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neoeno/chain.js

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Revisions

  1. neoeno revised this gist Dec 24, 2017. No changes.
  2. neoeno created this gist Dec 24, 2017.
    58 changes: 58 additions & 0 deletions chain.js
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    Original file line number Diff line number Diff line change
    @@ -0,0 +1,58 @@
    const hashMaker = require("hash.js");

    const hashString = string =>
    hashMaker
    .sha256()
    .update(string)
    .digest("hex");

    const findBlockWithHashPrefix = (signedGenerator, prefix) => {
    let nonce = 0;
    while (true) {
    nonce++;
    const signed = signedGenerator(nonce);
    const hash = hashString(signed);
    if (hash.slice(0, prefix.length) == prefix) {
    return { signed, hash };
    }
    }
    };

    const makeSigned = (chain, payload) => nonce => {
    return JSON.stringify({
    lastBlockHash: chain[chain.length - 1].hash,
    payload,
    nonce
    });
    };

    const addBlock = (chain, payload) => {
    const signedGenerator = makeSigned(chain, payload);
    return [...chain, findBlockWithHashPrefix(signedGenerator, "0")];
    };

    const verifyChain = chain => {
    return chain.every((block, idx) => {
    return (
    verifyBlockHashMatchesContent(block) &&
    verifyBlockContainsPreviousHash(block, chain[idx - 1])
    );
    });
    };

    const verifyBlockHashMatchesContent = block => {
    return hashString(block.signed) === block.hash;
    };

    const verifyBlockContainsPreviousHash = (block, prevBlock) => {
    // If prevBlock is undefined, we're the genesis block and we can do what we like
    if (prevBlock === undefined) {
    return true;
    }
    return JSON.parse(block.signed).lastBlockHash === prevBlock.hash;
    };

    module.exports = {
    addBlock,
    verifyChain
    };
    53 changes: 53 additions & 0 deletions chain.test.js
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    Original file line number Diff line number Diff line change
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    const hashMaker = require("hash.js");
    const Chain = require("./chain");

    const GENESIS_BLOCK = {
    hash: "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
    signed: ""
    };

    describe("addBlock", () => {
    test("adds a block", () => {
    const chain = Chain.addBlock([GENESIS_BLOCK], "hi!");
    expect(chain).toEqual([
    GENESIS_BLOCK,
    {
    hash:
    "0574f789c3b7f5cbd10470f2fdec7d9c590d51e8663d69f96dcf0a775b263449",
    signed:
    '{"lastBlockHash":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855","payload":"hi!","nonce":2}'
    }
    ]);
    });
    });

    describe("verifyChain", () => {
    test("verifies a correct chain", () => {
    const correctChain = Chain.addBlock([GENESIS_BLOCK], "hi!");
    expect(Chain.verifyChain(correctChain)).toBe(true);
    });

    test("invalidates an incorrectly hashed chain", () => {
    const correctChain = [
    GENESIS_BLOCK,
    {
    hash: "badhash",
    signed:
    '{"lastBlockHash":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855","payload":"hi!","nonce":2}'
    }
    ];
    expect(Chain.verifyChain(correctChain)).toBe(false);
    });

    test("invalidates an incorrectly chained chain", () => {
    const correctChain = [
    GENESIS_BLOCK,
    {
    hash:
    "0574f789c3b7f5cbd10470f2fdec7d9c590d51e8663d69f96dcf0a775b263449",
    signed: '{"lastBlockHash":"badhash","payload":"hi!","nonce":2}'
    }
    ];
    expect(Chain.verifyChain(correctChain)).toBe(false);
    });
    });
    13 changes: 13 additions & 0 deletions package.json
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    {
    "name": "bchain",
    "version": "1.0.0",
    "main": "index.js",
    "license": "MIT",
    "dependencies": {
    "hash.js": "^1.1.3",
    "jest": "^22.0.3"
    },
    "scripts": {
    "test": "jest"
    }
    }