pylightning: Add a compatibility mode for pre-\n\n versions

We inadvertently broke the compatibility between the python library
and the binary when switching to \n\n-delimiters. This reintroduces
the old inefficient parsing, and dynamically upgrades to the faster
version if it detects the \n\n-delimiter.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - JSON API: `pay` and `decodepay` accept and ignore `lightning:` prefixes.
 - pylightning: Allow either keyword arguments or positional arguments.
+- JSON-RPC: messages are now separated by 2 consecutive newlines. The pylightning client library has temporary support for both separators, but will eventually drop the single newline separator, which may cause it to stop working on older clients (see #2135 for details).
 
 ### Deprecated
 

contrib/pylightning/lightning/lightning.py

@@ -20,11 +20,38 @@ class UnixDomainSocketRpc(object):
         self.executor = executor
         self.logger = logger
 
+        # Do we require the compatibility mode?
+        self._compat = True
+
     @staticmethod
     def _writeobj(sock, obj):
         s = json.dumps(obj)
         sock.sendall(bytearray(s, 'UTF-8'))
 
+    def _readobj_compat(self, sock, buff=b''):
+        if not self._compat:
+            return self._readobj(sock, buff)
+        while True:
+            try:
+                b = sock.recv(1024)
+                buff += b
+
+                if b'\n\n' in buff:
+                    # The next read will use the non-compatible read instead
+                    self._compat = False
+
+                if len(b) == 0:
+                    return {'error': 'Connection to RPC server lost.'}
+                if b' }\n' not in buff:
+                    continue
+                # Convert late to UTF-8 so glyphs split across recvs do not
+                # impact us
+                objs, len_used = self.decoder.raw_decode(buff.decode("UTF-8"))
+                return objs, buff[len_used:].lstrip()
+            except ValueError:
+                # Probably didn't read enough
+                pass
+
     def _readobj(self, sock, buff=b''):
         """Read a JSON object, starting with buff; returns object and any buffer left over"""
         while True:
@@ -74,7 +101,7 @@ class UnixDomainSocketRpc(object):
             "params": payload,
             "id": 0
         })
-        resp, _ = self._readobj(sock)
+        resp, _ = self._readobj_compat(sock)
         sock.close()
 
         self.logger.debug("Received response for %s call: %r", method, resp)