Fix difficulty change error #4

[ivanhuay]

what occurred to me to solve the problem is to use the index of each block to validate the difficulty.

To verify that the difficulty change works, add a test that performs the mining operation 25 times

running the test with the previous version of the code breaks and returns the error that is mentioned in the issue

[0xs34n]

Hey @ivanhuay, thanks again for the PR!

I think this.chain.size - 1 on the get difficulty() function should fix the issue. I ran it on your fork and it passed the test. Do you want to add it to ur PR? :)

[ivanhuay]

Using the function with this.chain.size -1 only delays the problem

  get difficulty(): number {
    return Math.round((this.chain.size - 1)/ 50) + 3;
  }

running the test on the master branch and mining 26 times gives the error again

../Dev/blockchain/coin-cli/src/Node.ts:35
                throw e;
                ^
Failed to add block: Invalid Chain Error: Invalid Block Error: Hash 000b16ea09d53796b722a6fba6605f423f4b53ac76a531bf91adc866233e7be4 does not meet difficulty 4

The problem is when a new block is added all the previous blocks are validated using the same difficulty thath process start here:

  set chain(chain: List<Block>) {
    try {
      this.shouldReplaceChain(chain);
      this._chain = chain;
    } catch (e) {
      throw e;
    }
  }

after running

addBlock(block: Block) {
    try {
      this.isValidNextBlock(block, this.latestBlock);
      this.chain = this.chain.push(block);//this line!
    } catch (e) {
      throw `Failed to add block: ${e}`;
    }
  }

shouldReplaceChain validate all blocks from chain using the same difficulty using isValidBlocks

a possible solution

in my pull request I use the function

getIndexDifficulty(index: number) {
    return Math.round(index / 50) + 3;
  }

that uses the index of each block to get the complexity

[ivanhuay]

@seanjameshan As a detail above, the problem is to validate all the blocks with the same difficulty

[0xs34n]

Hey @ivanhuay, thank you so much for the detailed response. I really appreciate your help on this issue and you are absolutely correct, my solution just delays the problem.

I feel like there is redundancy in getting the difficulty. How about we have one function called getDifficulty(index) that calculates the difficulty given the index?

Blockchain.js

  // remove get difficulty() 
  getDifficulty(index: number) {
    return Math.round(index / 50) + 3;
  }

inside isHashDifficult() function

return i >= this.getDifficulty(index);

inside isValidDifficulty() function

  isValidDifficulty(block: Block) {
    const hash = block.hash;
    if (!this.isHashDifficult(hash, block.index)) {
      throw `Hash ${hash} does not meet difficulty ${this.getDifficulty(block.index)}`; // add the block index when throwing the error
    }
  }

inside generateNextBlock() function

while (!this.isHashDifficult(hash, index)) { // add the index here

Ran it to mine 25 and 26 blocks and it passed! :)

Would love to get your feedback on this! Sorry for the late response - It's approaching the end of the school semester, so it's getting quite busy! But I'll definitely get back to you as soon as I can.

[ivanhuay]

I agree that solution looks good

I updated my pull request with those changes

[0xs34n]

Thank you @ivanhuay !!