BUILDING BLOCKCHAIN
Revanth Kumar
Co-director @ StartupGrind
Senior Freelance R & D Engineer at Anvira Edustation
Mobile: 7093-113-123
FB: revanth.kumar.connect | IGTV: rave.kumr | Twitter: TweetRevanth
Step1: Create new block and test
the block
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Write create new block method in blockchain.js
Export the blockchain method to use
it in test.js
In dev folder run the command
node <space> test.js
CREATE NEW BLOCK WITH
DUMMY DATA
OUTPUT OF CREATE NEW
BLOCK IS THIS – run the node
test.js command again
crosscheck
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Create more blocks with different
values
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Create three different blocks
Step 2: Get last block
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Returns last block in our block chain
Step 3: create new transaction
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All new transactions are pending transactions
until a new block is created.
Change the param – new trsanscations to
pending transactions
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They get recorded when a new block is created
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All new trs are pending trs
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Change the variable name to pending trs
Return index of last block
Step 4: Test create new block
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CREATE NEW BLOCK
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CREATE NEW TRANSACTION
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O/P should be one block created and one
pending tr in the pendingTrs array
NOTE: We did not create new block after
creating transaction (new)
Test output should be
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But the pending transaction is not added to a
block
Bcoz we did not create a new block after doing
the transaction
Now, create new block after creating new tr
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A new array is created in second block
Now access the new array that is created and
check
Create new multiple trs
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Create multiple trs
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Create three blocks
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All the pending trs must be stored in last block
chain
Pending trs array must be empty
Look at third block
Hash block
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Take in a block and hash the block in to fixed length
string
Use hashing function
SHA256: converts string in to random long digit string –
very secured – change input then the entire op changes
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Show in realtime website
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Same hash for any specific string
Search sha256 npm
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Be in blockchain directory
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Execute sha256 --save
Create hash function
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Generate hash for blocks
Creating hash func
Testing hash
Hash to be created
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Any part of data changes,
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The whole hash would change
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This adds lot of security
Proof of work
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Very essential
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High security
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Make sure every block is legitimate
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Every time we create a new block, we need to
make sure it is legitimate
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Takes current block data and previous block
hash
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Get hash that have four zeros in beginning
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Its creates hash until you get specific string
code
Test proof of work
Output nonce value
Print all hash values until we see the
actual value we need
Proof of work should be very difficult
to calculate
check block is valid or not by using
hadblock method and passing
correct nonce
Creating genesis block
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First block in a BC
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Use createnew block method
Section 2
Building APIs to interact with BC
create new file api.js
Install expressjs
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npm install express --save
Start server
End point – 1 - blockchain
Run api.js and see it is listening at
port 3000
Making dev easy
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npm i nodemon –save --> in bc directory
When ever we make change it will
automatically restart the server
Blockchain end point
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Get previously created blockchain by hitting the
URL
Transaction endpoint
CHECK BC AGAIN – NEW TR
CREATED
Mining blocks via API
Send bitcoins to whomever mines
the blocks
Install uuid for unique network
nodes
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Npm i uuid –save ->> blockchain dir
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Hit blockchain endpoint in browser
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Localhost:3000/blockchain
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hit mine endpoint
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Check blockchain endpoint again
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Mine again
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Check block endpoint
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Repeat.... creating blocks..