In this section, we will download a sample contract, and compile to it to a wasm binary executable.
Please first review the client setup instructions, and configure a client before proceeding. Either the Node.js REPL or Go CLI will work.
Compiling and Testing Contract
Let's download the repo in which we collect
cw-contracts and try out an existing simple name service contract where
mimics a name service marketplace. Also this tutorial is the defacto cosmos-sdk entrance tutorial. First, clone the
repo and try to build the wasm bundle:
# get the code
git clone https://github.com/InterWasm/cw-contracts
git checkout main
# compile the wasm contract with stable toolchain
rustup default stable
After this compiles, it should produce a file in
target/wasm32-unknown-unknown/release/cw_nameservice.wasm. A quick
ls -lh should show around 1.7MB. This is a
release build, but not stripped of all unneeded code. To produce a much smaller version, you can run this which tells
the compiler to strip all unused code out:
RUSTFLAGS='-C link-arg=-s' cargo wasm
This produces a file about 162kB. We use this and another optimizer in the optimized compilation section to produce the final product uploaded to the blockchain. You don't need to worry about running this yourself (unless you are curious), but you should have an idea of the final size of your contract this way.
Let's try running the unit tests:
RUST_BACKTRACE=1 cargo unit-test
After some compilation steps, you should see:
running 5 tests
test contract::tests::cannot_initialize_expired ... ok
test contract::tests::proper_initialization ... ok
test contract::tests::init_and_query ... ok
test contract::tests::handle_refund ... ok
test contract::tests::handle_approve ... ok
test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
RUST_BACKTRACE=1 will provide you with full stack traces on any error, which is super useful. This only works for unit
tests (which test native rust code, not the compiled wasm). Also, if you want to know where
cargo unit-test come from, they are just aliases defined in
.cargo/config. Take a look there to understand the
cargo flags better.
To reduce gas costs, the binary size should be as small as possible. This will result in a less costly deployment, and lower fees on every interaction. Luckily, there is tooling to help with this. You can optimize production code using rust-optimizer. rust-optimizer produces reproducible builds of CosmWasm smart contracts. This means third parties can verify the contract is actually the claimed code.
docker run --rm -v "$(pwd)":/code \
--mount type=volume,source="$(basename "$(pwd)")_cache",target=/code/target \
--mount type=volume,source=registry_cache,target=/usr/local/cargo/registry \
Binary will be at
artifacts and its size will be