fix: add method for writing the RB6 db key cache manually (#64)

If the extraction of the Rekordbox database key fails (>6.6.5), the user can now write the key manually to the cache file. After updating the cache the database can be opened without providing the key each time.
To make this work pyrekordbox now caches the decrypted key, not the password for decrypting the key. If an old cache file is found it is upgraded automatically.

.gitignore

@@ -4,7 +4,7 @@
 .chglog/
 docs/source/generated/
 data/
-pyrekordbox/rb.cache
+*.cache
 
 # setuptools_scm version file
 #  Use this if the project uses pyproject.toml with setuptools_scm instead of setup.py

README.md

@@ -235,8 +235,15 @@ db = Rekordbox6Database(key="<insert key here>")
 ````
 
 The key can be found in some other projects, see issue
-[#77](https://github.com/dylanljones/pyrekordbox/issues/77).
+[#77](https://github.com/dylanljones/pyrekordbox/issues/77). Alternatively you can update the cache file of the Rekordbox database key
+manually. Once the key is cached the database can be opened without providing the key:
+````python
+from pyrekordbox.config import write_db6_key_cache
+from pyrekordbox import Rekordbox6Database
 
+write_db6_key_cache("<insert key here>")  # call once
+db = Rekordbox6Database()
+````
 
 ## 💡 File formats
 

pyrekordbox/config.py

@@ -23,6 +23,7 @@
 logger = logging.getLogger(__name__)
 
 # Cache file for pyrekordbox data
+_cache_file_version = 2
 _cache_file = os.path.join(os.path.dirname(__file__), "rb.cache")
 
 # Define empty pyrekordbox configuration
@@ -119,6 +120,40 @@ def _extract_pw(pioneer_install_dir: str):
     return pw
 
 
+def write_db6_key_cache(key: str) -> None:
+    """Writes the decrypted Rekordbox6 database key to the cache file.
+
+    This method can also be used to manually cache the database key, provided
+    the user has found the key somewhere else. The key can be, for example,
+    found in some other projects that hard-coded it.
+
+    Parameters
+    ----------
+    key : str
+        The decrypted database key. To make sure the key is valid, the first
+        five characters are checked before writing the key to the cache file.
+        The key should start with '402fd'.
+
+    Examples
+    --------
+    >>> from pyrekordbox.config import write_db6_key_cache
+    >>> from pyrekordbox import Rekordbox6Database
+    >>> write_db6_key_cache("402fd...")
+    >>> db = Rekordbox6Database()  # The db can now be opened without providing the key
+    """
+    # Check if the key looks like a valid key
+    if not key.startswith("402fd"):
+        raise ValueError("The provided database key doesn't look valid!")
+    lines = list()
+    lines.append(f"version: {_cache_file_version}")
+    lines.append("dp: " + key)
+    text = "\n".join(lines)
+    with open(_cache_file, "w") as fh:
+        fh.write(text)
+    # Set the config key to make sure the key is present after calling method
+    __config__["rekordbox6"]["dp"] = key
+
+
 def _get_rb6_config(pioneer_prog_dir: str, pioneer_app_dir: str):
     conf = _get_rb_config(pioneer_prog_dir, pioneer_app_dir, version=6)
 
@@ -131,24 +166,40 @@ def _get_rb6_config(pioneer_prog_dir: str, pioneer_app_dir: str):
         raise FileNotFoundError(f"The Rekordbox database '{db_path}' doesn't exist!")
 
     conf["db_path"] = db_path
-    if not os.path.exists(_cache_file):
-        # Read password from app.asar, see
-        # https://www.reddit.com/r/Rekordbox/comments/qou6nm/key_to_open_masterdb_file/
-        pw = _extract_pw(conf["install_dir"])
-        if pw:
-            # Write pw to cache file
-            with open(_cache_file, "w") as fp:
-                fp.write(pw)
-    else:
-        # Read pw from cache file
-        with open(_cache_file, "r") as fp:
-            pw = fp.read()
-
-    # Decrypt db
-    if pw:
-        cipher = blowfish.Cipher(pw.encode())
-        dp = base64.standard_b64decode(opts["dp"])
-        dp = b"".join(cipher.decrypt_ecb(dp)).decode()
+    cache_version = 0
+    pw, dp = "", ""
+    if os.path.exists(_cache_file):
+        # Read cache file
+        with open(_cache_file, "r") as fh:
+            text = fh.read()
+        lines = text.splitlines()
+        if lines[0].startswith("version:"):
+            cache_version = int(lines[0].split(":")[1].strip())
+        else:
+            cache_version = 1
+        if cache_version == 1:
+            # Cache file introduced in pyrekordbox 0.1.6 contains only the password
+            pw = lines[0]
+        elif cache_version == 2:
+            # Cache file introduced in pyrekordbox 0.1.7 contains version and db key
+            dp = lines[1].split(":")[1].strip()
+        else:
+            raise ValueError(f"Invalid cache version: {cache_version}")
+
+    if cache_version < _cache_file_version:
+        # Update cache file
+        if not pw:
+            logger.debug("Extracting pw")
+            pw = _extract_pw(conf["install_dir"])
+        if not dp and pw:
+            cipher = blowfish.Cipher(pw.encode())
+            dp = base64.standard_b64decode(opts["dp"])
+            dp = b"".join(cipher.decrypt_ecb(dp)).decode()
+        if dp:
+            write_db6_key_cache(dp)
+
+    # Add database key to config if found
+    if dp:
         conf["dp"] = dp
 
     return conf