RPC chain example

[evanlinjin]

RPC Chain example.

[LLFourn]

Thanks @evanlinjin. Quick review of how bdk core APIs are used. I think it can be simplified quite a bit by changing the API to return last_active_index.

I would love to see the sync/scan command to have a --live option where after doing the sync it prints out some basic stuff like balance and utxos maybe and then sits there polling for new blocks and prints out details about new transactions that come in that spend/create new wallet utxos.

Since the codebase is getting more mature now it'd be great if you could add docs and even example usage for new APIs (or even old ones). I find writing an explanation of the API helps me figure out early if the API actually makes sense.

[codecov-commenter]

Codecov Report

Merging #89 (35ef8ec) into master (ab0de04) will increase coverage by 0.99%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   50.33%   51.32%   +0.99%     
==========================================
  Files           9        9              
  Lines         602      602              
==========================================
+ Hits          303      309       +6     
+ Misses        299      293       -6     

Impacted Files	Coverage Δ
bdk_core/src/chain_graph.rs	0.00% <ø> (ø)
bdk_core/src/sparse_chain.rs	78.57% <ø> (ø)
bdk_core/src/tx_graph.rs	64.23% <0.00%> (+4.37%)	⬆️

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[LLFourn]

I think this is unsound -- you have to scan the txs first before deciding if it's relevant. scan the block when it comes in and each tx individually when the mempool comes in. From the docs of is_relevant:

    /// Whether any of the inputs of this transaction spend a txout tracked or whether any output
    /// matches one of our script pubkeys.
    ///
    /// It is easily possible to misuse this method and get false negatives by calling it before you
    /// have scanned the `TxOut`s the transaction is spending. For example if you want to filter out
    /// all the transactions in a block that are irrelevant you **must first scan all the
    /// transactions in the block** and only then use this method.

[evanlinjin]

But we are scanning transactions in order so the previous outputs will be scanned before the current transaction right?

[LLFourn]

Oh that's a good point but that only applies to the block txs. In the mempool are you guaranteed some kind of logical traversal order when you get the response. Maybe? But we shouldn't depend on it.

[evanlinjin]

@LLFourn I'm not a fan of having changesets for last_used_indicies

[evanlinjin]

Replaced by #157

All of @LLFourn 's pointers here should be addressed.