RPC transforms API

Definition and installation

defineTransform<TTarget, TContext>()

Starts a transform definition. Chain .caller(factory) and/or .callee(factory).

registerTransform(transform, options?)

Binds callee options for applyTransforms. Parameterless transforms omit options.

applyTransforms(TargetClass, config)

Installs transforms on all async methods or selected methods. Installation mutates the prototype and is cumulative.

Caller wrapping

.with(transform, options?)

Added to configured bindings by the Vite plugin. Returns a target with transformed async method types.

createTransformStub(rawTarget)

Manually wraps one Durable Object stub or Worker service binding.

withTransforms(namespace)

Manually wraps a Durable Object namespace so returned stubs expose .with().

Context

createTransformContextTarget(target, context)

Creates a promise-pipelined target carrying typed context. Return it from setContext() when a caller transform invokes next({ context }).

TransformContextTarget

The underlying context-target class. Prefer the factory in normal integrations.

Vite

doTransforms(options?)

Import from @durability/transforms/vite:

doTransforms({ wrangler: './wrangler.jsonc' })

The plugin validates Wrangler configuration, wraps matching bindings, and emits do-transforms.generated.d.ts by default.

Built-in return types

Transform	Caller-visible return
betterResultCodec	Preserved or rehydrated Result<T, E>
errorBoundary	Result<T, unknown>
abortAsSuccess	Result<T | undefined, never>
timeout	Original method return type
retry	Original method return type
largeObjectStream	Original method return type after runtime validation

Built-in errors

• CallerTimeoutError
• LargeObjectEncodeLimitError
• LargeObjectDecodeLimitError
• LargeObjectValidationError

Transform chains check target compatibility, caller and callee options, context compatibility, async method names, and transformed return types at compile time.