
+                            "listener"
+                        )
+                        print("is using raw protobuf format.")
+                        print(
+                            "\nTo fix this, run the dialer with the --raw-format flag:"
+                        )
+                        print(f"identify-demo --raw-format -d {destination}")
+                    else:
+                        print("You are using raw protobuf format but the listener")
+                        print("is using length-prefixed format (default).")
+                        print(
+                            "\nTo fix this, run the dialer without the --raw-format "
+                            "flag:"
+                        )
+                        print(f"identify-demo -d {destination}")
+                    print("=" * 60)
+                else:
+                    import traceback
+
+                    traceback.print_exc()
 
             return
 

libp2p/pubsub/pubsub.py

@@ -102,6 +102,9 @@ class TopicValidator(NamedTuple):
     is_async: bool
 
 
+MAX_CONCURRENT_VALIDATORS = 10
+
+
 class Pubsub(Service, IPubsub):
     host: IHost
 
@@ -109,6 +112,7 @@ class Pubsub(Service, IPubsub):
 
     peer_receive_channel: trio.MemoryReceiveChannel[ID]
     dead_peer_receive_channel: trio.MemoryReceiveChannel[ID]
+    _validator_semaphore: trio.Semaphore
 
     seen_messages: LastSeenCache
 
@@ -143,6 +147,7 @@ class Pubsub(Service, IPubsub):
         msg_id_constructor: Callable[
             [rpc_pb2.Message], bytes
         ] = get_peer_and_seqno_msg_id,
+        max_concurrent_validator_count: int = MAX_CONCURRENT_VALIDATORS,
     ) -> None:
         """
         Construct a new Pubsub object, which is responsible for handling all
@@ -168,6 +173,7 @@ class Pubsub(Service, IPubsub):
         # Therefore, we can only close from the receive side.
         self.peer_receive_channel = peer_receive
         self.dead_peer_receive_channel = dead_peer_receive
+        self._validator_semaphore = trio.Semaphore(max_concurrent_validator_count)
         # Register a notifee
         self.host.get_network().register_notifee(
             PubsubNotifee(peer_send, dead_peer_send)
@@ -657,7 +663,11 @@ class Pubsub(Service, IPubsub):
 
         logger.debug("successfully published message %s", msg)
 
-    async def validate_msg(self, msg_forwarder: ID, msg: rpc_pb2.Message) -> None:
+    async def validate_msg(
+        self,
+        msg_forwarder: ID,
+        msg: rpc_pb2.Message,
+    ) -> None:
         """
         Validate the received message.
 
@@ -680,23 +690,34 @@ class Pubsub(Service, IPubsub):
             if not validator(msg_forwarder, msg):
                 raise ValidationError(f"Validation failed for msg={msg}")
 
-        # TODO: Implement throttle on async validators
-
         if len(async_topic_validators) > 0:
             # Appends to lists are thread safe in CPython
-            results = []
-
-            async def run_async_validator(func: AsyncValidatorFn) -> None:
-                result = await func(msg_forwarder, msg)
-                results.append(result)
+            results: list[bool] = []
 
             async with trio.open_nursery() as nursery:
                 for async_validator in async_topic_validators:
-                    nursery.start_soon(run_async_validator, async_validator)
+                    nursery.start_soon(
+                        self._run_async_validator,
+                        async_validator,
+                        msg_forwarder,
+                        msg,
+                        results,
+                    )
 
             if not all(results):
                 raise ValidationError(f"Validation failed for msg={msg}")
 
+    async def _run_async_validator(
+        self,
+        func: AsyncValidatorFn,
+        msg_forwarder: ID,
+        msg: rpc_pb2.Message,
+        results: list[bool],
+    ) -> None:
+        async with self._validator_semaphore:
+            result = await func(msg_forwarder, msg)
+            results.append(result)
+
     async def push_msg(self, msg_forwarder: ID, msg: rpc_pb2.Message) -> None:
         """
         Push a pubsub message to others.

libp2p/stream_muxer/mplex/mplex_stream.py

@@ -1,3 +1,5 @@
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
 from types import (
     TracebackType,
 )
@@ -32,6 +34,72 @@ if TYPE_CHECKING:
     )
 
 
+class ReadWriteLock:
+    """
+    A read-write lock that allows multiple concurrent readers
+    or one exclusive writer, implemented using Trio primitives.
+    """
+
+    def __init__(self) -> None:
+        self._readers = 0
+        self._readers_lock = trio.Lock()  # Protects access to _readers count
+        self._writer_lock = trio.Semaphore(1)  # Allows only one writer at a time
+
+    async def acquire_read(self) -> None:
+        """Acquire a read lock. Multiple readers can hold it simultaneously."""
+        try:
+            async with self._readers_lock:
+                if self._readers == 0:
+                    await self._writer_lock.acquire()
+                self._readers += 1
+        except trio.Cancelled:
+            raise
+
+    async def release_read(self) -> None:
+        """Release a read lock."""
+        async with self._readers_lock:
+            if self._readers == 1:
+                self._writer_lock.release()
+            self._readers -= 1
+
+    async def acquire_write(self) -> None:
+        """Acquire an exclusive write lock."""
+        try:
+            await self._writer_lock.acquire()
+        except trio.Cancelled:
+            raise
+
+    def release_write(self) -> None:
+        """Release the exclusive write lock."""
+        self._writer_lock.release()
+
+    @asynccontextmanager
+    async def read_lock(self) -> AsyncGenerator[None, None]:
+        """Context manager for acquiring and releasing a read lock safely."""
+        acquire = False
+        try:
+            await self.acquire_read()
+            acquire = True
+            yield
+        finally:
+            if acquire:
+                with trio.CancelScope() as scope:
+                    scope.shield = True
+                    await self.release_read()
+
+    @asynccontextmanager
+    async def write_lock(self) -> AsyncGenerator[None, None]:
+        """Context manager for acquiring and releasing a write lock safely."""
+        acquire = False
+        try:
+            await self.acquire_write()
+            acquire = True
+            yield
+        finally:
+            if acquire:
+                self.release_write()
+
+
 class MplexStream(IMuxedStream):
     """
     reference: https://github.com/libp2p/go-mplex/blob/master/stream.go
@@ -46,7 +114,7 @@ class MplexStream(IMuxedStream):
     read_deadline: int | None
     write_deadline: int | None
 
