stream: _write takes an encoding argument

This vastly reduces the overhead of decodeStrings:false streams,
such as net and http.

1 files changed, 24 insertions, 12 deletions

diff --git a/doc/api/stream.markdown b/doc/api/stream.markdown
index 2b192d6b4a..c419266bc3 100644
--- a/doc/api/stream.markdown
+++ b/doc/api/stream.markdown
@@ -436,8 +436,8 @@ Resumes the incoming `'data'` events after a `pause()`.
 A `Writable` Stream has the following methods, members, and events.
 
 Note that `stream.Writable` is an abstract class designed to be
-extended with an underlying implementation of the `_write(chunk, cb)`
-method. (See below.)
+extended with an underlying implementation of the
+`_write(chunk, encoding, cb)` method. (See below.)
 
 ### new stream.Writable([options])
 
@@ -451,10 +451,16 @@ In classes that extend the Writable class, make sure to call the
 constructor so that the buffering settings can be properly
 initialized.
 
-### writable.\_write(chunk, callback)
+### writable.\_write(chunk, encoding, callback)
 
-* `chunk` {Buffer | Array} The data to be written
-* `callback` {Function} Called with an error, or null when finished
+* `chunk` {Buffer | String} The chunk to be written.  Will always
+  be a buffer unless the `decodeStrings` option was set to `false`.
+* `encoding` {String} If the chunk is a string, then this is the
+  encoding type.  Ignore chunk is a buffer.  Note that chunk will
+  **always** be a buffer unless the `decodeStrings` option is
+  explicitly set to `false`.
+* `callback` {Function} Call this function (optionally with an error
+  argument) when you are done processing the supplied chunk.
 
 All Writable stream implementations must provide a `_write` method to
 send data to the underlying resource.
@@ -467,9 +473,12 @@ Call the callback using the standard `callback(error)` pattern to
 signal that the write completed successfully or with an error.
 
 If the `decodeStrings` flag is set in the constructor options, then
-`chunk` will be an array rather than a Buffer.  This is to support
+`chunk` may be a string rather than a Buffer, and `encoding` will
+indicate the sort of string that it is.  This is to support
 implementations that have an optimized handling for certain string
-data encodings.
+data encodings.  If you do not explicitly set the `decodeStrings`
+option to `false`, then you can safely ignore the `encoding` argument,
+and assume that `chunk` will always be a Buffer.
 
 This method is prefixed with an underscore because it is internal to
 the class that defines it, and should not be called directly by user
@@ -543,13 +552,13 @@ TCP socket connection.
 
 Note that `stream.Duplex` is an abstract class designed to be
 extended with an underlying implementation of the `_read(size)`
-and `_write(chunk, callback)` methods as you would with a Readable or
+and `_write(chunk, encoding, callback)` methods as you would with a Readable or
 Writable stream class.
 
 Since JavaScript doesn't have multiple prototypal inheritance, this
 class prototypally inherits from Readable, and then parasitically from
 Writable.  It is thus up to the user to implement both the lowlevel
-`_read(n)` method as well as the lowlevel `_write(chunk,cb)` method
+`_read(n)` method as well as the lowlevel `_write(chunk, encoding, cb)` method
 on extension duplex classes.
 
 ### new stream.Duplex(options)
@@ -589,9 +598,12 @@ In classes that extend the Transform class, make sure to call the
 constructor so that the buffering settings can be properly
 initialized.
 
-### transform.\_transform(chunk, callback)
+### transform.\_transform(chunk, encoding, callback)
 
-* `chunk` {Buffer} The chunk to be transformed.
+* `chunk` {Buffer | String} The chunk to be transformed.  Will always
+  be a buffer unless the `decodeStrings` option was set to `false`.
+* `encoding` {String} If the chunk is a string, then this is the
+  encoding type.  (Ignore if `decodeStrings` chunk is a buffer.)
 * `callback` {Function} Call this function (optionally with an error
   argument) when you are done processing the supplied chunk.
 
@@ -671,7 +683,7 @@ function SimpleProtocol(options) {
 SimpleProtocol.prototype = Object.create(
   Transform.prototype, { constructor: { value: SimpleProtocol }});
 
-SimpleProtocol.prototype._transform = function(chunk, done) {
+SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
   if (!this._inBody) {
     // check if the chunk has a \n\n
     var split = -1;