Add option to refund unused deposit for set method

[agostbiro]

Hi,

This PR adds an option to the set method to refund part of the deposit that covers unused storage to the caller (fixes #6).

Invariants

I think there are three invariants to maintain with this feature:

1. No refunds for storage that is in use.
2. No double spending: same deposit cannot be withdrawn multiple times.
3. A caller cannot withdraw more than they deposited in the call.

I ensured the first two invariants by reusing the existing storage_withdraw implementation.

I ensured the third invariant by checking that we don't refund more than what was in the attached balance:

4e0581d#diff-bc8da1acc242fddbedebb84935fc8bb893ed6bb4044090dbed4b2e53fc817b02R153

Integration tests

I added an integration test suite to convince myself that the implementation is correct. If you want to keep the integration tests, I'm happy to add CI for them in a follow up PR.

Rust 1.69

I added a rust-toolchain.toml file to pin Rust 1.69 as nearcore doesn't support Rust 1.70 yet (more info: near/near-sdk-rs#1035)

Reviewing

I implemented this feature to gain more experience with NEAR smart contract development. As a result, in spite of my best efforts, it's possible that I overlooked something important, so please review carefully.

[frol]

Overall, looks good to me, but I’m not a code owner here to make any decisions

[frol]

Was there some limitation using the standard Rust tests folder for integration tests?

[agostbiro]

Good question! I put the integration tests in a separate crate so that its build script can build the WASM contract before running the tests. We could potentially make this work if the integration tests lived in the contract crate, but it would be quite hacky as the build target for tests would be native, but the contract needs to be compiled with WASM target.

Regarding naming of the integration tests directory, I followed the pattern in create-near-app, but happy to adjust.

Note that there is a top level tests folder in the repo with a single noop test that is not part of a crate and is not a member of the workspace. Maybe we could remove that?

[agostbiro]

I removed the tests folder now in ae24bfe

[evgenykuzyakov]

Since we're pinning this to a 1.69.0 for Rust, it makes sense to update Rust version in build_release.sh to match it. Then rebuild it (requires linux machine or non M-mac).

Also, please update CHANGELOG.md and bump the version to 0.11.0

[agostbiro]

Thanks for the review @evgenykuzyakov! I updated the Rust version in build_docker.sh, bumped the change log and built a new release contract. I tested the release contract by deploying it to the test net. Apologies for the delay -- I'm on an M1 mac and needed to get my hands on an x86 build server.

[agostbiro]

Ooops closed by accident.