Krister's coding adventures

Node.js encode/decode hex and publishing data to the bitcoin blockchain

Krister Viirsaar -

Okay so I'm trying to publish data on the bitcoin blockchain from bash using createrawtransaction and decoderawtransaction and here's what I've learned. Hopefully this will save someone from suffering.

How to encode and decode hex strings and decimals in Node.js

String to hex

Buffer(str).toString('hex')

hex to string

Buffer(hexstr, 'hex').toString()

decimal to hex

(5).toString(16)

hex to decimal

parseInt('4e', 16)

How to create a data transaction in Node.js with OP_RETURN

This SO question helped a lot.

I'm not going to repeat everything that's already said there, but a few pointers:

  1. If you don't use the dummy_address he gives then this method will not work.
  2. Don't even try putting the data straight into createrawtransaction, it's not possible.
  3. Unless you're using bitcoin version 0.11 or newer, then all you need to do is put {"data": "your hexified data"} into vout - much easier.
  4. child_process.execFile is much safer and maybe even more confy than child_process.exec, BUT decoderawtransaction doesn't seem wo work for me with execFile.
  5. move is not send. The former only moves numbers between accounts on your local machine. Send actually creates a transaction.

Summary

Always check the version of software you're using :) This has been a terrible week and getting the thing to work feels like I've broken through a brick wall.