HTTP Request and Response Parameter Mapping (TypeScript)

Overview

When an agent is exposed over HTTP, Golem maps parts of each HTTP request to constructor and method parameters. This skill covers how path segments, query parameters, headers, and request bodies are mapped, which types are supported for each, and how return types map to HTTP responses.

Path Variables

Path variables {varName} in mount or endpoint paths map to parameters by name:

// Mount path variables → constructor parameters
@agent({ mount: '/api/tasks/{name}' })
class TaskAgent extends BaseAgent {
  constructor(readonly name: string) { super(); }
 
  // Endpoint path variables → method parameters
  @endpoint({ get: '/items/{itemId}' })
  async getItem(itemId: string): Promise<Item> { ... }
}

Remaining (catch-all) path variables capture everything after a prefix:

@endpoint({ get: '/files/{*path}' })
async getFile(path: string): Promise<FileContent> { ... }
// GET .../files/docs/readme.md → path = "docs/readme.md"

Catch-all variables can only appear as the last path segment and are not allowed in mount paths.

Query Parameters

Specified in the endpoint path using ?key={var} syntax:

@endpoint({ get: '/search?q={query}&limit={maxResults}' })
async search(query: string, maxResults: number): Promise<SearchResult[]> { ... }
// GET .../search?q=hello&limit=10

Header Variables

Map HTTP headers to parameters using the headers option on @endpoint():

@endpoint({
  get: '/data',
  headers: { 'X-Request-Id': 'requestId', 'Authorization': 'token' }
})
async getData(requestId: string, token: string): Promise<Data> { ... }

Headers can also be mapped to constructor parameters at the mount level:

@agent({
  mount: '/api',
  headers: { 'X-Api-Key': 'apiKey' }
})
class ApiAgent extends BaseAgent {
  constructor(readonly apiKey: string) { super(); }
}

When using mount-level headers, all constructor parameters must be satisfied by either path variables or header variables.

Supported Types for Path, Query, and Header Variables

Only these types can be used for parameters bound to path/query/header variables (the value is parsed from the URL/header string):

For query parameters and headers only (not path variables), two additional wrapper types are supported:

All other types (objects, interfaces, nested arrays, Map, etc.) can only be used as body parameters.

POST Request Body Mapping

For POST/PUT/DELETE endpoints, method parameters not bound to path variables, query parameters, or headers are populated from the JSON request body:

@endpoint({ post: '/items/{id}' })
async updateItem(id: string, name: string, count: number): Promise<Item> { ... }
// POST .../items/123
// Body: { "name": "Widget", "count": 5 }
// → id from path, name and count from body

Each unmapped parameter becomes a top-level field in the expected JSON body object. Field names use the original camelCase parameter names.

⚠️ Important: The request body is always a JSON object with parameter names as keys — even when there is only a single body parameter. For example, an endpoint decide(decision: string) expects {"decision": "approved"}, never a bare string like "approved". Sending a non-object JSON value or plain text will fail with REQUEST_JSON_BODY_PARSING_FAILED.

Binary Request and Response Bodies

Use UnstructuredBinary from the SDK for raw binary payloads:

import { UnstructuredBinary } from '@golemcloud/golem-ts-sdk';
 
// Accepting any binary content type
@endpoint({ post: '/upload/{bucket}' })
async upload(bucket: string, payload: UnstructuredBinary): Promise<number> {
  if (payload.tag === 'url') return -1;
  return payload.val.byteLength;
}
 
// Restricting to specific MIME types
@endpoint({ post: '/upload-image/{bucket}' })
async uploadImage(
  bucket: string,
  payload: UnstructuredBinary<["image/gif"]>
): Promise<number> { ... }
 
// Returning binary data
@endpoint({ get: '/download' })
async download(): Promise<UnstructuredBinary> {
  return UnstructuredBinary.fromInline(
    new Uint8Array([1, 2, 3]),
    'application/octet-stream'
  );
}

Return Type to HTTP Response Mapping

Data Type to JSON Mapping

Principal Parameter

When authentication is enabled, methods can receive a Principal parameter with info about the authenticated user. Principal parameters are automatically populated and must not be mapped to path/query/header variables:

import { Principal } from '@golemcloud/golem-ts-sdk';
 
@endpoint({ get: '/whoami', auth: true })
async whoAmI(principal: Principal): Promise<{ value: Principal }> {
  return { value: principal };
}
 
// Principal can appear at any position among parameters
@endpoint({ get: '/data/{id}' })
async getData(id: string, principal: Principal): Promise<Data> { ... }