PoC: TAP 19 - Add support for Content Addressable Systems like IPFS in TUF

tuf/adapter/adapter.py

@@ -0,0 +1,91 @@
+# Copyright 2020, New York University and the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
+"""Implementation of content addressable targets"""
+import os
+import sys
+import inspect
+from abc import ABC, abstractmethod
+from typing import Optional
+import requests
+
+class Adapter(ABC):
+    """Abstract class for content addressable systems"""
+
+    @staticmethod
+    @abstractmethod
+    def scheme_name() -> str:
+        """Return the scheme of the URI.
+
+        Used to find out the correct adapter of a target file.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def fetch_target(self, target_dir: str) -> str:
+        """Download the target file and return the target directory.
+
+        Different adapters have different methods to fetch a file from its ecosystem.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def find_target_in_local_cache(self, target_dir: str) -> str:
+        """Check whether the target file exists in the local cache.
+
+        If found, return the location of the file.
+        """
+        raise NotImplementedError
+
+class IPFS(Adapter):
+    """Implements Adapter for IPFS targets"""
+
+    ipfs_gateway_url = 'http://127.0.0.1:8081/ipfs/'
+    scheme = 'ipfs'
+
+    def __init__(self, cid: str):
+        self.cid = cid
+
+    @staticmethod
+    def scheme_name() -> str:
+        return IPFS.scheme
+
+    def fetch_target(self, target_dir: str) -> str:
+        file_url = self.ipfs_gateway_url + self.cid
+        response = requests.get(file_url, timeout=5)
+        if response.status_code == 200:
+            filepath = self._generate_target_file_path(target_dir)
+            with open(filepath, 'wb') as file:
+                file.write(response.content)
+
+            return filepath
+
+        print('Failed to retrieve file:', response.status_code)
+        return ''
+
+    def find_target_in_local_cache(self, target_dir: str) -> Optional[str]:
+        filepath = self._generate_target_file_path(target_dir)
+        if os.path.exists(filepath):
+            return filepath
+
+        return None
+
+    def _generate_target_file_path(self, target_dir: str) -> str:
+        # TODO: Add the correct extension to the file name using Content-Type response header.
+        file_name = self.cid
+        return os.path.join(target_dir, file_name)
+
+def get_adapter_class(scheme: str) -> Adapter:
+    """Return the class of the provided scheme"""
+    classType = Adapter
+    subclasses = []
+    classes = inspect.getmembers(sys.modules[__name__], inspect.isclass)
+    for name, obj in classes:
+        if (obj is not classType) and (classType in inspect.getmro(obj)):
+            subclasses.append((obj, name))
+
+    for cls, name in subclasses:
+        if cls.scheme_name() == scheme:
+            return cls
+
+    return None

tuf/api/metadata.py

@@ -62,6 +62,7 @@
     MetadataSerializer,
     SignedSerializer,
 )
+from tuf.adapter import adapter
 
 _ROOT = "root"
 _SNAPSHOT = "snapshot"
@@ -1609,6 +1610,7 @@ def __init__(
             unrecognized_fields = {}
 
         self.unrecognized_fields = unrecognized_fields
+        self.adapter: Optional[adapter.Adapter] = None
 
     @property
     def custom(self) -> Any:

tuf/ngclient/updater.py

@@ -56,6 +56,7 @@
 from tuf.ngclient._internal import requests_fetcher, trusted_metadata_set
 from tuf.ngclient.config import UpdaterConfig
 from tuf.ngclient.fetcher import FetcherInterface
+from tuf.adapter import adapter
 
 logger = logging.getLogger(__name__)
 
@@ -192,6 +193,10 @@ def find_cached_target(
             ``None`` if file is not found or it is not up to date.
         """
 
+        if targetinfo.adapter is not None:
+            filepath = filepath or self.target_dir
+            return targetinfo.adapter.find_target_in_local_cache(filepath)
+
         if filepath is None:
             filepath = self._generate_target_file_path(targetinfo)
 
@@ -229,6 +234,10 @@ def download_target(
             Local path to downloaded file
         """
 
+        if targetinfo.adapter is not None:
+            target_dir = filepath or self.target_dir
+            return targetinfo.adapter.fetch_target(target_dir)
+
         if filepath is None:
             filepath = self._generate_target_file_path(targetinfo)
 
@@ -444,6 +453,14 @@ def _preorder_depth_first_walk(
 
             if target is not None:
                 logger.debug("Found target in current role %s", role_name)
+                scheme, identifer = _get_scheme_and_identifer(target_filepath)
+                if scheme is not None or identifer is not None:
+                    cls = adapter.get_adapter_class(scheme)
+                    if cls is None:
+                        logger.debug("Invalid scheme name. No implementation of scheme %s exists", scheme)
+                        return target
+                    target.adapter = cls(identifer)
+
                 return target
 
             # After preorder check, add current role to set of visited roles.
@@ -483,3 +500,12 @@ def _preorder_depth_first_walk(
 def _ensure_trailing_slash(url: str) -> str:
     """Return url guaranteed to end in a slash."""
     return url if url.endswith("/") else f"{url}/"
+
+def _get_scheme_and_identifer(uri):
+    try:
+        parsed_uri = parse.urlparse(uri)
+        scheme = parsed_uri.scheme
+        identifer = parsed_uri.path
+        return scheme, identifer
+    except ValueError:
+        return None, None