Initial JavaScript (node) implementation
This commit is contained in:
Tony Garnock-Jones
parent
97f6c1291b
commit
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node_modules/
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package-lock.json
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{
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"name": "preserves",
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"version": "0.0.0",
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"description": "Data serialization format",
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"homepage": "https://gitlab.com/tonyg/preserves",
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"license": "MIT",
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"publishConfig": {
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"access": "public"
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},
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"repository": "gitlab:tonyg/preserves",
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"scripts": {
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"test": "mocha",
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"cover": "nyc --reporter=html mocha"
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},
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"main": "src/index.js",
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"author": "Tony Garnock-Jones <tonyg@leastfixedpoint.com>",
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"devDependencies": {
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"chai": "^4.2.0",
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"chai-immutable": "^2.0.0-rc.2",
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"mocha": "^5.2.0",
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"nyc": "^13.1.0"
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},
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"dependencies": {
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"immutable": "^3.8.2"
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}
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}
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"use strict";
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const Immutable = require('immutable');
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const { List, Map, Set, fromJS } = Immutable;
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const PreserveOn = Symbol('PreserveOn');
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class DecodeError extends Error {}
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class EncodeError extends Error {
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constructor(message, irritant) {
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super(message);
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this.irritant = irritant;
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}
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}
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class Decoder {
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constructor(packet, options) {
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options = options || {};
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this.packet = packet;
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this.index = 0;
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this.shortForms = options.shortForms || {};
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}
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peekbyte() {
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if (this.index >= this.packet.length) throw new DecodeError("Short packet");
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// ^ NOTE: greater-than-or-equal-to, not greater-than.
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return this.packet[this.index];
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}
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advance(count) {
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const start = this.index;
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this.index += (count === void 0 ? 1 : count);
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return start;
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}
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nextbyte() {
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const val = this.peekbyte();
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this.advance();
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return val;
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}
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wirelength(arg) {
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if (arg < 15) return arg;
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return this.varint();
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}
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varint() {
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// TODO: Bignums :-/
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const v = this.nextbyte();
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if (v < 128) return v;
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return this.varint() * 128 + (v - 128);
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}
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nextbytes(n) {
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const start = this.advance(n);
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if (this.index > this.packet.length) throw new DecodeError("Short packet");
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// ^ NOTE: greater-than, not greater-than-or-equal-to.
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return this.packet.slice(start, this.index); // pretend it is immutable, please
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}
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nextvalues(n) {
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const result = [];
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for (let i = 0; i < n; i++) result.push(this.next());
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return result;
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}
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peekop() {
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const b = this.peekbyte();
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const major = b >> 6;
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const minor = (b >> 4) & 3;
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const arg = b & 15;
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return [major, minor, arg];
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}
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nextop() {
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const op = this.peekop();
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this.advance();
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return op;
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}
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peekend(arg) {
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const [a,i,r] = this.peekop();
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return (a === 0) && (i === 3) && (r === arg);
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}
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binarystream(arg, minor) {
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const result = [];
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while (!this.peekend(arg)) {
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chunk = this.next();
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if (!Buffer.isBuffer(chunk)) throw new DecodeError("Unexpected non-binary chunk");
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result.push(chunk);
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}
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return Buffer.concat(result); // pretend it is immutable, please
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}
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valuestream(arg, minor, decoder) {
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const result = [];
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while (!this.peekend(arg)) result.push(this.next());
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return decoder(minor, result);
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}
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decodeint(bs) {
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// TODO: Bignums :-/
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if (bs.length === 0) return 0;
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let acc = bs[0];
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if (acc & 0x80) acc -= 256;
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for (let i = 1; i < bs.length; i++) acc = (acc << 8) | b[i];
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return acc;
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}
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decodebinary(minor, bs) {
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switch (minor) {
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case 0: return this.decodeint(bs);
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case 1: return bs.toString('utf-8');
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case 2: return bs; // again, pretend it is immutable, please
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case 3: return Symbol.for(bs.toString('utf-8'));
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}
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}
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decoderecord(minor, vs) {
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if (minor === 3) {
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if (vs.length === 0) throw new DecodeError("Too few elements in encoded record");
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return new Record(vs[0], vs.slice(1));
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} else {
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const label = shortForms[minor];
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if (label === void 0) throw new DecodeError("Use of unconfigured short form " + minor);
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return new Record(label, vs);
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}
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}
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decodecollection(minor, vs) {
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switch (minor) {
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case 0: return List(vs);
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case 1: return Set(vs);
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case 2: return mapFromArray(vs);
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case 3: throw new DecodeError("Invalid collection type");
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}
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}
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next() {
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const [major, minor, arg] = this.nextop();
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switch (major) {
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case 0:
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switch (minor) {
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case 0:
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switch (arg) {
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case 0: return false;
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case 1: return true;
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case 2: return Float(this.nextbytes(4).readFloatBE());
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case 3: return this.nextbytes(8).readDoubleBE();
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}
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case 1:
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return (arg > 12) ? arg - 16 : arg;
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case 2: {
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const t = arg >> 2;
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const n = arg & 3;
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switch (t) {
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case 0: throw new DecodeError("Invalid format C start byte");
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case 1: return this.binarystream(arg, n);
