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A few updates for editable metadata

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* add and update many comments
* correctly handle metadata for young channels and range requests
* add a simple implementation of 'writeMetadata'
This commit is contained in:
ansuz 2019-08-14 14:37:18 +02:00
parent f5c318f155
commit 1c89e8d6ac
2 changed files with 58 additions and 37 deletions
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88
historyKeeper.js
View file

@ -91,6 +91,8 @@ module.exports.create = function (cfg) {
* offsetByHash:
* a map containing message offsets by their hash
* this is for every message in history, so it could be very large...
* XXX OFFSET
* except we remove offsets from the map if they occur before the oldest relevant checkpoint
* size: in bytes
* metadata:
* validationKey
@ -248,6 +250,7 @@ module.exports.create = function (cfg) {
* the fix is to use callbacks and implement queueing for writes
* to guarantee that offset computation is always atomic with writes
TODO rename maybeMsgHash to optionalMsgHash
*/
const storeMessage = function (ctx, channel, msg, isCp, maybeMsgHash) {
const msgBin = new Buffer(msg + '\n', 'utf8');
@ -272,6 +275,7 @@ module.exports.create = function (cfg) {
if (isCp) {
index.cpIndex = sliceCpIndex(index.cpIndex, index.line || 0);
for (let k in index.offsetByHash) {
// XXX OFFSET
if (index.offsetByHash[k] < index.cpIndex[0]) {
delete index.offsetByHash[k];
}
@ -325,6 +329,7 @@ module.exports.create = function (cfg) {
let signedMsg = (isCp) ? msgStruct[4].replace(CHECKPOINT_PATTERN, '') : msgStruct[4];
signedMsg = Nacl.util.decodeBase64(signedMsg);
// FIXME PERFORMANCE: cache the decoded key instead of decoding it every time
// CPU/Memory tradeoff
const validateKey = Nacl.util.decodeBase64(metadata_cache[channel.id].validateKey);
const validated = Nacl.sign.open(signedMsg, validateKey);
if (!validated) {
@ -337,6 +342,7 @@ module.exports.create = function (cfg) {
// is a potential source of bugs if one editor has high latency and
// pushes a duplicate of an earlier checkpoint than the latest which
// has been pushed by editors with low latency
// FIXME
if (Array.isArray(id) && id[2]) {
// Store new checkpoint hash
channel.lastSavedCp = id[2];
@ -360,14 +366,17 @@ module.exports.create = function (cfg) {
returns a number representing the byte offset from the start of the log
for whatever history you're seeking.
query by providing a 'lastKnownHash', which is really just a string of
the first 64 characters of an encrypted message.
query by providing a 'lastKnownHash',
which is really just a string of the first 64 characters of an encrypted message.
OR by -1 which indicates that we want the full history (byte offset 0)
OR nothing, which indicates that you want whatever messages the historyKeeper deems relevant
(typically the last few checkpoints)
this function embeds a lot of the history keeper's logic:
0. if you passed -1 as the lastKnownHash it means you want the complete history
* I'm not sure why you'd need to call this function if you know it will return 0 in this case...
* ansuz
* it has a side-effect of filling the index cache if it's empty
1. if you provided a lastKnownHash and that message does not exist in the history:
* either the client has made a mistake or the history they knew about no longer exists
* call back with EINVAL
@ -378,7 +387,7 @@ module.exports.create = function (cfg) {
* return the offset of the earliest checkpoint which 'sliceCpIndex' considers relevant
3. if you did provide a lastKnownHash
* read through the log until you find the hash that you're looking for
* call back with either the bytee offset of the message that you found OR
* call back with either the byte offset of the message that you found OR
* -1 if you didn't find it
*/
@ -390,9 +399,20 @@ module.exports.create = function (cfg) {
getIndex(ctx, channelName, waitFor((err, index) => {
if (err) { waitFor.abort(); return void cb(err); }
// check if the "hash" the client is requesting exists in the index
const lkh = index.offsetByHash[lastKnownHash];
// we evict old hashes from the index as new checkpoints are discovered.
// if someone connects and asks for a hash that is no longer relevant,
// we tell them it's an invalid request. This is because of the semantics of "GET_HISTORY"
// which is only ever used when connecting or reconnecting in typical uses of history...
// this assumption should hold for uses by chainpad, but perhaps not for other uses cases.
// EXCEPT: other cases don't use checkpoints!
// clients that are told that their request is invalid should just make another request
// without specifying the hash, and just trust the server to give them the relevant data.
// QUESTION: does this mean mailboxes are causing the server to store too much stuff in memory?
if (lastKnownHash && typeof(lkh) !== "number") {
waitFor.abort();
// XXX this smells bad
return void cb(new Error('EINVAL'));
}
@ -420,6 +440,8 @@ module.exports.create = function (cfg) {
// returning falls through to the next block and therefore returns -1
if (offset !== -1) { return; }
// do a lookup from the index
// XXX maybe we don't need this anymore?
// otherwise we have a non-negative offset and we can start to read from there
store.readMessagesBin(channelName, 0, (msgObj, readMore, abort) => {
// tryParse return a parsed message or undefined
@ -444,6 +466,9 @@ module.exports.create = function (cfg) {
* streams through the rest of the messages, safely parsing them and returning the parsed content to the handler
