Implement write_to_disk for uri backends

ethpm/backends/base.py

@@ -1,8 +1,13 @@
 from abc import ABC, abstractmethod
+from pathlib import Path
+import shutil
+import tempfile
 from typing import Union
 
 from eth_typing import URI
 
+from ethpm.exceptions import CannotHandleURI
+
 
 class BaseURIBackend(ABC):
     """
@@ -34,3 +39,19 @@ def fetch_uri_contents(self, uri: URI) -> Union[bytes, URI]:
         Fetch the contents stored at a URI.
         """
         pass
+
+    def write_to_disk(self, uri: URI, target_path: Path) -> None:
+        """
+        Writes the contents of target URI to target path.
+        Raises exception if target path exists.
+        """
+        contents = self.fetch_uri_contents(uri)
+        if target_path.exists():
+            raise CannotHandleURI(
+                f"Uri: {uri} cannot be written to disk since target path ({target_path}) "
+                "already exists. Please provide a target_path that does not exist."
+            )
+        with tempfile.NamedTemporaryFile() as temp:
+            temp.write(contents)
+            temp.seek(0)
+            shutil.copyfile(temp.name, target_path)

ethpm/backends/http.py

@@ -18,6 +18,10 @@ class GithubOverHTTPSBackend(BaseURIBackend):
     Base class for all URIs pointing to a content-addressed Github URI.
     """
 
+    @property
+    def base_uri(self) -> str:
+        return GITHUB_API_AUTHORITY
+
     def can_resolve_uri(self, uri: URI) -> bool:
         return is_valid_content_addressed_github_uri(uri)
 
@@ -43,7 +47,3 @@ def fetch_uri_contents(self, uri: URI) -> bytes:
         decoded_contents = base64.b64decode(contents["content"])
         validate_blob_uri_contents(decoded_contents, uri)
         return decoded_contents
-
-    @property
-    def base_uri(self) -> str:
-        return GITHUB_API_AUTHORITY

ethpm/backends/ipfs.py

@@ -3,6 +3,7 @@
 from pathlib import Path
 from typing import Dict, List, Type
 
+from eth_typing import URI
 from eth_utils import import_string, to_bytes
 import ipfshttpclient
 
@@ -59,7 +60,7 @@ class IPFSOverHTTPBackend(BaseIPFSBackend):
     def __init__(self) -> None:
         self.client = ipfshttpclient.connect(self.base_uri)
 
-    def fetch_uri_contents(self, uri: str) -> bytes:
+    def fetch_uri_contents(self, uri: URI) -> bytes:
         ipfs_hash = extract_ipfs_path_from_uri(uri)
         contents = self.client.cat(ipfs_hash)
         validation_hash = generate_file_hash(contents)
@@ -108,6 +109,11 @@ def fetch_uri_contents(self, uri: str) -> bytes:
             "IPFS gateway is currently disabled, please use a different IPFS backend."
         )
 
+    def write_to_disk(self, uri: URI, target_path: Path) -> None:
+        raise CannotHandleURI(
+            "IPFS gateway is currently disabled, please use a different IPFS backend."
+        )
+
 
 class InfuraIPFSBackend(IPFSOverHTTPBackend):
     """

tests/ethpm/backends/test_http_backends.py

@@ -6,23 +6,34 @@
 from ethpm.constants import GITHUB_API_AUTHORITY
 from ethpm.exceptions import CannotHandleURI, ValidationError
 
+BLOB_URI = "https://api.github.com/repos/ethpm/py-ethpm/git/blobs/a7232a93f1e9e75d606f6c1da18aa16037e03480"
 
-@pytest.mark.parametrize(
-    "uri",
-    (
-        "https://api.github.com/repos/ethpm/py-ethpm/git/blobs/a7232a93f1e9e75d606f6c1da18aa16037e03480",
-    ),
-)
-def test_github_over_https_backend_fetch_uri_contents(uri, owned_contract, w3):
+
+def test_github_over_https_backend_fetch_uri_contents(owned_contract, w3):
     # these tests may occassionally fail CI as a result of their network requests
     backend = GithubOverHTTPSBackend()
     assert backend.base_uri == GITHUB_API_AUTHORITY
     # integration with Package.from_uri
-    owned_package = Package.from_uri(uri, w3)
+    owned_package = Package.from_uri(BLOB_URI, w3)
     assert owned_package.name == "owned"
 
 
 def test_github_over_https_backend_raises_error_with_invalid_content_hash(w3):
     invalid_uri = "https://api.github.com/repos/ethpm/py-ethpm/git/blobs/a7232a93f1e9e75d606f6c1da18aa16037e03123"
     with pytest.raises(HTTPError):
         Package.from_uri(invalid_uri, w3)
+
+
+def test_github_backend_writes_to_disk(tmp_path):
+    backend = GithubOverHTTPSBackend()
+    contents = backend.fetch_uri_contents(BLOB_URI)
+    target_path = tmp_path / "github_uri.txt"
+    backend.write_to_disk(BLOB_URI, target_path)
+    assert target_path.read_bytes() == contents
+
+
+def test_github_backend_write_to_disk_raises_exception_if_target_exists(tmp_path):
+    target_path = tmp_path / "test.txt"
+    target_path.touch()
+    with pytest.raises(CannotHandleURI, match="cannot be written to disk."):
+        GithubOverHTTPSBackend().write_to_disk(BLOB_URI, target_path)

tests/ethpm/backends/test_ipfs_backends.py

@@ -13,6 +13,7 @@
     get_ipfs_backend_class,
 )
 from ethpm.constants import INFURA_GATEWAY_MULTIADDR
+from ethpm.exceptions import CannotHandleURI
 
 OWNED_MANIFEST_PATH = V2_PACKAGES_DIR / "owned" / "1.0.0.json"
 
@@ -116,3 +117,20 @@ def test_pin_assets_to_dummy_backend(dummy_ipfs_backend):
     assert "StandardToken.sol" in dir_names
     assert "QmRJHLmPVct2rbBpdGjP3xkXbF7romQigtmcs8TRfV1yC7" in dir_hashes
     assert "2865" in dir_sizes
+
+
+def test_ipfs_backend_write_to_disk(tmp_path):
+    ipfs_uri = "ipfs://Qme4otpS88NV8yQi8TfTP89EsQC5bko3F5N1yhRoi6cwGV"
+    backend = LocalIPFSBackend()
+    contents = backend.fetch_uri_contents(ipfs_uri)
+    target_path = tmp_path / "ipfs_uri.txt"
+    backend.write_to_disk(ipfs_uri, target_path)
+    assert target_path.read_bytes() == contents
+
+
+def test_ipfs_backend_write_to_disk_raises_exception_if_target_exists(tmp_path):
+    ipfs_uri = "ipfs://Qme4otpS88NV8yQi8TfTP89EsQC5bko3F5N1yhRoi6cwGV"
+    target_path = tmp_path / "test.txt"
+    target_path.touch()
+    with pytest.raises(CannotHandleURI, match="cannot be written to disk."):
+        LocalIPFSBackend().write_to_disk(ipfs_uri, target_path)