Add validation of smart contract calls

[netboz]

Description

Provide an endpoint to pre-validate smart contract execution

Fixes #57

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[bchamagne]

When I go to localhost:4000/api/transaction/contract/simulator I get this error:

[bchamagne]

Here's a few comments (some very biased) based only on reading the code. I'm going to need your help for a real word test.

[bchamagne]

It look like this {false, _} is not handled in the Stream.map? Did you mean a %{valid: false, ...} struct?

[bchamagne]

Works great!

Tested with the transaction builder & curl.
I tested 3 scenarios:

valid contract:
[{"address":"00002223BBD4EC3D64AE597696C7D7ADE1CEE65C639D885450AD2D7B75592AC76AFA","valid":true}]

invalid contract:
[{"address":"00002223BBD4EC3D64AE597696C7D7ADE1CEE65C639D885450AD2D7B75592AC76AFA","reason":"invalid_inherit_conditions","valid":false}]

exception throwing contract:
[{"reason":"A contract exited while simulating","valid":false}]

I found an issue with the transaction condition, but this is not the goal of this PR, I'll create an issue for that.

ps: maybe add the address to the exit message for consistency?

[bchamagne]

We are not going to merge that one yet, we will integrate it as soon as interpreter v1 is merged. We want to check the conditions in the Interpreter.exectute functions directly. Then we can use Interpreter.execute directly in the validate_contract function and in the worker as well.

[samuelmanzanera]

I think a if would do the job instead of a case ;)

[samuelmanzanera]

you could even use a with

[bchamagne]

I'm going to do one last thing on this PR:

• move the Contracts.simulate_contract_execution into Interpreter.execute. And then I'm going to use from both the simulate endpoint and from the worker (the only difference is the worker will actually persist the next transaction).

[samuelmanzanera]

Code is nicer ;)