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# Handling handlers


<!-- WARNING: THIS FILE WAS AUTOGENERATED! DO NOT EDIT! -->

``` python
from fasthtml.common import *
from collections import namedtuple
from typing import TypedDict
from datetime import datetime
import json,time
```

``` python
app = FastHTML()
```

The [`FastHTML`](https://www.fastht.ml/docs/api/core.html#fasthtml)
class is the main application class for FastHTML apps.

``` python
rt = app.route
```

`app.route` is used to register route handlers. It is a decorator, which
means we place it before a function that is used as a handler. Because
it’s used frequently in most FastHTML applications, we often alias it as
`rt`, as we do here.

## Basic Route Handling

``` python
@rt("/hi")
def get(): return 'Hi there'
```

Handler functions can return strings directly. These strings are sent as
the response body to the client.

``` python
cli = Client(app)
```

[`Client`](https://www.fastht.ml/docs/api/core.html#client) is a test
client for FastHTML applications. It allows you to simulate requests to
your app without running a server.

``` python
cli.get('/hi').text
```

    'Hi there'

The `get` method on a
[`Client`](https://www.fastht.ml/docs/api/core.html#client) instance
simulates GET requests to the app. It returns a response object that has
a `.text` attribute, which you can use to access the body of the
response. It calls `httpx.get` internally – all httpx HTTP verbs are
supported.

``` python
@rt("/hi")
def post(): return 'Postal'
cli.post('/hi').text
```

    'Postal'

Handler functions can be defined for different HTTP methods on the same
route. Here, we define a
[`post`](https://www.fastht.ml/docs/explains/stripe.html#post) handler
for the `/hi` route. The
[`Client`](https://www.fastht.ml/docs/api/core.html#client) instance can
simulate different HTTP methods, including POST requests.

## Request and Response Objects

``` python
@app.get("/hostie")
def show_host(req): return req.headers['host']
cli.get('/hostie').text
```

    'testserver'

Handler functions can accept a `req` (or `request`) parameter, which
represents the incoming request. This object contains information about
the request, including headers. In this example, we return the `host`
header from the request. The test client uses ‘testserver’ as the
default host.

In this example, we use `@app.get("/hostie")` instead of
`@rt("/hostie")`. The `@app.get()` decorator explicitly specifies the
HTTP method (GET) for the route, while `@rt()` by default handles both
GET and POST requests.

``` python
@rt
def yoyo(): return 'a yoyo'
cli.post('/yoyo').text
```

    'a yoyo'

If the `@rt` decorator is used without arguments, it uses the function
name as the route path. Here, the `yoyo` function becomes the handler
for the `/yoyo` route. This handler responds to GET and POST methods,
since a specific method wasn’t provided.

``` python
@rt
def ft1(): return Html(Div('Text.'))
print(cli.get('/ft1').text)
```

     <!doctype html>
     <html>
       <div>Text.</div>
     </html>

Handler functions can return
[`FT`](https://www.fastht.ml/docs/explains/explaining_xt_components.html)
objects, which are automatically converted to HTML strings. The `FT`
class can take other `FT` components as arguments, such as `Div`. This
allows for easy composition of HTML elements in your responses.

``` python
@app.get
def autopost(): return Html(Div('Text.', hx_post=yoyo.to()))
print(cli.get('/autopost').text)
```

     <!doctype html>
     <html>
       <div hx-post="/yoyo">Text.</div>
     </html>

The `rt` decorator modifies the `yoyo` function by adding a `to()`
method. This method returns the route path associated with the handler.
It’s a convenient way to reference the route of a handler function
dynamically.

In the example, `yoyo.to()` is used as the value for `hx_post`. This
means when the div is clicked, it will trigger an HTMX POST request to
the route of the `yoyo` handler. This approach allows for flexible, DRY
code by avoiding hardcoded route strings and automatically updating if
the route changes.

This pattern is particularly useful in larger applications where routes
might change, or when building reusable components that need to
reference their own routes dynamically.

``` python
@app.get
def autoget(): return Html(Body(Div('Text.', cls='px-2', hx_post=show_host.to(a='b'))))
print(cli.get('/autoget').text)
```

     <!doctype html>
     <html>
       <body>
         <div hx-post="/hostie?a=b" class="px-2">Text.</div>
       </body>
     </html>

The `rt()` method of handler functions can also accept parameters. When
called with parameters, it returns the route path with a query string
appended. In this example, `show_host.to(a='b')` generates the path
`/hostie?a=b`.

The `Body` component is used here to demonstrate nesting of FT
components. `Div` is nested inside `Body`, showcasing how you can create
more complex HTML structures.

