New upstream version 1.11.0+dfsgupstream/1.11.0+dfsg

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+# python.d.plugin
+
+`python.d.plugin` is a netdata external plugin. It is an **orchestrator** for data collection modules written in `python`.
+
+1. It runs as an independent process `ps fax` shows it
+2. It is started and stopped automatically by netdata
+3. It communicates with netdata via a unidirectional pipe (sending data to the netdata daemon)
+4. Supports any number of data collection **modules**
+5. Allows each **module** to have one or more data collection **jobs**
+6. Each **job** is collecting one or more metrics from a single data source
+
+
+## Disclaimer
+
+Every module should be compatible with python2 and python3.
+All third party libraries should be installed system-wide or in `python_modules` directory.
+Module configurations are written in YAML and **pyYAML is required**.
+
+Every configuration file must have one of two formats:
+
+- Configuration for only one job:
+
+```yaml
+update_every : 2 # update frequency
+retries      : 1 # how many failures in update() is tolerated
+priority     : 20000 # where it is shown on dashboard
+
+other_var1   : bla  # variables passed to module
+other_var2   : alb
+```
+
+- Configuration for many jobs (ex. mysql):
+
+```yaml
+# module defaults:
+update_every : 2
+retries      : 1
+priority     : 20000
+
+local:  # job name
+  update_every : 5 # job update frequency
+  other_var1   : some_val # module specific variable
+
+other_job:
+  priority     : 5 # job position on dashboard
+  retries      : 20 # job retries
+  other_var2   : val # module specific variable
+```
+
+`update_every`, `retries`, and `priority` are always optional.
+
+---
+
+## How to write a new module
+
+Writing new python module is simple. You just need to remember to include 5 major things:
+- **ORDER** global list
+- **CHART** global dictionary
+- **Service** class
+- **_get_data** method
+- all code needs to be compatible with Python 2 (**≥ 2.7**) *and* 3 (**≥ 3.1**)
+
+If you plan to submit the module in a PR, make sure and go through the [PR checklist for new modules](https://github.com/netdata/netdata/wiki/New-Module-PR-Checklist) beforehand to make sure you have updated all the files you need to.
+
+### Global variables `ORDER` and `CHART`
+
+`ORDER` list should contain the order of chart ids. Example:
+```py
+ORDER = ['first_chart', 'second_chart', 'third_chart']
+```
+
+`CHART` dictionary is a little bit trickier. It should contain the chart definition in following format:
+```py
+CHART = {
+    id: {
+        'options': [name, title, units, family, context, charttype],
+        'lines': [
+            [unique_dimension_name, name, algorithm, multiplier, divisor]
+        ]}
+```
+
+All names are better explained in the [External Plugins](../) section.
+Parameters like `priority` and `update_every` are handled by `python.d.plugin`.
+
+### `Service` class
+
+Every module needs to implement its own `Service` class. This class should inherit from one of the framework classes:
+
+- `SimpleService`
+- `UrlService`
+- `SocketService`
+- `LogService`
+- `ExecutableService`
+
+Also it needs to invoke the parent class constructor in a specific way as well as assign global variables to class variables. 
+
+Simple example:
+```py
+from base import UrlService
+class Service(UrlService):
+    def __init__(self, configuration=None, name=None):
+        UrlService.__init__(self, configuration=configuration, name=name)
+        self.order = ORDER
+        self.definitions = CHARTS
+```
+
+### `_get_data` collector/parser
+
+This method should grab raw data from `_get_raw_data`, parse it, and return a dictionary where keys are unique dimension names or `None` if no data is collected.
+
+Example:
+```py
+def _get_data(self):
+    try:
+        raw = self._get_raw_data().split(" ")
+        return {'active': int(raw[2])}
+    except (ValueError, AttributeError):
+        return None
+```
+
+More about framework classes
+============================
+
+Every framework class has some user-configurable variables which are specific to this particular class. Those variables should have default values initialized in the child class constructor.
+
+If module needs some additional user-configurable variable, it can be accessed from the `self.configuration` list and assigned in constructor or custom `check` method. Example:
+```py
+def __init__(self, configuration=None, name=None):
+    UrlService.__init__(self, configuration=configuration, name=name)
+    try:
+        self.baseurl = str(self.configuration['baseurl'])
+    except (KeyError, TypeError):
+        self.baseurl = "http://localhost:5001"
+```
+
+Classes implement `_get_raw_data` which should be used to grab raw data. This method usually returns a list of strings.
+
+### `SimpleService`
+
+_This is last resort class, if a new module cannot be written by using other framework class this one can be used._
+
+_Example: `mysql`, `sensors`_
+
+It is the lowest-level class which implements most of module logic, like:
+- threading
+- handling run times
+- chart formatting
+- logging
+- chart creation and updating
+
+### `LogService`
+
+_Examples: `apache_cache`, `nginx_log`_
+
+_Variable from config file_: `log_path`.
+
+Object created from this class reads new lines from file specified in `log_path` variable. It will check if file exists and is readable. Also `_get_raw_data` returns list of strings where each string is one line from file specified in `log_path`.
+
+### `ExecutableService`
+
+_Examples: `exim`, `postfix`_
+
+_Variable from config file_: `command`.
+
+This allows to execute a shell command in a secure way. It will check for invalid characters in `command` variable and won't proceed if there is one of:
+- '&'
+- '|'
+- ';'
+- '>'
+- '<'
+
+For additional security it uses python `subprocess.Popen` (without `shell=True` option) to execute command. Command can be specified with absolute or relative name. When using relative name, it will try to find `command` in `PATH` environment variable as well as in `/sbin` and `/usr/sbin`.
+
+`_get_raw_data` returns list of decoded lines returned by `command`.
+
+### UrlService
+
+_Examples: `apache`, `nginx`, `tomcat`_
+
+_Variables from config file_: `url`, `user`, `pass`.
+
+If data is grabbed by accessing service via HTTP protocol, this class can be used. It can handle HTTP Basic Auth when specified with `user` and `pass` credentials.
+
+`_get_raw_data` returns list of utf-8 decoded strings (lines).
+
+### SocketService
+
+_Examples: `dovecot`, `redis`_
+
+_Variables from config file_: `unix_socket`, `host`, `port`, `request`.
+
+Object will try execute `request` using either `unix_socket` or TCP/IP socket with combination of `host` and `port`. This can access unix sockets with SOCK_STREAM or SOCK_DGRAM protocols and TCP/IP sockets in version 4 and 6 with SOCK_STREAM setting.
+
+Sockets are accessed in non-blocking mode with 15 second timeout.
+
+After every execution of `_get_raw_data` socket is closed, to prevent this module needs to set `_keep_alive` variable to `True` and implement custom `_check_raw_data` method.
+
+`_check_raw_data` should take raw data and return `True` if all data is received otherwise it should return `False`. Also it should do it in fast and efficient way.
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