Add native LLM core foundation (#24712)

packages/llm/src/route/endpoint.ts

@@ -0,0 +1,41 @@
+import type { LLMRequest } from "../schema"
+import * as ProviderShared from "../protocols/shared"
+
+export interface EndpointInput<Body> {
+  readonly request: LLMRequest
+  readonly body: Body
+}
+
+export type EndpointPart<Body> = string | ((input: EndpointInput<Body>) => string)
+
+/**
+ * Declarative URL construction for one route.
+ *
+ * `Endpoint` carries only the path. The host always lives on `model.baseURL`,
+ * supplied by the provider helper that constructs the model. `render(...)`
+ * just appends the path (and any `model.queryParams`) to that host.
+ *
+ * `path` may be a string or a function of `EndpointInput`, for routes whose
+ * URL embeds the model id, region, or another body field (e.g. Bedrock,
+ * Gemini).
+ */
+export interface Endpoint<Body> {
+  readonly path: EndpointPart<Body>
+}
+
+/** Construct an `Endpoint` from a path string or path function. */
+export const path = <Body>(value: EndpointPart<Body>): Endpoint<Body> => ({ path: value })
+
+const renderPart = <Body>(part: EndpointPart<Body>, input: EndpointInput<Body>) =>
+  typeof part === "function" ? part(input) : part
+
+export const render = <Body>(endpoint: Endpoint<Body>, input: EndpointInput<Body>) => {
+  const url = new URL(
+    `${ProviderShared.trimBaseUrl(input.request.model.baseURL)}${renderPart(endpoint.path, input)}`,
+  )
+  const params = input.request.model.queryParams
+  if (params) for (const [key, value] of Object.entries(params)) url.searchParams.set(key, value)
+  return url
+}
+
+export * as Endpoint from "./endpoint"