script/client/sseclient.py

@@ -0,0 +1,163 @@
+import codecs
+import re
+import time
+import warnings
+
+import six
+
+import requests
+
+
+# Technically, we should support streams that mix line endings.  This regex,
+# however, assumes that a system will provide consistent line endings.
+end_of_field = re.compile(r'\r\n\r\n|\r\r|\n\n')
+
+class SSEClient(object):
+    def __init__(self, url, last_id=None, retry=3000, session=None, chunk_size=1024, **kwargs):
+        self.url = url
+        self.last_id = last_id
+        self.retry = retry
+        self.chunk_size = chunk_size
+
+        # Optional support for passing in a requests.Session()
+        self.session = session
+
+        # Any extra kwargs will be fed into the requests.get call later.
+        self.requests_kwargs = kwargs
+
+        # The SSE spec requires making requests with Cache-Control: nocache
+        if 'headers' not in self.requests_kwargs:
+            self.requests_kwargs['headers'] = {}
+        self.requests_kwargs['headers']['Cache-Control'] = 'no-cache'
+
+        # The 'Accept' header is not required, but explicit > implicit
+        self.requests_kwargs['headers']['Accept'] = 'text/event-stream'
+
+        # Keep data here as it streams in
+        self.buf = u''
+
+        self._connect()
+
+    def _connect(self):
+        if self.last_id:
+            self.requests_kwargs['headers']['Last-Event-ID'] = self.last_id
+
+        # Use session if set.  Otherwise fall back to requests module.
+        requester = self.session or requests
+        self.resp = requester.get(self.url, stream=True, **self.requests_kwargs)
+        self.resp_iterator = self.resp.iter_content(chunk_size=self.chunk_size)
+
+        # TODO: Ensure we're handling redirects.  Might also stick the 'origin'
+        # attribute on Events like the Javascript spec requires.
+        self.resp.raise_for_status()
+
+    def _event_complete(self):
+        return re.search(end_of_field, self.buf) is not None
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        decoder = codecs.getincrementaldecoder(
+            self.resp.encoding)(errors='replace')
+        while not self._event_complete():
+            try:
+                next_chunk = next(self.resp_iterator)
+                if not next_chunk:
+                    raise EOFError()
+                self.buf += decoder.decode(next_chunk)
+
+            except (StopIteration, requests.RequestException, EOFError) as e:
+                time.sleep(self.retry / 1000.0)
+                self._connect()
+
+                # The SSE spec only supports resuming from a whole message, so
+                # if we have half a message we should throw it out.
+                head, sep, tail = self.buf.rpartition('\n')
+                self.buf = head + sep
+                continue
+
+        # Split the complete event (up to the end_of_field) into event_string,
+        # and retain anything after the current complete event in self.buf
+        # for next time.
+        (event_string, self.buf) = re.split(end_of_field, self.buf, maxsplit=1)
+        msg = Event.parse(event_string)
+
+        # If the server requests a specific retry delay, we need to honor it.
+        if msg.retry:
+            self.retry = msg.retry
+
+        # last_id should only be set if included in the message.  It's not
+        # forgotten if a message omits it.
+        if msg.id:
+            self.last_id = msg.id
+
+        return msg
+
+    if six.PY2:
+        next = __next__
+
+
+class Event(object):
+
+    sse_line_pattern = re.compile('(?P<name>[^:]*):?( ?(?P<value>.*))?')
+
+    def __init__(self, data='', event='message', id=None, retry=None):
+        self.data = data
+        self.event = event
+        self.id = id
+        self.retry = retry
+
+    def dump(self):
+        lines = []
+        if self.id:
+            lines.append('id: %s' % self.id)
+
+        # Only include an event line if it's not the default already.
+        if self.event != 'message':
+            lines.append('event: %s' % self.event)
+
+        if self.retry:
+            lines.append('retry: %s' % self.retry)
+
+        lines.extend('data: %s' % d for d in self.data.split('\n'))
+        return '\n'.join(lines) + '\n\n'
+
+    @classmethod
+    def parse(cls, raw):
+        """
+        Given a possibly-multiline string representing an SSE message, parse it
+        and return a Event object.
+        """
+        msg = cls()
+        for line in raw.splitlines():
+            m = cls.sse_line_pattern.match(line)
+            if m is None:
+                # Malformed line.  Discard but warn.
+                warnings.warn('Invalid SSE line: "%s"' % line, SyntaxWarning)
+                continue
+
+            name = m.group('name')
+            if name == '':
+                # line began with a ":", so is a comment.  Ignore
+                continue
+            value = m.group('value')
+
+            if name == 'data':
+                # If we already have some data, then join to it with a newline.
+                # Else this is it.
+                if msg.data:
+                    msg.data = '%s\n%s' % (msg.data, value)
+                else:
+                    msg.data = value
+            elif name == 'event':
+                msg.event = value
+            elif name == 'id':
+                msg.id = value
+            elif name == 'retry':
+                msg.retry = int(value)
+
+        return msg
+
+    def __str__(self):
+        return self.data