# FAQ

## Does Guzzle require cURL?

No. Guzzle can use any HTTP handler to send requests. This means that Guzzle can be used with cURL, PHP's stream wrapper, sockets, and non-blocking libraries like [React](https://reactphp.org/). You just need to configure an HTTP handler to use a different method of sending requests.

> [!NOTE]
> Guzzle has historically only utilized cURL to send HTTP requests. cURL is an amazing HTTP client (arguably the best), and Guzzle will continue to use it by default when it is available. It is rare, but some developers don't have cURL installed on their systems or run into version specific issues. By allowing swappable HTTP handlers, Guzzle is now much more customizable and able to adapt to fit the needs of more developers.

## Can Guzzle send asynchronous requests?

Yes. You can use the `requestAsync`, `sendAsync`, `getAsync`, `headAsync`, `putAsync`, `postAsync`, `deleteAsync`, and `patchAsync` methods of a client to send an asynchronous request. The client will return a `GuzzleHttp\Promise\PromiseInterface` object. You can chain `then` functions off of the promise for fulfilled responses and rejected reasons.

> [!NOTE]
> In Guzzle 7, `optionsAsync()` still works through deprecated `Client::__call()` compatibility. This deprecation does not affect named async shortcuts such as `getAsync()` and `postAsync()`, which are real client methods. Prefer `requestAsync('OPTIONS', ...)` in new code. `Client::__call()` is removed in Guzzle 8.

```php
$promise = $client->requestAsync('GET', 'http://httpbin.org/get');
$promise->then(function ($response) {
    echo 'Got a response! ' . $response->getStatusCode();
}, function ($reason) {
    // The rejection reason is often a Guzzle exception, but custom handlers can
    // reject with other values.
});
```

You can force an asynchronous response to complete using the `wait()` method of the returned promise. It returns the response on fulfillment and throws when the promise is rejected.

```php
$promise = $client->requestAsync('GET', 'http://httpbin.org/get');
$response = $promise->wait();
```

## How can I add custom cURL options?

cURL offers a huge number of
[customizable options](https://www.php.net/curl_setopt). While Guzzle
normalizes many of these options across different handlers, there are times
when you need to set custom cURL options. This can be accomplished by passing
an array keyed by allow-listed integer `CURLOPT_*` constants in the **curl**
key of a request. Raw cURL options outside the built-in cURL handlers'
allow-list are deprecated. The special `body_as_string` key is also recognized
by Guzzle's cURL handler.

For example, let's say you need to customize the outgoing network interface used
with a client.

```php
$client->request('GET', '/', [
    'curl' => [
        CURLOPT_INTERFACE => 'xxx.xxx.xxx.xxx'
    ]
]);
```

Custom cURL request options remain active during redirects unless Guzzle
documents otherwise. See [`allow_redirects`](request-options.md#allow_redirects)
for cross-origin redirect credential behavior.

Callbacks supplied through the raw `curl` request option are passed directly to
PHP's cURL extension. Guzzle does not normalize exception or abort behavior for
raw cURL callbacks. Prefer Guzzle's `progress`, `on_headers`, and `on_stats`
request options when you need Guzzle's documented callback semantics.

## How can I limit concurrent connections?

If you use asynchronous requests with the cURL multi handler, the client can
bound concurrent connections with named constructor options:

```php
use GuzzleHttp\Client;

$client = new Client([
    'max_total_connections' => 50,
    'max_host_connections' => 5,
]);
```

When constructing a cURL multi handler yourself, pass the same named options to
the handler:

```php
use GuzzleHttp\Client;
use GuzzleHttp\Handler\CurlMultiHandler;
use GuzzleHttp\HandlerStack;

$handler = new CurlMultiHandler([
    'max_total_connections' => 50,
    'max_host_connections' => 5,
]);

$client = new Client(['handler' => HandlerStack::create($handler)]);
```

Additional cURL multi options that do not have named Guzzle options can still be
specified as an array keyed by integer `CURLMOPT_*` constants in the **options**
key of the `CurlMultiHandler` constructor. For example,
`CURLMOPT_MAX_CONCURRENT_STREAMS` can be used on PHP versions that expose it.

