Wasm

Since Camel 4.4

Only producer is supported

WebAssembly (Wasm) is a low-level bytecode format designed as a portable target for the compilation of high-level languages like C, C++, and Rust, enabling deployment on the web for client and server applications.

This component provides support to leverage Wasm functions for message transformation.

Maven users will need to add the following dependency to their pom.xml for this component:

    <dependency>
        <groupId>org.apache.camel</groupId>
        <artifactId>camel-wasm</artifactId>
        <version>${camel-version}</version>
    </dependency>

URI format

wasm://functionName?[options]

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The Wasm component supports 2 options, which are listed below.

Name Description Default Type

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

Endpoint Options

The Wasm endpoint is configured using URI syntax:

wasm:functionName

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

functionName (producer)

Required The Function Name.

String

Query Parameters (2 parameters)

Name Description Default Type

module (producer)

Required Set the module (the distributable, loadable, and executable unit of code in WebAssembly) resource that provides the producer function.

String

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

Writing A Wasm processor

In Wasm, sharing objects between the host, in this case the JVM, and the Wasm module is deliberately restricted and as of today, it requires a number of steps:

  1. From the host, call a function inside the webassembly module that allocates a block of memory and returns its address, then save it

  2. From the host, write the data that should be exchanged with the Wasm module to the saved address

  3. From the host, invoke the required function passing both the address where the data is written and its size

  4. From the Wasm module, read the data and process it

  5. From the host, release the memory when done

Providing functions for memory management

The module hosting the function must provide the functions to allocate/deallocate memory that must be named alloc and dealloc respectively.

Here an example of the mentioned functions implemented in Rust:

pub extern "C" fn alloc(size: u32) -> *mut u8 {
    let mut buf = Vec::with_capacity(size as usize);
    let ptr = buf.as_mut_ptr();

    // tell Rust not to clean this up
    mem::forget(buf);

    ptr
}

pub unsafe extern "C" fn dealloc(ptr: &mut u8, len: i32) {
    // Retakes the pointer which allows its memory to be freed.
    let _ = Vec::from_raw_parts(ptr, 0, len as usize);
}

Data shapes

It is not possible to share a Java object with the Wasm module directly and as mentioned before, data exchange leverages Wasm’s memory that can be accessed by both the host and the guest runtimes. At this stage, the data structure that the component exchange with the Wasm function is a subset of the Apache Camel Message, containing headers the body encoded as a base64 string:

public static class Wrapper {
    @JsonProperty
    public Map<String, String> headers = new HashMap<>();

    @JsonProperty
    public byte[] body;
}

Data processing

The component expects the processing function to have the following signature:

fn function(ptr: u32, len: u32) -> u64

  • it accepts two 32bit unsigned integers arguments

    • a pointer to the memory location when the input data has been written (ptr)

    • the size of the input data (len)

  • it returns a 64bit unsigned integer where:

    • the first 32bit represent a pointer to the return data

    • the last 31bit represent the size of the return data, which must have the same data shape discussed above unless there is an error (see below)

    • the most significant bit of the returned data size, is reserved to signal an error, so if it is set, then the return data could contain an error message/code/etc

Here an example of a complete function:

#[derive(Serialize, Deserialize)]
struct Message {
    headers: HashMap<String, serde_json::Value>,

    #[serde(with = "Base64Standard")]
    body: Vec<u8>,
}

#[cfg_attr(all(target_arch = "wasm32"), export_name = "process")]
#[no_mangle]
pub extern fn process(ptr: u32, len: u32) -> u64 {
    let bytes = unsafe {
        slice::from_raw_parts_mut(
            ptr as *mut u8,
            len as usize)
    };

    let mut msg: Message = serde_json::from_slice(bytes).unwrap();



    let out_vec = serde_json::to_vec(&msg).unwrap();
    let out_len = out_vec.len();
    let out_ptr = alloc(out_len as u32);

    unsafe {
        std::ptr::copy_nonoverlapping(
            out_vec.as_ptr(),
            out_ptr,
            out_len as usize)
    };

    return ((out_ptr as u64) << 32) | out_len as u64;
}

Examples

Supposing we have compiled a Wasm module containing the function above, then it can be called in a Camel Route by its name and module resource location:

 try (CamelContext cc = new DefaultCamelContext()) {
    FluentProducerTemplate pt = cc.createFluentProducerTemplate();

    cc.addRoutes(new RouteBuilder() {
        @Override
        public void configure() throws Exception {
            from("direct:in")
                    .toF("wasm:process?module=classpath://functions.wasm");
        }
    });
    cc.start();

    Exchange out = pt.to("direct:in")
            .withHeader("foo", "bar")
            .withBody("hello")
            .request(Exchange.class);

    assertThat(out.getMessage().getHeaders())
            .containsEntry("foo", "bar");
    assertThat(out.getMessage().getBody(String.class))
            .isEqualTo("HELLO");
}