### Create Scylla Function with Wasm UDF

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

An example CQL statement to create a ScyllaDB function using a compiled WebAssembly module. It highlights the `LANGUAGE xwasm` (or `wasm` in older versions) and how to embed the `.wat` content.

```cql
CREATE FUNCTION commas(string list<text>) CALLED ON NULL INPUT RETURNS text LANGUAGE wasm AS ' (module ...) '

```

--------------------------------

### Optimize and Strip Wasm Binary

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Demonstrates optional steps to optimize and reduce the size of the compiled WebAssembly binary using `wasm-opt` and `wasm-strip`.

```bash
wasm-opt -O3 target/wasm32-wasip1/debug/my_udf_library.wasm -o target/wasm32-wasip1/debug/my_udf_library.wasm
wasm-strip target/wasm32-wasip1/debug/my_udf_library.wasm

```

--------------------------------

### Running WASM Tests with Wasmtime

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Provides the command to execute Rust tests for the WASM32 WASIP1 target using the Wasmtime runtime, ensuring compatibility with WASM-specific code.

```bash
CARGO_TARGET_WASM32_RUNNER="wasmtime --allow-unknown-exports" cargo test --target=wasm32-wasip1
```

--------------------------------

### CQL to Rust Type Mappings for Tuples

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Shows the mapping of CQL TUPLE types to Rust tuple types, enabling the use of tuples in ScyllaDB User Defined Functions.

```rust
/*
CQL Type | Rust type
----------------------------------
TUPLE<T1, T2, ...>  | (RustT1, RustT2, ...)
*/
```

--------------------------------

### Convert Wasm to WAT

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Converts a compiled WebAssembly binary (`.wasm`) into the WebAssembly Text format (`.wat`) using the `wasm2wat` tool.

```bash
wasm2wat target/wasm32-wasip1/debug/my_udf_library.wasm > target/wasm32-wasip1/debug/my_udf_library.wat

```

--------------------------------

### Scylla UDF CQL Type Mapping (Native Types)

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Provides a mapping between ScyllaDB CQL data types and their corresponding Rust types for use in User Defined Functions.

```APIDOC
CQL Type Mapping:

Native types:

| CQL Type  | Rust type                     |
| --------- | ----------------------------- |
| ASCII     | String                        |
| BIGINT    | i64                           |
| BLOB      | Vec<u8>                       |
| BOOLEAN   | bool                          |
| COUNTER   | scylla_udf::Counter           |
| DATE      | chrono::NaiveDate             |
| DECIMAL   | bigdecimal::Decimal           |
| DOUBLE    | f64                           |
| DURATION  | scylla_udf::CqlDuration       |
| FLOAT     | f32                           |
| INET      | std::net::IpAddr              |
| INT       | i32                           |
| SMALLINT  | i16                           |
| TEXT      | String                        |
| TIME      | scylla_udf::Time              |
| TIMESTAMP | scylla_udf::Timestamp         |
| TIMEUUID | uuid::Uuid                    |
| TINYINT   | i8                            |
| UUID      | uuid::Uuid                    |
| VARCHAR   | String                        |
| VARINT    | num_bigint::BigInt            |

```

--------------------------------

### CQL to Rust Type Mappings for Collections

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Illustrates how CQL collection types like LIST, MAP, and SET are mapped to their corresponding Rust types (Vec, BTreeMap, HashMap, BTreeSet, HashSet) for use in ScyllaDB User Defined Functions.

```rust
/*
CQL Type   | Rust type
-------------------------------------------------------------------------------------
LIST<T>  | Vec<RustT>
MAP<T>   | std::collections::BTreeMap<RustT>, std::collections::HashMap<RustT>
SET<T>   | Vec<RustT>, std::collections::BTreeSet<RustT>, std::collections::HashSet<RustT>
*/
```

--------------------------------

### Build Scylla UDF for Wasm Target

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Compiles a Rust project targeting `wasm32-wasip1` with specific RUSTFLAGS to set the stack size, a common requirement for Scylla UDFs.

```bash
RUSTFLAGS="-C link-args=-zstack-size=131072" cargo build --target=wasm32-wasip1

```

--------------------------------

### Configure Crate Type for Scylla UDFs

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Configures the Rust project's `Cargo.toml` to build as a dynamic library (`cdylib`), which is required for Scylla UDFs.

```toml
[lib]
crate-type = ["cdylib"]

```

--------------------------------

### Handling Nulls in Rust UDFs

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

Explains how to handle potentially null CQL values in Rust User Defined Functions by mapping the corresponding Rust type to Option<RustT>.

```rust
/*
If a CQL Value of type T that's mapped to type RustT may be a null (all parameter and return types in `CALLED ON NULL INPUT` UDFs), then the type used in the Rust function should be Option<RustT>.
*/
```

--------------------------------

### Add Scylla UDF Dependency

Source: https://github.com/scylladb/scylla-rust-udf/blob/main/README.md

This snippet shows how to add the `scylla-udf` dependency to your Rust project's Cargo.toml file, which is necessary for creating Scylla UDFs.

```rust
cargo add scylla-udf
```

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