If the runtime libcurl cannot apply a named connection cap, the handler fails
closed: the first request fails with an exception instead of continuing
without the cap. Raw `CURLMOPT_*` options in the **options** array keep their
Guzzle 7 compatibility behavior and only trigger a warning when they cannot be
applied. Named connection caps also cannot be combined with a request-level
`CURLOPT_SHARE` option because Guzzle cannot verify that a caller-managed
shared connection pool honors the caps.

Multiplexing on the multi handle is controlled by the named `multiplex`
option rather than a raw cURL multi option: pass `Multiplexing::NONE` as the
`multiplex` client option or, when constructing the handler yourself, to the
`CurlMultiHandler` constructor to disallow multiplexing for every transfer
the handler runs; like the named caps, it fails closed when the runtime
libcurl cannot apply it. `Multiplexing::NONE` is also accepted as a request
option value exactly where its guarantee - the transfer does not share its
connection with any concurrent transfer - holds and can be verified. Passing
`CURLMOPT_PIPELINING` in the **options** array is deprecated and will be
rejected by Guzzle 8.0. Multiplexing is on by default
from libcurl 7.62, except for a regression that turned the default back off in
7.65.0 and 7.65.1. On libcurl 7.43 to 7.61, and on 7.65.0 and 7.65.1, a raw
multiplex-enabling mask is the only way to turn it on, so keep the raw option
there until the runtime is upgraded.

### Which transfers do the caps govern?

Numeric connection caps apply to transfers managed by `CurlMultiHandler`. When
the caps are configured, the default handler routes synchronous requests through
the capped `CurlMultiHandler` as well, and a cap-configured fallback
`StreamHandler` rejects enabled response streaming (`stream => true`) because
streamed connections cannot be capped. Accepted stream-handler transfers are
buffered and hold at most one connection per in-flight call, including in stream
fallback environments without a cap-capable cURL where every request uses the
stream handler. Overlapping buffered calls are not collectively limited by the
configured numbers.

Manually constructed `CurlHandler` or custom handlers are outside these caps. A
custom `handle_factory` is likewise caller-controlled and must not attach an
external connection-sharing `CURLOPT_SHARE` pool when the caps must hold,
because Guzzle cannot inspect that native handle state.

### How do the caps compose with connection sharing?

Guzzle-managed transport sharing shares only DNS and, when supported, TLS
session data and composes with the caps unchanged. A deprecated raw
`CURLOPT_SHARE` cURL option whose share handle shares connection data is outside
the caps, because libcurl 8.13.0 and newer does not apply the cURL multi
connection cap options to transfers that use a shared connection pool (older
libcurl checked the requesting transfer's own limits against the shared pool,
which is not a coherent cap). Guzzle 7.15 rejects request-level `CURLOPT_SHARE`
combined with the caps, and Guzzle 8 rejects the raw option entirely.

### What do the caps count?

The caps bound open connections, including idle pooled connections, rather than
in-flight requests.

`max_host_connections` follows libcurl's connection-bundle grouping. Proxy
forwarding, CONNECT tunnels, SOCKS proxies, and older libcurl versions do not
necessarily group connections under the same host key, so it is not a portable
per-proxy or per-credential socket limit.

### What happens when a cap is reached?

At the limit, libcurl queues transfers waiting for a connection slot. On libcurl
8.8.0 and newer, transfers queued behind a cap keep consuming the request
`timeout`; older libcurl does not run timeout checks on queued transfers, so a
queued transfer can overstay its `timeout` until a connection slot frees (curl
issue #13276). On libcurl 8.16.0 through 8.19.x, queued transfers resume one at
a time in an order that can starve some transfers under sustained load (fixed in
8.20.0). A transfer that must open a fresh connection, such as a proxied
transfer Guzzle isolates for credential safety, does not bypass the caps: it can
evict an eligible idle connection, and otherwise it stays pending until the
applicable per-host or total cap frees.

