Class: BTC::AssetProcessor

Inherits:
Object
  • Object
show all
Defined in:
lib/btcruby/open_assets/asset_processor.rb

Overview

AssetProcessor implements verification and discovery of assets. This assumes that underlying Bitcoin transactions are valid and not double-spent. Only OpenAssets validation is applied to determine which outputs are holding which assets and how much.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(source: nil, network: nil) ⇒ AssetProcessor

Returns a new instance of AssetProcessor.

Raises:

  • (ArgumentError) 


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# File 'lib/btcruby/open_assets/asset_processor.rb', line 16

def initialize(source: nil, network: nil)
  raise ArgumentError, "Source is missing." if !source
  @source = source
  @network = network || Network.default
end

Instance Attribute Details

#network ⇒ Object

Network to use for encoding AssetIDs. Default is Network.default.



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 14

def network
  @network
end

#source ⇒ Object

AssetProcessorSource instance that provides transactions.



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 11

def source
  @source
end

Instance Method Details

#color_transaction_inputs(atx) ⇒ Object 



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 93

def color_transaction_inputs(atx)
  atx.inputs.each do |ain|
    if !ain.verified?
      prev_atx = ain.previous_asset_transaction
      BTC::Invariant(!!prev_atx, "Must have previous asset transaction")
      if !prev_atx.verified?
        #puts "\n Prev ATX not fully verified: #{prev_atx.inspect} -> input #{ain.index} of #{atx.inspect}"
      end
      BTC::Invariant(prev_atx.verified?, "Must have previous asset transaction outputs fully verified")
      output = prev_atx.outputs[ain.transaction_input.previous_index]
      BTC::Invariant(output && output.verified?, "Must have a valid reference to a previous verified output")
      # Copy over color information. The output can be colored or uncolored.
      ain.asset_id = output.asset_id
      ain.value = output.value
      ain.verified = true
    end
  end
end

#discover_asset(asset_id: nil) ⇒ Object

scans forward and validates every AssetTransaction on the way.



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 308

def discover_asset(asset_id: nil)
  # TODO: ...
end

#partial_verify_asset_transaction(asset_transaction) ⇒ Object

Returns a list of asset transactions remaining to verify. Returns an empty array if verification succeeded and there is nothing more to verify. Returns nil if verification failed.

Raises:

  • (ArgumentError) 


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# File 'lib/btcruby/open_assets/asset_processor.rb', line 116

def partial_verify_asset_transaction(asset_transaction)
  raise ArgumentError, "Asset Transaction is missing" if !asset_transaction

  # 1. Verify issuing transactions and collect transfer outputs
  cache_transactions do
    if !verify_issues(asset_transaction)
      return nil
    end

    # No transfer outputs, this transaction is verified.
    # If there are assets on some inputs, they are destroyed.
    if asset_transaction.transfer_outputs.size == 0
      # We keep inputs unverified to indicate that they were not even processed.
      return []
    end

    # 2. Fetch parent transactions to verify.
    # * Verify inputs from non-OpenAsset transactions.
    # * Return OA transactions for verification.
    # * Link each input to its OA transaction output.
    prev_unverified_atxs_by_hash = {}
    asset_transaction.inputs.each do |ain|
      txin = ain.transaction_input
      # Ask source if it has a cached verified transaction for this input.
      prev_atx = @source.verified_asset_transaction_for_hash(txin.previous_hash)
      if prev_atx
        BTC::Invariant(prev_atx.verified?, "Cached verified tx must be fully verified")
      end
      prev_atx ||= prev_unverified_atxs_by_hash[txin.previous_hash]
      if !prev_atx
        prev_tx = transaction_for_input(txin)
        if !prev_tx
          Diagnostics.current.add_message("Failed to load previous transaction for input #{ain.index}: #{txin.previous_id}")
          return nil
        end
        begin
          prev_atx = AssetTransaction.new(transaction: prev_tx)
          prev_unverified_atxs_by_hash[prev_atx.transaction_hash] = prev_atx
        rescue FormatError => e
          # Previous transaction is not a valid Open Assets transaction,
          # so we mark the input as uncolored and verified as such.
          ain.asset_id = nil
          ain.value = nil
          ain.verified = true
        end
      end
      # Remember a reference to this transaction so we can validate the whole `asset_transaction` when all previous ones are set and verified.
      ain.previous_asset_transaction = prev_atx
    end # each input

