130 lines
3.6 KiB
JavaScript
130 lines
3.6 KiB
JavaScript
//binary data writer tuned for creating
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//postgres message packets as effeciently as possible by reusing the
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//same buffer to avoid memcpy and limit memory allocations
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var Writer = module.exports = function (size) {
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this.size = size || 1024;
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this.buffer = Buffer.alloc(this.size + 5);
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this.offset = 5;
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this.headerPosition = 0;
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};
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//resizes internal buffer if not enough size left
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Writer.prototype._ensure = function (size) {
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var remaining = this.buffer.length - this.offset;
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if (remaining < size) {
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var oldBuffer = this.buffer;
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// exponential growth factor of around ~ 1.5
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// https://stackoverflow.com/questions/2269063/buffer-growth-strategy
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var newSize = oldBuffer.length + (oldBuffer.length >> 1) + size;
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this.buffer = Buffer.alloc(newSize);
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oldBuffer.copy(this.buffer);
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}
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};
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Writer.prototype.addInt32 = function (num) {
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this._ensure(4);
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this.buffer[this.offset++] = (num >>> 24 & 0xFF);
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this.buffer[this.offset++] = (num >>> 16 & 0xFF);
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this.buffer[this.offset++] = (num >>> 8 & 0xFF);
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this.buffer[this.offset++] = (num >>> 0 & 0xFF);
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return this;
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};
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Writer.prototype.addInt16 = function (num) {
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this._ensure(2);
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this.buffer[this.offset++] = (num >>> 8 & 0xFF);
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this.buffer[this.offset++] = (num >>> 0 & 0xFF);
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return this;
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};
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//for versions of node requiring 'length' as 3rd argument to buffer.write
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var writeString = function (buffer, string, offset, len) {
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buffer.write(string, offset, len);
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};
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//overwrite function for older versions of node
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if (Buffer.prototype.write.length === 3) {
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writeString = function (buffer, string, offset, len) {
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buffer.write(string, offset);
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};
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}
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Writer.prototype.addCString = function (string) {
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//just write a 0 for empty or null strings
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if (!string) {
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this._ensure(1);
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} else {
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var len = Buffer.byteLength(string);
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this._ensure(len + 1); //+1 for null terminator
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writeString(this.buffer, string, this.offset, len);
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this.offset += len;
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}
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this.buffer[this.offset++] = 0; // null terminator
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return this;
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};
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Writer.prototype.addChar = function (c) {
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this._ensure(1);
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writeString(this.buffer, c, this.offset, 1);
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this.offset++;
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return this;
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};
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Writer.prototype.addString = function (string) {
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string = string || "";
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var len = Buffer.byteLength(string);
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this._ensure(len);
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this.buffer.write(string, this.offset);
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this.offset += len;
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return this;
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};
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Writer.prototype.getByteLength = function () {
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return this.offset - 5;
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};
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Writer.prototype.add = function (otherBuffer) {
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this._ensure(otherBuffer.length);
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otherBuffer.copy(this.buffer, this.offset);
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this.offset += otherBuffer.length;
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return this;
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};
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Writer.prototype.clear = function () {
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this.offset = 5;
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this.headerPosition = 0;
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this.lastEnd = 0;
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};
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//appends a header block to all the written data since the last
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//subsequent header or to the beginning if there is only one data block
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Writer.prototype.addHeader = function (code, last) {
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var origOffset = this.offset;
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this.offset = this.headerPosition;
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this.buffer[this.offset++] = code;
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//length is everything in this packet minus the code
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this.addInt32(origOffset - (this.headerPosition + 1));
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//set next header position
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this.headerPosition = origOffset;
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//make space for next header
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this.offset = origOffset;
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if (!last) {
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this._ensure(5);
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this.offset += 5;
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}
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};
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Writer.prototype.join = function (code) {
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if (code) {
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this.addHeader(code, true);
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}
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return this.buffer.slice(code ? 0 : 5, this.offset);
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};
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Writer.prototype.flush = function (code) {
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var result = this.join(code);
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this.clear();
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return result;
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};
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