The `cls` parameter is used to add a CSS class to the `Div`. This
translates to the `class` attribute in the rendered HTML. (`class` can’t
be used as a parameter name directly in Python since it’s a reserved
word.)

``` python
@rt('/ft2')
def get(): return Title('Foo'),H1('bar')
print(cli.get('/ft2').text)
```

     <!doctype html>
     <html>
       <head>
         <title>Foo</title>
         <meta charset="utf-8">
         <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
    <script src="https://unpkg.com/[email protected]/dist/htmx.min.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/[email protected]/fasthtml.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/surreal@main/surreal.js"></script><script src="https://cdn.jsdelivr.net/gh/gnat/css-scope-inline@main/script.js"></script><script>
        function sendmsg() {
            window.parent.postMessage({height: document.documentElement.offsetHeight}, '*');
        }
        window.onload = function() {
            sendmsg();
            document.body.addEventListener('htmx:afterSettle',    sendmsg);
            document.body.addEventListener('htmx:wsAfterMessage', sendmsg);
        };</script>   </head>
       <body>
         <h1>bar</h1>
       </body>
     </html>

Handler functions can return multiple `FT` objects as a tuple. The first
item is treated as the `Title`, and the rest are added to the `Body`.
When the request is not an HTMX request, FastHTML automatically adds
necessary HTML boilerplate, including default `head` content with
required scripts.

When using `app.route` (or `rt`), if the function name matches an HTTP
verb (e.g., `get`,
[`post`](https://www.fastht.ml/docs/explains/stripe.html#post), `put`,
`delete`), that HTTP method is automatically used for the route. In this
case, a path must be explicitly provided as an argument to the
decorator.

``` python
hxhdr = {'headers':{'hx-request':"1"}}
print(cli.get('/ft2', **hxhdr).text)
```

     <title>Foo</title>
     <h1>bar</h1>

For HTMX requests (indicated by the `hx-request` header), FastHTML
returns only the specified components without the full HTML structure.
This allows for efficient partial page updates in HTMX applications.

``` python
@rt('/ft3')
def get(): return H1('bar')
print(cli.get('/ft3', **hxhdr).text)
```

     <h1>bar</h1>

When a handler function returns a single `FT` object for an HTMX
request, it’s rendered as a single HTML partial.

``` python
@rt('/ft4')
def get(): return Html(Head(Title('hi')), Body(P('there')))

print(cli.get('/ft4').text)
```

     <!doctype html>
     <html>
       <head>
         <title>hi</title>
       </head>
       <body>
         <p>there</p>
       </body>
     </html>

Handler functions can return a complete `Html` structure, including
`Head` and `Body` components. When a full HTML structure is returned,
FastHTML doesn’t add any additional boilerplate. This gives you full
control over the HTML output when needed.

``` python
@rt
def index(): return "welcome!"
print(cli.get('/').text)
```

    welcome!

The `index` function is a special handler in FastHTML. When defined
without arguments to the `@rt` decorator, it automatically becomes the
handler for the root path (`'/'`). This is a convenient way to define
the main page or entry point of your application.

## Path and Query Parameters

``` python
@rt('/user/{nm}', name='gday')
def get(nm:str=''): return f"Good day to you, {nm}!"
cli.get('/user/Alexis').text
```

    'Good day to you, Alexis!'

Handler functions can use path parameters, defined using curly braces in
the route – this is implemented by Starlette directly, so all Starlette
path parameters can be used. These parameters are passed as arguments to
the function.

The `name` parameter in the decorator allows you to give the route a
name, which can be used for URL generation.

In this example, `{nm}` in the route becomes the `nm` parameter in the
function. The function uses this parameter to create a personalized
greeting.

``` python
@app.get
def autolink(): return Html(Div('Text.', link=uri('gday', nm='Alexis')))
print(cli.get('/autolink').text)
```

     <!doctype html>
     <html>
       <div href="/user/Alexis">Text.</div>
     </html>

The [`uri`](https://www.fastht.ml/docs/api/core.html#uri) function is
used to generate URLs for named routes. It takes the route name as its
first argument, followed by any path or query parameters needed for that
route.

In this example, `uri('gday', nm='Alexis')` generates the URL for the
route named ‘gday’ (which we defined earlier as ‘/user/{nm}’), with
‘Alexis’ as the value for the ‘nm’ parameter.

The `link` parameter in FT components sets the `href` attribute of the
rendered HTML element. By using
[`uri()`](https://www.fastht.ml/docs/api/core.html#uri), we can
dynamically generate correct URLs even if the underlying route structure
changes.

This approach promotes maintainable code by centralizing route
definitions and avoiding hardcoded URLs throughout the application.

``` python
@rt('/link')
def get(req): return f"{req.url_for('gday', nm='Alexis')}; {req.url_for('show_host')}"

cli.get('/link').text
```

    'http://testserver/user/Alexis; http://testserver/hostie'

The `url_for` method of the request object can be used to generate URLs
for named routes. It takes the route name as its first argument,
followed by any path parameters needed for that route.

