Recursively watch a directory for modifications and publish file content to an MQTT broker
This simple Python program portably watches a directory recursively and publishes the content of newly created and modified files as payload to an MQTT broker. Files which are deleted are published with a NULL payload.
The path to the directory to watch recursively (default .), as well as a list of files to ignore (*.swp, *.o, *.pyc), the broker host (localhost) and port number (1883) must be specified in via environment variables , together with the topic prefix to which to publish to (watch/).
git clone https://github.com/jpmens/mqtt-watchdir.git cd mqtt-watchdir virtualenv watchdir source watchdir/bin/activate pip install -e .
Set the following optional environment variables before invoking mqtt-watchdir.py:
- MQTTHOST (default "localhost") is the name/address of the MQTT broker.
- MQTTPORT (default 1883) is the TCP port number of the broker.
- MQTTWATCHDIR (default: ".") is the path to the directory to watch.
- MQTTQOS (default: 0) is the MQTT Quality of Service (QoS) to use on publish. Allowed values are 0, 1, or 2.
- MQTTRETAIN (default: 0) specifies whether the “retain” flag should be set on publish. Set to 1 if you want messages to be retained.
- MQTTPREFIX (default: "watch") is the prefix to be prepended (with a slash) to the MQTT topic name. The topic name is formed from this prefix plus the path name of the file that is being modified (i.e. watched). You can set this to an empty string ("") to avoid prefixing the topic name.
- MQTTFILTER (default None) allows modifying payload (see below). Takes path to a Python file (e.g. "/path/to/example-filter.py".
- MQTTFIXEDTOPIC (default None) sets a MQTT topic to which all messages are published. If set, the MQTTPREFIX setting is overruled and ignored.
- Set WATCHDEBUG (default: 0) to 1 to show debugging information.
mosquitto_sub -v -t 'watch/#'
Launch this program and, in another terminal, try something like this:
echo Hello World > message echo JP > myname rm myname
whereupon, on the first window, you should see:
watch/message Hello World watch/myname JP watch/myname (null)
Without a filter (the default), mqtt-watchdir reads the content of a newly created or modified file and uses that as the MQTT payload. By creating and enabling a so-called filter, mqtt-watchdir can pass the payload into said filter (a Python function) to have a payload translated.
Consider the included example-filter.py:
def mfilter(filename, topic, payload): '''Return a tuple [pub, newpayload] indicating whether this event should be published (True or False) and a new payload string or None''' print "Filter for topic %s" % topic if filename.endswith('.jpg'): return False, None if payload is not None: return True, payload.replace("\n", "-").replace(" ", "+") return True, None
The mfilter function is passed the fully qualified path to the file, the (possibly prefixed) MQTT topic name and the payload. In this simple example, spaces and newlines in the payload are replaced by dashes and plusses.
The function must return a tuple with two elements:
- The first specifies whether the payload will be published (True) or not (False)
- The second is a string with a possibly modified payload or None. If the returned payload is None, the original payload is not modified.
Possible uses of filters include
- Limiting payload lengths
- Conversion to JSON
- Ignore certain file types (e.g. binary data)
- Process content of files, say, YAML or JSON, and extract elements returning as string
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