--- title: "Execution Context" description: "The Context class manages the complete execution lifecycle for incoming HTTP requests src/context.ts. It encapsulates routing parameters, request headers, environment bindings, and response generat..." last_updated: "2026-10-12T08:14:12.710392+00:00" canonical_url: "https://www.doc0.dev/docs/552ca36e-f67e-41c3-a07a-def9bd9551b0/technical/core-engine/execution-context" ---
Relevant source files The following files were used as context for generating this wiki page: - [src/context.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts) - [src/request.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/request.ts) - [src/types.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/types.ts) - [src/adapter/aws-lambda/handler.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts) - [src/helper/streaming/sse.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts) - [src/helper/route/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/route/index.ts) - [src/middleware/jsx-renderer/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/jsx-renderer/index.ts) - [src/hono-base.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/hono-base.ts) - [src/middleware/request-id/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/request-id/index.ts) - [src/helper/streaming/stream.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/stream.ts) - [src/helper/streaming/text.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/text.ts) - [src/middleware/timing/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/timing/index.ts) - [src/adapter/cloudflare-pages/handler.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts) - [src/adapter/aws-lambda/types.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/types.ts) - [src/middleware/context-storage/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/context-storage/index.ts) - [src/jsx/context.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/jsx/context.ts) - [src/helper/adapter/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts) - [src/adapter/bun/server.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/bun/server.ts) - [src/adapter/lambda-edge/conninfo.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/lambda-edge/conninfo.ts) - [src/middleware/language/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/language/index.ts) - [src/middleware/secure-headers/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/secure-headers/index.ts) - [src/adapter/netlify/handler.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/netlify/handler.ts) - [src/helper/testing/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/testing/index.ts) - [src/middleware/jwt/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/jwt/index.ts) - [src/middleware/ip-restriction/index.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/middleware/ip-restriction/index.ts)
## Overview The `Context` class manages the complete execution lifecycle for incoming HTTP requests [src/context.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L293-L361). It encapsulates routing parameters, request headers, environment bindings, and response generation utilities within a unified interface passed to handlers and middleware [src/context.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L315-L434), [src/request.ts](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/request.ts#L94-L198). Sources: [src/context.ts:293-361](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L293-L361) Sources: [src/context.ts:315-434](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L315-L434), [src/request.ts:94-198](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/request.ts#L94-L198) ## Context Lifecycle and Internal State ### Constructor Initialization and Request Wrapping The `Context` class constructor takes a raw Web Standard `Request` object and an optional `ContextOptions` record [src/context.ts:352-361](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L352-L361). It retains the underlying request as `#rawRequest` and initializes instance parameters such as execution contexts, environment bindings, not-found handlers, path specifications, and routing match results if provided [src/context.ts:300-360](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L300-L360). Sources: [src/context.ts:352-361](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L352-L361) Request parsing is deferred via the `.req` getter property, which lazily instantiates a `HonoRequest` wrapper around `#rawRequest`, `#path`, and `#matchResult` upon first access [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369). Similarly, Cloudflare Pages middleware integration constructs a `Context` instance by passing the event execution context alongside extended bindings [src/adapter/cloudflare-pages/handler.ts:60-64](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L60-L64). Sources: [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369) Sources: [src/adapter/cloudflare-pages/handler.ts:60-64](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L60-L64) ```typescript constructor(req: Request, options?: ContextOptions) { this.#rawRequest = req if (options) { this.#executionCtx = options.executionCtx this.env = options.env this.#notFoundHandler = options.notFoundHandler this.#path = options.path this.