In this example, `req.url_for('gday', nm='Alexis')` generates the full
URL for the route named ‘gday’, including the scheme and host.
Similarly, `req.url_for('show_host')` generates the URL for the
‘show_host’ route.

This method is particularly useful when you need to generate absolute
URLs, such as for email links or API responses. It ensures that the
correct host and scheme are included, even if the application is
accessed through different domains or protocols.

``` python
app.url_path_for('gday', nm='Jeremy')
```

    '/user/Jeremy'

The `url_path_for` method of the application can be used to generate URL
paths for named routes. Unlike `url_for`, it returns only the path
component of the URL, without the scheme or host.

In this example, `app.url_path_for('gday', nm='Jeremy')` generates the
path ‘/user/Jeremy’ for the route named ‘gday’.

This method is useful when you need relative URLs or just the path
component, such as for internal links or when constructing URLs in a
host-agnostic manner.

``` python
@rt('/oops')
def get(nope): return nope
r = cli.get('/oops?nope=1')
print(r)
r.text
```

    <Response [200 OK]>

    /Users/iflath/git/AnswerDotAI/fasthtml/build/__editable__.python_fasthtml-0.12.1-py3-none-any/fasthtml/core.py:188: UserWarning: `nope has no type annotation and is not a recognised special name, so is ignored.
      if arg!='resp': warn(f"`{arg} has no type annotation and is not a recognised special name, so is ignored.")

    ''

Handler functions can include parameters, but they must be
type-annotated or have special names (like `req`) to be recognized. In
this example, the `nope` parameter is not annotated, so it’s ignored,
resulting in a warning.

When a parameter is ignored, it doesn’t receive the value from the query
string. This can lead to unexpected behavior, as the function attempts
to return `nope`, which is undefined.

The `cli.get('/oops?nope=1')` call succeeds with a 200 OK status because
the handler doesn’t raise an exception, but it returns an empty
response, rather than the intended value.

To fix this, you should either add a type annotation to the parameter
(e.g., `def get(nope: str):`) or use a recognized special name like
`req`.

``` python
@rt('/html/{idx}')
def get(idx:int): return Body(H4(f'Next is {idx+1}.'))
print(cli.get('/html/1', **hxhdr).text)
```

     <body>
       <h4>Next is 2.</h4>
     </body>

Path parameters can be type-annotated, and FastHTML will automatically
convert them to the specified type if possible. In this example, `idx`
is annotated as `int`, so it’s converted from the string in the URL to
an integer.

``` python
reg_re_param("imgext", "ico|gif|jpg|jpeg|webm")

@rt(r'/static/{path:path}{fn}.{ext:imgext}')
def get(fn:str, path:str, ext:str): return f"Getting {fn}.{ext} from /{path}"

print(cli.get('/static/foo/jph.ico').text)
```

    Getting jph.ico from /foo/

The
[`reg_re_param`](https://www.fastht.ml/docs/api/core.html#reg_re_param)
function is used to register custom path parameter types using regular
expressions. Here, we define a new path parameter type called “imgext”
that matches common image file extensions.

Handler functions can use complex path patterns with multiple parameters
and custom types. In this example, the route pattern
`r'/static/{path:path}{fn}.{ext:imgext}'` uses three path parameters:

1.  `path`: A Starlette built-in type that matches any path segments
2.  `fn`: The filename without extension
3.  `ext`: Our custom “imgext” type that matches specific image
    extensions

``` python
ModelName = str_enum('ModelName', "alexnet", "resnet", "lenet")

@rt("/models/{nm}")
def get(nm:ModelName): return nm

print(cli.get('/models/alexnet').text)
```

    alexnet

We define `ModelName` as an enum with three possible values: “alexnet”,
“resnet”, and “lenet”. Handler functions can use these enum types as
parameter annotations. In this example, the `nm` parameter is annotated
with `ModelName`, which ensures that only valid model names are
accepted.

When a request is made with a valid model name, the handler function
returns that name. This pattern is useful for creating type-safe APIs
with a predefined set of valid values.

``` python
@rt("/files/{path}")
async def get(path: Path): return path.with_suffix('.txt')
print(cli.get('/files/foo').text)
```

    foo.txt

Handler functions can use
[`Path`](https://www.fastht.ml/docs/api/svg.html#path) objects as
parameter types. The
[`Path`](https://www.fastht.ml/docs/api/svg.html#path) type is from
Python’s standard library `pathlib` module, which provides an
object-oriented interface for working with file paths. In this example,
the `path` parameter is annotated with
[`Path`](https://www.fastht.ml/docs/api/svg.html#path), so FastHTML
automatically converts the string from the URL to a
[`Path`](https://www.fastht.ml/docs/api/svg.html#path) object.

