Simulate transactions in CLI & REST by default

[cwgoes]

Simulate transactions against current state for:

• Transaction outputs, where applicable (e.g. proposal ID)
• Catching invalid transactions before committing them
• Estimating gas usage

[cwgoes]

Oh, since we're writing a TracingKVStore anyways, we should an a --dry-run option which doesn't actually sign or broadcast the transaction, but instead runs it against the state and reports all keys read/written.

[alessio]

Side note: --dry-run requires transactions to be signed anyway, simulation via query wouldn't go through otherwise

[cwgoes]

Side note: --dry-run requires transactions to be signed anyway, simulation via query wouldn't go through otherwise

I think we should actually remove this requirement, it isn't strictly necessary and is a bit confusing from a UX perspective. We can just skip the ante check for dry run.

[alessio]

We could skip the ante handler, though the gas estimate would be surely wrong. If a --dry-run is somewhtat desirable, then I think it is worth to open a separate issue.

[cwgoes]

We could skip the ante handler, though the gas estimate would be surely wrong. If a --dry-run is somewhtat desirable, then I think it is worth to open a separate issue.

No, sorry, was unclear - run the ante handler, consuming gas as normal, but just don't require a valid signature (specifically for simulation).

[alessio]

Are you perhaps suggesting to skip processSig() whilst consuming the gas that would be consumed by a successful call?

[cwgoes]

Are you perhaps suggesting to skip processSig() whilst consuming the gas that would be consumed by a successful call?

Yes, don't have the code in front of me but that's the idea.

[alessio]

This happens when ante handler is called via simulateTx:

[ConsumeGas] [memo] amount: 0 - consumed: 0
[ConsumeGas] [ReadFlat] amount: 10 - consumed: 10
[ConsumeGas] [ReadPerByte] amount: 42 - consumed: 52
[ConsumeGas] [ante verify] amount: 100 - consumed: 152
[ConsumeGas] [WriteFlat] amount: 10 - consumed: 162
[ConsumeGas] [WritePerByte] amount: 440 - consumed: 602

Note that signature verification is skipped as no sigs are sent.
The following excerpt instead shows the gas consumption of ante handler via runTx():

[ConsumeGas] [memo] amount: 0 - consumed: 0
[ConsumeGas] [ReadFlat] amount: 10 - consumed: 10
[ConsumeGas] [ReadPerByte] amount: 42 - consumed: 52
[ConsumeGas] [ante verify] amount: 100 - consumed: 152
[ConsumeGas] [WriteFlat] amount: 10 - consumed: 162
[ConsumeGas] [WritePerByte] amount: 840 - consumed: 1002

Thus if the UI's requirement is to simulate the execution to then expect an accurate estimate, the latter would be likely pretty wrong since store write ops depend on bytes stored, i.e. no sigs, fewer bytes written.

[cwgoes]

Can we write a fake signature during the simulation?

[jackzampolin]

cc @mslipper