I receive the same data from network twice after connection hang up error!

[BartolomeoItaliano]

Hi!

I have got small dapp which tracks transactions on EOS network and it is very important for me to not receive over your library duplicated data and I am pretty sure I do.

After library hangs connection for a moment with error:

{
  type: 'error',
  errors: [
    {
      message: 'graphql: hammer search result: rpc error: code = Unknown desc = Internal server error (trace_id: 
      56c9fe4be60757f244e32b37e56ce125)'
    }
  ],
  terminal: true
}

I receive the same data I already received before error being thrown.
This is very dangerous for my app. I plan to receive and send from my contract money in form of EOS and other tokens to users.
Please advice what to do.

[maoueh]

Please provide full logs so I can see more what is happening.

[BartolomeoItaliano]

It happens very rarely once per few days or even rarer I will try to provide you proper logs, but it can take.

[BartolomeoItaliano]

dfuse-issue-logs.txt

I think I already see the problem in logs when this Internal server error is called stream is restarted with the initial cursor.
Please confirm, if I am right and if you gonna handle it somehow or what can I do on my side now.

[matthewdarwin]

You need to send the latest cursor you received on reconnect.

[BartolomeoItaliano]

But reconnect is automatic. It's your library which handles it.
How can I handle it?

[BartolomeoItaliano]

I know I might provided you with logs in poor format.
Here I attach them in txt file.
dfuse-issue-logs.txt

[maoueh]

@BartolomeoItaliano Three things is required for proper tracking of chain and ensure no duplicated trx is found:

• It's required to mark the cursor on the stream to save the active cursor, the active cursor is used to re-connect
• It's required to have a $cursor variable in the GraphQL document, it you have an active cursor, it's automatically used and passed to the GraphQL variables
• If you deal with head blocks that can fork, you need to deal with the undo: true flag which is set when a transaction is part of a forked block and must be reverted.

From the logs you have, you seems to have the cursor inlined inside your GraphQL document:

2022-01-11T16:18:02.393Z dfuse:socket:graphql Sending message { id: 'dc-cff18860357fa-0', type: 'start', payload: { query: '\n' + '             
 subscription {\n' + '                
 searchTransactionsForward(query: "receiver:eosio.token action:transfer data.to:eosgamesdepo",\n' + '                 
 cursor: "yzs7YNIzWmXlCrbClmtHQ_e7JpQ9BV9vUgPlIBEVg97_9HWW2J6uAjAgPBXVkP_53EPrS1yk1o7IF3l_9pZU79Xvw7wyuHU4FHMvl4_sqby6e_umbV9KIr1mV-2EMN-NCDveYAzycrUF",\n' + ' 
                 irreversibleOnly: false) {\n' + '                  cursor\n' + '                  undo\n' + '                  trace {\n' + '                  
                   matchingActions {\n' + '                      json\n' + '                    }\n' + '                  }\n' + '                }\n' + '            
                    }\n' + '            ', variables: { cursor: '' } } } through socket.
                    ```
                    
You should do something more like this:

subscription($cursor: String!) { searchTransactionsForward(query: "...", cursor: $cursor) ...

This should work as expected and re-connect at the right location.

[maoueh]

See the commit function which is called when each data is received and and calls mark here

[BartolomeoItaliano]

One more question, in case I use query with cursor provided like this:
subscription($cursor: String!) { searchTransactionsForward(query: "...", cursor: $cursor) ...

How can I provide query with initial cursor when I am restarting whole appllication?

[BartolomeoItaliano]

Ok, here I found some good example:
https://docs.dfuse.io/ethereum/public-apis/tutorials/searching-transactions/

[maoueh]

subscription($cursor: String!) { searchTransactionsForward(query: "...", cursor: $cursor) ...

You pass it in your initial variables. See https://github.com/dfuse-io/client-js/blob/master/examples/advanced/common/graphql-never-miss-a-beat.ts#L152

[BartolomeoItaliano]

For people with this problem in the future.
Here is proper stream setup:

https://github.com/dfuse-io/client-js/blob/HEAD/examples/basic/eosio/stream-transfers-graphql.ts

Like @maoueh said you need to set initial parameters and then after each message mark their change, otherwise still initial params would be used for reconection:
stream.mark({ cursor: data.cursor })