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Diffstat (limited to 'common/src/main/webapp/usageguide/appserver/node_modules/mongodb/node_modules/readable-stream/lib/_stream_transform.js')
-rw-r--r-- | common/src/main/webapp/usageguide/appserver/node_modules/mongodb/node_modules/readable-stream/lib/_stream_transform.js | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/common/src/main/webapp/usageguide/appserver/node_modules/mongodb/node_modules/readable-stream/lib/_stream_transform.js b/common/src/main/webapp/usageguide/appserver/node_modules/mongodb/node_modules/readable-stream/lib/_stream_transform.js new file mode 100644 index 00000000..dbc996ed --- /dev/null +++ b/common/src/main/webapp/usageguide/appserver/node_modules/mongodb/node_modules/readable-stream/lib/_stream_transform.js @@ -0,0 +1,180 @@ +// 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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