Feature request: emit post-processing 'info' event

[salzhrani]

I am using sharp's raw input and output to do some color manipulation on images in addition to resize and crop.

var input = sharp().raw().resize(600).max().withoutEnlargement();
var process = new ColorSaturationStream();
var output = sharp(null, {raw: {
    width: newWidth,
    height: newHeight,
    channels: newChannels
}}).toFormat('jpg');

someImageStream.pipe(input).pipe(process).pipe(output).pipe(response);

the challenge is that output must have the correct newWidth and newHeight or it will throw an error like:
libc++abi.dylib: terminating with uncaught exception of type vips::VError
while knowing the original image size I can calculate what newWidth and newHeight can be, but since there is a possibility of using different rounding methods than sharp I might get the wrong values.

I currently use Math.round as sharp does but is it always going to be the case ?

One way that might help with this is to add a utility function that exposes sharp internal calculations so we can have the same values.

[lovell]

Hello, we could add a feature where an instance of sharp will emit an info event with the same details as the info parameter provided to the toBuffer callback. Do you think this might provide what you need?

Given the async nature of this, you would probably need to cork the output Stream of your example until this event was emitted by the input Stream.

As an aside, we also need to check why you're seeing "terminating with uncaught exception of type vips::VError" as that should have been caught and emitted as an error event.

[salzhrani]

this error message is on mac os, in linux I got more details which point to this line which is becuase of the difference in size

[salzhrani]

an info event is useful, preferably if emitted early or even before pushing to the stream.

[lovell]

Commit 86815bc on the needle branch adds the info event for Stream-based output.

[lovell]

v0.14.0 now available via npm, thanks for the original suggestion!