fix(compress): don't compress server-sent events

[dmitri-gb]

Using both compress middleware and the streamSSE helper from hono/streaming doesn't work correctly -- the SSE messages are not streamed, instead they get buffered by the compression mechanism.

According to expressjs/compression it should be possible to compress server-sent events, if the underlying compression mechanism supports manual flushing. As far as I can tell though, CompressionStream (used by Hono's compress middleware) doesn't offer this functionality, so the best we can do is not compress SSE streams at all.

[EdamAme-x]

Nice work
I think need to add tests about this

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.71%. Comparing base (2a68c59) to head (aee7f69).
Report is 1 commits behind head on main.

Additional details and impacted files

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##             main    #3833   +/-   ##
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  Coverage   91.71%   91.71%           
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  Files         160      160           
  Lines       10195    10195           
  Branches     2925     2868   -57     
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  Hits         9350     9350           
  Misses        844      844           
  Partials        1        1           

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[yusukebe]

Hi @dmitri-gb

Thank you for the PR. I also realized that the problem and your idea are good! As @EdamAme-x mentioned, you need to add a test. I think it's a little unsuitable if you add it to src/helper/streaming/sse.test.tsx because this fix is about Compress Middleware. So it will be okay to test if it will not be compressed if the content type is text/event-stream in src/middleware/compress/index.test.ts.

[dmitri-gb]

Hi! I added a test in src/middleware/compress/index.test.ts that uses the streamSSE helper.

[yusukebe]

LGTM!

[yusukebe]

@dmitri-gb

Great! Thank you for your contribution.

[mfulton26]

related issues for tracking ability to control flushing on CompressionStream:

• On-demand flush whatwg/compression#56
• Supply parameters for compression algorithms whatwg/compression#22