server: Add zmq based event and data interface to the server

To allow easily extracting or streaming the data to an external
analysis system, zeromq can be configured (and reconfigured). The
system works as fire and forget and no loss detection is present.

A simple go based client application is provided to subscribe to
the publisher.

Change-Id: I4f3e6d675023a81b7d2ee19bf1f44a2be0ca003c

1 files changed, 41 insertions, 0 deletions

diff --git a/doc/zmq_data.txt b/doc/zmq_data.txt
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+ZeroMQ data protocol v1
+=======================
+
+The osmo-pcap-server can be configured to publish PCAP data to
+zero to many subscribers. The following document describes the
+data format used.
+
+Multiple clients might be connected to the osmo-pcap-server and
+use different link headers depending on the underlying device
+data is being captured from.
+
+The messages published are in two categories. These are client
+events and client data. Client events are generated on connect,
+disconnect, link type change and client data is sent for each
+frame.
+
+Client Events
+^^^^^^^^^^^^^
+
+A multi-part message with event.v1.<EVENT_NAME>.<CLIENT_NAME>
+as the first part followed by textual data will be generated.
+<CLIENT_NAME> is the configured name and <EVENT_NAME> can be
+any of:
+
+	* connect
+	* disconnect
+	* closingtracefile
+
+It might contain more information, such as the filename of the
+tracefile that was closed. There is no guarantee for the order
+and amount of connect/disconnect messages.
+
+
+Client Data
+^^^^^^^^^^^
+
+A multi-part message with data.v1.<CLIENT_NAME> to allow to
+filter for data and a specific client if wanted.
+
+It is followed by the pcap_file_header structure as the second
+part and then the data as third part.