-    # TODO: Add lock for read/write to avoid interleaving receiving messages?
+    rw_lock: ReadWriteLock
     close_lock: trio.Lock
 
     # NOTE: `dataIn` is size of 8 in Go implementation.
@@ -80,6 +148,7 @@ class MplexStream(IMuxedStream):
         self.event_remote_closed = trio.Event()
         self.event_reset = trio.Event()
         self.close_lock = trio.Lock()
+        self.rw_lock = ReadWriteLock()
         self.incoming_data_channel = incoming_data_channel
         self._buf = bytearray()
 
@@ -113,48 +182,49 @@ class MplexStream(IMuxedStream):
         :param n: number of bytes to read
         :return: bytes actually read
         """
-        if n is not None and n < 0:
-            raise ValueError(
-                "the number of bytes to read `n` must be non-negative or "
-                f"`None` to indicate read until EOF, got n={n}"
-            )
-        if self.event_reset.is_set():
-            raise MplexStreamReset
-        if n is None:
-            return await self._read_until_eof()
-        if len(self._buf) == 0:
-            data: bytes
-            # Peek whether there is data available. If yes, we just read until there is
-            # no data, then return.
-            try:
-                data = self.incoming_data_channel.receive_nowait()
-                self._buf.extend(data)
-            except trio.EndOfChannel:
-                raise MplexStreamEOF
-            except trio.WouldBlock:
-                # We know `receive` will be blocked here. Wait for data here with
-                # `receive` and catch all kinds of errors here.
+        async with self.rw_lock.read_lock():
+            if n is not None and n < 0:
+                raise ValueError(
+                    "the number of bytes to read `n` must be non-negative or "
+                    f"`None` to indicate read until EOF, got n={n}"
+                )
+            if self.event_reset.is_set():
+                raise MplexStreamReset
+            if n is None:
+                return await self._read_until_eof()
+            if len(self._buf) == 0:
+                data: bytes
+                # Peek whether there is data available. If yes, we just read until
+                # there is no data, then return.
                 try:
-                    data = await self.incoming_data_channel.receive()
+                    data = self.incoming_data_channel.receive_nowait()
                     self._buf.extend(data)
                 except trio.EndOfChannel:
-                    if self.event_reset.is_set():
-                        raise MplexStreamReset
-                    if self.event_remote_closed.is_set():
-                        raise MplexStreamEOF
-                except trio.ClosedResourceError as error:
-                    # Probably `incoming_data_channel` is closed in `reset` when we are
-                    # waiting for `receive`.
-                    if self.event_reset.is_set():
-                        raise MplexStreamReset
-                    raise Exception(
-                        "`incoming_data_channel` is closed but stream is not reset. "
-                        "This should never happen."
-                    ) from error
-        self._buf.extend(self._read_return_when_blocked())
-        payload = self._buf[:n]
-        self._buf = self._buf[len(payload) :]
-        return bytes(payload)
+                    raise MplexStreamEOF
+                except trio.WouldBlock:
+                    # We know `receive` will be blocked here. Wait for data here with
+                    # `receive` and catch all kinds of errors here.
+                    try:
+                        data = await self.incoming_data_channel.receive()
+                        self._buf.extend(data)
+                    except trio.EndOfChannel:
+                        if self.event_reset.is_set():
+                            raise MplexStreamReset
+                        if self.event_remote_closed.is_set():
+                            raise MplexStreamEOF
+                    except trio.ClosedResourceError as error:
+                        # Probably `incoming_data_channel` is closed in `reset` when
+                        # we are waiting for `receive`.
+                        if self.event_reset.is_set():
+                            raise MplexStreamReset
+                        raise Exception(
+                            "`incoming_data_channel` is closed but stream is not reset."
+                            "This should never happen."
+                        ) from error
+            self._buf.extend(self._read_return_when_blocked())
+            payload = self._buf[:n]
+            self._buf = self._buf[len(payload) :]
+            return bytes(payload)
 
     async def write(self, data: bytes) -> None:
         """
@@ -162,14 +232,15 @@ class MplexStream(IMuxedStream):
 
         :return: number of bytes written
         """
-        if self.event_local_closed.is_set():
-            raise MplexStreamClosed(f"cannot write to closed stream: data={data!r}")
-        flag = (
-            HeaderTags.MessageInitiator
-            if self.is_initiator
-            else HeaderTags.MessageReceiver
-        )
-        await self.muxed_conn.send_message(flag, data, self.stream_id)
+        async with self.rw_lock.write_lock():
+            if self.event_local_closed.is_set():
+                raise MplexStreamClosed(f"cannot write to closed stream: data={data!r}")
+            flag = (
+                HeaderTags.MessageInitiator
+                if self.is_initiator
+                else HeaderTags.MessageReceiver
+            )
+            await self.muxed_conn.send_message(flag, data, self.stream_id)
 
     async def close(self) -> None:
         """

newsfragments/748.feature.rst

@@ -0,0 +1 @@
+ Add lock for read/write to avoid interleaving receiving messages in mplex_stream.py

newsfragments/755.performance.rst

@@ -0,0 +1,2 @@
+Added throttling for async topic validators in validate_msg, enforcing a
+concurrency limit to prevent resource exhaustion under heavy load.

newsfragments/778.bugfix.rst

@@ -0,0 +1 @@
+Fixed incorrect handling of raw protobuf format in identify protocol. The identify example now properly handles both raw and length-prefixed (varint) message formats, provides better error messages, and displays connection status with peer IDs. Replaced mock-based tests with comprehensive real network integration tests for both formats.

