h3/dist/docs/0.guide/1.basics/0.lifecycle.md

Minimal H(TTP) framework built for high performance and portability.

# Request Lifecycle

> H3 dispatches incoming web requests to final web responses.

Below is an overview of what happens in a H3 server from when an HTTP request arrives until a response is generated.

## 1. Incoming Request

When An HTTP request is made by Browser or [fetch()](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API), server fetch handler receives a [Request](https://developer.mozilla.org/en-US/docs/Web/API/Request) object.

```mermaid
%%{init: {'theme':'neutral'}}%%
flowchart LR
  A1["<code>fetch(request)</code>"] --> A2["<code>server.fetch(request)</code>"]

click A2 "/guide/api/h3#h3fetch"
```

> [!TIP]
> ​[💥 Srvx](https://srvx.h3.dev) provides unified `server.fetch` interface and adds [Node.js compatibility](https://srvx.h3.dev/guide/node).

## 2. Accept Request

H3 Initializes an [`H3Event`](/guide/api/h3event) instance from incoming request, calls [`onRequest`](/guide/api/h3#global-hooks) global hook and finally [`H3.handler`](/guide/api/h3#h3handler) with the initialized event.

```mermaid
%%{init: {'theme':'neutral'}}%%
flowchart LR
  B1["<code>new H3Event(request)</code>"] --> B2["<code>onRequest(event)</code>"] --> B3["<code>h3.handler(event)</code>"]

click B1 "/guide/api/h3event"
click B2 "/guide/api/h3#global-hooks"
click B3 "/guide/api/h3#apphandler"
```

## 3. Dispatch Request

H3 [matches route](/guide/basics/routing) based on `request.url` and `request.method`, calls global [middleware](/guide/basics/middleware) and finally matched route handler function with event.

```mermaid
%%{init: {'theme':'neutral'}}%%
sequenceDiagram
    participant MiddlewareA as Middleware1(event, next)
    participant MiddlewareB as Middleware2(event, next)
    participant Route as RouteHandler(event)

    MiddlewareA->>+MiddlewareB: await next()
    MiddlewareB->>+Route: await next()
    Route-->>-MiddlewareB: rawBody
    MiddlewareB-->>-MiddlewareA: rawBody

```

> [!TIP]
> 🚀 Internally, H3 uses srvx `FastURL` instead of `new URL(req.url).pathname`.

## 4. Send Response

H3 [converts](/guide/basics/response#response-types) returned value and [prepared headers](/guide/basics/response#preparing-response) into a [Response](https://developer.mozilla.org/en-US/docs/Web/API/Response), calls [`onResponse`](/guide/api/h3#global-hooks) global hook and finally returns response back to the server fetch handler.

```mermaid
%%{init: {'theme':'neutral'}}%%
flowchart LR
 D1["Returned Value => Response"] --> D2["<code>onResponse(response)</code>"] --> D3["Response"]

click D1 "/guide/basics/response"
click D2 "/guide/api/h3#global-hooks"
```