Support read(n=-1)

Now, `n=-1` indicates that we want to read until EOF. However, now we
only read until we have no new message.

libp2p/stream_muxer/mplex/mplex.py

@@ -1,5 +1,5 @@
 import asyncio
-from typing import Dict, Tuple, Optional
+from typing import Dict, Optional, Tuple
 
 from multiaddr import Multiaddr
 

libp2p/stream_muxer/mplex/mplex_stream.py

@@ -39,28 +39,39 @@ class MplexStream(IMuxedStream):
         self.stream_lock = asyncio.Lock()
         self._buf = b""
 
-    async def read(self, n) -> bytes:
+    async def read(self, n: int = -1) -> bytes:
         """
         Read up to n bytes. Read possibly returns fewer than `n` bytes,
         if there are not enough bytes in the Mplex buffer.
+        If `n == -1`, read until EOF.
         :param n: number of bytes to read
         :return: bytes actually read
         """
+        if n < 0 and n != -1:
+            raise ValueError("`n` can only be -1 if it is negative")
         # If the buffer is empty at first, blocking wait for data.
         if len(self._buf) == 0:
             self._buf = await self.mplex_conn.read_buffer(self.stream_id)
-        # Here, `self._buf` should never be `None`.
+        # Sanity check: `self._buf` should never be empty here.
         if self._buf is None or len(self._buf) == 0:
-            raise Exception("start to `read_buffer_nonblocking` only when there are bytes read.")
+            raise Exception("`self._buf` should never be empty here")
 
-        while len(self._buf) < n:
+        # FIXME: If `n == -1`, we should blocking read until EOF, instead of returning when
+        #   no message is available.
+        # If `n >= 0`, read up to `n` bytes.
+        # Else, read until no message is available.
+        while len(self._buf) < n or n == -1:
             new_bytes = await self.mplex_conn.read_buffer_nonblocking(self.stream_id)
             if new_bytes is None:
                 # Nothing to read in the `MplexConn` buffer
                 break
             self._buf += new_bytes
+        payload: bytes
+        if n == -1:
+            payload = self._buf
+        else:
             payload = self._buf[:n]
-        self._buf = self._buf[n:]
+        self._buf = self._buf[len(payload) :]
         return payload
 
     async def write(self, data: bytes) -> int: