The resolve module now computes a sha256 sum if the link doesn't alre…

…ady have one

Resolves #22

src/piprules/resolve.py

@@ -168,9 +168,12 @@ def _create_resolved_requirement(self, requirement):
 
         link = requirement.link
         source = ResolvedRequirementSource(link.url_without_fragment)
-        if link.hash:
-            # TODO this assumes the hash is sha256
-            source.sha256 = link.hash
+
+        source.sha256 = (
+            link.hash
+            if link.hash and link.hash_name == "sha256"
+            else self._compute_sha256_sum(requirement)
+        )
 
         return ResolvedRequirement(
             pipcompat.canonicalize_name(requirement.name),
@@ -199,6 +202,11 @@ def _set_link_to_local_wheel(self, requirement):
             session=self._session,
         )
 
+    def _compute_sha256_sum(self, requirement):
+        LOG.debug(f"Computing sha256 sum for {requirement.name}")
+        temp_wheel_path = _find_wheel(self._work_dirs.wheel, requirement.name)
+        return util.compute_file_hash(temp_wheel_path)
+
 
 def _find_wheel(directory, name):
     canon_name = pipcompat.canonicalize_name(name)

src/piprules/util.py

@@ -1,5 +1,6 @@
-import errno
 import contextlib
+import errno
+import hashlib
 import itertools
 import os
 
@@ -42,3 +43,16 @@ def prepend_to_pythonpath(paths):
 def full_groupby(iterable, key=None):
     """Like itertools.groupby(), but sorts the input on the group key first."""
     return itertools.groupby(sorted(iterable, key=key), key=key)
+
+
+def compute_file_hash(path, algorithm="sha256"):
+    hasher = hashlib.new(algorithm)
+    block_size = 4096
+
+    with open(path, mode='rb') as file_:
+        buf = file_.read(block_size)
+        while buf:
+            hasher.update(buf)
+            buf = file_.read(block_size)
+
+    return hasher.hexdigest()