* calls back when it has reached the end of the log
Used by:
* GET_HISTORY
*/
const getHistoryAsync = (ctx, channelName, lastKnownHash, beforeHash, handler, cb) => {
let offset = -1;
@ -472,6 +497,9 @@ module.exports.create = function (cfg) {
* stores all messages in history as they are read
* can therefore be very expensive for memory
* should probably be converted to a streaming interface
Used by:
* GET_HISTORY_RANGE
*/
const getOlderHistory = function (channelName, oldestKnownHash, cb) {
var messageBuffer = [];
@ -482,10 +510,11 @@ module.exports.create = function (cfg) {
let parsed = tryParse(msgStr);
if (typeof parsed === "undefined") { return; }
if (parsed.validateKey) {
metadata_cache[channelName] = parsed;
return;
}
// identify classic metadata messages by their inclusion of a channel.
// and don't send metadata, since:
// 1. the user won't be interested in it
// 2. this metadata is potentially incomplete/incorrect
if (parsed.channel) { return; }
var content = parsed[4];
if (typeof(content) !== 'string') { return; }
@ -547,6 +576,10 @@ module.exports.create = function (cfg) {
// Check if the selected channel is expired
// If it is, remove it from memory and broadcast a message to its members
const onChannelMetadataChanged = function (ctx, channel) {
// XXX
};
/* checkExpired
* synchronously returns true or undefined to indicate whether the channel is expired
* according to its metadata
@ -616,7 +649,9 @@ module.exports.create = function (cfg) {
var lastKnownHash = parsed[3];
var owners;
var expire;
if (parsed[2] && typeof parsed[2] === "object") { // FIXME METADATA RECEIVE
// XXX we can be a bit more strict in our validation here
// maybe we should check that it's an object and not an array?
if (parsed[2] && typeof parsed[2] === "object") {
validateKey = parsed[2].validateKey;
lastKnownHash = parsed[2].lastKnownHash;
owners = parsed[2].owners;
@ -663,39 +698,24 @@ module.exports.create = function (cfg) {
// And then check if the channel is expired. If it is, send the error and abort
// FIXME this is hard to read because 'checkExpired' has side effects
if (checkExpired(ctx, channelName)) { return void waitFor.abort(); }
// Send the metadata to the user
if (!lastKnownHash && index.cpIndex.length > 1) {
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify(index.metadata)], w);
return;
}
w();
// always send metadata with GET_HISTORY requests
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify(index.metadata)], w);
}));
}).nThen(() => {
let msgCount = 0;
let expired = false;
// XXX a lot of this logic is currently wrong
// we should have already sent the most up to data metadata (if it exists)
// we should have also already checked if the channel has expired
// we just need to avoid sending metadata a second time
// we should have already sent the most up-to-date metadata (if it exists)
// TODO compute lastKnownHash in a manner such that it will always skip past the metadata line?
getHistoryAsync(ctx, channelName, lastKnownHash, false, (msg, readMore) => {
if (!msg) { return; }
if (msg.validateKey) {
// If it is a young channel, this is the part where we get the metadata
// Check if the channel is expired and abort if it is.
if (!metadata_cache[channelName]) { metadata_cache[channelName] = msg; }
expired = checkExpired(ctx, channelName);
}
if (expired) { return void readMore(); }
msgCount++;
// check for the channel because it's the one thing that should
// always exist in "classic metadata"
if (msg.channel && metadata_cache[channelName]) { return readMore(); }
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify(msg)], readMore);
}, (err) => {
// If the pad is expired, stop here, we've already sent the error message
if (expired) { return; }
if (err && err.code !== 'ENOENT') {
if (err.message !== 'EINVAL') { Log.error("HK_GET_HISTORY", err); }
const parsedMsg = {error:err.message, channel: channelName};
@ -726,10 +746,10 @@ module.exports.create = function (cfg) {
store.writeMetadata(channelName, JSON.stringify(metadata), function (err) {
if (err) {
// XXX handle errors
return void console.error(err);
}
});
//storeMessage(ctx, chan, JSON.stringify(metadata), false, undefined); // FIXME METADATA WRITE
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify(metadata)]); // FIXME METADATA SEND
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify(metadata)]);
}
// End of history message:
@ -820,15 +840,13 @@ module.exports.create = function (cfg) {
}
// FIXME METADATA CHANGE
/*
if (msg[3] === 'SET_METADATA') { // or whatever we call the RPC????
// make sure we update our cache of metadata
// or at least invalidate it and force other mechanisms to recompute its state
// 'output' could be the new state as computed by rpc
onChannelMetadataChanged(ctx, msg[4]);
}
*/
sendMsg(ctx, user, [0, HISTORY_KEEPER_ID, 'MSG', user.id, JSON.stringify([parsed[0]].concat(output))]);
});
} catch (e) {

7
storage/file.js
View file

@ -221,8 +221,10 @@ How to proceed
};
var writeMetadata = function (env, channelId, data, cb) {
// XXX
cb("NOT_IMPLEMENTED");
var path = mkMetadataPath(env, channelId);
// XXX appendFile isn't great
// but this is a simple way to get things working
Fs.appendFile(path, data + '\n', cb);
};
const NEWLINE_CHR = ('\n').charCodeAt(0);
@ -268,6 +270,7 @@ const mkOffsetCounter = () => {
});
};
// XXX write some docs for this magic
const readMessagesBin = (env, id, start, msgHandler, cb) => {
const stream = Fs.createReadStream(mkPath(env, id), { start: start });
let keepReading = true;