tests/core/identity/identify/test_identify_integration.py

@@ -0,0 +1,241 @@
+import logging
+
+import pytest
+
+from libp2p.custom_types import TProtocol
+from libp2p.identity.identify.identify import (
+    AGENT_VERSION,
+    ID,
+    PROTOCOL_VERSION,
+    _multiaddr_to_bytes,
+    identify_handler_for,
+    parse_identify_response,
+)
+from tests.utils.factories import host_pair_factory
+
+logger = logging.getLogger("libp2p.identity.identify-integration-test")
+
+
+@pytest.mark.trio
+async def test_identify_protocol_varint_format_integration(security_protocol):
+    """Test identify protocol with varint format in real network scenario."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=True)
+        )
+
+        # Make identify request
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+        assert result.listen_addrs == [
+            _multiaddr_to_bytes(addr) for addr in host_a.get_addrs()
+        ]
+
+
+@pytest.mark.trio
+async def test_identify_protocol_raw_format_integration(security_protocol):
+    """Test identify protocol with raw format in real network scenario."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=False)
+        )
+
+        # Make identify request
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+        assert result.listen_addrs == [
+            _multiaddr_to_bytes(addr) for addr in host_a.get_addrs()
+        ]
+
+
+@pytest.mark.trio
+async def test_identify_default_format_behavior(security_protocol):
+    """Test identify protocol uses correct default format."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Use default identify handler (should use varint format)
+        host_a.set_stream_handler(ID, identify_handler_for(host_a))
+
+        # Make identify request
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+
+
+@pytest.mark.trio
+async def test_identify_cross_format_compatibility_varint_to_raw(security_protocol):
+    """Test varint dialer with raw listener compatibility."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Host A uses raw format
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=False)
+        )
+
+        # Host B makes request (will automatically detect format)
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response (should work with automatic format detection)
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+
+
+@pytest.mark.trio
+async def test_identify_cross_format_compatibility_raw_to_varint(security_protocol):
+    """Test raw dialer with varint listener compatibility."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Host A uses varint format
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=True)
+        )
+
+        # Host B makes request (will automatically detect format)
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response (should work with automatic format detection)
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+
+
+@pytest.mark.trio
+async def test_identify_format_detection_robustness(security_protocol):
+    """Test identify protocol format detection is robust with various message sizes."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Test both formats with different message sizes
+        for use_varint in [True, False]:
+            host_a.set_stream_handler(
+                ID, identify_handler_for(host_a, use_varint_format=use_varint)
+            )
+
+            # Make identify request
+            stream = await host_b.new_stream(host_a.get_id(), (ID,))
+            response = await stream.read(8192)
+            await stream.close()
+
+            # Parse response
+            result = parse_identify_response(response)
+
+            # Verify response content
+            assert result.agent_version == AGENT_VERSION
+            assert result.protocol_version == PROTOCOL_VERSION
+            assert result.public_key == host_a.get_public_key().serialize()
+
+
+@pytest.mark.trio
+async def test_identify_large_message_handling(security_protocol):
+    """Test identify protocol handles large messages with many protocols."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Add many protocols to make the message larger
+        async def dummy_handler(stream):
+            pass
+
+        for i in range(10):
+            host_a.set_stream_handler(TProtocol(f"/test/protocol/{i}"), dummy_handler)
+
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=True)
+        )
+
+        # Make identify request
+        stream = await host_b.new_stream(host_a.get_id(), (ID,))
+        response = await stream.read(8192)
+        await stream.close()
+
+        # Parse response
+        result = parse_identify_response(response)
+
+        # Verify response content
+        assert result.agent_version == AGENT_VERSION
+        assert result.protocol_version == PROTOCOL_VERSION
+        assert result.public_key == host_a.get_public_key().serialize()
+
+
+@pytest.mark.trio
+async def test_identify_message_equivalence_real_network(security_protocol):
+    """Test that both formats produce equivalent messages in real network."""
+    async with host_pair_factory(security_protocol=security_protocol) as (
+        host_a,
+        host_b,
+    ):
+        # Test varint format
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=True)
+        )
+        stream_varint = await host_b.new_stream(host_a.get_id(), (ID,))
+        response_varint = await stream_varint.read(8192)
+        await stream_varint.close()
+
+        # Test raw format
+        host_a.set_stream_handler(
+            ID, identify_handler_for(host_a, use_varint_format=False)
+        )
+        stream_raw = await host_b.new_stream(host_a.get_id(), (ID,))
+        response_raw = await stream_raw.read(8192)
+        await stream_raw.close()
+
+        # Parse both responses
+        result_varint = parse_identify_response(response_varint)
+        result_raw = parse_identify_response(response_raw)
+
+        # Both should produce identical parsed results
+        assert result_varint.agent_version == result_raw.agent_version
+        assert result_varint.protocol_version == result_raw.protocol_version
+        assert result_varint.public_key == result_raw.public_key
+        assert result_varint.listen_addrs == result_raw.listen_addrs

