Add support for customizing compress encodings

[arunoda]

Related: #555

By default we only do if for gzip.

For an example, here how to add support for bothbr and gzip compress encodings.

var zlib = require('zlib')
var iltorb = require('iltorb')

module.exports = {
  // Returns a map of compression streams for the types of encodings you want to support
  // Here's a list of common encoding types: https://goo.gl/ke7zOK

  // The first listed encoding has the higher priority over others.
  //  In this case, first it'll try to serve the `br` version if the browser supports it.
  //  Otherwise, it'll serve the gzipped version.
  compress: {
    br: function () {
      return iltorb.compressStream()
    },
    gzip: function () {
      // You can also return a promise which resolve a compression stream
      return new Promise(function (resolve) {
        resolve(zlib.createGzip())
      })
    }
  }
}

[nkzawa]

I think we should accept Promise instead of ReadableStream since errors might occur in the middle of compression process.

[arunoda]

But we capture it inside our code. We convert this into a promise.

Why I like this approach is, this is how most of the compression API works. So, it's pretty simple for the user. We handle the rest.

[nkzawa]

But we capture it inside our code.

Actually, it doesn't capture all errors since errors are emitted on each stream. http://stackoverflow.com/questions/21771220/error-handling-with-node-js-streams

Additionally, we should consider the case you do something async inside the callback.

br (path) {
  something(path).then(() => {
    ..
  }).catch((err) => {
    // handle err
  })
}

[arunoda]

@nkzawa so what what do get from the promise?

• Stream
• Nothing: Let them to write to the disk.

We can do something like this too:

{
  br: function(inputPath, outputPath) {
    return new Promise()
  }
}

[nkzawa]

👍 That seems the simplest way.

Another idea is to accept only a transform stream.

    gzip: function() {
      return zlib.createGzip()
    }

• We can catch all errors since other streams are prepared by us.
• Maybe you can still do any async operations by wrapping them inside a stream.

I'm not so sure if this would cover all cases though.

[arunoda]

@nkzawa I like that approach. And we can also also accept a promise from that function. (Which returns a stream)

[rauchg]

What's br ?

[rauchg]

Will leave this for post 2.0

[arunoda]

@rauchg this is br: https://github.com/google/brotli (AKA: Realistic version of Pied Piper)

[arunoda]

@nkzawa check now.

[rauchg]

What I don't get is why we need the br key. Why don't we have a general callback directly?

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[arunoda]

@rauchg That's for the type of compress encodings we support.
Different browsers support different types of encodings. (They all do gzip, but if you get more optimizations, you need to do browser specific stuff like br)

We use this key (like 'br', 'gzip') to save the compressed file with that extension. Also we use this to detect which type of encodings we support and serve which is suits for the given browser.

See:

[msand]

Looks great, many thanks!

[rauchg]

@arunoda should next do the accept-encoding parsing, or should we hand the header (or even request) to the function?

[msand]

@rauchg The compression is currently done statically on build, and next checks the supported and accepted encoding to decide what file to serve, which seems reasonable.

Compress on build: https://github.com/zeit/next.js/pull/657/files#diff-1634f71f56280340be4063732d469343R12
Choose encoding: https://github.com/zeit/next.js/pull/657/files#diff-bec864430eb5752a683c8798d0c6bd6cR146

[impronunciable]

It would be cool to use styled-jsx

[arunoda]

I just wanna talk about this feature in this example.
Anyway, I don't mind using that too.

[impronunciable]

How about compress the syntax to something like:

  br: iltorb.compressStream,
  gzip: () => new Promise(resolve => resolve(zlib.createGzip()))
}

[arunoda]

Isn't is the same as right now except it should be br: iltorb.compressStream()?

If you are looking at ES2015 features, I didn't use them because we don't transpile the next.config.js.

[timneutkens]

@arunoda since we're moving to not use compression in next.js but let it be handled by the server, should this PR be closed?

[arunoda]

Yeah! let's close this.