    # Return all unverified transactions.
    # Note: this won't include the already verified one.
    prev_unverified_atxs_by_hash.values
  end
end

#verify_asset_transaction(asset_transaction) ⇒ Object

Scans backwards and validates every AssetTransaction on the way. Does not verify Bitcoin transactions (assumes amounts and scripts are already validated). Updates verified flags on the asset transaction. Returns true if asset transaction is verified succesfully. Returns false otherwise.

Raises:

  • (ArgumentError) 


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# File 'lib/btcruby/open_assets/asset_processor.rb', line 27

def verify_asset_transaction(asset_transaction)
  raise ArgumentError, "Asset Transaction is missing" if !asset_transaction

  # Perform a depth-first scanning.
  # When completed, we'll only have transactions that have all previous txs fully verified.
  atx_stack = [ asset_transaction ]
  i = 0
  max_size = atx_stack.size
  while i < atx_stack.size # note: array dynamically changes as we scan it
    atx = atx_stack[i]
    BTC::Invariant(atx.is_a?(AssetTransaction), "Must be AssetTransaction instance")

    more_atxs_to_verify = partial_verify_asset_transaction(atx)
    if more_atxs_to_verify == nil # Validation failed - return immediately
      return false
    elsif more_atxs_to_verify.size == 0 # atx is fully verifiable (issue-only or we used cached parents), remove it from the list
      
      # outputs may not be all verified because they can be transfers with cached verified inputs.
      # so we need to verify local balance and apply asset ids from inputs to outputs
      if !verify_transfers(atx) 
        return false
      end

      if i == 0 # that was the topmost transaction, we are done.
        return true
      end

      @source.asset_transaction_was_verified(atx)
      atx_stack.delete_at(i)
      i -= 1
      # If this is was the last parent to check, then the previous item would be :parents marker
      # Once we validate the child behind that marker, we might have another child or the marker again.
      # Unroll the stack until the previous item is not a child with all parents verified.
      while (child_atx = atx_stack[i]) == :parents
        BTC::Invariant(i >= 1, ":parents marker should be preceded by an asset transaction")
        atx_stack.delete_at(i)
        i -= 1
        child_atx = atx_stack.delete_at(i)

        # Now all inputs are verified, we only need to verify the transfer outputs against them.
        # This will make outputs verified for the later transactions (earlier in the list).
        if !verify_transfers(child_atx)
          return false
        end

        # Now transaction is fully verified.
        # Source can cache it if needed.
        @source.asset_transaction_was_verified(child_atx)

        if i == 0 # this was the topmost child, return
          return true
        end
        i -= 1
      end
    else
      # we have more things to verify - dig inside these transactions
      # Start with the last one so once any tx is verifed, we can move back and color inputs of the child transaction.
      atx_stack.insert(i+1, :parents, *more_atxs_to_verify)
      max_size = atx_stack.size if atx_stack.size > max_size
      j = i
      i += more_atxs_to_verify.size + 1
    end
  end
  return true
end

#verify_issues(asset_transaction) ⇒ Object

Attempts to verify issues. Fetches parent transactions to determine AssetID. Returns true if verified all issue outputs. Returns false if previous tx defining AssetID is not found.



