Refactor libssl import path workarounds (#1202)

This amends the logic introduced for #1167 to only run when a plain
import of the library fails, thus avoiding the slow path traversal
needed to find the underlying library file.

telethon/crypto/libssl.py

@@ -3,13 +3,28 @@ Helper module around the system's libssl library if available for IGE mode.
 """
 import ctypes
 import ctypes.util
+try:
+    import ctypes.macholib.dyld
+except ImportError:
+    pass
 import logging
 import os
 
 __log__ = logging.getLogger(__name__)
 
 
+def _find_ssl_lib():
     lib = ctypes.util.find_library('ssl')
+    if not lib:
+        raise OSError('no library called "ssl" found')
+
+    # First, let ctypes try to handle it itself.
+    try:
+        libssl = ctypes.cdll.LoadLibrary(lib)
+    except OSError:
+        pass
+    else:
+        return libssl
 
     # This is a best-effort attempt at finding the full real path of lib.
     #
@@ -17,9 +32,8 @@ lib = ctypes.util.find_library('ssl')
     # so we have to do that ourselves.
     try:
         # This is not documented, so it could fail. Be on the safe side.
-    import ctypes.macholib.dyld
         paths = ctypes.macholib.dyld.DEFAULT_LIBRARY_FALLBACK
-except (ImportError, AttributeError):
+    except AttributeError:
         paths = [
             os.path.expanduser("~/lib"),
             "/usr/local/lib",
@@ -34,18 +48,17 @@ for path in paths:
                     # Manually follow symbolic links on *nix systems.
                     # Fix for https://github.com/LonamiWebs/Telethon/issues/1167
                     lib = os.path.realpath(os.path.join(root, lib))
-                break
+                    return ctypes.cdll.LoadLibrary(lib)
+    else:
+        raise OSError('no absolute path for "%s" and cannot load by name' % lib)
 
 
 try:
-    if not lib:
-        raise OSError('no library called "ssl" found')
-
-    _libssl = ctypes.cdll.LoadLibrary(lib)
+    _libssl = _find_ssl_lib()
 except OSError as e:
     # See https://github.com/LonamiWebs/Telethon/issues/1167
     # Sometimes `find_library` returns improper filenames.
-    __log__.info('Failed to load %s: %s (%s)', lib, type(e), e)
+    __log__.info('Failed to load SSL library: %s (%s)', type(e), e)
     _libssl = None
 
 if not _libssl: