Is it possible to use gzip compression with Server-Sent Events (SSE)?

Question

I would like to know if it is possible to enable gzip compression for Server-Sent Events (SSE ; Content-Type: text/event-stream). It seems it is possible, according to this book: http://chimera.labs.oreilly.com/books/1230000000545/ch16.html But I can't find any example of SSE with gzip compression. I tried to send gzipped messages with the response header field Content-Encoding set to "gzip" without success. For experimenting around SSE, I am testing a small web application made in Python with the bottle framework + gevent ; I am just running the bottle WSGI server: ``` @bottle.get('/data_stream') def stream_data(): bottle.response.content_type = "text/event-stream" bottle.response.add_header("Connection", "keep-alive") bottle.response.add_header("Cache-Control", "no-cache") bottle.response.add_header("Content-Encoding", "gzip") while True: # new_data is a gevent AsyncResult object, # .get() just returns a data string when new # data is available data = new_data.get() yield zlib.compr…

Accepted Answer

TL;DR: If the requests are not cached, you likely want to use zlib and declare Content-Encoding to be 'deflate'. That change alone should make your code work.

If you declare Content-Encoding to be gzip, you need to actually use gzip. They are based on the the same compression algorithm, but gzip has some extra framing. This works, for example:

```
import gzip
import StringIO
from bottle import response, route
@route('/')
def get_data():
    response.add_header("Content-Encoding", "gzip")
    s = StringIO.StringIO()
    with gzip.GzipFile(fileobj=s, mode='w') as f:
        f.write('Hello World')
    return s.getvalue()
```

That only really makes sense if you use an actual file as a cache, though.

Is it possible to use gzip compression with Server-Sent Events (SSE)?

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