This approach is particularly useful when working with file-related
routes, as it provides a convenient and platform-independent way to
handle file paths.

``` python
fake_db = [{"name": "Foo"}, {"name": "Bar"}]

@rt("/items/")
def get(idx:int|None = 0): return fake_db[idx]
print(cli.get('/items/?idx=1').text)
```

    {"name":"Bar"}

Handler functions can use query parameters, which are automatically
parsed from the URL. In this example, `idx` is a query parameter with a
default value of 0. It’s annotated as `int|None`, allowing it to be
either an integer or None.

The function uses this parameter to index into a fake database
(`fake_db`). When a request is made with a valid `idx` query parameter,
the handler returns the corresponding item from the database.

``` python
print(cli.get('/items/').text)
```

    {"name":"Foo"}

When no `idx` query parameter is provided, the handler function uses the
default value of 0. This results in returning the first item from the
`fake_db` list, which is `{"name":"Foo"}`.

This behavior demonstrates how default values for query parameters work
in FastHTML. They allow the API to have a sensible default behavior when
optional parameters are not provided.

``` python
print(cli.get('/items/?idx=g'))
```

    <Response [404 Not Found]>

When an invalid value is provided for a typed query parameter, FastHTML
returns a 404 Not Found response. In this example, ‘g’ is not a valid
integer for the `idx` parameter, so the request fails with a 404 status.

This behavior ensures type safety and prevents invalid inputs from
reaching the handler function.

``` python
@app.get("/booly/")
def _(coming:bool=True): return 'Coming' if coming else 'Not coming'
print(cli.get('/booly/?coming=true').text)
print(cli.get('/booly/?coming=no').text)
```

    Coming
    Not coming

Handler functions can use boolean query parameters. In this example,
`coming` is a boolean parameter with a default value of `True`. FastHTML
automatically converts string values like ‘true’, ‘false’, ‘1’, ‘0’,
‘on’, ‘off’, ‘yes’, and ‘no’ to their corresponding boolean values.

The underscore `_` is used as the function name in this example to
indicate that the function’s name is not important or won’t be
referenced elsewhere. This is a common Python convention for throwaway
or unused variables, and it works here because FastHTML uses the route
decorator parameter, when provided, to determine the URL path, not the
function name. By default, both `get` and
[`post`](https://www.fastht.ml/docs/explains/stripe.html#post) methods
can be used in routes that don’t specify an http method (by either using
`app.get`, `def get`, or the `methods` parameter to `app.route`).

``` python
@app.get("/datie/")
def _(d:parsed_date): return d
date_str = "17th of May, 2024, 2p"
print(cli.get(f'/datie/?d={date_str}').text)
```

    2024-05-17 14:00:00

Handler functions can use `date` objects as parameter types. FastHTML
uses `dateutil.parser` library to automatically parse a wide variety of
date string formats into `date` objects.

``` python
@app.get("/ua")
async def _(user_agent:str): return user_agent
print(cli.get('/ua', headers={'User-Agent':'FastHTML'}).text)
```

    FastHTML

Handler functions can access HTTP headers by using parameter names that
match the header names. In this example, `user_agent` is used as a
parameter name, which automatically captures the value of the
‘User-Agent’ header from the request.

The [`Client`](https://www.fastht.ml/docs/api/core.html#client) instance
allows setting custom headers for test requests. Here, we set the
‘User-Agent’ header to ‘FastHTML’ in the test request.

``` python
@app.get("/hxtest")
def _(htmx): return htmx.request
print(cli.get('/hxtest', headers={'HX-Request':'1'}).text)

@app.get("/hxtest2")
def _(foo:HtmxHeaders, req): return foo.request
print(cli.get('/hxtest2', headers={'HX-Request':'1'}).text)
```

    1
    1

Handler functions can access HTMX-specific headers using either the
special `htmx` parameter name, or a parameter annotated with
[`HtmxHeaders`](https://www.fastht.ml/docs/api/core.html#htmxheaders).
Both approaches provide access to HTMX-related information.

In these examples, the `htmx.request` attribute returns the value of the
‘HX-Request’ header.

``` python
app.chk = 'foo'
@app.get("/app")
def _(app): return app.chk
print(cli.get('/app').text)
```

    foo

Handler functions can access the
[`FastHTML`](https://www.fastht.ml/docs/api/core.html#fasthtml)
application instance using the special `app` parameter name. This allows
handlers to access application-level attributes and methods.

