At the moment we should have 3 possible options to check return state
during vm context unloading:
* no check
* ensure the stack is empty
* ensure the stack is not empty
It is necessary to distinguish them because new _deploy method shouldn't
left anything on stack. Example: if we use _deploy method before some
ordinary contract method which returns one value. Without these changes
the contract invocation will fail due to 2 elements on stack left after
invocation (the first `null` element is from _deploy, the second element
is return-value from the ordinary contract method).
Most often we only need to read them and it doesn't require copying. Make an
explicit copy (and copy only things we need!) where needed.
After the recent neo-vm tests update our vm package testing time jumped to
~12s, with this change it's now more like ~8s.
Inspired by neo-project/neo-vm#352. We can't directly compare slices, so we're
better optimize things we already have. At the same time this code would
behave a bit different if A is to call B and then B is call A and then some
pointer from the first A invocation is to be compared with a pointer from the
second A invocation. Not sure it really matters.
1. `Run()` must be able to continue execution after a breakpoint.
2. VM must stop right before the breakpoint, not after.
3. Initial vm state is NONE, not HALT.
When calling external contracts we expect exactly 1 value to be on
stack. For methods returning nothing, `Null` value is pushed, otherwise
it is an error.`
It's not needed any more with Go 1.13 as we have wrapping/unwrapping in base
packages. All errors.Wrap calls are replaced with fmt.Errorf, some strings are
improved along the way.
Allow to invoke methods by offset:
1. Every invoked contract must have manifest.
2. Check arguments count on invocation.
3. Change AppCall to a regular syscall.
4. Add test suite for `System.Contract.Call`.
Implement 3 new instructions: TRY,ENDTRY,ENDFINALLY.
1. TRY marks the start of the block where exceptions are catched.
It has 2 arguments which are relative offsets of exception handler
and the end of the whole try/catch construction.
2. ENDTRY denotes either end of try or catch block.
3. ENDFINALLY denotes end of finally block which is executed
irregardless of whether an exception has occured.
We were accepting transactions with zero system fee, but we shouldn't do
that. Also, transaction's verification execution has to be limited by network
fee.
