stream: add comments to pipeline implementation

ronag · MylesBorins · commit 2585b814b0da · 2020-03-09T19:01:18.000-04:00
Fixes: #32039 PR-URL: #32042 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/lib/internal/streams/pipeline.js b/lib/internal/streams/pipeline.js
@@ -219,6 +219,11 @@ function pipeline(...streams) {
           PassThrough = require('_stream_passthrough');
         }
 
+        // If the last argument to pipeline is not a stream
+        // we must create a proxy stream so that pipeline(...)
+        // always returns a stream which can be further
+        // composed through `.pipe(stream)`.
+
         const pt = new PassThrough();
         if (isPromise(ret)) {
           ret
@@ -253,6 +258,9 @@ function pipeline(...streams) {
     }
   }
 
+  // TODO(ronag): Consider returning a Duplex proxy if the first argument
+  // is a writable. Would improve composability.
+  // See, https://github.com/nodejs/node/issues/32020
   return ret;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -219,6 +219,11 @@ function pipeline(...streams) {`
`219`	`219`	`PassThrough = require('_stream_p 8000 assthrough');`
`220`	`220`	`}`
`221`	`221`
	`222`	`+ // If the last argument to pipeline is not a stream`
	`223`	`+ // we must create a proxy stream so that pipeline(...)`
	`224`	`+ // always returns a stream which can be further`
	`225`	+ // composed through `.pipe(stream)`.
	`226`	`+`
`222`	`227`	`const pt = new PassThrough();`
`223`	`228`	`if (isPromise(ret)) {`
`224`	`229`	`ret`
`@@ -253,6 +258,9 @@ function pipeline(...streams) {`
`253`	`258`	`}`
`254`	`259`	`}`
`255`	`260`
	`261`	`+ // TODO(ronag): Consider returning a Duplex proxy if the first argument`
	`262`	`+ // is a writable. Would improve composability.`
	`263`	`+ // See, https://github.com/nodejs/node/issues/32020`
`256`	`264`	`return ret;`
`257`	`265`	`}`
`258`	`266`