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+## Hello Darkmap
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+
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+In this part, we will walk through a simple Darkfi contract.
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+
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+First, pull down the Darkmap repository, we'd use this example to understand how
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+to write a simple yet powerful Darkfi contract!
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+
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+> Note: This book assumes basic familiarity with smart contracts and blockchain.
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+> It's good if you are familiar with Rust. You'd still be able to follow along
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+> even if you aren't by inferring from the context.
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+
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+```
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+git clone https://github.com/darkrenaissance/darkmap
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+```
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+
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+In Darkfi, a contract is deployed as a wasm module. Rust has one of the best wasm support, so Darkmap is implemented in Rust.
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+
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+## entrypoint.rs
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+
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+Take a look at `Cargo.toml`, the package's configurations.
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+
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+There is macro defining 4 entrypoints the contract runtime calls.
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+They are called in order:
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+1. init
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+1. metadata
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+1. exec
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+1. apply
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+
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+```
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+darkfi_sdk::define_contract!(
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+ init: init_contract,
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+ exec: process_instruction,
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+ apply: process_update,
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+ metadata: get_metadata
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+);
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+```
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+
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+## Init
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+
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+Init is responsible for 2 tasks:
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+1. from the zkas binary, compute and store the corresponding verifying key
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+2. initialize any number of databases (e.g. for the contract's business logic)
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+
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+```
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+fn init_contract(cid: ContractId, ix: &[u8]) -> ContractResult {
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+
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+ // The way to load zkas binary as native contracts, it will probably be different regular contracts
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+ let set_v1_bincode = include_bytes!("../proof/set_v1.zk.bin");
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+
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+ // Compute and store verifying key if it's not already stored
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+ zkas_db_set(&set_v1_bincode[..])?;
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+
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+ // Check if a db is already initialized
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+ if db_lookup(cid, MAP_CONTRACT_ENTRIES_TREE).is_err() {
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+ // db for business logic
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+ db_init(cid, MAP_CONTRACT_ENTRIES_TREE)?;
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+ }
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+
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+ Ok(())
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+}
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+```
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+
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+### Under the hood
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+
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+```
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+// https://github.com/darkrenaissance/darkfi/blob/85c53aa7b086652ed6d2428bf748f841485ee0e2/src/runtime/import/db.rs#L522
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+
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+/// Only `deploy()` can call this. Given a zkas circuit, create a VerifyingKey and insert
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+/// them both into the db.
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+pub(crate) fn zkas_db_set(ctx: FunctionEnvMut<Env>, ptr: WasmPtr<u8>, len: u32) -> i32 {
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+```
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+
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+## Metadata
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+
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+## Exec
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+
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+## Apply
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+
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+## Others
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+
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+* Where are the states stored?
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+ * There is no memory, there is calldata
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+* What are the runtime functions you can call?
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+ * db_init
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+ * db_lookup
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+ * zkas_db_set
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+
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x