In this example, we set a custom attribute `chk` on the application
instance. The handler function then uses the `app` parameter to access
this attribute and return its value.

``` python
@app.get("/app2")
def _(foo:FastHTML): return foo.chk,HttpHeader("mykey", "myval")
r = cli.get('/app2', **hxhdr)
print(r.text)
print(r.headers)
```

    foo
    Headers({'mykey': 'myval', 'content-length': '3', 'content-type': 'text/html; charset=utf-8'})

Handler functions can access the
[`FastHTML`](https://www.fastht.ml/docs/api/core.html#fasthtml)
application instance using a parameter annotated with
[`FastHTML`](https://www.fastht.ml/docs/api/core.html#fasthtml). This
allows handlers to access application-level attributes and methods, just
like using the special `app` parameter name.

Handlers can return tuples containing both content and
[`HttpHeader`](https://www.fastht.ml/docs/api/core.html#httpheader)
objects.
[`HttpHeader`](https://www.fastht.ml/docs/api/core.html#httpheader)
allows setting custom HTTP headers in the response.

In this example:

- We define a handler that returns both the `chk` attribute from the
  application and a custom header.
- The `HttpHeader("mykey", "myval")` sets a custom header in the
  response.
- We use the test client to make a request and examine both the response
  text and headers.
- The response includes the custom header “mykey” along with standard
  headers like content-length and content-type.

``` python
@app.get("/app3")
def _(foo:FastHTML): return HtmxResponseHeaders(location="http://example.org")
r = cli.get('/app3')
print(r.headers)
```

    Headers({'hx-location': 'http://example.org', 'content-length': '0', 'content-type': 'text/html; charset=utf-8'})

Handler functions can return
[`HtmxResponseHeaders`](https://www.fastht.ml/docs/api/core.html#htmxresponseheaders)
objects to set HTMX-specific response headers. This is useful for
HTMX-specific behaviors like client-side redirects.

In this example we define a handler that returns an
[`HtmxResponseHeaders`](https://www.fastht.ml/docs/api/core.html#htmxresponseheaders)
object with a `location` parameter, which sets the `HX-Location` header
in the response. HTMX uses this for client-side redirects.

``` python
@app.get("/app4")
def _(foo:FastHTML): return Redirect("http://example.org")
cli.get('/app4', follow_redirects=False)
```

    <Response [303 See Other]>

Handler functions can return
[`Redirect`](https://www.fastht.ml/docs/api/core.html#redirect) objects
to perform HTTP redirects. This is useful for redirecting users to
different pages or external URLs.

In this example:

- We define a handler that returns a
  [`Redirect`](https://www.fastht.ml/docs/api/core.html#redirect) object
  with the URL “http://example.org”.
- The `cli.get('/app4', follow_redirects=False)` call simulates a GET
  request to the ‘/app4’ route without following redirects.
- The response has a 303 See Other status code, indicating a redirect.

The `follow_redirects=False` parameter is used to prevent the test
client from automatically following the redirect, allowing us to inspect
the redirect response itself.

``` python
Redirect.__response__
```

    <function fasthtml.core.Redirect.__response__(self, req)>

The [`Redirect`](https://www.fastht.ml/docs/api/core.html#redirect)
class in FastHTML implements a `__response__` method, which is a special
method recognized by the framework. When a handler returns a
[`Redirect`](https://www.fastht.ml/docs/api/core.html#redirect) object,
FastHTML internally calls this `__response__` method to replace the
original response.

The `__response__` method takes a `req` parameter, which represents the
incoming request. This allows the method to access request information
if needed when constructing the redirect response.

``` python
@rt
def meta(): 
    return ((Title('hi'),H1('hi')),
        (Meta(property='image'), Meta(property='site_name')))

print(cli.post('/meta').text)
```

     <!doctype html>
     <html>
       <head>
         <title>hi</title>
         <meta property="image">
         <meta property="site_name">
         <meta charset="utf-8">
         <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
    <script src="https://unpkg.com/[email protected]/dist/htmx.min.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/[email protected]/fasthtml.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/surreal@main/surreal.js"></script><script src="https://cdn.jsdelivr.net/gh/gnat/css-scope-inline@main/script.js"></script><script>
        function sendmsg() {
            window.parent.postMessage({height: document.documentElement.offsetHeight}, '*');
        }
        window.onload = function() {
            sendmsg();
            document.body.addEventListener('htmx:afterSettle',    sendmsg);
            document.body.addEventListener('htmx:wsAfterMessage', sendmsg);
        };</script>   </head>
       <body>
         <h1>hi</h1>
       </body>
     </html>

FastHTML automatically identifies elements typically placed in the
`<head>` (like `Title` and `Meta`) and positions them accordingly, while
other elements go in the `<body>`.

