pipe should have a continuation callback.
a.pipe(b, function(err) { ... });
This is the simplest way to hook up code which will be executed after the
pipe operation: no need to trap two events (one for success, one for
error), a good old callback does the job.
With a callback API, you don't need domains, you can get the error context
from a closure.
Bruno
On Thursday, August 15, 2013 11:06:33 AM UTC+2, greelgorke wrote:
>
> the error handling is something domains should do. i haven't tried them
> yet, but generally i think it's a good idea to separate error handling from
> the business logic. I don't see a good point to let errors bubble up the
> pipe, you need to transform them in most cases anyway. but it would be cool
> to be trigger a shutdown sequence that bubbles up the pipe.
>
> // in domain
>
> a.pipe(b).pipe(c)
>
> domain.on('error', function(){
> a.destroy() //buubles up the chain.
> })
>
> every stream could implement the bubbled destroy reaction different,
> eighter by destroy self or just unpipe.
>
>
> Am Mittwoch, 14. August 2013 19:02:19 UTC+2 schrieb Eldar:
>>
>> Node completely shutdowns because emitter.emit('error') triggers
>> exception when there is no listeners for error event.
>> The ".pipe()" listens for errors but doesn't change that behavior.
>>
>> So strictly speaking above server will shutdown on file error because of
>> uncaught exception
>> and leak on socket hang up, because "close" not an "error" event will be
>> emitted.
>>
>> среда, 14 августа 2013 г., 13:47:14 UTC+4 пользователь Floby написал:
>>>
>>> file.pipe(res) does clean the resources on error because node completely
>>> shuts down, doesn't it?
>>>
>>> On Tuesday, 13 August 2013 12:08:30 UTC+2, Eldar wrote:
>>>>
>>>> file.pipe(res)
>>>>
>>>> On response error (say client clicked close window button) the file
>>>> will remain open.
>>>> And vice versa on file error response will hang. So the correct way to
>>>> pipe is
>>>>
>>>> file.pipe(res)
>>>> file.on('error', res.destroy.bind(res))
>>>> res.on('error', file.destroy.bind(res))
>>>>
>>>> вторник, 13 августа 2013 г., 12:58:09 UTC+4 пользователь Floby написал:
>>>>>
>>>>> ok.
>>>>> I didn't understand the part about " `.pipe()` doesn't cleanup any
>>>>> resources.
>>>>> Everything works fine until the streaming process completes
>>>>> successfully. "
>>>>>
>>>>> Is there an example where that becomes obvious?
>>>>>
>>>>> On Monday, 12 August 2013 18:05:02 UTC+2, Eldar wrote:
>>>>>>
>>>>>> If you want to create some function which accepts a stream and can
>>>>>> affect
>>>>>> it's state you should be able to destroy the given stream on demand
>>>>>> e.g. when something went wrong and/or you are not interested in
>>>>>> receiving data anymore.
>>>>>> Unfortunately that's impossible with current node readable streams
>>>>>> because they:
>>>>>>
>>>>>> 1. Support multiple consumers
>>>>>> 2. Don't have common cleanup interface
>>>>>>
>>>>>> So you can't touch another's stream because someone else may use it
>>>>>> and if you could you don't know how.
>>>>>>
>>>>>> The absence of ability to pass streams as arguments is a huge flow. You
>>>>>> can build almost nothing
>>>>>> without that. Now someone may wonder: but there are so many useful
>>>>>> modules about streams in npm!?
>>>>>> Right. They all rely on `.pipe()`. For some reason all kind of blog
>>>>>> posts, tutorials and even node's
>>>>>> own documentation teach that for passing readable you can do
>>>>>> `readable.pipe(writable)`.
>>>>>> E.g. http file server could be:
>>>>>>
>>>>>> ```javascript
>>>>>> var http = require('http')
>>>>>> var fs = require('fs')
>>>>>> http.createServer(function(req, res) {
>>>>>> res.writeHead(200, {'Content-Type': 'text/plain'})
>>>>>> fs.createReadStream(req.url.slice(1)).pipe(res)
>>>>>> }).listen(3000)
>>>>>> ```
>>>>>>
>>>>>> That's a lie. Exactly for the reasons above `.pipe()` doesn't cleanup
>>>>>> any resources.
>>>>>> Everything works fine until the streaming process completes
>>>>>> successfully.
>>>>>> But if something fails you get horrible leaks and hangs.
>>>>>> Almost every module doing stream processing have this flow. Obvious or
>>>>>> not.
>>>>>>
>>>>>> That all is sad. We need another, simpler API. Although I believe
>>>>>> incompatible changes should be made
>>>>>> to node core that is not what I am calling about (at least not at the
>>>>>> first place).
>>>>>> But we definitely should stop to expose node streams in userland modules,
>>>>>> stop to extend "stream base classes", just stop to use it in userland.
>>>>>>
>>>>>> Now the constructive part. Tim Caswell proposed recently simple-stream
>>>>>> <https://github.com/creationix/js-git/blob/master/specs/simple-stream.md>
>>>>>> and build many things on top of it.
>>>>>>
>>>>>> Let's just peek this API as a standard and start using it.
>>>>>> Here is readable-to-simple-stream
>>>>>> <https://github.com/eldargab/stream-simple> converter which can be used
>>>>>> for dealing with node core.
>>>>>>
>>>>>> It also contains slightly more detailed version of original spec which
>>>>>> could be discussed.
>>>>>>
>>>>>> That's it.
>>>>>>
>>>>>>
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