tests/core/identity/identify/test_identify_parsing.py

@@ -1,410 +0,0 @@
-import pytest
-
-from libp2p.identity.identify.identify import (
-    _mk_identify_protobuf,
-)
-from libp2p.identity.identify.pb.identify_pb2 import (
-    Identify,
-)
-from libp2p.io.abc import Closer, Reader, Writer
-from libp2p.utils.varint import (
-    decode_varint_from_bytes,
-    encode_varint_prefixed,
-)
-from tests.utils.factories import (
-    host_pair_factory,
-)
-
-
-class MockStream(Reader, Writer, Closer):
-    """Mock stream for testing identify protocol compatibility."""
-
-    def __init__(self, data: bytes):
-        self.data = data
-        self.position = 0
-        self.closed = False
-
-    async def read(self, n: int | None = None) -> bytes:
-        if self.closed or self.position >= len(self.data):
-            return b""
-        if n is None:
-            n = len(self.data) - self.position
-        result = self.data[self.position : self.position + n]
-        self.position += len(result)
-        return result
-
-    async def write(self, data: bytes) -> None:
-        # Mock write - just store the data
-        pass
-
-    async def close(self) -> None:
-        self.closed = True
-
-
-def create_identify_message(host, observed_multiaddr=None):
-    """Create an identify protobuf message."""
-    return _mk_identify_protobuf(host, observed_multiaddr)
-
-
-def create_new_format_message(identify_msg):
-    """Create a new format (length-prefixed) identify message."""
-    msg_bytes = identify_msg.SerializeToString()
-    return encode_varint_prefixed(msg_bytes)
-
-
-def create_old_format_message(identify_msg):
-    """Create an old format (raw protobuf) identify message."""
-    return identify_msg.SerializeToString()
-
-
-async def read_new_format_message(stream) -> bytes:
-    """Read a new format (length-prefixed) identify message."""
-    # Read varint length prefix
-    length_bytes = b""
-    while True:
-        b = await stream.read(1)
-        if not b:
-            break
-        length_bytes += b
-        if b[0] & 0x80 == 0:
-            break
-
-    if not length_bytes:
-        raise ValueError("No length prefix received")
-
-    msg_length = decode_varint_from_bytes(length_bytes)
-
-    # Read the protobuf message
-    response = await stream.read(msg_length)
-    if len(response) != msg_length:
-        raise ValueError("Incomplete message received")
-
-    return response
-
-
-async def read_old_format_message(stream) -> bytes:
-    """Read an old format (raw protobuf) identify message."""
-    # Read all available data
-    response = b""
-    while True:
-        chunk = await stream.read(4096)
-        if not chunk:
-            break
-        response += chunk
-
-    return response
-
-
-async def read_compatible_message(stream) -> bytes:
-    """Read an identify message in either old or new format."""
-    # Try to read a few bytes to detect the format
-    first_bytes = await stream.read(10)
-    if not first_bytes:
-        raise ValueError("No data received")
-
-    # Try to decode as varint length prefix (new format)
-    try:
-        msg_length = decode_varint_from_bytes(first_bytes)
-
-        # Validate that the length is reasonable (not too large)
-        if msg_length > 0 and msg_length <= 1024 * 1024:  # Max 1MB
-            # Calculate how many bytes the varint consumed
-            varint_len = 0
-            for i, byte in enumerate(first_bytes):
-                varint_len += 1
-                if (byte & 0x80) == 0:
-                    break
-
-            # Read the remaining protobuf message
-            remaining_bytes = await stream.read(
-                msg_length - (len(first_bytes) - varint_len)
-            )
-            if len(remaining_bytes) == msg_length - (len(first_bytes) - varint_len):
-                message_data = first_bytes[varint_len:] + remaining_bytes
-
-                # Try to parse as protobuf to validate
-                try:
-                    Identify().ParseFromString(message_data)
-                    return message_data
-                except Exception:
-                    # If protobuf parsing fails, fall back to old format
-                    pass
-    except Exception:
-        pass
-
-    # Fall back to old format (raw protobuf)
-    response = first_bytes
-
-    # Read more data if available
-    while True:
-        chunk = await stream.read(4096)
-        if not chunk:
-            break
-        response += chunk
-
-    return response
-
-
-async def read_compatible_message_simple(stream) -> bytes:
-    """Read a message in either old or new format (simplified version for testing)."""
-    # Try to read a few bytes to detect the format
-    first_bytes = await stream.read(10)
-    if not first_bytes:
-        raise ValueError("No data received")
-
-    # Try to decode as varint length prefix (new format)
-    try:
-        msg_length = decode_varint_from_bytes(first_bytes)
-
-        # Validate that the length is reasonable (not too large)
-        if msg_length > 0 and msg_length <= 1024 * 1024:  # Max 1MB
-            # Calculate how many bytes the varint consumed
-            varint_len = 0
-            for i, byte in enumerate(first_bytes):
-                varint_len += 1
-                if (byte & 0x80) == 0:
-                    break
-
-            # Read the remaining message
-            remaining_bytes = await stream.read(
-                msg_length - (len(first_bytes) - varint_len)
-            )
-            if len(remaining_bytes) == msg_length - (len(first_bytes) - varint_len):
-                return first_bytes[varint_len:] + remaining_bytes
-    except Exception:
-        pass
-
-    # Fall back to old format (raw data)
-    response = first_bytes
-
-    # Read more data if available
-    while True:
-        chunk = await stream.read(4096)
-        if not chunk:
-            break
-        response += chunk
-
-    return response
-
-
-def detect_format(data):
-    """Detect if data is in new or old format (varint-prefixed or raw protobuf)."""
-    if not data:
-        return "unknown"
-
-    # Try to decode as varint
-    try:
-        msg_length = decode_varint_from_bytes(data)
-
-        # Validate that the length is reasonable
-        if msg_length > 0 and msg_length <= 1024 * 1024:  # Max 1MB
-            # Calculate varint length
-            varint_len = 0
-            for i, byte in enumerate(data):
-                varint_len += 1
-                if (byte & 0x80) == 0:
-                    break
-
-            # Check if we have enough data for the message
-            if len(data) >= varint_len + msg_length:
-                # Additional check: try to parse the message as protobuf
-                try:
-                    message_data = data[varint_len : varint_len + msg_length]
-                    Identify().ParseFromString(message_data)
-                    return "new"
-                except Exception:
-                    # If protobuf parsing fails, it's probably not a valid new format
-                    pass
-    except Exception:
-        pass
-
-    # If varint decoding fails or length is unreasonable, assume old format
-    return "old"
-
-
-@pytest.mark.trio
-async def test_identify_new_format_compatibility(security_protocol):
-    """Test that identify protocol works with new format (length-prefixed) messages."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Create new format message
-        new_format_data = create_new_format_message(identify_msg)
-
-        # Create mock stream with new format data
-        stream = MockStream(new_format_data)
-
-        # Read using new format reader
-        response = await read_new_format_message(stream)
-
-        # Parse the response
-        parsed_msg = Identify()
-        parsed_msg.ParseFromString(response)
-
-        # Verify the message content
-        assert parsed_msg.protocol_version == identify_msg.protocol_version
-        assert parsed_msg.agent_version == identify_msg.agent_version
-        assert parsed_msg.public_key == identify_msg.public_key
-
-
-@pytest.mark.trio
-async def test_identify_old_format_compatibility(security_protocol):
-    """Test that identify protocol works with old format (raw protobuf) messages."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Create old format message
-        old_format_data = create_old_format_message(identify_msg)
-
-        # Create mock stream with old format data
-        stream = MockStream(old_format_data)
-
-        # Read using old format reader
-        response = await read_old_format_message(stream)
-
-        # Parse the response
-        parsed_msg = Identify()
-        parsed_msg.ParseFromString(response)
-
-        # Verify the message content
-        assert parsed_msg.protocol_version == identify_msg.protocol_version
-        assert parsed_msg.agent_version == identify_msg.agent_version
-        assert parsed_msg.public_key == identify_msg.public_key
-
-
-@pytest.mark.trio
-async def test_identify_backward_compatibility_old_format(security_protocol):
-    """Test backward compatibility reader with old format messages."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Create old format message
-        old_format_data = create_old_format_message(identify_msg)
-
-        # Create mock stream with old format data
-        stream = MockStream(old_format_data)
-
-        # Read using old format reader (which should work reliably)
-        response = await read_old_format_message(stream)
-
-        # Parse the response
-        parsed_msg = Identify()
-        parsed_msg.ParseFromString(response)
-
-        # Verify the message content
-        assert parsed_msg.protocol_version == identify_msg.protocol_version
-        assert parsed_msg.agent_version == identify_msg.agent_version
-        assert parsed_msg.public_key == identify_msg.public_key
-
-
-@pytest.mark.trio
-async def test_identify_backward_compatibility_new_format(security_protocol):
-    """Test backward compatibility reader with new format messages."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Create new format message
-        new_format_data = create_new_format_message(identify_msg)
-
-        # Create mock stream with new format data
-        stream = MockStream(new_format_data)
-
-        # Read using new format reader (which should work reliably)
-        response = await read_new_format_message(stream)
-
-        # Parse the response
-        parsed_msg = Identify()
-        parsed_msg.ParseFromString(response)
-
-        # Verify the message content
-        assert parsed_msg.protocol_version == identify_msg.protocol_version
-        assert parsed_msg.agent_version == identify_msg.agent_version
-        assert parsed_msg.public_key == identify_msg.public_key
-
-
-@pytest.mark.trio
-async def test_identify_format_detection(security_protocol):
-    """Test that the format detection works correctly."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Test new format detection
-        new_format_data = create_new_format_message(identify_msg)
-        format_type = detect_format(new_format_data)
-        assert format_type == "new", "New format should be detected correctly"
-
-        # Test old format detection
-        old_format_data = create_old_format_message(identify_msg)
-        format_type = detect_format(old_format_data)
-        assert format_type == "old", "Old format should be detected correctly"
-
-
-@pytest.mark.trio
-async def test_identify_error_handling(security_protocol):
-    """Test error handling for malformed messages."""
-    from libp2p.exceptions import ParseError
-
-    # Test with empty data
-    stream = MockStream(b"")
-    with pytest.raises(ValueError, match="No data received"):
-        await read_compatible_message(stream)
-
-    # Test with incomplete varint
-    stream = MockStream(b"\x80")  # Incomplete varint
-    with pytest.raises(ParseError, match="Unexpected end of data"):
-        await read_new_format_message(stream)
-
-    # Test with invalid protobuf data
-    stream = MockStream(b"\x05invalid")  # Length prefix but invalid protobuf
-    with pytest.raises(Exception):  # Should fail when parsing protobuf
-        response = await read_new_format_message(stream)
-        Identify().ParseFromString(response)
-
-
-@pytest.mark.trio
-async def test_identify_message_equivalence(security_protocol):
-    """Test that old and new format messages are equivalent."""
-    async with host_pair_factory(security_protocol=security_protocol) as (
-        host_a,
-        host_b,
-    ):
-        # Create identify message
-        identify_msg = create_identify_message(host_a)
-
-        # Create both formats
-        new_format_data = create_new_format_message(identify_msg)
-        old_format_data = create_old_format_message(identify_msg)
-
-        # Extract the protobuf message from new format
-        varint_len = 0
-        for i, byte in enumerate(new_format_data):
-            varint_len += 1
-            if (byte & 0x80) == 0:
-                break
-
-        new_format_protobuf = new_format_data[varint_len:]
-
-        # The protobuf messages should be identical
-        assert new_format_protobuf == old_format_data, (
-            "Protobuf messages should be identical in both formats"
-        )

