Improve error reporting with missing binaries

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

src/extractcode/libarchive2.py

@@ -93,10 +93,16 @@ def load_lib():
     """
     from plugincode.location_provider import get_location
 
-    # get paths from plugins
     dll = get_location(EXTRACTCODE_LIBARCHIVE_DLL)
     libdir = get_location(EXTRACTCODE_LIBARCHIVE_LIBDIR)
+    if not (dll and libdir) or not os.path.isfile(dll) or not os.path.isdir(libdir):
+        raise Exception(
+            'CRITICAL: libarchive DLL is not installed. '
+            'Unable to continue: you need to install a valid extractcode-libarchive '
+            'plugin with a valid libarchive DLL available.'
+    )
     return command.load_shared_library(dll, libdir)
+    
 
 
 def set_env_with_tz():

src/extractcode/sevenzip.py

@@ -1,4 +1,3 @@
-
 #
 # Copyright (c) nexB Inc. and others.
 # SPDX-License-Identifier: Apache-2.0
@@ -73,6 +72,24 @@
 UNKNOWN_ERROR = 'Unknown extraction error'
 
 
+def get_bin_locations():
+    """
+    Return a tuple of (lib_dir, cmd_loc) for 7zip loaded from plugin-provided path.
+    """
+    from plugincode.location_provider import get_location
+
+    cmd_loc = get_location(EXTRACTCODE_7ZIP_EXE)
+    libdir = get_location(EXTRACTCODE_7ZIP_LIBDIR)
+    if not (cmd_loc and libdir) or not os.path.isfile(cmd_loc) or not os.path.isdir(libdir):
+        raise Exception(
+            'CRITICAL: 7zip executable is not installed. '
+            'Unable to continue: you need to install a valid extractcode-7z '
+            'plugin with a valid executable available.'
+    )
+
+    return libdir, cmd_loc
+
+
 def get_7z_errors(stdout, stderr):
     """
     Return error messages extracted from a 7zip command output `stdout` and
@@ -160,18 +177,6 @@ def is_rar(location):
     return T.filetype_file.lower().startswith('rar archive')
 
 
-def get_bin_locations():
-    """
-    Return a tuple of (lib_dir, cmd_loc) for 7zip loaded from plugin-provided path.
-    """
-    from plugincode.location_provider import get_location
-
-    # get paths from plugins
-    lib_dir = get_location(EXTRACTCODE_7ZIP_LIBDIR)
-    cmd_loc = get_location(EXTRACTCODE_7ZIP_EXE)
-    return lib_dir, cmd_loc
-
-
 def extract(location, target_dir, arch_type='*', file_by_file=on_mac, skip_symlinks=True):
     """
     Extract all files from a 7zip-supported archive file at location in the