compute indexes in child processes
ansuz
5 years ago
parent
d1b16af160
commit
4522ffa18a
@ -0,0 +1,173 @@
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/* jshint esversion: 6 */
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/* global process */
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const HK = require("./hk-util");
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const Store = require("./storage/file");
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const Util = require("./common-util");
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const nThen = require("nthen");
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const Env = {};
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var ready = false;
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var store;
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const init = function (config, cb) {
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if (!config) {
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return void cb('E_INVALID_CONFIG');
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}
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Store.create(config, function (_store) {
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store = _store;
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cb();
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});
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};
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const tryParse = function (Env, str) {
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try {
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return JSON.parse(str);
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} catch (err) {
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// XXX
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}
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};
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/* computeIndex
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can call back with an error or a computed index which includes:
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* cpIndex:
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* array including any checkpoints pushed within the last 100 messages
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* processed by 'sliceCpIndex(cpIndex, line)'
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* offsetByHash:
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* a map containing message offsets by their hash
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* this is for every message in history, so it could be very large...
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* except we remove offsets from the map if they occur before the oldest relevant checkpoint
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* size: in bytes
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* metadata:
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* validationKey
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* expiration time
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* owners
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* ??? (anything else we might add in the future)
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* line
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* the number of messages in history
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* including the initial metadata line, if it exists
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*/
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const computeIndex = function (channelName, cb) {
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const cpIndex = [];
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let messageBuf = [];
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let i = 0;
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const CB = Util.once(cb);
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const offsetByHash = {};
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let size = 0;
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nThen(function (w) {
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// iterate over all messages in the channel log
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// old channels can contain metadata as the first message of the log
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// skip over metadata as that is handled elsewhere
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// otherwise index important messages in the log
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store.readMessagesBin(channelName, 0, (msgObj, readMore) => {
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let msg;
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// keep an eye out for the metadata line if you haven't already seen it
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// but only check for metadata on the first line
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if (!i && msgObj.buff.indexOf('{') === 0) {
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i++; // always increment the message counter
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msg = tryParse(Env, msgObj.buff.toString('utf8'));
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if (typeof msg === "undefined") { return readMore(); }
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// validate that the current line really is metadata before storing it as such
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// skip this, as you already have metadata...
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if (HK.isMetadataMessage(msg)) { return readMore(); }
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}
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i++;
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if (msgObj.buff.indexOf('cp|') > -1) {
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msg = msg || tryParse(Env, msgObj.buff.toString('utf8'));
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if (typeof msg === "undefined") { return readMore(); }
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// cache the offsets of checkpoints if they can be parsed
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if (msg[2] === 'MSG' && msg[4].indexOf('cp|') === 0) {
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cpIndex.push({
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offset: msgObj.offset,
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line: i
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});
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// we only want to store messages since the latest checkpoint
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// so clear the buffer every time you see a new one
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messageBuf = [];
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}
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}
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// if it's not metadata or a checkpoint then it should be a regular message
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// store it in the buffer
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messageBuf.push(msgObj);
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return readMore();
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}, w((err) => {
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if (err && err.code !== 'ENOENT') {
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w.abort();
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return void CB(err);
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}
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// once indexing is complete you should have a buffer of messages since the latest checkpoint
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// map the 'hash' of each message to its byte offset in the log, to be used for reconnecting clients
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messageBuf.forEach((msgObj) => {
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const msg = tryParse(Env, msgObj.buff.toString('utf8'));
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if (typeof msg === "undefined") { return; }
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if (msg[0] === 0 && msg[2] === 'MSG' && typeof(msg[4]) === 'string') {
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// msgObj.offset is API guaranteed by our storage module
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// it should always be a valid positive integer
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offsetByHash[HK.getHash(msg[4])] = msgObj.offset;
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}
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// There is a trailing \n at the end of the file
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size = msgObj.offset + msgObj.buff.length + 1;
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});
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}));
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}).nThen(function () {
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// return the computed index
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CB(null, {
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// Only keep the checkpoints included in the last 100 messages
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cpIndex: HK.sliceCpIndex(cpIndex, i),
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offsetByHash: offsetByHash,
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size: size,
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//metadata: metadata,
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line: i
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});
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});
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};
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process.on('message', function (data) {
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if (!data || !data.txid) {
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return void process.send({
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error:'E_INVAL'
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});
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}
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const txid = data.txid;
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if (!ready) {
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return void init(data.config, function (err) {
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if (err) {
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return void process.send({
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txid: txid,
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error: err,
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});
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}
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ready = true;
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process.send({txid: txid,});
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});
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}
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const channel = data.args;
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if (!channel) {
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return void process.send({
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error: 'E_NO_CHANNEL',
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});
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}
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// computeIndex
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computeIndex(channel, function (err, index) {
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if (err) {
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return void process.send({
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txid: txid,
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error: err,
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});
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}
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return void process.send({
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txid: txid,
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value: index,
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});
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});
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});
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