In this example: - `(Title('hi'), H1('hi'))` defines the title and main
heading. The title is placed in the head, and the H1 in the body. -
`(Meta(property='image'), Meta(property='site_name'))` defines two meta
tags, which are both placed in the head.

## APIRouter

[`APIRouter`](https://www.fastht.ml/docs/api/core.html#apirouter) is
useful when you want to split your application routes across multiple
`.py` files that are part of a single FastHTMl application. It accepts
an optional `prefix` argument that will be applied to all routes within
that instance of
[`APIRouter`](https://www.fastht.ml/docs/api/core.html#apirouter).

Below we define several hypothetical product related routes in a
`products.py` and then demonstrate how they can seamlessly be
incorporated into a FastHTML app instance.

``` python
# products.py
ar = APIRouter(prefix="/products")

@ar("/all")
def all_products(req):
    return Div(
        "Welcome to the Products Page! Click the button below to look at the details for product 42",
        Div(
            Button(
                "Details",
                hx_get=req.url_for("details", pid=42),
                hx_target="#products_list",
                hx_swap="outerHTML",
            ),
        ),
        id="products_list",
    )


@ar.get("/{pid}", name="details")
def details(pid: int):
    return f"Here are the product details for ID: {pid}"
```

Since we specified the `prefix=/products` in our hypothetical
`products.py` file, all routes defined in that file will be found under
`/products`.

``` python
print(str(ar.rt_funcs.all_products))
print(str(ar.rt_funcs.details))
```

    /products/all
    /products/{pid}

``` python
# main.py
# from products import ar

app, rt = fast_app()
ar.to_app(app)

@rt
def index():
    return Div(
        "Click me for a look at our products",
        hx_get=ar.rt_funcs.all_products,
        hx_swap="outerHTML",
    )
```

Note how you can reference our python route functions via
`APIRouter.rt_funcs` in your `hx_{http_method}` calls like normal.

## Form Data and JSON Handling

``` python
app = FastHTML()
rt = app.route
cli = Client(app)
```

``` python
@app.post('/profile/me')
def profile_update(username: str): return username

r = cli.post('/profile/me', data={'username' : 'Alexis'}).text
assert r == 'Alexis'
print(r)
```

    Alexis

Handler functions can accept form data parameters, without needing to
manually extract it from the request. In this example, `username` is
expected to be sent as form data.

The `data` parameter in the `cli.post()` method simulates sending form
data in the request.

``` python
r = cli.post('/profile/me', data={})
assert r.status_code == 400
print(r.text)
r
```

    Missing required field: username

    <Response [400 Bad Request]>

If required form data is missing, FastHTML automatically returns a 400
Bad Request response with an error message.

``` python
@app.post('/pet/dog')
def pet_dog(dogname: str = None): return dogname or 'unknown name'
r = cli.post('/pet/dog', data={}).text
r
```

    'unknown name'

Handlers can have optional form data parameters with default values. In
this example, `dogname` is an optional parameter with a default value of
`None`.

Here, if the form data doesn’t include the `dogname` field, the function
uses the default value. The function returns either the provided
`dogname` or ‘unknown name’ if `dogname` is `None`.

``` python
@dataclass
class Bodie: a:int;b:str

@rt("/bodie/{nm}")
def post(nm:str, data:Bodie):
    res = asdict(data)
    res['nm'] = nm
    return res

print(cli.post('/bodie/me', data=dict(a=1, b='foo', nm='me')).text)
```

    {"a":1,"b":"foo","nm":"me"}

You can use dataclasses to define structured form data. In this example,
`Bodie` is a dataclass with `a` (int) and `b` (str) fields.

FastHTML automatically converts the incoming form data to a `Bodie`
instance where attribute names match parameter names. Other form data
elements are matched with parameters with the same names (in this case,
`nm`).

Handler functions can return dictionaries, which FastHTML automatically
JSON-encodes.

``` python
@app.post("/bodied/")
def bodied(data:dict): return data

d = dict(a=1, b='foo')
print(cli.post('/bodied/', data=d).text)
```

    {"a":"1","b":"foo"}

`dict` parameters capture all form data as a dictionary. In this
example, the `data` parameter is annotated with `dict`, so FastHTML
automatically converts all incoming form data into a dictionary.

Note that when form data is converted to a dictionary, all values become
strings, even if they were originally numbers. This is why the ‘a’ key
in the response has a string value “1” instead of the integer 1.

``` python
nt = namedtuple('Bodient', ['a','b'])

@app.post("/bodient/")
def bodient(data:nt): return asdict(data)
print(cli.post('/bodient/', data=d).text)
```

    {"a":"1","b":"foo"}

Handler functions can use named tuples to define structured form data.
In this example, `Bodient` is a named tuple with `a` and `b` fields.