Low caps combined with aggressive timeouts and large request bursts can
therefore time out, or wait longer than expected, before a connection becomes
available. To bound in-flight requests and memory, combine the caps with
request-level concurrency controls such as `GuzzleHttp\Pool` or
`GuzzleHttp\Promise\Each::ofLimit()`.

## How can I add custom stream context options?

You can pass allow-listed custom
[stream context options](https://www.php.net/manual/en/context.php) using the
**stream_context** key of the request option. The **stream_context** array is an
associative array where each key is a PHP transport, and each value is an
associative array of transport options. Stream context options outside the
built-in stream handler allow-list are deprecated.

For example, let's say you need to customize the outgoing network interface used
with a client.

```php
$client->request('GET', '/', [
    'stream' => true,
    'stream_context' => [
        'socket' => [
            'bindto' => 'xxx.xxx.xxx.xxx'
        ]
    ]
]);
```

Custom stream context options remain active during redirects unless Guzzle
documents otherwise. See [`allow_redirects`](request-options.md#allow_redirects)
for cross-origin redirect credential behavior.

## Why am I getting an SSL verification error?

You need to specify the path on disk to the CA bundle used by Guzzle for verifying the peer certificate. See the [`verify` option](request-options.md#verify).

## What is this Maximum function nesting error?

> Maximum function nesting level of '100' reached, aborting

You could run into this error if you have the XDebug extension installed and you execute a lot of requests in callbacks. This error message comes specifically from the XDebug extension. PHP itself does not have a function nesting limit. Change this setting in your php.ini to increase the limit:

    xdebug.max_nesting_level = 1000

## Why am I getting a 417 error response?

This can occur for a number of reasons, but if you are sending PUT, POST, or PATCH requests with an `Expect: 100-Continue` header, a server that does not support this header will return a 417 response. You can work around this by setting the `expect` request option to `false`:

```php
$client = new GuzzleHttp\Client();

// Disable the expect header on a single request
$response = $client->request('PUT', '/', ['expect' => false]);

// Disable the expect header on all client requests
$client = new GuzzleHttp\Client(['expect' => false]);
```

## How can I track redirected requests?

You can enable tracking of redirected URIs and status codes via the `track_redirects` option. Each redirected URI and status code will be stored in the `X-Guzzle-Redirect-History` and the `X-Guzzle-Redirect-Status-History` header respectively.

The initial request's URI and the final status code will be excluded from the results. With this in mind you should be able to easily track a request's full redirect path.

For example, let's say you need to track redirects and provide both results together in a single report:

```php
// First you configure Guzzle with redirect tracking and make a request
$client = new Client([
    RequestOptions::ALLOW_REDIRECTS => [
        'max'             => 10,        // allow at most 10 redirects.
        'strict'          => true,      // use "strict" RFC compliant redirects.
        'referer'         => true,      // add a Referer header
        'track_redirects' => true,
    ],
]);
$initialRequest = '/redirect/3'; // Store the request URI for later use
$response = $client->request('GET', $initialRequest); // Make your request

// Retrieve both Redirect History headers
$redirectUriHistory = $response->getHeader('X-Guzzle-Redirect-History'); // retrieve Redirect URI history
$redirectCodeHistory = $response->getHeader('X-Guzzle-Redirect-Status-History'); // retrieve Redirect HTTP Status history

// Add the initial URI requested to the (beginning of) URI history
array_unshift($redirectUriHistory, $initialRequest);

// Add the final HTTP status code to the end of HTTP response history
array_push($redirectCodeHistory, $response->getStatusCode());

// (Optional) Combine the items of each array into a single result set
$fullRedirectReport = [];
foreach ($redirectUriHistory as $key => $value) {
    $fullRedirectReport[$key] = ['location' => $value, 'code' => $redirectCodeHistory[$key]];
}
echo json_encode($fullRedirectReport);
```
