I have walked through the official document and found a page about how to transfer using polkadot-js https://polkadot.js.org/docs/api/examples/promise/make-transfer
const transfer = api.tx.balances.transfer(BOB, 12345);
const hash = await transfer.signAndSend(alice);
I want to know if I can split the signAndSend method into two and execute at different machines. like in a client machine, in the browser compute the signature.
const transfer = api.tx.balances.transfer(BOB, 12345);
const signature = await transfer.signAsync(alice);
and then in the server side send the transfer transaction.
const mockSigner = createMockSigner(signature); // signature is computed from the client side and send to server over HTTP
const transfer = api.tx.balances.transfer(BOB, 12345);
const res = transfer.send({signer: mockSigner});
The above example doesn't work, I just want to express if I can do sign and send in different machines.
Signing a transaction on one computer and sending it from a second computer is definitely possible.
PolkadotJS Tools contains a method for building and signing a transaction offline. You can find the source here. Please note that building the transaction in the browser will still require access to a polkadot node (the endpoint in the code).
The signer sendOffline command has the exact same API, but will not broadcast the transaction. submit and sendOffline must be connected to a node to fetch the current metadata and construct a valid transaction. Their API has the format:
Therefore, you'd need to run a light client in the browser in order to have access to current block information or attach to some other node endpoint outwith the browser.
The offline sign version: https://gist.github.com/xcaptain/4d190232411dcf27441d9fadd7ff6988
The online sign version:
const transfer = api.tx.balances.transfer(BOB, 12345);
const signedExtrinsic = await transfer.signAsync(alice).toJSON();
await api.rpc.author.submitExtrinsic(signedExtrinsic);
Don't know what's the difference, but they both work.