tests/core/pubsub/test_pubsub.py

@@ -5,10 +5,12 @@ import inspect
 from typing import (
     NamedTuple,
 )
+from unittest.mock import patch
 
 import pytest
 import trio
 
+from libp2p.custom_types import AsyncValidatorFn
 from libp2p.exceptions import (
     ValidationError,
 )
@@ -243,7 +245,37 @@ async def test_get_msg_validators():
     ((False, True), (True, False), (True, True)),
 )
 @pytest.mark.trio
-async def test_validate_msg(is_topic_1_val_passed, is_topic_2_val_passed):
+async def test_validate_msg_with_throttle_condition(
+    is_topic_1_val_passed, is_topic_2_val_passed
+):
+    CONCURRENCY_LIMIT = 10
+
+    state = {
+        "concurrency_counter": 0,
+        "max_observed": 0,
+    }
+    lock = trio.Lock()
+
+    async def mock_run_async_validator(
+        self,
+        func: AsyncValidatorFn,
+        msg_forwarder: ID,
+        msg: rpc_pb2.Message,
+        results: list[bool],
+    ) -> None:
+        async with self._validator_semaphore:
+            async with lock:
+                state["concurrency_counter"] += 1
+                if state["concurrency_counter"] > state["max_observed"]:
+                    state["max_observed"] = state["concurrency_counter"]
+
+            try:
+                result = await func(msg_forwarder, msg)
+                results.append(result)
+            finally:
+                async with lock:
+                    state["concurrency_counter"] -= 1
+
     async with PubsubFactory.create_batch_with_floodsub(1) as pubsubs_fsub:
 
         def passed_sync_validator(peer_id: ID, msg: rpc_pb2.Message) -> bool:
@@ -280,11 +312,19 @@ async def test_validate_msg(is_topic_1_val_passed, is_topic_2_val_passed):
             seqno=b"\x00" * 8,
         )
 
-        if is_topic_1_val_passed and is_topic_2_val_passed:
-            await pubsubs_fsub[0].validate_msg(pubsubs_fsub[0].my_id, msg)
-        else:
-            with pytest.raises(ValidationError):
+        with patch(
+            "libp2p.pubsub.pubsub.Pubsub._run_async_validator",
+            new=mock_run_async_validator,
+        ):
+            if is_topic_1_val_passed and is_topic_2_val_passed:
                 await pubsubs_fsub[0].validate_msg(pubsubs_fsub[0].my_id, msg)
+            else:
+                with pytest.raises(ValidationError):
+                    await pubsubs_fsub[0].validate_msg(pubsubs_fsub[0].my_id, msg)
+
+    assert state["max_observed"] <= CONCURRENCY_LIMIT, (
+        f"Max concurrency observed: {state['max_observed']}"
+    )
 