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 175

def verify_issues(asset_transaction)
  previous_txout = nil # fetch only when we have > 0 issue outputs
  asset_transaction.outputs.each do |aout|
    if !aout.verified?
      if aout.value && aout.value > 0
        if aout.issue?
          previous_txout ||= transaction_output_for_input(asset_transaction.inputs[0].transaction_input)
          if !previous_txout
            Diagnostics.current.add_message("Failed to assign AssetID to issue output #{aout.index}: can't find output for input #0")
            return false
          end
          aout.asset_id = AssetID.new(script: previous_txout.script, network: self.network)
          # Output issues some known asset and amount and therefore it is verified.
          aout.verified = true
        else
          # Transfer outputs must be matched with known asset ids on the inputs.
        end
      else
        # Output without a value is uncolored.
        aout.asset_id = nil
        aout.value = nil
        aout.verified = true
      end
    end
  end
  true
end

#verify_transfers(asset_transaction) ⇒ Object

Attempts to verify transfer transactions assuming all inputs are verified. Returns true if all transfers are verified (also updates verified and asset_id on them). Returns false if any transfer is invalid or some inputs are not verified.



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# File 'lib/btcruby/open_assets/asset_processor.rb', line 206

def verify_transfers(asset_transaction)
  # Do not verify colors on inputs if no transfers occur. 
  # Typically it's an issuance tx. If there are assets on inputs, they are destroyed.
  if asset_transaction.transfer_outputs.size == 0
    return true
  end

  color_transaction_inputs(asset_transaction)

  current_asset_id = nil

  inputs = asset_transaction.inputs.dup
  current_asset_id = nil
  current_input = nil
  current_input_remainder = 0

  asset_transaction.outputs.each do |aout|
    # Only check outputs that can be colored (value > 0) and are transfer outputs (after the marker)
    if aout.has_value? && !aout.marker? && !aout.issue?

      aout.asset_id = nil
      remaining_value = aout.value

      # Try to fill in the output with available inputs.
      while remaining_value > 0

        BTC::Invariant((current_input_remainder == 0) ? (current_input == nil) : true,
          "Remainder must be == 0 only when current_input is nil")

        BTC::Invariant((current_input_remainder > 0) ? (current_input && current_input.colored?) : true,
          "Remainder must be > 0 only when transfer input is colored")

        current_input ||= inputs.shift

        # skip uncolored inputs
        while current_input && !current_input.colored?
          current_input = inputs.shift
        end

        if !current_input
          Diagnostics.current.add_message("Failed to assign AssetID to transfer output #{aout.index}: not enough colored inputs (#{remaining_value} missing for output #{aout.index}).")
          return false
        end

        # Need to consume aout.value units from inputs and extract the asset ID
        if !current_input.verified?
          Diagnostics.current.add_message("Failed to assign AssetID to transfer output #{aout.index}: input #{current_input.index} is not verified.")
          return false
        end

        # Make sure asset ID matches.
        # If output gets assigned units from 2 or more inputs, all asset ids must be the same.
        if !aout.asset_id
          aout.asset_id = current_input.asset_id
        else
          if aout.asset_id != current_input.asset_id
            Diagnostics.current.add_message("Failed to assign AssetID to transfer output #{aout.index}: already assigned another AssetID.")
            return false
          end
        end

        # If we have remainder from the previous output, use it.
        # Otherwise use the whole input's value.
        qty = if current_input_remainder > 0
          current_input_remainder
        else
          current_input.value
        end

        if qty <= remaining_value
          remaining_value -= qty
          # choose next input, clear remainder.
          current_input_remainder = 0
          current_input = nil
        else
          current_input_remainder = qty - remaining_value
          remaining_value = 0
          # keep the current input to use with `current_input_remainder` in the next output
        end
      end # filling in the output

      aout.verified = true

      BTC::Invariant(aout.verified && aout.asset_id && aout.value > 0, "Transfer output should be fully verified")
    end # only transfer outputs with value > 0
  end # each output

  # Some inputs may have remained. If those have some assets, they'll be destroyed.
  if current_input_remainder > 0
    Diagnostics.current.add_message("Warning: #{current_input_remainder} units left over from input #{current_input.index} will be destroyed.")
  end

  while current_input = inputs.shift
    if current_input.colored?
      Diagnostics.current.add_message("Warning: #{current_input.value} units from input #{current_input.index} will be destroyed.")
    end
  end

  return true
end