TBlockChain

Source: source/internal/TBlockChain.prg

Standalone class

TBlockChain is a pure Harbour blockchain implementation with SHA-256 hashing, proof-of-work mining, and block validation. It uses a CLASSDATA hash (aBlocks) so all instances share the same chain, enabling multi-window applications to operate on the same data. The chain stores an array of hashed blocks, each containing a timestamp, data payload, once (nonce), and the previous block's hash. Mining iterates through nonce values until the hash matches the difficulty prefix.

Key DATA Members

DATA	Type	Description
`aBlocks`	Hash (CLASSDATA)	All blocks in the chain, shared across all instances
`cJson`	Character	JSON representation of the entire chain
`uDifficulty`	Character	Mining difficulty prefix (default: "0000")
`nIterations`	Numeric	Total mining iterations performed
`cPrivateKey`	Character	Private key for signing blocks
`cPublicKey`	Character	Public key for signature verification
`cSignature`	Character	Block signature string

Methods

Method	Description
`New( cKey )`	Create a new blockchain with genesis block, keyed by cKey
`AddNewBlock( uOnce, cData )`	Add a new block with optional nonce and data string
`BlockToHash( nIdx, uOnce, cData )`	Compute the hash for a given block index and data
`MineBlock( nIdx )`	Mine block nIdx by iterating nonces until hash matches difficulty
`IsValidHash( nIdx )`	Check whether block nIdx has a valid hash matching difficulty
`IsValidBlock( nIdx, cHash )`	Validate block nIdx against the provided hash
`CountBlocks()`	Return the total number of blocks in the chain
`UpdateAllBlocks()`	Recompute hashes for all blocks in the chain

Example: Creating a Chain

#include "FiveWin.ch"

function Main()

   local oChain := TBlockChain():New( "myapp" )

   // Add blocks with data
   oChain:AddNewBlock( , "Genesis: Base record" )
   oChain:AddNewBlock( , "Block 2: Transaction data" )
   oChain:AddNewBlock( , "Block 3: Verification record" )

   // Mine the second block
   oChain:MineBlock( 2 )

   // Validate
   if oChain:IsValidHash( 2 )
      MsgInfo( "Block 2 is valid. Total blocks: " + ;
               Str( oChain:CountBlocks() ) )
   endif

   // Output chain as JSON
   if ! Empty( oChain:cJson )
      MemoWrit( "chain.json", oChain:cJson )
   endif

   oChain:End()

return nil

Notes

The aBlocks data member is marked CLASSDATA and stored as a hash keyed by the cKey parameter passed to New(). All instances using the same key share the same chain data.
The default difficulty (uDifficulty) is "0000", requiring the first four hex digits of the SHA-256 hash to be zero. Increase the string length (e.g. "000000") to make mining exponentially harder.
MineBlock() increments the nonce and re-hashes until the hash matches the difficulty prefix. The number of iterations is accumulated in nIterations.
Written by Cristobal Navarro.

TBlockChain

Key DATA Members

Methods

Example: Creating a Chain

Notes

See Also