#matchResult = options.matchResult } } ``` Sources: [src/context.ts:352-361](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L352-L361) ```typescript return async (executionCtx) => { const context = new Context(executionCtx.request, { env: { ...executionCtx.env, eventContext: executionCtx }, executionCtx, }) ``` Sources: [src/adapter/cloudflare-pages/handler.ts:60-64](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L60-L64) ### Execution State and Response Tracking An active `Context` instance maintains internal tracking flags and response fields throughout the handler execution cycle [src/context.ts:315-345](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L315-L345). The `finalized` boolean flag marks whether a response has been committed or set [src/context.ts:317](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L317). Platform-specific capabilities such as Cloudflare Workers event bindings are accessed through strict getters: the `event` getter verifies the presence of `respondWith` on the execution context, while the `executionCtx` getter validates standard platform contexts, throwing errors if accessed outside a supported environment [src/context.ts:377-397](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L377-L397). Sources: [src/context.ts:315-345](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L315-L345) Sources: [src/context.ts:317](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L317) Sources: [src/context.ts:377-397](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L377-L397) ```typescript get res(): Response { return (this.#res ||= createResponseInstance(null, { headers: (this.#preparedHeaders ??= new Headers()), })) } /** * Sets the Response object for the current request. * * @param _res - The Response object to set. */ set res(_res: Response | undefined) { if (this.#res && _res) { _res = createResponseInstance(_res.body, _res) for (const [k, v] of this.#res.headers.entries()) { if (k === 'content-type') { continue } if (k === 'set-cookie') { const cookies = this.#res.headers.getSetCookie() _res.headers.delete('set-cookie') for (const cookie of cookies) { _res.headers.append('set-cookie', cookie) } } else { _res.headers.set(k, v) } } } this.#res = _res this.finalized = true } ``` Sources: [src/context.ts:403-434](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L403-L434) > [!NOTE] > Setting the response property (`c.res = ...`) automatically marks the context as finalized and copies existing header entries—such as preserving set-cookie arrays and skipping duplicate content types—into the incoming response instance [src/context.ts:414-434](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L414-L434). Sources: [src/context.ts:414-434](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L414-L434) The table below details the internal state properties managed directly within the `Context` class instance. | Field / Property | Internal Variable | Type | Description | | :--- | :--- | :--- | :--- | | `req` | `#req`, `#rawRequest` | `HonoRequest \| undefined`, `Request` | Lazily wrapped request accessor and underlying fetch request [src/context.ts:300-301, 366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L300-L301) | | `env` | `env` | `E['Bindings']` | Environment variables, secrets, and bindings object [src/context.ts:315](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L315) | | `error` | `error` | `Error \| undefined` | Captured error object thrown during middleware or handler execution [src/context.ts:333](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L333) | | `event` | `#executionCtx` | `FetchEventLike` | FetchEvent instance supporting `respondWith` [src/context.ts:336, 377-383](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L336) | | `executionCtx` | `#executionCtx` | `ExecutionContext` | Platform execution context supporting methods like `waitUntil` [src/context.ts:336, 391-397](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L336) | | `res` | `#res`, `#preparedHeaders` | `Response`, `Headers \| undefined` | Current response object and prepared headers buffer [src/context.ts:337, 341, 403-407](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L337) | | `finalized` | `finalized` | `boolean` | Flag indicating whether the response has been sent or locked [src/context.ts:317](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L317) | Sources: [src/context.ts:300-434](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L300-L434) ## Request Parameter and Header Accessors ### HonoRequest Initialization and Parameter Retrieval The `Context` instance exposes incoming request properties through its `.req` property [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369). Accessing `c.req` triggers the lazy instantiation of a `HonoRequest` wrapper, combining the raw underlying `Request` object with route path variables and match results [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369). Sources: [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369) ```typescript get req(): HonoRequest { this.#req ??= new HonoRequest(this.#rawRequest, this.#path, this.#matchResult) return this.#req } ``` Sources: [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369) > [!NOTE] > The `HonoRequest` instance is initialized precisely on first access (`this.#req ??= ...