[WIP] base contentproviders commit

Very much a WIP, but some thougts on how we can support more
than just git.

repo2docker/contentproviders/base.py

@@ -0,0 +1,26 @@
+"""
+Base classes for repo2docker ContentProviders
+
+ContentProviders accept a `spec` of various kinds, and 
+provide the contents from the spec to a given output directory.
+"""
+class ContentProviderException(Exception):
+    """Exception raised when a ContentProvider can not provide content
+    """
+    pass
+
+class ContentProvider:
+    kind = ""
+
+    def provide(self, spec, output_dir, yield_output=False):
+        """Provide the contents of given spec to output_dir
+
+        This is a generator, and so should be yielded from or iterated over.
+        
+        Arguments:
+            spec -- Dict / String specification understood by this ContentProvider
+            output_dir {string} -- Path to output directory (must already exist)
+            yield_output {bool} -- If True, return output line by line. If not, output just goes to stdout.
+        """
+        raise NotImplementedError()
+

repo2docker/contentproviders/git.py

@@ -0,0 +1,28 @@
+import subprocess
+
+from .base import ContentProvider, ContentProviderException
+from ..utils import execute_cmd
+
+class GitContentProvider(ContentProvider):
+    """Provides contents of a git repository (optionally at a given ref)
+    """
+    kind = "git"
+
+    def provide(self, spec, output_dir, yield_output=False):
+        url = spec['url']
+        ref = spec.get('ref', None)
+        try:
+            for line in execute_cmd(['git', 'clone', url, output_dir],
+                                    capture=yield_output):
+                yield line
+        except subprocess.CalledProcessError as e:
+            raise ContentProviderException("Failed to clone repository!") from e
+
+        if ref:
+            try:
+                for line in execute_cmd(['git', 'reset', '--hard', ref],
+                                        cwd=output_dir,
+                                        capture=yield_output):
+                    yield line
+            except subprocess.CalledProcessError:
+                raise ContentProviderException("Failed to checkout ref {}!".format(ref)) from e

tests/contentproviders/test_git.py

@@ -0,0 +1,38 @@
+from contextlib import contextmanager
+import shutil
+import os
+import subprocess
+from tempfile import TemporaryDirectory
+from repo2docker.contentproviders.git import GitContentProvider
+
+
+@contextmanager
+def git_repo():
+    """
+    Makes a dummy git repo in which user can perform git operations
+
+    Should be used as a contextmanager, it will delete directory when done
+    """
+
+    with TemporaryDirectory() as gitdir:
+        subprocess.check_call(['git', 'init'], cwd=gitdir)
+
+        yield gitdir
+
+def test_clone():
+    """Test simple git clone to a target dir
+    """
+    with git_repo() as upstream:
+        with open(os.path.join(upstream, 'test'), 'w') as f:
+            f.write("Hello")
+
+        subprocess.check_call(['git', 'add', 'test'], cwd=upstream)
+        subprocess.check_call(['git', 'commit', '-m', 'Test commit'], cwd=upstream)
+
+        with TemporaryDirectory() as clone_dir:
+            spec = {
+                'url': upstream
+            }
+            for _ in GitContentProvider().provide(spec, clone_dir, False):
+                pass
+            assert os.path.exists(os.path.join(clone_dir, 'test'))