Improve error handling in PrologEngine

1 files changed, 84 insertions, 25 deletions

diff --git a/prolog/engine.py b/prolog/engine.py
index 6627b9a..a25a07d 100644
--- a/prolog/engine.py
+++ b/prolog/engine.py
@@ -2,43 +2,53 @@
 
 import http.client
 import json
+import re
 import urllib
 
 address, port = 'localhost', 3030
 
 class PrologEngine(object):
-    def __init__(self, address=address, port=port, code=''):
-        self.id = None
+    def __init__(self, address=address, port=port, code='', destroy=False, id=None):
         self.conn = http.client.HTTPConnection(address, port, timeout=10)
 
-        hdrs = {'Content-Type': 'application/json; charset=utf-8'}
-        opts = json.dumps({'destroy': False, 'src_text': code, 'format': 'json'})
-        self.conn.request('POST', '/pengine/create', body=opts, headers=hdrs)
+        # If existing engine ID is given, use it.
+        if id:
+            self.id = id
+            return
 
-        response = self.conn.getresponse()
-        data = response.read()
-        reply = json.loads(str(data, encoding='utf-8'))
-        if reply['event'] == 'create':
-            self.id = reply['id']
-        else:
-            raise Exception('could not create engine: ' + reply['code'])
+        # Otherwise, create a new engine.
+        hdrs = {'Content-Type': 'application/json;charset=utf-8'}
+        opts = json.dumps({'destroy': destroy, 'src_text': code, 'format': 'json-s'})
+        reply, outputs = self.request('POST', '/pengine/create', body=opts, headers=hdrs)
+
+        failed = (reply['event'] != 'create')
+        warnings = []
+        errors = []
+        for output in outputs:
+            print(output)
+            message = PrologEngine.parse_prolog_output(output)
+            if output['message'] == 'warning':
+                warnings.append(message)
+            elif output['message'] == 'error':
+                failed = True
+                errors.append(message)
+
+        if failed:
+            raise Exception('\n'.join(errors))
 
-    def send(self, event, fmt='json'):
+        self.id = reply['id']
+
+    def send(self, event):
         params = urllib.parse.urlencode({
             'id': self.id,
             'event': event,
-            'format': fmt})
-        self.conn.request('GET', '/pengine/send?' + params)
-
-        response = self.conn.getresponse()
-        data = str(response.read(), encoding='utf-8')
-        if response.status == http.client.OK:
-            return json.loads(data) if fmt == 'json' else data
-        return None
-
-    def ask(self, query, template='', fmt='json'):
-        event = 'ask(({}),[template({})])'.format(query, template)
-        reply = self.send(event, fmt=fmt)
+            'format': 'json-s'})
+        reply, outputs = self.request('GET', '/pengine/send?' + params)
+        return reply
+
+    def ask(self, query):
+        event = 'ask(({}),[])'.format(query)
+        reply = self.send(event)
         return reply
 
     def next(self, n=1):
@@ -55,6 +65,55 @@ class PrologEngine(object):
         self.conn.close()
         self.conn = None
 
+    # Return the main reply and possible output replies.
+    def request(self, method, path, body=None, headers={}):
+        self.conn.request(method, path, body, headers)
+        outputs = []
+        while True:
+            response = self.conn.getresponse()
+            if response.status != http.client.OK:
+                raise Exception('server returned {}'.format(response.status))
+            reply = json.loads(response.read().decode('utf-8'))
+            self.id = reply['id']
+            if reply['event'] == 'output':
+                outputs.append(reply)
+                params = urllib.parse.urlencode({
+                    'id': self.id,
+                    'format': 'json-s'})
+                self.conn.request('GET', '/pengine/pull_response?' + params)
+            else:
+                return reply, outputs
+
+    # Check if output is an error message and return a prettified version of it.
+    def parse_prolog_output(output):
+        match = re.match(r'.*<pre class="[^"]*">(.*)</pre>.*',
+                         output['data'], flags=re.DOTALL)
+        data = match.group(1).strip()
+        message = ''
+        if output['message'] == 'error':
+            if 'location' in output:
+                loc = output['location']
+                message += 'near line ' + str(loc['line'])
+                if 'ch' in loc:
+                    message += ', character ' + str(loc['ch'])
+                message += ': '
+
+            if output.get('code') == 'syntax_error':
+                match = re.match(r'^.*Syntax error: (.*)$', data, flags=re.DOTALL)
+                message += match.group(1)
+            elif output.get('code') == 'permission_error':
+                match = re.match(r'^.*(No permission [^\n]*)', data, flags=re.DOTALL)
+                message += match.group(1)
+            elif output.get('code') == 'type_error':
+                match = re.match(r'^.*(Type error: [^\n]*)', data, flags=re.DOTALL)
+                message += match.group(1)
+            else:
+                message += data
+
+        # Replace anonymous variable names with _.
+        message = re.sub(r'_G[0-9]*', '_', message)
+        return message
+
 # Basic sanity check.
 if __name__ == '__main__':
     engine = PrologEngine(code='dup([],[]). dup([H|T],[H,H|TT]) :- dup(T,TT).')