`), avoiding parsing overhead for requests that do not inspect parameters, headers, or query strings [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369). Sources: [src/context.ts:366-369](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L366-L369) ## Variable Storage and Context Typing ### Context Variable Map and Generic Constraints The `Context` class manages scoped variables across middleware and request handlers via a private `#var` instance of JavaScript's `Map` [src/context.ts:316](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L316). These variables are typed through the generic `E` constraint parameter extending `Env`, allowing applications to define strict typing for key-value pairs shared during request execution [src/context.ts:293-295](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L293-L295). Sources: [src/context.ts:316](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L316) Sources: [src/context.ts:293-295](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L293-L295) ```typescript #var: Map | undefined ``` Sources: [src/context.ts:316](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L316) > [!NOTE] > The internal `#var` map is lazily initialized on first write or read operation, preventing unnecessary allocation for request contexts that do not utilize scoped variables [src/context.ts:316](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L316). Sources: [src/context.ts:316](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L316) ## Response Construction and Helpers ### Response Instance Creation and Default Types Response generation relies on underlying Web Standard constructor wrappers [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291). The helper `createResponseInstance` wraps `new Response(body, init)`, providing the foundation for text, stream, and binary outputs [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291). Additionally, `TEXT_PLAIN` defines the default UTF-8 plain text content type string [src/context.ts:279](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L279), while `setDefaultContentType` merges content type headers with existing header records [src/context.ts:281-286](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L281-L286). Sources: [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291) Sources: [src/context.ts:279](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L279), [src/context.ts:281-286](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L281-L286) ```typescript export const TEXT_PLAIN = 'text/plain; charset=UTF-8' const setDefaultContentType = (contentType: string, headers?: HeaderRecord): HeaderRecord => { return { 'Content-Type': contentType, ...headers, } } const createResponseInstance = ( body?: BodyInit | null | undefined, init?: globalThis.ResponseInit ): Response => new Response(body, init) ``` Sources: [src/context.ts:279-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L279-L291) > [!WARNING] > Modifying headers after a response has been finalized forces Hono to instantiate a new underlying `Response` object to prevent mutation errors on immutable response streams [src/context.ts:516-518](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L516-L518). Sources: [src/context.ts:516-518](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L516-L518) ### Stream SSE Execution Walkthrough The `streamSSE` helper orchestrates Server-Sent Events by initializing a transform stream, invoking `c.header` to configure transport headers, and utilizing `createResponseInstance` to generate the final response [src/helper/streaming/sse.ts:72-100](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L72-L100), [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291). Sources: [src/helper/streaming/sse.ts:72-100](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L72-L100), [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291) 1. `streamSSE` initializes a `TransformStream` and wraps it in an `SSEStreamingApi` instance [src/helper/streaming/sse.ts:77-78](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L77-L78). 2. `isOldBunVersion()` checks for legacy runtime behavior, binding an abort listener to `c.req.raw.signal` if necessary [src/helper/streaming/sse.ts:80-87](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L80-L87). 3. `contextStash.set` caches the context against the response readable stream to prevent premature garbage collection in Bun [src/helper/streaming/sse.ts:89-90](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L89-L90). 4. `c.header` sets required transport and protocol headers including `Transfer-Encoding`, `Content-Type`, `Cache-Control`, and `Connection` [src/helper/streaming/sse.ts:92-95](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L92-L95), [src/context.ts:515-527](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L515-L527). 5. `run` executes the user callback with error handling and automatic stream closure [src/helper/streaming/sse.ts:47-68](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L47-L68), [97](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L97). 