Remove tx_history and ledger_header in API version 2

[Bronek]

High Level Overview of Change

Remove tx_history and ledger_header methods from API version 2. Also update RPC::Handler to allow for methods (or methods implementation) to be version specific. This partially resolves #4727 and fully resolves #3638 and #3539

Context of Change

Note design change in RPC::Handler - we can now store multiple handlers with the same name, as long as they belong to different (non-overlapping) API versions. This necessarily impacts the handler lookup algorithm and its complexity, however there is no performance loss on x86_64 architecture, and only minimal performance loss on arm64 (around 10ns). This design change gives us extra flexibility evolving API in the future, including other parts of #4727

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Tests (You added tests for code that already exists, or your new feature included in this PR)
• Documentation Updates
• Release

Before / After

Before

In any API version tx_history and ledger_header are recognised methods

After

In API version 1 tx_history and ledger_header are a valid API method
In API version 2 tx_history and ledger_header are not recognised method; rippled will return error unknownCmd if they are called.

[mDuo13]

Fixes #3638

[mDuo13]

P.S. while we're at it, maybe do #3539 also?

[mDuo13]

Excited to finally get rid of some of this old cruft!

[Bronek]

Apologies to reviewers about all these forced push, I was trying to make the micro-benchmark Handler_test.cpp little less stupid. Which happens to be first commit in the series because I use it to establish baseline ...

[intelliot]

Yes, I think we can always default to the most recent API version for command line. As stated here, the command line is intended for ad-hoc usage by humans, not programs or automated scripts. The command line is not meant for use in production code.

I don't think anyone is using tx_history, not even from the command line. If they are, they are welcome to later open an issue, where we can direct them to use alternative method to get the data they're looking for.

[ximinez]

@ckeshava Change apiMaximumSupportedVersion to 2 and rebuild. The command line uses the maximum non-beta API version.
https://github.com/XRPLF/rippled/blob/1.12.0/src/ripple/net/impl/RPCCall.cpp#L1485

[intelliot]

note: we intend to promote API version 2 to non-beta after #4733 is merged, and maybe after #4775; and almost certainly before the first 2.0.0-rc

[ximinez]

A few minor comments. Overall looks great.

[intelliot]

@Bronek please comment here to let us know when you think all suggestions have been addressed

[Bronek]

@Bronek please comment here to let us know when you think all suggestions have been addressed

Yes, all addressed

[Bronek]

This is ready to merge

[intelliot]

awaiting updated review from ximinez (verifying the changes that were made)

[Bronek]

awaiting updated review from ximinez (verifying the changes that were made)

Well in that case I will have one more minor improvement ...

[ximinez]

Looks good!

[intelliot]

Suggested commit message:

APIv2: remove tx_history and ledger_header (#4759)

Remove `tx_history` and `ledger_header` methods from API version 2.

Update `RPC::Handler` to allow for methods (or method implementations)
to be API version specific. This partially resolves #4727. We can now
store multiple handlers with the same name, as long as they belong to
different (non-overlapping) API versions. This necessarily impacts the
handler lookup algorithm and its complexity; however, there is no
performance loss on x86_64 architecture, and only minimal performance
loss on arm64 (around 10ns). This design change gives us extra
flexibility evolving the API in the future, including other parts of
#4727.

In API version 2, `tx_history` and `ledger_header` are no longer
recognised; if they are called, `rippled` will return error
`unknownCmd`

Resolve #3638

Resolve #3539