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file.js
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file.js
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var fs = require("fs"),
events = require("events");
exports.readStream = function(filename) {
var emitter = new events.EventEmitter(),
read,
readAll = false,
bytesNeeded,
bytesAvailable = 0,
bytesChunk = 0,
chunkHead,
chunkTail;
fs.createReadStream(filename)
.on("data", data)
.on("end", end)
.on("error", error);
function maybeRead() {
if (bytesAvailable >= bytesNeeded) {
var buffer = consume(bytesNeeded);
bytesAvailable -= bytesNeeded;
bytesNeeded = undefined;
read.call(emitter, buffer);
}
}
function maybeEnd() {
if (bytesAvailable < bytesNeeded) {
bytesNeeded = undefined;
emitter.emit("end");
}
}
function consume(bytes) {
if (bytesChunk + bytes <= chunkHead.length) {
return chunkHead.slice(bytesChunk, bytesChunk += bytes);
}
var buffer = new Buffer(bytes),
bytesCopied = chunkHead.length - bytesChunk;
chunkHead.copy(buffer, 0, bytesChunk);
chunkHead = chunkHead.next;
bytesChunk = 0;
while (bytes - bytesCopied > chunkHead.length) {
chunkHead.copy(buffer, bytesCopied);
bytesCopied += chunkHead.length;
chunkHead = chunkHead.next;
}
chunkHead.copy(buffer, bytesCopied, 0, bytesChunk = bytes - bytesCopied);
return buffer;
}
function data(chunk) {
if (chunkTail) chunkTail.next = chunk;
if (!chunkHead) chunkHead = chunk;
chunkTail = chunk;
bytesAvailable += chunk.length;
maybeRead();
}
function error(e) {
emitter.emit("error", e);
}
function end() {
readAll = true;
process.nextTick(maybeEnd);
}
emitter.read = function(bytes, callback) {
bytesNeeded = bytes;
if (readAll && bytesAvailable < bytesNeeded) return void process.nextTick(maybeEnd);
read = callback;
process.nextTick(maybeRead);
};
return emitter;
};