Fix error handling gaps

Author: JeremiahM37

scripts/build_ffi.py

@@ -332,7 +332,7 @@ def get_features(local_wolfssl, features):
 
     for d in include_dirs:
         if not os.path.exists(d):
-            e = "Invalid wolfSSL include dir: .".format(d)
+            e = "Invalid wolfSSL include dir: {}.".format(d)
             raise FileNotFoundError(e)
 
         options = os.path.join(d, "wolfssl", "options.h")

wolfcrypt/__init__.py

@@ -46,6 +46,7 @@
 if top_level_py not in ["setup.py", "build_ffi.py"]:
     from wolfcrypt._ffi import ffi as _ffi
     from wolfcrypt._ffi import lib as _lib
+    from wolfcrypt.exceptions import WolfCryptError
 
     if hasattr(_lib, 'WC_RNG_SEED_CB_ENABLED'):
         if _lib.WC_RNG_SEED_CB_ENABLED:

wolfcrypt/hkdf.py

@@ -34,7 +34,7 @@ def HKDF(hash_cls, in_key, salt=None, info=None, out_len=None):
         Perform HKDF Extract-and-Expand in one call (wraps wc_HKDF).
 
         Parameters:
-        - hash_cls: hash class, see `wolfcrypt.hashes`.
+        - hash_cls: HMAC class, e.g. HmacSha256, see `wolfcrypt.hashes`.
         - in_key: input key material (IKM) as bytes or str.
         - salt: optional salt value (bytes or str). If None, treated as empty.
         - info: optional context/application info (bytes or str). If None,
@@ -79,7 +79,7 @@ def HKDF_Extract(hash_cls, salt, in_key):
         Wraps wc_HKDF_Extract.
 
         Parameters:
-        - hash_cls: hash class, see `wolfcrypt.hashes`.
+        - hash_cls: HMAC class, e.g. HmacSha256, see `wolfcrypt.hashes`.
         - salt: bytes/str (can be None -> treated as empty).
         - in_key: input key material (IKM) as bytes/str.
 
@@ -106,7 +106,7 @@ def HKDF_Expand(hash_cls, prk, info, out_len):
         Wraps wc_HKDF_Expand.
 
         Parameters:
-        - hash_cls: hash class, see `wolfcrypt.hashes`.
+        - hash_cls: HMAC class, e.g. HmacSha256, see `wolfcrypt.hashes`.
         - prk: pseudorandom key (output from HKDF-Extract) as bytes/str.
         - info: optional context/application info (bytes/str). If None, treated as empty.
         - out_len: length of output keying material in bytes.