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SessionManager: Use .setSub() and parallel queries to avoid races

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This also simplfies the code.
This commit is contained in:
Richard Hansen 2021-11-12 21:26:01 -05:00
parent 3070cee9ca
commit 9d63700da0
1 changed files with 17 additions and 51 deletions
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68
src/node/db/SessionManager.js
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@ -134,41 +134,14 @@ exports.createSession = async (groupID, authorID, validUntil) => {
// set the session into the database
await db.set(`session:${sessionID}`, {groupID, authorID, validUntil});
// get the entry
let group2sessions = await db.get(`group2sessions:${groupID}`);
/*
* In some cases, the db layer could return "undefined" as well as "null".
* Thus, it is not possible to perform strict null checks on group2sessions.
* In a previous version of this code, a strict check broke session
* management.
*
* See: https://github.com/ether/etherpad-lite/issues/3567#issuecomment-468613960
*/
if (!group2sessions || !group2sessions.sessionIDs) {
// the entry doesn't exist so far, let's create it
group2sessions = {sessionIDs: {}};
}
// add the entry for this session
group2sessions.sessionIDs[sessionID] = 1;
// save the new element back
await db.set(`group2sessions:${groupID}`, group2sessions);
// get the author2sessions entry
let author2sessions = await db.get(`author2sessions:${authorID}`);
if (author2sessions == null || author2sessions.sessionIDs == null) {
// the entry doesn't exist so far, let's create it
author2sessions = {sessionIDs: {}};
}
// add the entry for this session
author2sessions.sessionIDs[sessionID] = 1;
// save the new element back
await db.set(`author2sessions:${authorID}`, author2sessions);
// Add the session ID to the group2sessions and author2sessions records after creating the session
// so that the state is consistent.
await Promise.all([
// UeberDB's setSub() method atomically reads the record, updates the appropriate (sub)object
// property, and writes the result.
db.setSub(`group2sessions:${groupID}`, ['sessionIDs', sessionID], 1),
db.setSub(`author2sessions:${authorID}`, ['sessionIDs', sessionID], 1),
]);
return {sessionID};
};
@ -200,23 +173,16 @@ exports.deleteSession = async (sessionID) => {
const groupID = session.groupID;
const authorID = session.authorID;
// get the group2sessions and author2sessions entries
const group2sessions = await db.get(`group2sessions:${groupID}`);
const author2sessions = await db.get(`author2sessions:${authorID}`);
await Promise.all([
// UeberDB's setSub() method atomically reads the record, updates the appropriate (sub)object
// property, and writes the result. Setting a property to `undefined` deletes that property
// (JSON.stringify() ignores such properties).
db.setSub(`group2sessions:${groupID}`, ['sessionIDs', sessionID], undefined),
db.setSub(`author2sessions:${authorID}`, ['sessionIDs', sessionID], undefined),
]);
// remove session from group2sessions
if (group2sessions != null) { // Maybe the group was already deleted
delete group2sessions.sessionIDs[sessionID];
await db.set(`group2sessions:${groupID}`, group2sessions);
}
// remove session from author2sessions
if (author2sessions != null) { // Maybe the author was already deleted
delete author2sessions.sessionIDs[sessionID];
await db.set(`author2sessions:${authorID}`, author2sessions);
}
// remove the session
// Delete the session record after updating group2sessions and author2sessions so that the state
// is consistent.
await db.remove(`session:${sessionID}`);
};