51Degrees Device Detection
--------------------------

You can also include 51Degrees for inbuilt device detection enabling attributes
such as screen size (physical & pixels), supported input methods, release date,
hardware vendor and model, browser information, and device price among many
others. Such information can be used to improve the user experience of a web
site by tailoring the page content, layout and business processes to the
precise characteristics of the device. Such customisations improve profit by
making it easier for customers to get to the information or services they
need. Attributes of the device making a web request can be added to HTTP
headers as configurable parameters.

In order to enable 51Degrees download the 51Degrees source code from the
official github repository :

    git clone https://github.com/51Degrees/Device-Detection

then run 'make' with USE_51DEGREES and 51DEGREES_SRC set. Both 51DEGREES_INC
and 51DEGREES_LIB may additionally be used to force specific different paths
for .o and .h, but will default to 51DEGREES_SRC. Make sure to replace
'51D_REPO_PATH' with the path to the 51Degrees repository.

51Degrees provide 2 different detection algorithms:

    1. Pattern - balances main memory usage and CPU.
    2. Trie - a very high performance detection solution which uses more main
       memory than Pattern.

To make with 51Degrees Pattern algorithm use the following command line.

    $ make TARGET=<target> USE_51DEGREES=1 51DEGREES_SRC='51D_REPO_PATH'/src/pattern

To use the 51Degrees Trie algorithm use the following command line.

    $ make TARGET=<target> USE_51DEGREES=1 51DEGREES_SRC='51D_REPO_PATH'/src/trie

A data file containing information about devices, browsers, operating systems
and their associated signatures is then needed. 51Degrees provide a free
database with Github repo for this purpose. These free data files are located
in '51D_REPO_PATH'/data with the extensions .dat for Pattern data and .trie for
Trie data.

The configuration file needs to set the following parameters:

    global
        51degrees-data-file           path to the Pattern or Trie data file
        51degrees-property-name-list  list of 51Degrees properties to detect
        51degrees-property-separator  separator to use between values
        51degrees-cache-size          LRU-based cache size (disabled by default)

The following is an example of the settings for Pattern.

    global
        51degrees-data-file '51D_REPO_PATH'/data/51Degrees-LiteV3.2.dat
        51degrees-property-name-list IsTablet DeviceType IsMobile
        51degrees-property-separator ,
        51degrees-cache-size 10000

HAProxy needs a way to pass device information to the backend servers. This is
done by using the 51d converter or fetch method, which intercepts the HTTP
headers and creates some new headers. This is controlled in the frontend
http-in section.

The following is an example which adds two new HTTP headers prefixed X-51D-

    frontend http-in
        bind *:8081
        default_backend servers
        http-request set-header X-51D-DeviceTypeMobileTablet %[51d.all(DeviceType,IsMobile,IsTablet)]
        http-request set-header X-51D-Tablet %[51d.all(IsTablet)]

Here, two headers are created with 51Degrees data, X-51D-DeviceTypeMobileTablet
and X-51D-Tablet. Any number of headers can be created this way and can be
named anything. 51d.all( ) invokes the 51degrees fetch. It can be passed up to
five property names of values to return. Values will be returned in the same
order, seperated by the 51-degrees-property-separator configured earlier. If a
property name can't be found the value 'NoData' is returned instead.

In addition to the device properties three additional properties related to the
validity of the result can be returned when used with the Pattern method. The
following example shows how Method, Difference and Rank could be included as one
new HTTP header X-51D-Stats.

    frontend http-in
        ...
        http-request set-header X-51D-Stats %[51d.all(Method,Difference,Rank)]

These values indicate how confident 51Degrees is in the result that that was
returned. More information is available on the 51Degrees web site at:

    https://51degrees.com/support/documentation/pattern

The above 51d.all fetch method uses all available HTTP headers for detection. A
modest performance improvement can be obtained by only passing one HTTP header
to the detection method with the 51d.single converter. The following example
uses the User-Agent HTTP header only for detection.

    frontend http-in
        ...
        http-request set-header X-51D-DeviceTypeMobileTablet %[req.fhdr(User-Agent),51d.single(DeviceType,IsMobile,IsTablet)]

Any HTTP header could be used inplace of User-Agent by changing the parameter
provided to req.fhdr.

When compiled to use the Trie detection method the trie format data file needs
to be provided. Changing the extension of the data file from dat to trie will
use the correct data.

    global
        51degrees-data-file '51D_REPO_PATH'/data/51Degrees-LiteV3.2.trie

When used with Trie the Method, Difference and Rank properties are not
available.

The free Lite data file contains information about screen size in pixels and
whether the device is a mobile. A full list of available properties is located
on the 51Degrees web site at:

    https://51degrees.com/resources/property-dictionary

Some properties are only available in the paid for Premium and Enterprise
versions of 51Degrees. These data sets not only contain more properties but
are updated weekly and daily and contain signatures for 100,000s of different
device combinations. For more information see the data options comparison web
page:

    https://51degrees.com/compare-data-options