6. `createResponseInstance` is invoked through response helpers to construct the final Response wrapping `stream.responseReadable` [src/helper/streaming/sse.ts:99](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L99), [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291). Sources: [src/helper/streaming/sse.ts:77-78](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L77-L78) Sources: [src/helper/streaming/sse.ts:80-87](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L80-L87) Sources: [src/helper/streaming/sse.ts:89-90](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L89-L90) Sources: [src/helper/streaming/sse.ts:92-95](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L92-L95), [src/context.ts:515-527](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L515-L527) Sources: [src/helper/streaming/sse.ts:47-68](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L47-L68), [src/helper/streaming/sse.ts:97](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L97) Sources: [src/helper/streaming/sse.ts:99](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L99), [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291) ```typescript export const streamSSE = ( c: Context, cb: (stream: SSEStreamingApi) => Promise, onError?: (e: Error, stream: SSEStreamingApi) => Promise ): Response => { const { readable, writable } = new TransformStream() const stream = new SSEStreamingApi(writable, readable) // Until Bun v1.1.27, Bun didn't call cancel() on the ReadableStream for Response objects from Bun.serve() if (isOldBunVersion()) { c.req.raw.signal.addEventListener('abort', () => { if (!stream.closed) { stream.abort() } }) } // in bun, `c` is destroyed when the request is returned, so hold it until the end of streaming contextStash.set(stream.responseReadable, c) c.header('Transfer-Encoding', 'chunked') c.header('Content-Type', 'text/event-stream') c.header('Cache-Control', 'no-cache') c.header('Connection', 'keep-alive') run(stream, cb, onError) return c.newResponse(stream.responseReadable) } ``` Sources: [src/helper/streaming/sse.ts:72-100](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L72-L100) ```mermaid sequenceDiagram participant streamSSE as streamSSE (sse.ts) participant Context as Context (context.ts) participant header as header (context.ts) participant createResponseInstance as createResponseInstance (context.ts) streamSSE->>Context: c.header('Transfer-Encoding', 'chunked') Context->>header: header(name, value, options) streamSSE->>Context: c.newResponse(stream.responseReadable) Context->>createResponseInstance: createResponseInstance(body, init) ``` Sources: [src/helper/streaming/sse.ts:72-100](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L72-L100), [src/context.ts:288-291](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L288-L291) > [!NOTE] An internal `contextStash` WeakMap holds a reference to the active `Context` keyed by `stream.responseReadable`, ensuring the request context remains accessible throughout long-lived streaming connections [src/helper/streaming/sse.ts:70-90](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L70-L90). Sources: [src/helper/streaming/sse.ts:70-90](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/streaming/sse.ts#L70-L90) ## Adapter Bindings and Environment Access ### Runtime Identification and Environment Resolution Hono resolves environment bindings and execution contexts across heterogeneous JavaScript runtimes by combining runtime detection helpers with platform-specific adapter handlers. The `getRuntimeKey()` utility inspects `globalThis` properties and user agent strings to classify the active platform into one of the supported runtime identifiers [src/helper/adapter/index.ts:50-84](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L50-L84). Once identified, the `env()` helper dynamically dispatches to the correct environment provider, returning process environment variables or platform-native binding stores [src/helper/adapter/index.ts:10-41](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L10-L41). Sources: [src/helper/adapter/index.ts:50-84](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L50-L84) Sources: [src/helper/adapter/index.ts:10-41](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L10-L41) | Runtime Key | Detection Mechanism | Environment Source | | :--- | :--- | :--- | | `bun` | `navigator.userAgent` starts with `Bun` | `process.env` | | `node` | `navigator.userAgent` starts with `Node.js` or `process.release.name === 'node'` | `process.env` | | `deno` | `navigator.userAgent` starts with `Deno` | `Deno.env.toObject()` | | `workerd` | `navigator.userAgent` starts with `Cloudflare-Workers` | `c.env` | | `edge-light` | `globalThis.EdgeRuntime` is a string | `process.env` | | `fastly` | `globalThis.fastly !== undefined` | `{}` | | `other` | Fallback when no platform signature matches | `{}` | Sources: [src/helper/adapter/index.ts:8-48](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L8-L48) ```typescript export type Runtime = 'node' | 'deno' | 'bun' | 'workerd' | 'fastly' | 'edge-light' | 'other' export const env = < T extends Record, C extends Context = Context<{ Bindings: T }>, >( c: T extends Record ? Context : C, runtime?: Runtime ): T & C['env'] => { // eslint-disable-next-line @typescript-eslint/no-explicit-any const global = globalThis as any const globalEnv = global?.process?.env as T runtime ??