it makes sense, that the Readable implementation gets not error
notification. Why should it. It's in the domain of the code, which does
r.pipe(w) to handle the errored state, the readable stream itself can't
know what is the right error reaction.
Am Dienstag, 3. Dezember 2013 14:32:59 UTC+1 schrieb Gagle:
>
> I have a writable stream piped into a readable stream. The writable stream
> at some point fails and emits an error. Me, as a readable stream
> implementor, how am I supposed to handle this situation? Do I receive any
> event from the writable stream?
>
> I have this example that shows what I'm trying to explain.
>
> --------------------------------------
>
> var fs = require ("fs");
>
> var rs = fs.createReadStream ("in", { highWaterMark: 1 })
> var ws = fs.createWriteStream ("out");
>
> var i = 5;
> var write = ws._write;
> ws._write = function (){
> if (!--i) this.emit ("error", new Error ());
> else write.apply (this, arguments)
> }
>
> rs.on ("error", function (){
> console.log("rs error")
> })
>
> rs.on ("end", function (){
> console.log("rs end")
> })
>
> rs.on ("close", function (){
> console.log("rs close")
> })
>
> ws.on ("error", function (error){
> console.log(error)
> })
>
> ws.on ("finish", function (error){
> console.log("ws finish")
> })
>
> ws.on ("open", function (error){
> console.log("ws open")
> })
>
> ws.on ("pipe", function (error){
> console.log("ws pipe")
> })
>
> ws.on ("unpipe", function (error){
> console.log("ws unpipe")
> })
>
> rs.pipe (ws);
>
> --------------------------------------
>
> File "in" has the content "1234567890".
> File "out" ends with the content "1234".
>
> The console output is:
>
> ws pipe
> ws open
> ws unpipe
> [Error]
>
> So, what I don't understand is what is occurring under the hood. I've been
> following the source code and what happens is:
>
> - When rs calls to pipe(), an "error" handler (Line
> 545<https://github.com/joyent/node/blob/master/lib/_stream_readable.js#L545>)
> and an "unpipe" handler (Line
> 489<https://github.com/joyent/node/blob/master/lib/_stream_readable.js#L489>)
> are attached to the ws.
> - When ws emits an error, the previous error handler is executed and it
> calls to unpipe() (Line
> 576<https://github.com/joyent/node/blob/master/lib/_stream_readable.js#L576>
> ).
> - Then the ws is unpiped from the rs, and emits an "unpipe" event (Line
> 628<https://github.com/joyent/node/blob/master/lib/_stream_readable.js#L628>).
>
> This event calls the previous "unpipe" handler.
> - When the "unpipe" handler is executed it calls to cleanup() (Line
> 509<https://github.com/joyent/node/blob/master/lib/_stream_readable.js#L509>).
>
> It basically removes some attached listeners.
>
> So... as you can see the readable stream never emits any event, just like
> the result of the previous example (none of the ws listeners are executed).
>
> I don't understand this, the readable stream magically stops emitting data
> just because the destination stream is unpiped, but I don't see in the code
> where the Readable stream notifies its implementor
> (ReadStream<https://github.com/joyent/node/blob/master/lib/fs.js#L1415>)
> to close the underlying resource and stop pushing more data into it.
>
> My readable stream implementation gets the data from internet. If the
> writable stream fails I need to close the socket. Right now I simply have
> an abort() function that is called when the writable stream fails:
>
> var rs = getMyReadStream ();
> var ws = fs.createWriteStream ("out");
>
> ws.on ("error", function (){
> rs.abort ();
> })
>
> rs.pipe (ws);
>
> I want to remove the call to abort(), it should be called implicitly from
> inside the readable stream. Maybe should I listen to an "unpipe" event?
> (the ReadStream
> <https://github.com/joyent/node/blob/master/lib/fs.js#L1415>doesn't do
> this)
>
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