[[http-meta-data]]
=== HTTP Meta Data

By default, the client sends some meta data about the HTTP connection using
custom headers.

You can disable or enable it using the following methods:


==== Elastic Meta Header

The client sends a `x-elastic-client-meta` header by default.
This header is used to collect meta data about the versions of the components
used by the client. For instance, a value of `x-elastic-client-meta` can be
`es=7.14.0-s,php=7.4.11,t=7.14.0-s,a=0,cu=7.68.0`, where each value is the
version of `es=Elasticsearch`, `t` is the transport version (same of client),
`a` is asyncronouts (`0=false` by default) and `cu=cURL`.

If you would like to disable it you can use the `setElasticMetaHeader()`
method, as follows:

[source,php]
----
$client = Elasticsearch\ClientBuilder::create()
    ->setElasticMetaHeader(false)
    ->build();
----

==== Include port number in Host header

This is a special setting for the client that enables the port in the
Host header. This setting has been introduced to prevent issues with
HTTP proxy layers (see issue https://github.com/elastic/elasticsearch-php/issues/993[#993]).

By default the port number is not included in the Host header.
If you want you can enable it using the `includePortInHostHeader()` function,
as follows:

[source,php]
----
$client = Elasticsearch\ClientBuilder::create()
    ->includePortInHostHeader(true)
    ->build();
----

==== Send the API compatibility layer

Starting from version 7.13, {es} supports a compatibility header in
`Content-Type` and `Accept`. The PHP client can be configured to emit the following HTTP headers:

[source]
----
Content-Type: application/vnd.elasticsearch+json; compatible-with=7
Accept: application/vnd.elasticsearch+json; compatible-with=7
----

which signals to {es} that the client is requesting 7.x version of request and response
bodies. This allows upgrading from 7.x to 8.x version of Elasticsearch without upgrading
everything at once. {es} should be upgraded first after the compatibility header is
configured and clients should be upgraded second.

To enable this compatibility header, you need to create an `ELASTIC_CLIENT_APIVERSIONING`
environment variable and set it to `true` or `1`, before the `Client` class initialization.

In PHP you can set this environment variable as follows:

[source,php]
----
putenv("ELASTIC_CLIENT_APIVERSIONING=true");
----