Network listeners and their services are specified via configuration.

application.conf (snippet)
    <consoles type="mtev_console" require_env="MTEV_CONTROL">
      <listener address="" port="32322">
    <web type="control_dispatch" address="*">
      <listener port="80" />
      <listener port="443" ssl="on" />

This example demonstrates many powerful concepts of the libmtev configuration system. There are three listener stanzas nested above and we'll walk through each. The first is the <listener address="" port="32322">. With this, you can telnet to port 32322 and talk with your libmtev application. The console is extensible so you can add application-specific command, control, and interrogation capabilities.

This listener has a <config> stanza underneath it that sets line_protocol to telnet. line_protocol is a configuration option for listeners of type mtev_console. You'll note that the listener's type attribute was actually set in a parent node. Most systems in libmtev will recusively merge from ancestors down to the a specimen node and use that result. Here type is simply an attribute, so merging is just replacing. This node also has an sslconfig, but it doesn't use it, so we'll ignore that for now. The require_env attribute requires the MTEV_CONTROL environment variable to be set for this listener to be active; if unspecified, it is active.

The next two listener stanzas are for port 80 and 443. They are in a web node that has both type and address attributes set (those are inherited by the listeners). The config node (child of web) and the sslconfig node (child of listeners) are also inherited into the listener nodes. The config is arbitrary and passed into the listener. The sslconfig is passed into the ssl subsystem and is uniform across all listener types.

The following attributes are supported for listeners:

  • type

    The type of listener simply references a named eventer callback in the system (one registered with eventer_name_callback(...). libmtev support four built-in listener types: http_rest_api, mtev_wire_rest_api/1.0, control_dispatch, and mtev_console. Applications can arbitrarily extend the system by naming callbacks.

  • require_env

    This optionally requires conditions around an environment variable. See require_env.

  • address

    The address is either a filesystem path (AF_UNIX), an IPv4 address or an IPv6 address. The type is intuited from the input string. If the special string * or inet:* is used, then the IPv4 in_addr_any address is used for listening. IF inet6:* is used, then the IPv6 in_addr_any address is used for listening.

  • port

    Specifies the port on which to listen. This has no meaning for AF_UNIX-based addresses.

  • ssl

    If the value here is on, then the socket passes through SSL negotiation before handed to the underlying system driving the specified listener type.

  • fanout

    If the value here is on, the new events created for accepted connections will be fanned out across threads in the event pool owning the listening socket (usually the default event pool). A different pool can be selected by additionally supplying fanout_pool.

  • fanout_pool

    If fanout is on, this will select a named pool on which to distribute new connection events. The value of this attribute should be the name of an event pool. If not pool exists with the specified name, the pool containing the listening event will be used.

  • accept_thread

    If accept_thread is on, a new dedicated thread will be spawned to handle accepting new connections in a blocking fashion.

  • no_delay

    If no_delay is off or false, then TCP_NODELAY will not be activated on the accepted socket. The default is on.

  • idle_timeout

    Specifies a time in milliseconds afterwhich if the connection remains idle (no read or write traffic) it will be terminated. The protocol driver must cooperate programmatically to inform the system of such activity; the mtev_console and http protocols do this.

Each listener can access the config passed to it; see type-specific documentation for other config keys.


The ssl config allow specification of many aspects of how SSL is negotiated with connecting clients. SSL config supports the follwing keys:

  • layer

    This specifies the SSL protocol options we present and is the form <protocol>[:<option>,[<option>[,...]]]. Options may be negated with an antecedent !. Tokens are matched case-insensitively.

    Protocols supported (depending on openssl): SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3

    Options supported (depending on openssl): SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, cipher_server_preference

    TLS version options can be prefixed with =, >=, or <=. The default layer string is tlsv1:>=tls1.2,cipher_server_preference

  • certificate_file or certificate

    Specifies the path to a PEM encoded certificate file. You may include the PEM block inline.

  • key_file or key

    Specifies the path to a PEM encoded key file. It must not be encrypted with a password. You may include the PEM block inline.

  • ca_chain or ca_file

    Specifies the CA verification list file (PEM encoded) that should be used to certificates from the client. You may include the PEM block inline.

  • ca_accept

    Specifies the CA certificates file (PEM encoded) that should be advertised to clients, if not specified ca_file is used. You may include the PEM block inline.

  • crl

    Specifies a PEM encoded certificate revocation list file. If not specified, no revocation is enforced.

  • ciphers

    Specifies which ciphers should be supported, expressed in the OpenSSL cipher list format. Check the OpenSSL manual for more details. If not specified, the default ciphers supported by the OpenSSL library are used.

  • npn or alpn

    Specifies which NPN (next-protocol-negotiation) to offer. If omitted, h2 is used and the http2 protocol is exposed. Specifying none will disable this NPN/ALPN registration.

  • optional_no_ca

    If set to "true", no checks on the validate of the signing CA will be performed. The default is "false".

  • ignore_dates

    If set to "true", expired or future certificates will be considered valid. The default is "false".

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