 
 @pytest.mark.trio

tests/core/stream_muxer/test_read_write_lock.py

@@ -0,0 +1,590 @@
+from typing import Any, cast
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+import trio
+from trio.testing import wait_all_tasks_blocked
+
+from libp2p.stream_muxer.exceptions import (
+    MuxedConnUnavailable,
+)
+from libp2p.stream_muxer.mplex.constants import HeaderTags
+from libp2p.stream_muxer.mplex.datastructures import StreamID
+from libp2p.stream_muxer.mplex.exceptions import (
+    MplexStreamClosed,
+    MplexStreamEOF,
+    MplexStreamReset,
+)
+from libp2p.stream_muxer.mplex.mplex_stream import MplexStream
+
+
+class MockMuxedConn:
+    """A mock Mplex connection for testing purposes."""
+
+    def __init__(self):
+        self.sent_messages = []
+        self.streams: dict[StreamID, MplexStream] = {}
+        self.streams_lock = trio.Lock()
+        self.is_unavailable = False
+
+    async def send_message(
+        self, flag: HeaderTags, data: bytes | None, stream_id: StreamID
+    ) -> None:
+        """Mocks sending a message over the connection."""
+        if self.is_unavailable:
+            raise MuxedConnUnavailable("Connection is unavailable")
+        self.sent_messages.append((flag, data, stream_id))
+        # Yield to allow other tasks to run
+        await trio.lowlevel.checkpoint()
+
+    def get_remote_address(self) -> tuple[str, int]:
+        """Mocks getting the remote address."""
+        return "127.0.0.1", 4001
+
+
+@pytest.fixture
+async def mplex_stream():
+    """Provides a fully initialized MplexStream and its communication channels."""
+    # Use a buffered channel to prevent deadlocks in simple tests
+    send_chan, recv_chan = trio.open_memory_channel(10)
+    stream_id = StreamID(1, is_initiator=True)
+    muxed_conn = MockMuxedConn()
+    stream = MplexStream("test-stream", stream_id, cast(Any, muxed_conn), recv_chan)
+    muxed_conn.streams[stream_id] = stream
+
+    yield stream, send_chan, muxed_conn
+
+    # Cleanup: Close channels and reset stream state
+    await send_chan.aclose()
+    await recv_chan.aclose()
+    # Reset stream state to prevent cross-test contamination
+    stream.event_local_closed = trio.Event()
+    stream.event_remote_closed = trio.Event()
+    stream.event_reset = trio.Event()
+
+
+# ===============================================
+# 1. Tests for Stream-Level Lock Integration
+# ===============================================
+
+
+@pytest.mark.trio
+async def test_stream_write_is_protected_by_rwlock(mplex_stream):
+    """Verify that stream.write() acquires and releases the write lock."""
+    stream, _, muxed_conn = mplex_stream
+
+    # Mock lock methods
+    original_acquire = stream.rw_lock.acquire_write
+    original_release = stream.rw_lock.release_write
+
+    stream.rw_lock.acquire_write = AsyncMock(wraps=original_acquire)
+    stream.rw_lock.release_write = MagicMock(wraps=original_release)
+
+    await stream.write(b"test data")
+
+    stream.rw_lock.acquire_write.assert_awaited_once()
+    stream.rw_lock.release_write.assert_called_once()
+
+    # Verify the message was actually sent
+    assert len(muxed_conn.sent_messages) == 1
+    flag, data, stream_id = muxed_conn.sent_messages[0]
+    assert flag == HeaderTags.MessageInitiator
+    assert data == b"test data"
+    assert stream_id == stream.stream_id
+
+
+@pytest.mark.trio
+async def test_stream_read_is_protected_by_rwlock(mplex_stream):
+    """Verify that stream.read() acquires and releases the read lock."""
+    stream, send_chan, _ = mplex_stream
+
+    # Mock lock methods
+    original_acquire = stream.rw_lock.acquire_read
+    original_release = stream.rw_lock.release_read
+
+    stream.rw_lock.acquire_read = AsyncMock(wraps=original_acquire)
+    stream.rw_lock.release_read = AsyncMock(wraps=original_release)
+
+    await send_chan.send(b"hello")
+    result = await stream.read(5)
+
+    stream.rw_lock.acquire_read.assert_awaited_once()
+    stream.rw_lock.release_read.assert_awaited_once()
+    assert result == b"hello"
+
+
+@pytest.mark.trio
+async def test_multiple_readers_can_coexist(mplex_stream):
+    """Verify multiple readers can operate concurrently."""
+    stream, send_chan, _ = mplex_stream
+
+    # Send enough data for both reads
+    await send_chan.send(b"data1")
+    await send_chan.send(b"data2")
+
+    # Track lock acquisition order
+    acquisition_order = []
+    release_order = []
+
+    # Patch lock methods to track concurrency
+    original_acquire = stream.rw_lock.acquire_read
+    original_release = stream.rw_lock.release_read
+
+    async def tracked_acquire():
+        nonlocal acquisition_order
+        acquisition_order.append("start")
+        await original_acquire()
+        acquisition_order.append("acquired")
+
+    async def tracked_release():
+        nonlocal release_order
+        release_order.append("start")
+        await original_release()
+        release_order.append("released")
+
+    with (
+        patch.object(
+            stream.rw_lock, "acquire_read", side_effect=tracked_acquire, autospec=True
+        ),
+        patch.object(
+            stream.rw_lock, "release_read", side_effect=tracked_release, autospec=True
+        ),
+    ):
+        # Execute concurrent reads
+        async with trio.open_nursery() as nursery:
+            nursery.start_soon(stream.read, 5)
+            nursery.start_soon(stream.read, 5)
+
+    # Verify both reads happened
+    assert acquisition_order.count("start") == 2
+    assert acquisition_order.count("acquired") == 2
+    assert release_order.count("start") == 2
+    assert release_order.count("released") == 2
+
+
+@pytest.mark.trio
+async def test_writer_blocks_readers(mplex_stream):
+    """Verify that a writer blocks all readers and new readers queue behind."""
+    stream, send_chan, _ = mplex_stream
+
+    writer_acquired = trio.Event()
+    readers_ready = trio.Event()
+    writer_finished = trio.Event()
+    all_readers_started = trio.Event()
+    all_readers_done = trio.Event()
+
+    counters = {"reader_start_count": 0, "reader_done_count": 0}
+    reader_target = 3
+    reader_start_lock = trio.Lock()
+
+    # Patch write lock to control test flow
+    original_acquire_write = stream.rw_lock.acquire_write
+    original_release_write = stream.rw_lock.release_write
+
+    async def tracked_acquire_write():
+        await original_acquire_write()
+        writer_acquired.set()
+        # Wait for readers to queue up
+        await readers_ready.wait()
+
+    # Must be synchronous since real release_write is sync
+    def tracked_release_write():
+        original_release_write()
+        writer_finished.set()
+
+    with (
+        patch.object(
+            stream.rw_lock, "acquire_write", side_effect=tracked_acquire_write
+        ),
+        patch.object(
+            stream.rw_lock, "release_write", side_effect=tracked_release_write
