Function parse_coinbase_height 

pub(crate) fn parse_coinbase_height(
    data: Vec<u8>,
) -> Result<(Height, CoinbaseData), SerializationError>

Split data into a block height and remaining miner-controlled coinbase data.

The height may consume 0..=5 bytes at the stat of the coinbase data. The genesis block does not include an encoded coinbase height.

Consensus

A coinbase transaction for a block at block height greater than 0 MUST have a script that, as its first item, encodes the block height height as follows. For height in the range {1..16}, the encoding is a single byte of value 0x50 + height. Otherwise, let heightBytes be the signed little-endian representation of height, using the minimum nonzero number of bytes such that the most significant byte is < 0x80. The length of heightBytes MUST be in the range {1..5}. Then the encoding is the length of heightBytes encoded as one byte, followed by heightBytes itself. This matches the encoding used by Bitcoin in the implementation of [BIP-34] (but the description here is to be considered normative).

https://zips.z.cash/protocol/protocol.pdf#txnconsensus https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki