Add the feature to mock the context object

A `MockContext` object is added which mimics the default behaviour and implements the necessary attributes and functions described here: http://docs.aws.amazon.com/lambda/latest/dg/python-context-object.html The script accepts a `context.json` file. The contents of the file can be accessed via the python object `context.client_context.custom` in your handler function.
nficano · quiqua · May 17, 2016 · May 17, 2016 · May 17, 2016 · May 17, 2016
commit 06884ab0ce8e86c2bfea22477af5dd2c8d918f60
diff --git a/aws_lambda/aws_lambda.py b/aws_lambda/aws_lambda.py
@@ -3,6 +3,7 @@
 import json
 import logging
 import os
+import sys
 import time
 from imp import load_source
 from shutil import copy, copyfile
@@ -12,6 +13,7 @@
 import pip
 import yaml
 from . import project_template
+from .context import MockContext
 from .helpers import mkdir, read, archive, timestamp
 
 
@@ -41,14 +43,32 @@ def deploy(src):
         create_function(cfg, path_to_zip_file)
 
 
-def invoke(src, alt_event=None, verbose=False):
+def _load_json(base_dir, filename, default):
+    if filename is None:
+        filename = default
+    path = os.path.join(base_dir, filename)
+    try:
+        return read(path, loader=json.loads)
+    except IOError:
+        print("File does not exist: {}".format(path))
+        # file does not exist or json is malformed
+        return None
+    except ValueError:
+        print("Could not decode JSON object: {}".format(path))
+        print("Aborting...")
+        sys.exit(1)
+
+
+def invoke(src, alt_event=None, alt_context=None, verbose=False):
     """Simulates a call to your function.
 
     :param str src:
         The path to your Lambda ready project (folder must contain a valid
         config.yaml and handler module (e.g.: service.py).
     :param str alt_event:
         An optional argument to override which event file to use.
+    :param str alt_context:
+        An optional argument to override which context file to use.
     :param bool verbose:
         Whether to print out verbose details.
     """
@@ -57,22 +77,16 @@ def invoke(src, alt_event=None, verbose=False):
     cfg = read(path_to_config_file, loader=yaml.load)
 
     # Load and parse event file.
-    if alt_event:
-        path_to_event_file = os.path.join(src, alt_event)
-    else:
-        path_to_event_file = os.path.join(src, 'event.json')
-    event = read(path_to_event_file, loader=json.loads)
+    event = _load_json(src, alt_event, 'event.json')
+    context = _load_json(src, alt_context, 'context.json')
 
     handler = cfg.get('handler')
     # Inspect the handler string (<module>.<function name>) and translate it
     # into a function we can execute.
     fn = get_callable_handler_function(src, handler)
 
-    # TODO: look into mocking the ``context`` variable, currently being passed
-    # as None.
-
     start = time.time()
-    results = fn(event, None)
+    results = fn(event, MockContext(context))
     end = time.time()
 
     print("{0}".format(results))

diff --git a/aws_lambda/context.py b/aws_lambda/context.py
@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+
+class MockContext(object):
+    def __init__(self, context):
+        self.function_name = 'Mock'
+        self.function_version = 'm1'
+        self.memory_limit_in_mb = '500'
+        self.aws_request_id = None
+        self.log_groupd_name = None
+        self.log_stream_name = None
+        self.identiy = FakeObject()
+        self.client_context = ClientContext(context)
+
+    def get_remaining_time_in_millis(self):
+        # Returns the remaining execution time, in milliseconds, until
+        # AWS Lambda terminates the function.
+        return 0
+
+
+class FakeObject(object):
+    def __init__(self, context=None):
+        self._context = context or {} # if None was passed
+
+    def __getattr__(self, attr):
+        return self._context.get(attr, None)
+
+
+class ClientContext(object):
+    def __init__(self, context):
+        self.custom = FakeObject(context)
+        self.client = FakeObject()
diff --git a/scripts/lambda b/scripts/lambda
@@ -27,9 +27,10 @@ def build():
 
 @click.command(help="Run a local test of your function.")
 @click.option('--event-file', default=None, help='Alternate event file.')
+@click.option('--context-file', default=None, help='Alternate context file.')
 @click.option('--verbose', '-v', is_flag=True)
-def invoke(event_file, verbose):
-    aws_lambda.invoke(CURRENT_DIR, event_file, verbose)
+def invoke(event_file, context_file, verbose):
+    aws_lambda.invoke(CURRENT_DIR, event_file, context_file, verbose)
 
 
 @click.command(help="Register and deploy your code to lambda.")