Tracking: Add parameters to Network::Testnet variant

[arya2]

Motivation

Zebra currently hard-codes some consensus parameters that may need to be changed for testing.

Scope

To be discussed in #7967.

Preparatory Refactors:

• Refactor tests to use is_mainnet() to look up test vectors using new functions in zebra-test #8325
• Refactor production code that matches on Testnet to use a new Network method for each consensus rule #8326
• Add an empty NetworkParameters struct to Network::Testnet #7968

After these changes are merged, we should decide which parameters we want to add and create more issues like #7970 for each of them.

Adding Parameters:

• Add a field for the network upgrade activation heights to TestnetParameters #7970
  • Add config field for accepting network upgrade activation heights #7840
• Add a disable_peers field to testnet::Parameters #8361
• Add a debug_disable_pow_check field to Network #8362
• Add a name field to NetworkParameters to be used at the end of the cache dir path #8327
• Copy or generate Regtest genesis block from zcashd #8412
• Add a default_port field to NetworkParameters (needed for custom Testnets but not Regtest)
• Move TESTNET_{MINIMUM_DIFFICULTY/MAX_TIME}_START_HEIGHT constants to fields on NetworkParameters #8364
• Implement zcash_primitives::consensus::Parameters for Network to pass network to try_sapling_output_recovery() directly #8365
• Add a genesis_hash field to NetworkParameters #8366
• Add protocol version information to fields on NetworkParameters #8367

Possible Design

• Turn the Testnet variant into:

Testnet(Arc<NetworkParameters { 
   cache_name,
   genesis_hash,
   network_id,
   default_port,
   activation_heights,
   ..
>)

• Consider adding fields for:
  • slow_start_interval (nSubsidySlowStartInterval)
  • target_difficulty_limit (powLimit)
  • key_prefixes
  • debug_mandatory_checkpoint_height: Option<Height>
  • checkpoints: Path
  • pow_avg_window (update logic to use min(num_blocks_in_cache, 17))
• Add a new_testnet() method or DEFAULT_TESTNET constant with the existing testnet defaults, to replace literal Testnet variant.
• Replace matching against Testnet with an is_mainnet() method. (This is only required when we're matching against Testnet, we can change the Mainnet matches gradually.)

[mpguerra]

Lowering priority as it's not clear that it's a blocker for ZSA testing anymore

[arya2]

Elevating priority so ZSAs can be tested with a new genesis block.

[teor2345]

Elevating priority so ZSAs can be tested with a new genesis block.

Mining a new genesis block is out of scope for this ticket. It's an extremely tricky process, let's check what zcashd does, and open another ticket?

(It's possible they just re-use the mainnet or testnet block for all networks.)

[daira]

zcashd uses a separate genesis block for testnet, and does not support multiple testnets without modifying code and rebuilding. Is it sufficient to just use that block and upgrade at height 1?

[teor2345]

zcashd uses a separate genesis block for testnet, and does not support multiple testnets without modifying code and rebuilding. Is it sufficient to just use that block and upgrade at height 1?

@arya2 let's ask the QEDIT team when we get in touch with them? (Along with everything else, it's not an urgent question.)

[mpguerra]

@arya2 can you split out what we're going to work on from here on Sprint 24?