+        ),
+    ):
+        async with trio.open_nursery() as nursery:
+            # Start writer
+            nursery.start_soon(stream.write, b"test")
+            await writer_acquired.wait()
+
+            # Start readers
+            async def reader_task():
+                async with reader_start_lock:
+                    counters["reader_start_count"] += 1
+                    if counters["reader_start_count"] == reader_target:
+                        all_readers_started.set()
+
+                try:
+                    # This will block until data is available
+                    await stream.read(5)
+                except (MplexStreamReset, MplexStreamEOF):
+                    pass
+                finally:
+                    async with reader_start_lock:
+                        counters["reader_done_count"] += 1
+                        if counters["reader_done_count"] == reader_target:
+                            all_readers_done.set()
+
+            for _ in range(reader_target):
+                nursery.start_soon(reader_task)
+
+            # Wait until all readers are started
+            await all_readers_started.wait()
+
+            # Let the writer finish and release the lock
+            readers_ready.set()
+            await writer_finished.wait()
+
+            # Send data to unblock the readers
+            for i in range(reader_target):
+                await send_chan.send(b"data" + str(i).encode())
+
+            # Wait for all readers to finish
+            await all_readers_done.wait()
+
+
+@pytest.mark.trio
+async def test_writer_waits_for_readers(mplex_stream):
+    """Verify a writer waits for existing readers to complete."""
+    stream, send_chan, _ = mplex_stream
+    readers_started = trio.Event()
+    writer_entered = trio.Event()
+    writer_acquiring = trio.Event()
+    readers_finished = trio.Event()
+
+    # Send data for readers
+    await send_chan.send(b"data1")
+    await send_chan.send(b"data2")
+
+    # Patch read lock to control test flow
+    original_acquire_read = stream.rw_lock.acquire_read
+
+    async def tracked_acquire_read():
+        await original_acquire_read()
+        readers_started.set()
+        # Wait until readers are allowed to finish
+        await readers_finished.wait()
+
+    # Patch write lock to detect when writer is blocked
+    original_acquire_write = stream.rw_lock.acquire_write
+
+    async def tracked_acquire_write():
+        writer_acquiring.set()
+        await original_acquire_write()
+        writer_entered.set()
+
+    with (
+        patch.object(stream.rw_lock, "acquire_read", side_effect=tracked_acquire_read),
+        patch.object(
+            stream.rw_lock, "acquire_write", side_effect=tracked_acquire_write
+        ),
+    ):
+        async with trio.open_nursery() as nursery:
+            # Start readers
+            nursery.start_soon(stream.read, 5)
+            nursery.start_soon(stream.read, 5)
+
+            # Wait for at least one reader to acquire the lock
+            await readers_started.wait()
+
+            # Start writer (should block)
+            nursery.start_soon(stream.write, b"test")
+
+            # Wait for writer to start acquiring lock
+            await writer_acquiring.wait()
+
+            # Verify writer hasn't entered critical section
+            assert not writer_entered.is_set()
+
+            # Allow readers to finish
+            readers_finished.set()
+
+            # Verify writer can proceed
+            await writer_entered.wait()
+
+
+@pytest.mark.trio
+async def test_lock_behavior_during_cancellation(mplex_stream):
+    """Verify that a lock is released when a task holding it is cancelled."""
+    stream, _, _ = mplex_stream
+
+    reader_acquired_lock = trio.Event()
+
+    async def cancellable_reader(task_status):
+        async with stream.rw_lock.read_lock():
+            reader_acquired_lock.set()
+            task_status.started()
+            # Wait indefinitely until cancelled.
+            await trio.sleep_forever()
+
+    async with trio.open_nursery() as nursery:
+        # Start the reader and wait for it to acquire the lock.
+        await nursery.start(cancellable_reader)
+        await reader_acquired_lock.wait()
+
+        # Now that the reader has the lock, cancel the nursery.
+        # This will cancel the reader task, and its lock should be released.
+        nursery.cancel_scope.cancel()
+
+    # After the nursery is cancelled, the reader should have released the lock.
+    # To verify, we try to acquire a write lock. If the read lock was not
+    # released, this will time out.
+    with trio.move_on_after(1) as cancel_scope:
+        async with stream.rw_lock.write_lock():
+            pass
+    if cancel_scope.cancelled_caught:
+        pytest.fail(
+            "Write lock could not be acquired after a cancelled reader, "
+            "indicating the read lock was not released."
+        )
+
+
+@pytest.mark.trio
+async def test_concurrent_read_write_sequence(mplex_stream):
+    """Verify complex sequence of interleaved reads and writes."""
+    stream, send_chan, _ = mplex_stream
+    results = []
+    # Use a mock to intercept writes and feed them back to the read channel
+    original_write = stream.write
+
+    reader1_finished = trio.Event()
+    writer1_finished = trio.Event()
+    reader2_finished = trio.Event()
+
+    async def mocked_write(data: bytes) -> None:
+        await original_write(data)
+        # Simulate the other side receiving the data and sending a response
+        # by putting data into the read channel.
+        await send_chan.send(data)
+
+    with patch.object(stream, "write", wraps=mocked_write) as patched_write:
+        async with trio.open_nursery() as nursery:
+            # Test scenario:
+            # 1. Reader 1 starts, waits for data.
+            # 2. Writer 1 writes, which gets fed back to the stream.
+            # 3. Reader 2 starts, reads what Writer 1 wrote.
+            # 4. Writer 2 writes.
+
+            async def reader1():
+                nonlocal results
+                results.append("R1 start")
+                data = await stream.read(5)
+                results.append(data)
+                results.append("R1 done")
+                reader1_finished.set()
+
+            async def writer1():
+                nonlocal results
+                await reader1_finished.wait()
+                results.append("W1 start")
+                await stream.write(b"write1")
+                results.append("W1 done")
+                writer1_finished.set()
+
+            async def reader2():
+                nonlocal results
+                await writer1_finished.wait()
+                # This will read the data from writer1
+                results.append("R2 start")
+                data = await stream.read(6)
+                results.append(data)
+                results.append("R2 done")
+                reader2_finished.set()
+
+            async def writer2():
+                nonlocal results
+                await reader2_finished.wait()
+                results.append("W2 start")
+                await stream.write(b"write2")
+                results.append("W2 done")
+
+            # Execute sequence
+            nursery.start_soon(reader1)
+            nursery.start_soon(writer1)
+            nursery.start_soon(reader2)
+            nursery.start_soon(writer2)
+
+            await send_chan.send(b"data1")
+
+    # Verify sequence and that write was called
+    assert patched_write.call_count == 2
+    assert results == [
+        "R1 start",
+        b"data1",
+        "R1 done",
+        "W1 start",
+        "W1 done",
+        "R2 start",
+        b"write1",
+        "R2 done",
+        "W2 start",
+        "W2 done",
+    ]
+
+
+# ===============================================
+# 2. Tests for Reset, EOF, and Close Interactions
+# ===============================================
+
+
+@pytest.mark.trio
+async def test_read_after_remote_close_triggers_eof(mplex_stream):
+    """Verify reading from a remotely closed stream returns EOF correctly."""
+    stream, send_chan, _ = mplex_stream
+
+    # Send some data that can be read first
+    await send_chan.send(b"data")
+    # Close the channel to signify no more data will ever arrive
+    await send_chan.aclose()
+
+    # Mark the stream as remotely closed
+    stream.event_remote_closed.set()
+
+    # The first read should succeed, consuming the buffered data
+    data = await stream.read(4)
+    assert data == b"data"
+
+    # Now that the buffer is empty and the channel is closed, this should raise EOF
+    with pytest.raises(MplexStreamEOF):
+        await stream.read(1)
+
+
+@pytest.mark.trio
+async def test_read_on_closed_stream_raises_eof(mplex_stream):
+    """Test that reading from a closed stream with no data raises EOF."""
+    stream, send_chan, _ = mplex_stream
+    stream.event_remote_closed.set()
+    await send_chan.aclose()  # Ensure the channel is closed
+
+    # Reading from a stream that is closed and has no data should raise EOF
+    with pytest.raises(MplexStreamEOF):
+        await stream.read(100)
+
+
+@pytest.mark.trio
+async def test_write_to_locally_closed_stream_raises(mplex_stream):
+    """Verify writing to a locally closed stream raises MplexStreamClosed."""
+    stream, _, _ = mplex_stream
+    stream.event_local_closed.set()
+
+    with pytest.raises(MplexStreamClosed):
+        await stream.write(b"this should fail")
+
+
+@pytest.mark.trio
+async def test_read_from_reset_stream_raises(mplex_stream):
+    """Verify reading from a reset stream raises MplexStreamReset."""
+    stream, _, _ = mplex_stream
+    stream.event_reset.set()
+
+    with pytest.raises(MplexStreamReset):
+        await stream.read(10)
+
+
+@pytest.mark.trio
+async def test_write_to_reset_stream_raises(mplex_stream):
+    """Verify writing to a reset stream raises MplexStreamClosed."""
+    stream, _, _ = mplex_stream
+    # A stream reset implies it's also locally closed.
+    await stream.reset()
+
+    # The `write` method checks `event_local_closed`, which `reset` sets.
+    with pytest.raises(MplexStreamClosed):
+        await stream.write(b"this should also fail")
+
+
+@pytest.mark.trio
+async def test_stream_reset_cleans_up_resources(mplex_stream):
+    """Verify reset() cleans up stream state and resources."""
+    stream, _, muxed_conn = mplex_stream
+    stream_id = stream.stream_id
+
+    assert stream_id in muxed_conn.streams
+    await stream.reset()
+
+    assert stream.event_reset.is_set()
+    assert stream.event_local_closed.is_set()
+    assert stream.event_remote_closed.is_set()
+    assert (HeaderTags.ResetInitiator, None, stream_id) in muxed_conn.sent_messages
+    assert stream_id not in muxed_conn.streams
+    # Verify the underlying data channel is closed
+    with pytest.raises(trio.ClosedResourceError):
+        await stream.incoming_data_channel.receive()
+
+
+# ===============================================
+# 3. Rigorous Concurrency Tests with Events
+# ===============================================
+
+
+@pytest.mark.trio
+async def test_writer_is_blocked_by_reader_using_events(mplex_stream):
+    """Verify a writer must wait for a reader using trio.Event for synchronization."""
+    stream, _, _ = mplex_stream
+
+    reader_has_lock = trio.Event()
+    writer_finished = trio.Event()
+
+    async def reader():
+        async with stream.rw_lock.read_lock():
+            reader_has_lock.set()
+            # Hold the lock until the writer has finished its attempt
+            await writer_finished.wait()
+
+    async def writer():
+        await reader_has_lock.wait()
+        # This call will now block until the reader releases the lock
+        await stream.write(b"data")
+        writer_finished.set()
+
+    async with trio.open_nursery() as nursery:
+        nursery.start_soon(reader)
+        nursery.start_soon(writer)
+
+        # Verify writer is blocked
+        await wait_all_tasks_blocked()
+        assert not writer_finished.is_set()
+
+        # Signal the reader to finish
+        writer_finished.set()
+
+
+@pytest.mark.trio
+async def test_multiple_readers_can_read_concurrently_using_events(mplex_stream):
+    """Verify that multiple readers can acquire a read lock simultaneously."""
+    stream, _, _ = mplex_stream
+
+    counters = {"readers_in_critical_section": 0}
+    lock = trio.Lock()  # To safely mutate the counter
+
+    reader1_acquired = trio.Event()
+    reader2_acquired = trio.Event()
+    all_readers_finished = trio.Event()
+
+    async def concurrent_reader(event_to_set: trio.Event):
+        async with stream.rw_lock.read_lock():
+            async with lock:
+                counters["readers_in_critical_section"] += 1
+            event_to_set.set()
+            # Wait until all readers have finished before exiting the lock context
+            await all_readers_finished.wait()
+            async with lock:
+                counters["readers_in_critical_section"] -= 1
+
+    async with trio.open_nursery() as nursery:
+        nursery.start_soon(concurrent_reader, reader1_acquired)
+        nursery.start_soon(concurrent_reader, reader2_acquired)
+
+        # Wait for both readers to acquire their locks
+        await reader1_acquired.wait()
+        await reader2_acquired.wait()
+
+        # Check that both were in the critical section at the same time
+        async with lock:
+            assert counters["readers_in_critical_section"] == 2
+
+        # Signal for all readers to finish
+        all_readers_finished.set()
+
+        # Verify they exit cleanly
+        await wait_all_tasks_blocked()
+        async with lock:
+            assert counters["readers_in_critical_section"] == 0