libmagic-sys-provided: let user override paths

let the user override assumed paths via environment.
lib_dir is probed first from LD_LIBRARY_PATH.
Location on libmagic.so can be overriden by passing path via LIBMAGIC
environment variable. If not found it falls back to lib_dir/libmagic.so.
Location of the magic database can be specified via MAGIC environment
variable. If not found it falls back to the previous bevahior.

With this patch it possible to run scancode is buildsystems like YOCTO,
which heaviily rely on overriding paths via environment to pick the
correct implementation from the build workspace

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>

Author: priv-kweihmann

builtins/typecode_libmagic_system_provided/src/typecode_libmagic/__init__.py

@@ -22,8 +22,9 @@
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
-from os import path
 import platform
+from os import environ
+from os import path
 
 from plugincode.location_provider import LocationProviderPlugin
 
@@ -35,38 +36,42 @@ def get_locations(self):
         locations of the libmagic shared library as installed on various Linux
         distros or on FreeBSD.
         """
-        system_arch = platform.machine()
-        mainstream_system = platform.system().lower()
-        if mainstream_system == 'linux':
-            distribution = platform.linux_distribution()[0].lower()
-            debian_based_distro = ['ubuntu', 'mint', 'debian']
-            rpm_based_distro = ['fedora', 'redhat']
-
-            if distribution in debian_based_distro:
-                data_dir = '/usr/lib/file'
-                lib_dir = '/usr/lib/'+system_arch+'-linux-gnu'
+        lib_dir = environ.get('LD_LIBRARY_PATH')
+        lib_dll = path.join(lib_dir, 'libmagic.so')
+        data_dir = '/usr/share'
+        if not lib_dir:
+            system_arch = platform.machine()
+            mainstream_system = platform.system().lower()
+            if mainstream_system == 'linux':
+                distribution = platform.linux_distribution()[0].lower()
+                debian_based_distro = ['ubuntu', 'mint', 'debian']
+                rpm_based_distro = ['fedora', 'redhat']
 
-            elif distribution in rpm_based_distro:
-                data_dir = '/usr/share/misc'
-                lib_dir = '/usr/lib64'
+                if distribution in debian_based_distro:
+                    data_dir = '/usr/lib/file'
+                    lib_dir = '/usr/lib/'+system_arch+'-linux-gnu'
 
-            else:
-                raise Exception('Unsupported system: {}'.format(distribution))
+                elif distribution in rpm_based_distro:
+                    data_dir = '/usr/share/misc'
+                    lib_dir = '/usr/lib64'
 
-            lib_dll = path.join(lib_dir, 'libmagic.so');
+                else:
+                    raise Exception('Unsupported system: {}'.format(distribution))
 
-        elif mainstream_system == 'freebsd':
-            if path.isdir('/usr/local/'):
-                lib_dir = '/usr/local'
-            else:
-                lib_dir = '/usr'
+            elif mainstream_system == 'freebsd':
+                if path.isdir('/usr/local/'):
+                    lib_dir = '/usr/local'
+                else:
+                    lib_dir = '/usr'
 
-            lib_dll = path.join(lib_dir, 'lib/libmagic.so')
-            data_dir = path.join(lib_dir,'share/file')
+                lib_dll = path.join(lib_dir, 'lib/libmagic.so')
+                data_dir = path.join(lib_dir,'share/file')
+        lib_magic = environ.get('LIBMAGIC', lib_dll)
+        file_magic_data = environ.get('MAGIC', path.join(data_dir, 'magic.mgc'))
 
         locations = {
             'typecode.libmagic.libdir': lib_dir,
-            'typecode.libmagic.dll': lib_dll,
-            'typecode.libmagic.db': path.join(data_dir, 'magic.mgc'),
+            'typecode.libmagic.dll': lib_magic,
+            'typecode.libmagic.db': file_magic_data,
             }
         return locations