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sseclient.py
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sseclient.py
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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, **kwargs):
self.url = url
self.last_id = last_id
self.retry = retry
# 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(decode_unicode=True)
# 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):
while not self._event_complete():
try:
nextchar = next(self.resp_iterator)
self.buf += nextchar
except (StopIteration, requests.RequestException):
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 = re.split(end_of_field, self.buf)
head = split[0]
tail = "".join(split[1:])
self.buf = tail
msg = Event.parse(head)
# 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.split('\n'):
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.groupdict()['name']
value = m.groupdict()['value']
if name == '':
# line began with a ":", so is a comment. Ignore
continue
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