FastHTML automatically converts the incoming form data to a `Bodient`
instance where field names match parameter names. As with the previous
example, all form data values are converted to strings in the process.

``` python
class BodieTD(TypedDict): a:int;b:str='foo'

@app.post("/bodietd/")
def bodient(data:BodieTD): return data
print(cli.post('/bodietd/', data=d).text)
```

    {"a":1,"b":"foo"}

You can use `TypedDict` to define structured form data with type hints.
In this example, `BodieTD` is a `TypedDict` with `a` (int) and `b` (str)
fields, where `b` has a default value of ‘foo’.

FastHTML automatically converts the incoming form data to a `BodieTD`
instance where keys match the defined fields. Unlike with regular
dictionaries or named tuples, FastHTML respects the type hints in
`TypedDict`, converting values to the specified types when possible
(e.g., converting ‘1’ to the integer 1 for the ‘a’ field).

``` python
class Bodie2:
    a:int|None; b:str
    def __init__(self, a, b='foo'): store_attr()

@app.post("/bodie2/")
def bodie(d:Bodie2): return f"a: {d.a}; b: {d.b}"
print(cli.post('/bodie2/', data={'a':1}).text)
```

    a: 1; b: foo

Custom classes can be used to define structured form data. Here,
`Bodie2` is a custom class with `a` (int|None) and `b` (str) attributes,
where `b` has a default value of ‘foo’. The `store_attr()` function
(from fastcore) automatically assigns constructor parameters to instance
attributes.

FastHTML automatically converts the incoming form data to a `Bodie2`
instance, matching form fields to constructor parameters. It respects
type hints and default values.

``` python
@app.post("/b")
def index(it: Bodie): return Titled("It worked!", P(f"{it.a}, {it.b}"))

s = json.dumps({"b": "Lorem", "a": 15})
print(cli.post('/b', headers={"Content-Type": "application/json", 'hx-request':"1"}, data=s).text)
```

     <title>It worked!</title>
    <main class="container">   <h1>It worked!</h1>
       <p>15, Lorem</p>
    </main>

Handler functions can accept JSON data as input, which is automatically
parsed into the specified type. In this example, `it` is of type
`Bodie`, and FastHTML converts the incoming JSON data to a `Bodie`
instance.

The [`Titled`](https://www.fastht.ml/docs/api/xtend.html#titled)
component is used to create a page with a title and main content. It
automatically generates an `<h1>` with the provided title, wraps the
content in a `<main>` tag with a “container” class, and adds a `title`
to the head.

When making a request with JSON data: - Set the “Content-Type” header to
“application/json” - Provide the JSON data as a string in the `data`
parameter of the request

## Cookies, Sessions, File Uploads, and more

``` python
@rt("/setcookie")
def get(): return cookie('now', datetime.now())

@rt("/getcookie")
def get(now:parsed_date): return f'Cookie was set at time {now.time()}'

print(cli.get('/setcookie').text)
time.sleep(0.01)
cli.get('/getcookie').text
```

    'Cookie was set at time 16:19:27.811570'

Handler functions can set and retrieve cookies. In this example:

- The `/setcookie` route sets a cookie named ‘now’ with the current
  datetime.
- The `/getcookie` route retrieves the ‘now’ cookie and returns its
  value.

The [`cookie()`](https://www.fastht.ml/docs/api/core.html#cookie)
function is used to create a cookie response. FastHTML automatically
converts the datetime object to a string when setting the cookie, and
parses it back to a date object when retrieving it.

``` python
cookie('now', datetime.now())
```

    HttpHeader(k='set-cookie', v='now="2025-01-30 16:19:29.997374"; Path=/; SameSite=lax')

The [`cookie()`](https://www.fastht.ml/docs/api/core.html#cookie)
function returns an
[`HttpHeader`](https://www.fastht.ml/docs/api/core.html#httpheader)
object with the ‘set-cookie’ key. You can return it in a tuple along
with `FT` elements, along with anything else FastHTML supports in
responses.

``` python
app = FastHTML(secret_key='soopersecret')
cli = Client(app)
rt = app.route
```

``` python
@rt("/setsess")
def get(sess, foo:str=''):
    now = datetime.now()
    sess['auth'] = str(now)
    return f'Set to {now}'

@rt("/getsess")
def get(sess): return f'Session time: {sess["auth"]}'

print(cli.get('/setsess').text)
time.sleep(0.01)

cli.get('/getsess').text
```

    Set to 2025-01-30 16:19:31.078650

    'Session time: 2025-01-30 16:19:31.078650'

Sessions store and retrieve data across requests. To use sessions, you
should to initialize the FastHTML application with a `secret_key`. This
is used to cryptographically sign the cookie used by the session.