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case 2: return this.valuestream(arg, n, this.decoderecord.bind(this));
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case 3: return this.valuestream(arg, n, this.decodecollection.bind(this));
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}
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}
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case 3:
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throw new DecodeError("Invalid format C end byte");
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}
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case 1: return this.decodebinary(minor, this.nextbytes(this.wirelength(arg)));
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case 2: return this.decoderecord(minor, this.nextvalues(this.wirelength(arg)));
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case 3: return this.decodecollection(minor, this.nextvalues(this.wirelength(arg)));
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}
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}
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}
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class Encoder {
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constructor(options) {
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options = options || {}
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this.chunks = [];
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this.buffer = Buffer.alloc(256);
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this.index = 0;
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this.shortForms = options.shortForms || {};
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}
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contents() {
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this.rotatebuffer(4096);
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return Buffer.concat(this.chunks);
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}
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rotatebuffer(size) {
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this.chunks.push(this.buffer.slice(0, this.index));
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this.buffer = Buffer.alloc(size);
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this.index = 0;
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}
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makeroom(amount) {
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if (this.index + amount > this.buffer.length) {
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this.rotatebuffer(amount + 4096);
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}
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}
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emitbyte(b) {
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this.makeroom(1);
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this.buffer[this.index++] = b;
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}
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emitbytes(bs) {
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this.makeroom(bs.length);
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this.buffer.fill(bs, this.index, this.index + bs.length);
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this.index += bs.length;
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}
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varint(v) {
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if (v < 128) {
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this.emitbyte(v);
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} else {
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this.emitbyte((v % 128) + 128);
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this.varint(Math.floor(v / 128));
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}
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}
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leadbyte(major, minor, arg) {
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this.emitbyte(((major & 3) << 6) | ((minor & 3) << 4) | (arg & 15));
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}
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header(major, minor, wirelength) {
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if (wirelength < 15) {
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this.leadbyte(major, minor, wirelength);
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} else {
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this.leadbyte(major, minor, 15);
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this.varint(wirelength);
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}
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}
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encodeint(v) {
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// TODO: Bignums :-/
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const plain_bitcount = Math.floor(Math.log2(Math.abs(v))) + 1;
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const signed_bitcount = plain_bitcount + 1;
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const bytecount = (signed_bitcount + 7) >> 3;
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this.header(1, 0, bytecount);
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const enc = (n, x) => {
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if (n > 0) {
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enc(n - 1, x >> 8);
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this.emitbyte(x & 255);
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}
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};
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enc(bytecount, v);
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}
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encodecollection(minor, items) {
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this.header(3, minor, items.size);
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for (const item of items) { this.push(item); }
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}
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encodestream(t, n, items) {
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const tn = ((t & 3) << 2) | (n & 3);
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this.header(0, 2, tn);
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for (const item of items) { this.push(item); }
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this.header(0, 3, tn);
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}
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push(v) {
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if (typeof v === 'object' && v !== null && typeof v[PreserveOn] === 'function') {
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v[PreserveOn](this);
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}
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if (v === false) return this.leadbyte(0, 0, 0);
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if (v === true) return this.leadbyte(0, 0, 1);
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if (typeof v === 'number') {
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if (v >= -3 && v <= 12) return this.leadbyte(0, 1, v >= 0 ? v : v + 16);
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return this.encodeint(v);
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}
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if (typeof v === 'string') {
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const bs = Buffer.from(v);
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this.header(1, 1, bs.length);
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return this.emitbytes(bs);
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}
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if (typeof v === 'symbol') {
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const key = Symbol.keyFor(v);
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if (key === void 0) throw new EncodeError("Cannot preserve non-global Symbol", v);
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const bs = Buffer.from(key);
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this.header(1, 3, bs.length);
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return this.emitbytes(bs);
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}
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if (Buffer.isBuffer(v)) {
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this.header(1, 2, v.length);
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return this.emitbytes(v);
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}
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if (List.isList(v)) return this.encodecollection(0, v);
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if (Set.isSet(v)) return this.encodecollection(1, v);
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if (Map.isMap(v)) {
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const kvs = [];
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v.forEach((val, key) => { kvs.push(key); kvs.push(val); });
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return this.encodecollection(2, kvs);
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}
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if (typeof v === 'object' && v !== null && typeof v[Symbol.iterator] === 'function') {
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return this.encodestream(3, 0, v);
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}
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throw new EncodeError("Cannot encode", v);
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}
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}
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class Record {
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constructor(label, fields) {
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this.label = label;
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this.fields = fromJS(fields);
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}
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[PreserveOn](encoder) {
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if (Immutable.is(encoder.shortForms[0], this.label)) {
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encoder.header(2, 0, this.fields.size);
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} else if (Immutable.is(encoder.shortForms[1], this.label)) {
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encoder.header(2, 1, this.fields.size);
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} else if (Immutable.is(encoder.shortForms[2], this.label)) {
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encoder.header(2, 2, this.fields.size);
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} else {
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encoder.header(2, 3, this.fields.size + 1);
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encoder.push(this.label);
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}
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for (const field in this.fields) { encoder.push(field); }
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}
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}
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class Float {
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constructor(value) {
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this.value = value;
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}
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[PreserveOn](encoder) {
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encoder.leadbyte(0, 0, 2);
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encoder.makeroom(4);
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encoder.buffer.writeFloatBE(this.value, encoder.index);
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encoder.index += 4;
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}
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}
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Object.assign(module.exports, {
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PreserveOn,
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DecodeError,
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EncodeError,
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Decoder,
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Encoder,
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Record,
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Float,
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});
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