fix: ensure bytes with null chars are returned

src/kasa_crypt/_crypt_impl.pyx

@@ -1,32 +1,43 @@
 import cython
 
-from libc.stdlib cimport malloc
+from libc.stdlib cimport free, malloc
 from libc.string cimport strlen
 
 
 cdef extern from "crypt_wrapper.h":
     void _encrypt_into(const char * unencrypted, char * encrypted)
     void _decrypt_into(const char * encrypted, char * unencrypted)
 
-cdef char* _decrypt(const char *encrypted):
+cdef void _decrypt(const char *encrypted, char **unencrypted, Py_ssize_t *length):
     cdef Py_ssize_t n = strlen(encrypted)
-    cdef char* unencrypted = <char *> malloc((n + 1) * sizeof(char))
-    if not unencrypted:
-        return NULL  # malloc failed
-    _decrypt_into(encrypted, unencrypted)
-    return unencrypted[:n]
+    unencrypted[0] = <char *> malloc((n + 1) * sizeof(char))
+    if not unencrypted[0]:
+        return  # malloc failed
+    _decrypt_into(encrypted, unencrypted[0] )
+    length[0] = n
 
-cdef char* _encrypt(const char *unencrypted):
+cdef void _encrypt(const char *unencrypted, char** encrypted, Py_ssize_t *length):
     cdef Py_ssize_t n = strlen(unencrypted)
-    cdef char* encrypted = <char *> malloc((n + 1) * sizeof(char))
-    if not encrypted:
-        return NULL  # malloc failed
-    _encrypt_into(unencrypted, encrypted)
-    return encrypted[:n]
+    encrypted[0] = <char *> malloc((n + 1) * sizeof(char))
+    if not encrypted[0]:
+        return  # malloc failed
+    _encrypt_into(unencrypted, encrypted[0])
+    length[0] = n
 
 def encrypt(string: str) -> bytes:
-    return _encrypt(string.encode('utf-8'))
-
+    cdef char* encrypted = NULL
+    cdef Py_ssize_t length = 0
+    _encrypt(string.encode('utf-8'), &encrypted, &length)
+    try:
+        return encrypted[:length]
+    finally:
+        free(encrypted)
 
 def decrypt(string: bytes) -> str:
-    return _decrypt(string).decode('utf-8')
+    cdef char* unencrypted = NULL
+    cdef Py_ssize_t length = 0
+    _decrypt(string, &unencrypted, &length)
+    try:
+        return unencrypted[:length].decode('utf-8')
+    finally:
+        free(unencrypted)

src/kasa_crypt/crypt_wrapper.h

@@ -14,18 +14,16 @@ void _encrypt_into(const char * unencrypted, char * encrypted) {
         key = key ^ unencrypted_byte;
         encrypted[i] = key;
     }
-    encrypted[len] = '\0';
 }
 void _decrypt_into(const char * encrypted, char * unencrypted) {
     uint8_t unencrypted_byte;
     uint8_t encrypted_byte;
     uint8_t key = 171;
     unsigned long len = strlen(encrypted);
-    for(unsigned i = 0; i < strlen(encrypted); i++) {
+    for(unsigned i = 0; i < len; i++) {
         encrypted_byte = encrypted[i];
         unencrypted_byte = key ^ encrypted_byte;
         key = encrypted_byte;
         unencrypted[i] = unencrypted_byte;
     }
-    unencrypted[len] = '\0';
 }