The `sess` parameter in handler functions provides access to the session
data. You can set and get session variables using dictionary-style
access.

``` python
@rt("/upload")
async def post(uf:UploadFile): return (await uf.read()).decode()

with open('../../CHANGELOG.md', 'rb') as f:
    print(cli.post('/upload', files={'uf':f}, data={'msg':'Hello'}).text[:15])
```

    # Release notes

Handler functions can accept file uploads using Starlette’s `UploadFile`
type. In this example:

- The `/upload` route accepts a file upload named `uf`.
- The `UploadFile` object provides an asynchronous `read()` method to
  access the file contents.
- We use `await` to read the file content asynchronously and decode it
  to a string.

We added `async` to the handler function because it uses `await` to read
the file content asynchronously. In Python, any function that uses
`await` must be declared as `async`. This allows the function to be run
asynchronously, potentially improving performance by not blocking other
operations while waiting for the file to be read.

``` python
app.static_route('.md', static_path='../..')
print(cli.get('/README.md').text[:10])
```

    # FastHTML

The `static_route` method of the FastHTML application allows serving
static files with specified extensions from a given directory. In this
example:

- `.md` files are served from the `../..` directory (two levels up from
  the current directory).
- Accessing `/README.md` returns the contents of the README.md file from
  that directory.

``` python
help(app.static_route_exts)
```

    Help on method static_route_exts in module fasthtml.core:

    static_route_exts(prefix='/', static_path='.', exts='static') method of fasthtml.core.FastHTML instance
        Add a static route at URL path `prefix` with files from `static_path` and `exts` defined by `reg_re_param()`

``` python
app.static_route_exts()
assert cli.get('/README.txt').status_code == 404
print(cli.get('/README.txt').text[:50])
```

    404 Not Found

The `static_route_exts` method of the FastHTML application allows
serving static files with specified extensions from a given directory.
By default:

- It serves files from the current directory (‘.’).
- It uses the ‘static’ regex, which includes common static file
  extensions like ‘ico’, ‘gif’, ‘jpg’, ‘css’, ‘js’, etc.
- The URL prefix is set to ‘/’.

The ‘static’ regex is defined by FastHTML using this code:

``` python
reg_re_param("static", "ico|gif|jpg|jpeg|webm|css|js|woff|png|svg|mp4|webp|ttf|otf|eot|woff2|txt|html|map")
```

``` python
@rt("/form-submit/{list_id}")
def options(list_id: str):
    headers = {
        'Access-Control-Allow-Origin': '*',
        'Access-Control-Allow-Methods': 'POST',
        'Access-Control-Allow-Headers': '*',
    }
    return Response(status_code=200, headers=headers)

print(cli.options('/form-submit/2').headers)
```

    Headers({'access-control-allow-origin': '*', 'access-control-allow-methods': 'POST', 'access-control-allow-headers': '*', 'content-length': '0', 'set-cookie': 'session_=eyJhdXRoIjogIjIwMjUtMDEtMzAgMTY6MTk6MzEuMDc4NjUwIn0=.Z5vtZA.1ooY2RCWopWAbLYDy6660g_LlHI; path=/; Max-Age=31536000; httponly; samesite=lax'})

FastHTML handlers can handle OPTIONS requests and set custom headers. In
this example:

- The `/form-submit/{list_id}` route handles OPTIONS requests.
- Custom headers are set to allow cross-origin requests (CORS).
- The function returns a Starlette `Response` object with a 200 status
  code and the custom headers.

You can return any Starlette Response type from a handler function,
giving you full control over the response when needed.

``` python
def _not_found(req, exc): return Div('nope')

app = FastHTML(exception_handlers={404:_not_found})
cli = Client(app)
rt = app.route

r = cli.get('/')
print(r.text)
```

     <!doctype html>
     <html>
       <head>
         <title>FastHTML page</title>
         <meta charset="utf-8">
         <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
    <script src="https://unpkg.com/[email protected]/dist/htmx.min.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/[email protected]/fasthtml.js"></script><script src="https://cdn.jsdelivr.net/gh/answerdotai/surreal@main/surreal.js"></script><script src="https://cdn.jsdelivr.net/gh/gnat/css-scope-inline@main/script.js"></script><script>
        function sendmsg() {
            window.parent.postMessage({height: document.documentElement.offsetHeight}, '*');
        }
        window.onload = function() {
            sendmsg();
            document.body.addEventListener('htmx:afterSettle',    sendmsg);
            document.body.addEventListener('htmx:wsAfterMessage', sendmsg);
        };</script>   </head>
       <body>
         <div>nope</div>
       </body>
     </html>

FastHTML allows you to define custom exception handlers – in this case,
a custom 404 (Not Found) handler function `_not_found`, which returns a
`Div` component with the text ‘nope’.