Detailed Explanation

1. decode_varint(stream) Function

• This function decodes a variable-length integer from the byte stream.
• It reads the first byte to determine the format of the integer:
  • If the byte is less than 0xFD, it’s a single-byte integer.
  • If the byte is 0xFD, the next 2 bytes represent the integer.
  • If the byte is 0xFE, the next 4 bytes represent the integer.
  • If the byte is 0xFF, the next 8 bytes represent the integer.
• The function returns the decoded integer and the number of bytes consumed.

2. deserialize_tx(serialized_tx) Function

• This function takes the raw byte format of a Bitcoin transaction and deserializes it into a dictionary.
• It begins by setting the offset to 0.
• It reads the transaction version (4 bytes, little-endian) from the byte stream.
• It decodes the number of transaction inputs (vin_count) and advances the offset accordingly.
• For each input (vin), it:
  • Reads the transaction ID (txid, 32 bytes, reversed) and converts it to hexadecimal.
  • Reads the output index (vout, 4 bytes, little-endian).
  • Decodes the length of the scriptSig (script_length) and reads the scriptSig.
  • Reads the sequence number (4 bytes, little-endian).
  • Appends these values to the vin list.
• It decodes the number of transaction outputs (vout_count) and advances the offset accordingly.
• For each output (vout), it:
  • Reads the output value (value, 8 bytes, little-endian).
  • Decodes the length of the scriptPubKey (script_length) and reads the scriptPubKey.
  • Appends these values to the vout list.
  • Finally, it reads the transaction locktime (4 bytes, little-endian).
  • It returns a dictionary containing the version, list of inputs (vin), list of outputs (vout), and locktime.

3. Deserialization of Serialized Transaction

• The serialized transaction is provided as a hexadecimal string.
• The deserialize_tx function is called with the byte format of the serialized transaction.
• The function returns a dictionary representing the deserialized transaction.
• The deserialized transaction is then printed, including its version, inputs (vin), outputs (vout), and locktime.

This process allows you to convert a raw Bitcoin transaction into a structured format for analysis or further processing.

When transactions are transmitted over the network or exchanged between applications, they are serialized. Serialization is most commonly used for encoding data structures for transmission over a network or for storage in a file. The serialization format of a transaction output is shown in Transaction output serialization. This article focuses on discussing steps to decode input data from a transaction.