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# Listen Options

This is a detailed description of each option allowed by the listening modules:

## access

AccessName

This option defines access to the port. The default value is `all`.

## backlog

Value

The backlog value defines the maximum length that the queue of pending connections may grow to. This should be increased if the server is going to handle lots of new incoming connections as they may be dropped if there is no space in the queue (and ejabberd was not able to accept them immediately). Default value is 5.

## cafile

Path

Path to a file of CA root certificates. The default is to use system defined file if possible.

This option is useful to define the file for a specific port listener. To set a file for all client listeners or for specific vhosts, you can use the `c2s_cafile` top-level option. To set a file for all server connections, you can use the `s2s_cafile` top-level option or the `ca_file` top-level option.

## certfile

Path

Path to the certificate file. Only makes sense when the `tls` options is set. If this option is not set, you should set the `certfiles` top-level option or configure ACME.

## check_from

true | false

This option can be used with `ejabberd_service` only. `XEP-0114` requires that the domain must match the hostname of the component. If this option is set to `false`, `ejabberd` will allow the component to send stanzas with any arbitrary domain in the ’from’ attribute. Only use this option if you are completely sure about it. The default value is `true`, to be compliant with `XEP-0114`.

## ciphers

Ciphers

OpenSSL ciphers list in the same format accepted by ‘`openssl ciphers`’ command.

## custom_headers

{Name: Value}

Specify additional HTTP headers to be included in all HTTP responses. Default value is: `[]`

## dhfile

Path

Full path to a file containing custom parameters for Diffie-Hellman key exchange. Such a file could be created with the command `openssl dhparam -out dh.pem 2048`. If this option is not specified, default parameters will be used, which might not provide the same level of security as using custom parameters.

## global_routes

true | false

This option emulates legacy behaviour which registers all routes defined in `hosts` on a component connected. This behaviour is considered harmful in the case when it's desired to multiplex different components on the same port, so, to disable it, set `global_routes` to `false`.

The default value is `true`, e.g. legacy behaviour is emulated: the only reason for this is to maintain backward compatibility with existing deployments.

## hosts

{Hostname: [HostOption, ...]}

The external Jabber component that connects to this `ejabberd_service` can serve one or more hostnames. As `HostOption` you can define options for the component; currently the only allowed option is the password required to the component when attempt to connect to ejabberd: `password: Secret`. Note that you cannot define in a single `ejabberd_service` components of different services: add an `ejabberd_service` for each service, as seen in an example below. This option may not be necessary if the component already provides the host in its packets; in that case, you can simply provide the password option that will be used for all the hosts (see port 5236 definition in the example below).

## max_fsm_queue

Size

This option specifies the maximum number of elements in the queue of the FSM (Finite State Machine). Roughly speaking, each message in such queues represents one XML stanza queued to be sent into its relevant outgoing stream. If queue size reaches the limit (because, for example, the receiver of stanzas is too slow), the FSM and the corresponding connection (if any) will be terminated and error message will be logged. The reasonable value for this option depends on your hardware configuration. This option can be specified for `ejabberd_service` and `ejabberd_c2s` listeners, or also globally for `ejabberd_s2s_out`. If the option is not specified for `ejabberd_service` or `ejabberd_c2s` listeners, the globally configured value is used. The allowed values are integers and ’undefined’. Default value: ’10000’.

## max_payload_size

Size

Specify the maximum payload size in bytes. It can be either an integer or the word `infinity`. The default value is `infinity`.

## max_stanza_size

Size

This option specifies an approximate maximum size in bytes of XML stanzas. Approximate, because it is calculated with the precision of one block of read data. For example `{max_stanza_size, 65536}`. The default value is `infinity`. Recommended values are 65536 for c2s connections and 131072 for s2s connections. s2s max stanza size must always much higher than c2s limit. Change this value with extreme care as it can cause unwanted disconnect if set too low.

## password

Secret

Specify the password to verify an external component that connects to the port.

## port

Port number, or unix domain socket path

Declares at which port/unix domain socket should be listening.

Can be set to number between `1` and `65535` to listen on TCP or UDP socket, or can be set to string in form `"unix:/path/to/socket"` to create and listen on unix domain socket `/path/to/socket`.

## protocol_options

ProtocolOpts

List of general options relating to SSL/TLS. These map to `OpenSSL’s set_options()`. The default entry is: `"no_sslv3|cipher_server_preference|no_compression"`

## request_handlers

{Path: Module}

To define one or several handlers that will serve HTTP requests in `ejabberd_http`. The Path is a string; so the URIs that start with that Path will be served by Module. For example, if you want `mod_foo` to serve the URIs that start with `/a/b/`, and you also want `mod_bosh` to serve the URIs `/bosh/`, use this option:

        request_handlers:
          /a/b: mod_foo
          /bosh: mod_bosh
          /mqtt: mod_mqtt

## shaper

none | ShaperName

This option defines a shaper for the port (see section Shapers). The default value is `none`.

## shaper_rule

none | ShaperRule

This option defines a shaper rule for `ejabberd_service` (see section Shapers). The recommended value is `fast`.

## starttls

true | false

This option specifies that STARTTLS encryption is available on connections to the port. You should also set the `certfiles` top-level option or configure ACME.

## starttls_required

true | false

This option specifies that STARTTLS encryption is required on connections to the port. No unencrypted connections will be allowed. You should also set the `certfiles` top-level option or configure ACME.

## tag

String

Allow specifying a tag in a `listen` section and later use it to have a special `api_permissions` just for it.

For example:

        listen:
          -
            port: 4000
            module: ejabberd_http
            tag: "magic_listener"

        api_permissions:
          "magic_access":
            from:
              - tag: "magic_listener"
            who: all
            what: "*"

The default value is the empty string: `""`.

## timeout

Integer

Timeout of the connections, expressed in milliseconds. Default: 5000

## tls

true | false

This option specifies that traffic on the port will be encrypted using SSL immediately after connecting. This was the traditional encryption method in the early Jabber software, commonly on port 5223 for client-to-server communications. But this method is nowadays deprecated and not recommended. The preferable encryption method is STARTTLS on port 5222, as defined `RFC 6120: XMPP Core`, which can be enabled in `ejabberd` with the option `starttls`.

If this option is set, you should also set the `certfiles` top-level option or configure ACME.

The option `tls` can also be used in `ejabberd_http` to support HTTPS.

## tls_compression

true | false

Whether to enable or disable TLS compression. The default value is `false`.

## tls_verify

false | true

This option specifies whether to verify the certificate or not when TLS is enabled.

The default value is `false`, which means no checks are performed.

The certificate will be checked against trusted CA roots, either defined at the operation system level or defined in the listener `cafile`. If trusted, it will accept the jid that is embedded in the certificate in the `subjectAltName` field of that certificate.

## use_proxy_protocol

true | false

Is this listener accessed by proxy service that is using proxy protocol for supplying real IP addresses to ejabberd server. You can read about this protocol in Proxy protocol specification. The default value of this option is`false`.

## zlib

true | false

This option specifies that Zlib stream compression (as defined in `XEP-0138`) is available on connections to the port.