Module wit_component::metadata

Definition for encoding of custom sections within core wasm modules of component-model related data.

When creating a component from a source language the high-level process for doing this is that code will be generated into the source language by wit-bindgen or a similar tool which will be compiled down to core wasm. The core wasm file is then fed into wit-component and a component is created. This means that the componentization process is decoupled from the binding generation process and intentionally affords for linking together libraries into the main core wasm module that import different interfaces.

The purpose of this module is to define an intermediate format to reside in a custom section in the core wasm output. This intermediate format is carried through the wasm linker through a custom section whose name starts with component-type. This custom section is created per-language-binding-generation and consumed by slurping up all the sections during the component creation process.

The custom section here contains World, the interpretation of a “world” of a component, along with how strings are encoded for all the specified interfaces. Currently the encoding is:

• First, a version byte (CURRENT_VERSION). This is intended to detect mismatches between different versions of the binding generator and wit-component which may or may not become a problem over time.

• Next a string encoding byte.

• Afterwards a “types only” component encoding of a World package through the ComponentEncoder::types_only configuration.

Structs

BindgenMetadata

Result of extracting interfaces embedded within a core wasm file.

Functions

decode

This function will parse the wasm binary given as input and return a BindgenMetadata which extracts the custom sections describing component-level types from within the binary itself.

encode

Creates a component-type* custom section to be decoded by decode above.