--- /dev/null
+// a transform stream is a readable/writable stream where you do
+// something with the data. Sometimes it's called a "filter",
+// but that's not a great name for it, since that implies a thing where
+// some bits pass through, and others are simply ignored. (That would
+// be a valid example of a transform, of course.)
+//
+// While the output is causally related to the input, it's not a
+// necessarily symmetric or synchronous transformation. For example,
+// a zlib stream might take multiple plain-text writes(), and then
+// emit a single compressed chunk some time in the future.
+//
+// Here's how this works:
+//
+// The Transform stream has all the aspects of the readable and writable
+// stream classes. When you write(chunk), that calls _write(chunk,cb)
+// internally, and returns false if there's a lot of pending writes
+// buffered up. When you call read(), that calls _read(n) until
+// there's enough pending readable data buffered up.
+//
+// In a transform stream, the written data is placed in a buffer. When
+// _read(n) is called, it transforms the queued up data, calling the
+// buffered _write cb's as it consumes chunks. If consuming a single
+// written chunk would result in multiple output chunks, then the first
+// outputted bit calls the readcb, and subsequent chunks just go into
+// the read buffer, and will cause it to emit 'readable' if necessary.
+//
+// This way, back-pressure is actually determined by the reading side,
+// since _read has to be called to start processing a new chunk. However,
+// a pathological inflate type of transform can cause excessive buffering
+// here. For example, imagine a stream where every byte of input is
+// interpreted as an integer from 0-255, and then results in that many
+// bytes of output. Writing the 4 bytes {ff,ff,ff,ff} would result in
+// 1kb of data being output. In this case, you could write a very small
+// amount of input, and end up with a very large amount of output. In
+// such a pathological inflating mechanism, there'd be no way to tell
+// the system to stop doing the transform. A single 4MB write could
+// cause the system to run out of memory.
+//
+// However, even in such a pathological case, only a single written chunk
+// would be consumed, and then the rest would wait (un-transformed) until
+// the results of the previous transformed chunk were consumed.
+
+'use strict';
+
+module.exports = Transform;
+
+var Duplex = require('./_stream_duplex');
+
+/*<replacement>*/
+var util = require('core-util-is');
+util.inherits = require('inherits');
+/*</replacement>*/
+
+util.inherits(Transform, Duplex);
+
+function TransformState(stream) {
+ this.afterTransform = function (er, data) {
+ return afterTransform(stream, er, data);
+ };
+
+ this.needTransform = false;
+ this.transforming = false;
+ this.writecb = null;
+ this.writechunk = null;
+ this.writeencoding = null;
+}
+
+function afterTransform(stream, er, data) {
+ var ts = stream._transformState;
+ ts.transforming = false;
+
+ var cb = ts.writecb;
+
+ if (!cb) return stream.emit('error', new Error('no writecb in Transform class'));
+
+ ts.writechunk = null;
+ ts.writecb = null;
+
+ if (data !== null && data !== undefined) stream.push(data);
+
+ cb(er);
+
+ var rs = stream._readableState;
+ rs.reading = false;
+ if (rs.needReadable || rs.length < rs.highWaterMark) {
+ stream._read(rs.highWaterMark);
+ }
+}
+
+function Transform(options) {
+ if (!(this instanceof Transform)) return new Transform(options);
+
+ Duplex.call(this, options);
+
+ this._transformState = new TransformState(this);
+
+ // when the writable side finishes, then flush out anything remaining.
+ var stream = this;
+
+ // start out asking for a readable event once data is transformed.
+ this._readableState.needReadable = true;
+
+ // we have implemented the _read method, and done the other things
+ // that Readable wants before the first _read call, so unset the
+ // sync guard flag.
+ this._readableState.sync = false;
+
+ if (options) {
+ if (typeof options.transform === 'function') this._transform = options.transform;
+
+ if (typeof options.flush === 'function') this._flush = options.flush;
+ }
+
+ this.once('prefinish', function () {
+ if (typeof this._flush === 'function') this._flush(function (er) {
+ done(stream, er);
+ });else done(stream);
+ });
+}
+
+Transform.prototype.push = function (chunk, encoding) {
+ this._transformState.needTransform = false;
+ return Duplex.prototype.push.call(this, chunk, encoding);
+};
+
+// This is the part where you do stuff!
+// override this function in implementation classes.
+// 'chunk' is an input chunk.
+//
+// Call `push(newChunk)` to pass along transformed output
+// to the readable side. You may call 'push' zero or more times.
+//
+// Call `cb(err)` when you are done with this chunk. If you pass
+// an error, then that'll put the hurt on the whole operation. If you
+// never call cb(), then you'll never get another chunk.
+Transform.prototype._transform = function (chunk, encoding, cb) {
+ throw new Error('not implemented');
+};
+
+Transform.prototype._write = function (chunk, encoding, cb) {
+ var ts = this._transformState;
+ ts.writecb = cb;
+ ts.writechunk = chunk;
+ ts.writeencoding = encoding;
+ if (!ts.transforming) {
+ var rs = this._readableState;
+ if (ts.needTransform || rs.needReadable || rs.length < rs.highWaterMark) this._read(rs.highWaterMark);
+ }
+};
+
+// Doesn't matter what the args are here.
+// _transform does all the work.
+// That we got here means that the readable side wants more data.
+Transform.prototype._read = function (n) {
+ var ts = this._transformState;
+
+ if (ts.writechunk !== null && ts.writecb && !ts.transforming) {
+ ts.transforming = true;
+ this._transform(ts.writechunk, ts.writeencoding, ts.afterTransform);
+ } else {
+ // mark that we need a transform, so that any data that comes in
+ // will get processed, now that we've asked for it.
+ ts.needTransform = true;
+ }
+};
+
+function done(stream, er) {
+ if (er) return stream.emit('error', er);
+
+ // if there's nothing in the write buffer, then that means
+ // that nothing more will ever be provided
+ var ws = stream._writableState;
+ var ts = stream._transformState;
+
+ if (ws.length) throw new Error('calling transform done when ws.length != 0');
+
+ if (ts.transforming) throw new Error('calling transform done when still transforming');
+
+ return stream.push(null);
+}
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projects / yaffs-website / blobdiff