[DRAFT] MpcContract using yields

[saketh-are]

No description provided.

[mikedotexe]

Excited to see this example, or something very similar merged into this SDK.
Great to have a reference in the examples directory for this, which is an intriguing update to the protocol

[DavidM-D]

@saketh-are what still needs to be done to this before it can be merged in?

[saketh-are]

@DavidM-D #1183 merges the imports for the host functions which is enough to unblock you. It is pending a review by a code owner.

[gagdiez]

Very interesting addition @saketh-are ! I am missing only one piece of the puzzle in the code:

How is the resume on pub fn sign_respond

env::promise_yield_resume(&data_id, &serde_json::to_vec(&signature).unwrap());

linked back to the yield_create in pub fn sign

        let yield_promise = env::promise_yield_create(
            "sign_on_finish",
            &serde_json::to_vec(&(index,)).unwrap(),
            SIGN_ON_FINISH_CALL_GAS,
            GasWeight(0),
            DATA_ID_REGISTER,
        );

Because multiple users will call sign, and they will want to get the Signature for their specific payloads

[gagdiez]

@saketh-are @DavidM-D I am working on a blogpost here:

• PR: https://github.com/near/docs/pull/1983/files
• Preview: https://docs-preview-pr-1983.onrender.com/blog/yield-resume

Will try to complete the first draft tomorrow

[saketh-are]

@gagdiez The way the example is written the sign function will give back the signature as its return value.

[gagdiez]

@saketh-are that part I get it, what I don't get is:

• saketh calls sign and a yield is created, now saketh is waiting for a reply
• gagdiez calls sign and a yield is created, now gagdiez is waiting for a reply
• The service calls sign_respond and provides a signature for gagdiez

Which part of the sign_respond code says: "please now resume computation for gagdiez"

[saketh-are]

sign_respond accepts an argument data_id which is used to identify the yield which is being resumed. It is a unique token produced by the host function promise_yield_create (it is written to a data register indicated by DATA_ID_REGISTER) and later expected as an argument to the host function promise_yield_resume.