init: provide a better error message for missing symbols

When the there is a difference in versions between build time and
run time libraries for the bindings there might be missing symbols.
So provide a slightly better error message when that happens, as the
usual message is not to clear.

Signed-off-by: Erik Larsson <who+github@cnackers.org>

src/tpm2_pytss/__init__.py

@@ -1,4 +1,21 @@
 import _cffi_backend
+
+# check that we can load the C bindings,
+# if we can't, provide a better message.
+try:
+    from ._libtpm2_pytss import lib
+except ImportError as e:
+    parts = e.msg.split(": ", 2)
+    if len(parts) != 3:
+        raise e
+    path, error, symbol = parts
+    if error != "undefined symbol":
+        raise e
+    raise ImportError(
+        f"failed to load tpm2-tss bindigs in {path} due to missing symbol {symbol}, "
+        + "ensure that you are using the same libraries the python module was built against."
+    )
+
 from .ESAPI import ESAPI
 
 try:

test/test_import.py

@@ -0,0 +1,47 @@
+#!/usr/bin/python3 -u
+# SPDX-License-Identifier: BSD-2
+
+import sys
+import unittest
+
+
+class mocklib:
+    def __init__(self, msg):
+        self.msg = msg
+
+    @property
+    def lib(self):
+        raise ImportError(self.msg)
+
+
+class ImportTest(unittest.TestCase):
+    def test_missing_symbol(self):
+        if "tpm2_pytss" in sys.modules:
+            del sys.modules["tpm2_pytss"]
+        sys.modules["tpm2_pytss._libtpm2_pytss"] = mocklib(
+            "/tmp/tpm2_pytss/_libtpm2_pytss.abi3.so: undefined symbol: test_symbol"
+        )
+        with self.assertRaises(ImportError) as e:
+            import tpm2_pytss
+        self.assertEqual(
+            e.exception.msg,
+            "failed to load tpm2-tss bindigs in /tmp/tpm2_pytss/_libtpm2_pytss.abi3.so"
+            + " due to missing symbol test_symbol, ensure that you are using the same"
+            + " libraries the python module was built against.",
+        )
+
+    def test_other_message(self):
+        if "tpm2_pytss" in sys.modules:
+            del sys.modules["tpm2_pytss"]
+        sys.modules["tpm2_pytss._libtpm2_pytss"] = mocklib("I am a teapot")
+        with self.assertRaises(ImportError) as e:
+            import tpm2_pytss
+        self.assertEqual(e.exception.msg, "I am a teapot")
+
+    def test_not_missing_symbol(self):
+        if "tpm2_pytss" in sys.modules:
+            del sys.modules["tpm2_pytss"]
+        sys.modules["tpm2_pytss._libtpm2_pytss"] = mocklib("/bin/ls: not a: teapot")
+        with self.assertRaises(ImportError) as e:
+            import tpm2_pytss
+        self.assertEqual(e.exception.msg, "/bin/ls: not a: teapot")