dubbo WASM api

中文

At present, Dubbo's SPI extensions can only be written in Java language, the dubbo-wasm module aims to overcome this limitation.

WASM(WebAssembly) bytecode is designed to be encoded in a size- and load-time-efficient binary format. WASM aims to leverage the common hardware features available on various platforms to execute in browsers at machine code speed.

WASI(WebAssembly System Interface) provide a portable interface for applications that run within a constrained sandbox environment, which allows WASM to run in non browser environments such as Linux. It's portable and secure.

We use wasmtime-java to run WASI in Java, as long as the language can be compiled into WASM bytecode, it can be used to write SPI extensions for dubbo.

Module structure

• dubbo-wasm-api: Responsible for defining basic exceptions and providing runtime for executing WASM bytecode (Dubbo API)
• dubbo-wasm-cluster-api: Provide the WASM version of the dubbo-cluster module SPIs
• dubbo-wasm-common-api: Provide the WASM version of the dubbo-common module SPIs
• dubbo-wasm-metrics-api(todo): Provide the WASM version of the dubbo-metrics module SPIs
• dubbo-wasm-registry-api: Provide the WASM version of the dubbo-registry-api module SPIs
• dubbo-wasm-remoting-api(todo): Provide the WASM version of the dubbo-remoting-api module SPIs
• dubbo-wasm-rpc-api: Provide the WASM version of the dubbo-rpc-api module SPIs

Note

Due to the strict requirements of WASM on parameter types and for simplicity reasons, types other than java.lang.Long/java.lang.Integer are not used as parameters or return value.

How to use

Below is an example of implementing org.apache.dubbo.rpc.cluster.LoadBalance SPI in rust.

1.Create subproject in another language

cargo new --lib your_subproject_name

2.Add methods to lib.rs

// Adding `#[no_mangle]` to prevent the Rust compiler from modifying method names is mandatory
#[no_mangle]
pub unsafe extern "C" fn doSelect(_arg_id: i64) -> i32 {
    1
}

3.Add [lib] to Cargo.toml and change crate-type to ["cdylib"]. Ultimately, your Cargo.toml should look like

[package]
name = "your_subproject_name"
version = "0.1.0"
edition = "2021"

[dependencies]
# ......

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

4.Generate the wasm file

cargo build --target wasm32-wasi --release

You will see {your_subproject_name}/target/wasm32-wasi/release/{your_subproject_name}.wasm.

5.Add dependency to pom.xml

<dependency>
    <groupId>org.apache.dubbo.extensions</groupId>
    <artifactId>dubbo-wasm-cluster-api</artifactId>
    <version>${revision}</version>
</dependency>

6.Add x.y.z.RustLoadBalance.java

package x.y.z;

public class RustLoadBalance extends AbstractWasmLoadBalance {
    public static final String NAME = "rust";
}

7.Add resources/META-INF/dubbo/org.apache.dubbo.rpc.cluster.LoadBalance

rust=x.y.z.RustLoadBalance

8.Rename the WASM file

Due to the class x.y.z.RustLoadBalance.java，the final wasm file name should be x.y.z.RustLoadBalance.wasm, finally, put the wasm file in the resources folder of your module.

Communicate with Java

Below is an example of using rust.

Pass args to another language

1.Export method to another language

public class RustLoadBalance extends AbstractWasmLoadBalance {
    //......
    @Override
    protected Map<String, Func> initWasmCallJavaFunc(Store<Void> store, Supplier<ByteBuffer> supplier) {
        Map<String, Func> funcMap = new HashMap<>();
        //......
        funcMap.put("get_args", WasmFunctions.wrap(store, WasmValType.I64, WasmValType.I64, WasmValType.I32, WasmValType.I32, 
            (argId, addr, len) -> {
                String config = "hello from java " + argId;
                System.out.println("java side->" + config);
                assertEquals("hello from java 0", config);
                ByteBuffer buf = supplier.get();
                for (int i = 0; i < len && i < config.length(); i++) {
                    buf.put(addr.intValue() + i, (byte) config.charAt(i));
                }
                return Math.min(config.length(), len);
            }));
        //......
        return funcMap;
    }
}

2.Import method in another language

#[link(wasm_import_module = "dubbo")]
extern "C" {
    fn get_args(arg_id: i64, addr: i64, len: i32) -> i32;
}

3.Get args in another language

#[no_mangle]
pub unsafe extern "C" fn doSelect(arg_id: i64) -> i32 {
    //......
    let mut buf = [0u8; 32];
    let buf_ptr = buf.as_mut_ptr() as i64;
    eprintln!("rust side-> buffer base address: {}", buf_ptr);
    // get arg from java
    let len = get_args(arg_id, buf_ptr, buf.len() as i32);
    let java_arg = std::str::from_utf8(&buf[..len as usize]).unwrap();
    eprintln!("rust side-> recv:{}", java_arg);
    //......
}

Pass result to Java

Below is an example of using rust.

1.Export method to another language

public class RustLoadBalance extends AbstractWasmLoadBalance {
    //......
    
    private static final Map<Long, String> RESULTS = new ConcurrentHashMap<>();
    
    @Override
    protected Map<String, Func> initWasmCallJavaFunc(Store<Void> store, Supplier<ByteBuffer> supplier) {
        Map<String, Func> funcMap = new HashMap<>();
        //......
        funcMap.put("put_result", WasmFunctions.wrap(store, WasmValType.I64, WasmValType.I64, WasmValType.I32, WasmValType.I32,
            (argId, addr, len) -> {
                ByteBuffer buf = supplier.get();
                byte[] bytes = new byte[len];
                for (int i = 0; i < len; i++) {
                    bytes[i] = buf.get(addr.intValue() + i);
                }
                String result = new String(bytes, StandardCharsets.UTF_8);
                assertEquals("rust result", result);
                RESULTS.put(argId, result);
                System.out.println("java side->" + result);
                return 0;
            }));
        //......
        return funcMap;
    }
}

2.Import method in another language

#[link(wasm_import_module = "dubbo")]
extern "C" {
    fn put_result(arg_id: i64, addr: i64, len: i32) -> i32;
}

3.Pass result in another language

#[no_mangle]
pub unsafe extern "C" fn doSelect(arg_id: i64) -> i32 {
    //......
    let rust_result = "rust result".as_bytes();
    let result_ptr = rust_result.as_ptr() as i64;
    _ = put_result(arg_id, result_ptr, rust_result.len() as i32);
    //......
}

4.Get result in Java

public class RustLoadBalance extends AbstractWasmLoadBalance {
    //......
    
    private static final Map<Long, String> RESULTS = new ConcurrentHashMap<>();

    @Override
    protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
        return wasmLoader.getWasmExtern(DO_SELECT_METHOD_NAME)
                .map(extern -> {
                    // call WASI function
                    final Long argumentId = getArgumentId(invokers, url, invocation);
                    ARGUMENTS.put(argumentId, new Argument<>(invokers, url, invocation));
                    // WASI cannot easily pass Java objects like JNI, here we pass Long
                    // then we can get the argument by Long
                    final Integer index = WasmFunctions.func(wasmLoader.getStore(), extern.func(), WasmValType.I64, WasmValType.I32)
                            .call(argumentId);
                    ARGUMENTS.remove(argumentId);
                    
                    // For demonstration purposes, the doSelect method has been overwritten
                    final String result = RESULTS.get(argumentId);
                    assertEquals("rust result", result);
                    return invokers.get(index);
                })
                .orElseThrow(() -> new DubboWasmException(
                        DO_SELECT_METHOD_NAME + " function not found in " + wasmLoader.getWasmName()));
    }
}