how to appropriate close(interrupt) stream result before end event ?

[jimmyolo]

as title, how to correctly interrupt stream results?
In mysqljs, I call .end(). that will trigger end event, then close stream
but in mysql2, TypeError: query.end is not a function
here is my code sample

// getConnection from pool
const query = conn.query('SELECT * FROM `table`')
    .on('result', (aRow)=>{
        // I handle one row and response to client, but if data is error or client disconnect, I need to stop res.
        // thus, i call query.end();
    })
    .on('end', ()=>{
        conn.release();
    });

I'm curiosity, query is readable stream or the other? but readable stream should not have end() method
should I call destroy() or close() preferable ?

[sidorares]

query.end() in mysqljs is from here - https://github.com/mysqljs/mysql/blob/e16c52da980e46012a391232be884b797b8af070/lib/protocol/sequences/Sequence.js#L62

At a protocol level there is no way to stop stream of data, at best yo set some flag on the client to ignore it and not waste memory/cpu. I think Query.end() basically does that ( need to double check ). As long as it's not implemeted in mysql2 you can achieve similar result like this:

const keepProcessing = true;

const done = () => {
   keepProcessing  = true;
   conn.release()
}

const query = conn.query('SELECT * FROM `table`')
    .on('result', (aRow)=>{
        if (!keepProcessing) {
          return; 
        }
        if (someBusinessLogic(dataThusFar) {
           done()          
        }
    })
    .on('end', ()=>{
        done()
    });
    .on('error', err => {
        if (!err.isFatal) {
           // not a disconnect - logic error like sql syntax etc
          done();
         }
         // for disconnects pool should handle error and remove connection from pool, no need to release()
     })

[jimmyolo]

This is exactly how I do in mysql2 now, thanks for help
I know if is sql relative error that will trigger .on('error') and then will trigger .on('end'), so release connection should be one time.
plus, in done function keepProcessing should = false;
for now, if is BusinessLogic error or not sql-relative error, we cannot interrupt stream data right ?
Thanks again.

[sidorares]

for now, if is BusinessLogic error or not sql-relative error, we cannot interrupt stream data right ?

mysql protocol is half duplex in it's design, communication is always one way ( from server of from client, not both ways at the same time ). For example, once server started sending big set of rows there is no way to tell it "wait wait, stop, I don't need rest of the data anymore" from the same connection. Your options are:

• just ignore data and wait until it's all sent ( as you already do )
• kill query using KILL QUERY sql query from another connection
• kill connection via KILL CONNECTION ( also from another connection )
• kill underlying tcp connection from client side ( connection.destroy() )

[sidorares]

https://dev.mysql.com/doc/refman/5.7/en/kill.html

[jimmyolo]

Thanks for summary,
should I close this issue or keep it since you tag its incompatible to mysqljs

[sidorares]

I'll keep it open to track missing Query.end() incompatibility

[dev-guy]

For mysql2, call connection.connection.query() instead of connection.query().

connection.destroy() (for mysql2 it's connection.connection.destroy()) is the only thing I've found that works. It seems to be instantaneous - the callback is never called