= getRuntimeKey() const runtimeEnvHandlers: Record T> = { bun: () => globalEnv, node: () => globalEnv, 'edge-light': () => globalEnv, deno: () => { // eslint-disable-next-line @typescript-eslint/ban-ts-comment // @ts-ignore return Deno.env.toObject() as T }, workerd: () => c.env, // On Fastly Compute, you can use the ConfigStore to manage user-defined data. fastly: () => ({}) as T, other: () => ({}) as T, } return runtimeEnvHandlers[runtime]() } export const knownUserAgents: Partial> = { deno: 'Deno', bun: 'Bun', workerd: 'Cloudflare-Workers', node: 'Node.js', } ``` Sources: [src/helper/adapter/index.ts:8-48](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L8-L48) > [!NOTE] > The `env()` helper requires an explicit runtime parameter or falls back to `getRuntimeKey()`, which inspects `navigator.userAgent` before checking runtime-specific global objects [src/helper/adapter/index.ts:17-23](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L17-L23). Sources: [src/helper/adapter/index.ts:17-23](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/helper/adapter/index.ts#L17-L23) ### Platform Adapter Handlers and Execution Contexts Cloudflare Pages, AWS Lambda, and Netlify integrate with Hono by mapping native platform events and execution contexts into the standard `app.fetch()` signature [src/adapter/aws-lambda/handler.ts:268-272](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts#L268-L272), [src/adapter/cloudflare-pages/handler.ts:37-45](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L37-L45), [src/adapter/netlify/handler.ts:8](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/netlify/handler.ts#L8). Cloudflare Pages passes `eventContext.request`, environment bindings augmented with `eventContext`, and an execution options object containing `waitUntil` and `passThroughOnException` callbacks [src/adapter/cloudflare-pages/handler.ts:37-45](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L37-L45). Sources: [src/adapter/aws-lambda/handler.ts:268-272](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts#L268-L272), [src/adapter/cloudflare-pages/handler.ts:37-45](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L37-L45), [src/adapter/netlify/handler.ts:8](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/netlify/handler.ts#L8) Sources: [src/adapter/cloudflare-pages/handler.ts:37-45](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L37-L45) ```typescript export const handle = ( app: Hono ): PagesFunction => (eventContext) => { return app.fetch( eventContext.request, { ...eventContext.env, eventContext }, { waitUntil: eventContext.waitUntil, passThroughOnException: eventContext.passThroughOnException, props: {}, } ) } ``` Sources: [src/adapter/cloudflare-pages/handler.ts:32-46](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/cloudflare-pages/handler.ts#L32-L46) AWS Lambda adapters process incoming API Gateway or ALB events via event processors (`EventV1Processor` and `EventV2Processor`), converting event payloads into standard `Request` instances and passing the raw `event`, `requestContext`, and `lambdaContext` through to `app.fetch()` [src/adapter/aws-lambda/handler.ts:252-272](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts#L252-L272). Similarly, Netlify's adapter delegates incoming requests directly to `app.fetch()` accompanied by the Netlify execution context object [src/adapter/netlify/handler.ts:4-10](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/netlify/handler.ts#L4-L10). Connection info helpers, such as the Lambda@Edge implementation, extract client IP addresses directly from nested event records stored within `c.env` [src/adapter/lambda-edge/conninfo.ts:11-14](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/lambda-edge/conninfo.ts#L11-L14). Sources: [src/adapter/aws-lambda/handler.ts:252-272](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts#L252-L272) Sources: [src/adapter/netlify/handler.ts:4-10](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/netlify/handler.ts#L4-L10) Sources: [src/adapter/lambda-edge/conninfo.ts:11-14](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/lambda-edge/conninfo.ts#L11-L14) ```typescript return async (event, lambdaContext?) => { const processor = getProcessor(event) let req, requestContext try { req = processor.createRequest(event) requestContext = getRequestContext(event) } catch (error) { console.error('Error processing request:', error) const errorResponse = error instanceof TypeError ? new Response('Invalid request', { status: 400 }) : new Response('Internal Server Error', { status: 500 }) return processor.createResult(event, errorResponse, { isContentTypeBinary }) } const res = await app.fetch(req, { event, requestContext, lambdaContext, }) return processor.createResult(event, res, { isContentTypeBinary }) } } ``` Sources: [src/adapter/aws-lambda/handler.ts:252-276](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/adapter/aws-lambda/handler.ts#L252-L276) > [!WARNING] > Accessing `c.event` or `c.executionCtx` on platforms that do not supply a matching execution context object will throw an explicit error (`This context has no FetchEvent` or `This context has no ExecutionContext`) [src/context.ts:377-397](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L377-L397). Sources: [src/context.ts:377-397](https://github.com/blade47/hono/blob/e50df01453e71b071c3e6136b161b160b9fdf916/src/context.ts#L377-L397) ## Related - [Request Lifecycle](https://www.doc0.dev/docs/552ca36e-f67e-41c3-a07a-def9bd9551b0/technical/core-engine/request-lifecycle) - [Application Core](https://www.doc0.dev/docs/552ca36e-f67e-41c3-a07a-def9bd9551b0/technical/core-engine/application-core) - [Context Storage](https://www.doc0.dev/docs/552ca36e-f67e-41c3-a07a-def9bd9551b0/technical/traffic-middleware/context-storage) ## Sitemap See the full [sitemap](https://www.doc0.dev/docs/552ca36e-f67e-41c3-a07a-def9bd9551b0/llms.txt) for all pages in this wiki.