pylightning: Wrap request in an object

We well need this in the next commit to be able to return from an
asynchronous call. We also guard stdout access with a reentrant lock
since we are no longer guaranteed that all communication happens on
the same thread.

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

contrib/pylightning/lightning/plugin.py

@@ -1,6 +1,7 @@
 from collections import OrderedDict
-from lightning import LightningRpc
 from enum import Enum
+from lightning import LightningRpc
+from threading import RLock
 
 import inspect
 import json
@@ -15,6 +16,12 @@ class MethodType(Enum):
     HOOK = 1
 
 
+class RequestState(Enum):
+    PENDING = 'pending'
+    FINISHED = 'finished'
+    FAILED = 'failed'
+
+
 class Method(object):
     """Description of methods that are registered with the plugin.
 
@@ -27,6 +34,59 @@ class Method(object):
         self.name = name
         self.func = func
         self.mtype = mtype
+        self.background = False
+
+
+class Request(dict):
+    """A request object that wraps params and allows async return
+    """
+    def __init__(self, plugin, req_id, method, params, background=False):
+        self.method = method
+        self.params = params
+        self.background = background
+        self.plugin = plugin
+        self.state = RequestState.PENDING
+        self.id = req_id
+
+    def getattr(self, key):
+        if key == "params":
+            return self.params
+        elif key == "id":
+            return self.id
+        elif key == "method":
+            return self.method
+
+    def set_result(self, result):
+        if self.state != RequestState.PENDING:
+            raise ValueError(
+                "Cannot set the result of a request that is not pending, "
+                "current state is {state}".format(self.state))
+        self.result = result
+        self._write_result({
+            'jsonrpc': '2.0',
+            'id': self.id,
+            'result': self.result
+        })
+
+    def set_exception(self, exc):
+        if self.state != RequestState.PENDING:
+            raise ValueError(
+                "Cannot set the exception of a request that is not pending, "
+                "current state is {state}".format(self.state))
+        self.exc = exc
+        self._write_result({
+            'jsonrpc': '2.0',
+            'id': self.id,
+            "error": "Error while processing {method}: {exc}".format(
+                method=self.method, exc=repr(exc)
+            ),
+        })
+
+    def _write_result(self, result):
+        with self.plugin.write_lock:
+            json.dump(result, fp=self.plugin.stdout)
+            self.plugin.stdout.write('\n\n')
+            self.plugin.stdout.flush()
 
 
 class Plugin(object):
@@ -59,6 +119,8 @@ class Plugin(object):
         self.rpc = None
         self.child_init = None
 
+        self.write_lock = RLock()
+
     def add_method(self, name, func):
         """Add a plugin method to the dispatch table.
 
@@ -185,7 +247,7 @@ class Plugin(object):
         return decorator
 
     def _exec_func(self, func, request):
-        params = request['params']
+        params = request.params
         sig = inspect.signature(func)
 
         arguments = OrderedDict()
@@ -223,36 +285,30 @@ class Plugin(object):
         return func(*ba.args, **ba.kwargs)
 
     def _dispatch_request(self, request):
-        name = request['method']
+        name = request.method
 
         if name not in self.methods:
             raise ValueError("No method {} found.".format(name))
         method = self.methods[name]
+        request.background = method.background
 
         try:
-            result = {
+            result = self._exec_func(method.func, request)
-                'jsonrpc': '2.0',
+            if not method.background:
-                'id': request['id'],
+                # Only if this is not an async (background) call do we need to
-                'result': self._exec_func(method.func, request)
+                # return the result, otherwise the callee will eventually need
-            }
+                # to call request.set_result or request.set_exception to
+                # return a result or raise an exception.
+                request.set_result(result)
         except Exception as e:
-            result = {
+            request.set_exception(e)
-                'jsonrpc': '2.0',
-                'id': request['id'],
-                "error": "Error while processing {}: {}".format(
-                    request['method'], repr(e)
-                ),
-            }
             self.log(traceback.format_exc())
-        json.dump(result, fp=self.stdout)
-        self.stdout.write('\n\n')
-        self.stdout.flush()
 
     def _dispatch_notification(self, request):
-        name = request['method']
+        if request.method not in self.subscriptions:
-        if name not in self.subscriptions:
+            raise ValueError("No subscription for {name} found.".format(
-            raise ValueError("No subscription for {} found.".format(name))
+                name=request.method))
-        func = self.subscriptions[name]
+        func = self.subscriptions[request.method]
 
         try:
             self._exec_func(func, request)
@@ -265,6 +321,7 @@ class Plugin(object):
             'method': method,
             'params': params,
         }
+        with self.write_lock:
             json.dump(payload, self.stdout)
             self.stdout.write("\n\n")
             self.stdout.flush()
@@ -282,11 +339,18 @@ class Plugin(object):
         """
         for payload in msgs[:-1]:
             request = json.loads(payload)
+            request = Request(
+                plugin=self,
+                req_id=request.get('id', None),
+                method=request['method'],
+                params=request['params'],
+                background=False,
+            )
 
             # If this has an 'id'-field, it's a request and returns a
             # result. Otherwise it's a notification and it doesn't
             # return anything.
-            if 'id' in request:
+            if request.id is not None:
                 self._dispatch_request(request)
             else:
                 self._dispatch_notification(request)

contrib/pylightning/lightning/test_plugin.py

@@ -1,22 +1,21 @@
-from .plugin import Plugin
+from .plugin import Plugin, Request
 import itertools
 
 
 def test_positional_inject():
     p = Plugin()
-    rdict = {
+    rdict = Request(
-        'id': 1,
+        plugin=p,
-        'jsonrpc':
+        req_id=1,
-        '2.0',
+        method='func',
-        'method': 'func',
+        params={'a': 1, 'b': 2, 'kwa': 3, 'kwb': 4}
-        'params': {'a': 1, 'b': 2, 'kwa': 3, 'kwb': 4}
+    )
-    }
+    rarr = Request(
-    rarr = {
+        plugin=p,
-        'id': 1,
+        req_id=1,
-        'jsonrpc': '2.0',
+        method='func',
-        'method': 'func',
+        params=[1, 2, 3, 4],
-        'params': [1, 2, 3, 4]
+    )
-    }
 
     def pre_args(plugin, a, b, kwa=3, kwb=4):
         assert (plugin, a, b, kwa, kwb) == (p, 1, 2, 3, 4)