kojikamid: write buildrequires files as bytes

Fix a TypeError when downloading buildrequires files on Python 3.
base64.b64decode() returns bytes, so we must open the file for writing
in bytes mode, not text mode.

Add a unit test that verifies this behavior.

tests/test_vm/test_kojikamid.py

@@ -0,0 +1,65 @@
+import base64
+import filecmp
+import importlib.machinery
+import importlib.util
+import os
+import tempfile
+from subprocess import check_call
+
+VM_TESTS_DIR = os.path.dirname(os.path.abspath(__file__))
+LOGO_FIXTURE = os.path.join(VM_TESTS_DIR, 'data', 'koji.png')
+TESTS_DIR = os.path.dirname(VM_TESTS_DIR)
+VM_DIR = os.path.join(os.path.dirname(TESTS_DIR), 'vm')
+
+# Generate the kojikamid file before importing.
+tmpfile = tempfile.NamedTemporaryFile(prefix='kojikamid.')
+check_call(['bash', 'fix_kojikamid.sh'], cwd=VM_DIR, stdout=tmpfile)
+print(tmpfile.name)
+
+# Dynamically import our temporary kojikamid file.
+loader = importlib.machinery.SourceFileLoader('kojikamid', tmpfile.name)
+spec = importlib.util.spec_from_loader(loader.name, loader)
+kojikamid = importlib.util.module_from_spec(spec)
+loader.exec_module(kojikamid)
+
+
+class FakeServer(object):
+    def getTaskInfo(self):
+        # Koji's getTaskInfo(..., request=True) returns the task's request
+        # data. kojivmd strips this down to the second element of that request
+        # and returns it here:
+        return ['git://example.com/ceph.git#abc123',
+                'ceph-6.1-win-build',
+                {'repo_id': 2,
+                 'winspec': 'git://example.com/pkg.git?ceph#def456'}]
+
+    def getFile(self, buildinfo, archiveinfo, offset, length, type):
+        # Return a base64-encoded static fixture (a PNG image).
+        offset = int(offset)
+        length = int(length)
+        with open(LOGO_FIXTURE, 'rb') as fileobj:
+            try:
+                fileobj.seek(offset)
+                data = fileobj.read(length)
+                encoded = base64.b64encode(data).decode()
+                del data
+                return encoded
+            finally:
+                fileobj.close()
+
+
+def test_fetch_file(tmpdir):
+    server = FakeServer()
+    build = kojikamid.WindowsBuild(server)
+    basedir = str(tmpdir)
+    buildinfo = {
+        'name': 'wnbd',
+    }
+    fileinfo = {
+        'localpath': 'koji.png',
+        'checksum_type': 2,  # sha256
+        'checksum': 'f78bc62287eec7641a85a7d1c0435c995672e7f46e33de72a82775b1fb16a93f',
+    }
+    build.fetchFile(basedir, buildinfo, fileinfo, 'win')
+    fetched = str(tmpdir.join('koji.png'))
+    assert filecmp.cmp(fetched, LOGO_FIXTURE)

vm/kojikamid.py

@@ -335,7 +335,7 @@ class WindowsBuild(object):
                 raise BuildError('Unknown checksum type %s for %s' % (  # noqa: F821
                                  checksum_type,
                                  os.path.basename(fileinfo['localpath'])))
-        with koji._open_text_file(destpath, 'wt') as destfile:
+        with open(destpath, 'wb') as destfile:
             offset = 0
             while True:
                 encoded = self.server.getFile(buildinfo, fileinfo, encode_int(offset), 1048576,