Tighten bytes/str boundaries and remove unnecessary coercing (#547)

Now that the project is Python 3 only, the boundaries between bytes and
Unicode strings is more explicit.

This allows removing several unnecessary force_bytes() and
force_unicode() calls that handled differences between Python 2 and
Python 3. All uses of force_unicode() have been removed.

For values that are known to be bytes, use `.decode()` instead. For
values are that known to be str, use `.encode()` instead. This strategy
makes the type explicit and reduces a function call.

Key handling continues to use force_bytes() to allow callers to pass
either bytes or str.

To help enforce bytes/str handling in the future, the `-b` option is
passed to Python when testing. This option will emit a warning if bytes
and str are improperly mixed together.

3 files changed, 15 insertions, 29 deletions

diff --git a/jwt/algorithms.py b/jwt/algorithms.py
index 2eb090c..c94f631 100644
--- a/jwt/algorithms.py
+++ b/jwt/algorithms.py
@@ -8,7 +8,6 @@ from .utils import (
     base64url_encode,
     der_to_raw_signature,
     force_bytes,
-    force_unicode,
     from_base64url_uint,
     raw_to_der_signature,
     to_base64url_uint,
@@ -194,7 +193,7 @@ class HMACAlgorithm(Algorithm):
     def to_jwk(key_obj):
         return json.dumps(
             {
-                "k": force_unicode(base64url_encode(force_bytes(key_obj))),
+                "k": base64url_encode(force_bytes(key_obj)).decode(),
                 "kty": "oct",
             }
         )
@@ -260,18 +259,14 @@ if has_crypto:  # noqa: C901
                 obj = {
                     "kty": "RSA",
                     "key_ops": ["sign"],
-                    "n": force_unicode(
-                        to_base64url_uint(numbers.public_numbers.n)
-                    ),
-                    "e": force_unicode(
-                        to_base64url_uint(numbers.public_numbers.e)
-                    ),
-                    "d": force_unicode(to_base64url_uint(numbers.d)),
-                    "p": force_unicode(to_base64url_uint(numbers.p)),
-                    "q": force_unicode(to_base64url_uint(numbers.q)),
-                    "dp": force_unicode(to_base64url_uint(numbers.dmp1)),
-                    "dq": force_unicode(to_base64url_uint(numbers.dmq1)),
-                    "qi": force_unicode(to_base64url_uint(numbers.iqmp)),
+                    "n": to_base64url_uint(numbers.public_numbers.n).decode(),
+                    "e": to_base64url_uint(numbers.public_numbers.e).decode(),
+                    "d": to_base64url_uint(numbers.d).decode(),
+                    "p": to_base64url_uint(numbers.p).decode(),
+                    "q": to_base64url_uint(numbers.q).decode(),
+                    "dp": to_base64url_uint(numbers.dmp1).decode(),
+                    "dq": to_base64url_uint(numbers.dmq1).decode(),
+                    "qi": to_base64url_uint(numbers.iqmp).decode(),
                 }
 
             elif getattr(key_obj, "verify", None):
@@ -281,8 +276,8 @@ if has_crypto:  # noqa: C901
                 obj = {
                     "kty": "RSA",
                     "key_ops": ["verify"],
-                    "n": force_unicode(to_base64url_uint(numbers.n)),
-                    "e": force_unicode(to_base64url_uint(numbers.e)),
+                    "n": to_base64url_uint(numbers.n).decode(),
+                    "e": to_base64url_uint(numbers.e).decode(),
                 }
             else:
                 raise InvalidKeyError("Not a public or private key")
diff --git a/jwt/api_jws.py b/jwt/api_jws.py
index bce7a1a..cf0d8fb 100644
--- a/jwt/api_jws.py
+++ b/jwt/api_jws.py
@@ -11,7 +11,7 @@ from .exceptions import (
     InvalidSignatureError,
     InvalidTokenError,
 )
-from .utils import base64url_decode, base64url_encode, force_bytes, merge_dict
+from .utils import base64url_decode, base64url_encode, merge_dict
 
 
 class PyJWS:
@@ -95,9 +95,9 @@ class PyJWS:
             self._validate_headers(headers)
             header.update(headers)
 
-        json_header = force_bytes(
-            json.dumps(header, separators=(",", ":"), cls=json_encoder)
-        )
+        json_header = json.dumps(
+            header, separators=(",", ":"), cls=json_encoder
+        ).encode()
 
         segments.append(base64url_encode(json_header))
         segments.append(base64url_encode(payload))
diff --git a/jwt/utils.py b/jwt/utils.py
index 0e8f210..a617342 100644
--- a/jwt/utils.py
+++ b/jwt/utils.py
@@ -11,15 +11,6 @@ except ImportError:
     pass
 
 
-def force_unicode(value):
-    if isinstance(value, bytes):
-        return value.decode("utf-8")
-    elif isinstance(value, str):
-        return value
-    else:
-        raise TypeError("Expected a string value")
-
-
 def force_bytes(value):
     if isinstance(value, str):
         return value.encode("utf-8")