Start using content providers

repo2docker/app.py

@@ -30,12 +30,12 @@ from traitlets.config import Application
 from . import __version__
 from .buildpacks import (
     PythonBuildPack, DockerBuildPack, LegacyBinderDockerBuildPack,
-    CondaBuildPack, JuliaBuildPack, BaseImage,
-    RBuildPack
+    CondaBuildPack, JuliaBuildPack, RBuildPack
 )
+from . import contentproviders
 from .utils import (
-    execute_cmd, ByteSpecification, maybe_cleanup, is_valid_docker_image_name,
-    validate_and_generate_port_mapping, check_ref
+    ByteSpecification, maybe_cleanup, is_valid_docker_image_name,
+    validate_and_generate_port_mapping
 )
 
 
@@ -95,6 +95,23 @@ class Repo2Docker(Application):
         """
     )
 
+    # Git is our content provider of last resort. This is to maintain the
+    # old behaviour when git and local directories were the only supported
+    # content providers. We can detect local directories from the path, but
+    # detecting if something will successfully `git clone` is very hard if all
+    # you can do is look at the path/URL to it.
+    content_providers = List(
+        [
+            contentproviders.Local,
+            contentproviders.Git,
+        ],
+        config=True,
+        help="""
+        Ordered list of ContentProviders to try in turn to fetch the contents
+        specified by the user.
+        """
+    )
+
     build_memory_limit = ByteSpecification(
         0,
         help="""
@@ -176,29 +193,24 @@ class Repo2Docker(Application):
 
     def fetch(self, url, ref, checkout_path):
         """Check out a repo using url and ref to the checkout_path location"""
-        try:
-            cmd = ['git', 'clone', '--recursive']
-            if not ref:
-                cmd.extend(['--depth', '1'])
-            cmd.extend([url, checkout_path])
-            for line in execute_cmd(cmd, capture=self.json_logs):
-                self.log.info(line, extra=dict(phase='fetching'))
-        except subprocess.CalledProcessError:
-            self.log.error('Failed to clone repository!',
-                           extra=dict(phase='failed'))
-            sys.exit(1)
+        # Pick a content provider based on URL
+        picked_content_provider = None
+        for CP in self.content_providers:
+            cp = CP(self.log)
+            spec = cp.detect(url, ref=ref)
+            if spec is not None:
+                picked_content_provider = cp
+                self.log.info("Picked {cp} content "
+                              "provider.\n".format(cp=cp.__class__.__name__))
+                break
 
-        if ref:
-            hash = check_ref(ref, checkout_path)
-            if hash is None:
-                self.log.error('Failed to check out ref %s', ref,
-                               extra=dict(phase='failed'))
-                sys.exit(1)
-            # If the hash is resolved above, we should be able to reset to it
-            for line in execute_cmd(['git', 'reset', '--hard', hash],
-                                    cwd=checkout_path,
-                                    capture=self.json_logs):
-                self.log.info(line, extra=dict(phase='fetching'))
+        if picked_content_provider is None:
+            self.log.error("No matching content provider found for "
+                           "{url}.".format(url=url))
+
+        for log_line in picked_content_provider.fetch(
+                spec, checkout_path, yield_output=self.json_logs):
+            self.log.info(log_line, extra=dict(phase='fetching'))
 
     def validate_image_name(self, image_name):
         """

repo2docker/contentproviders/__init__.py

@@ -0,0 +1,2 @@
+from .git import Git
+from .base import Local

repo2docker/contentproviders/base.py

@@ -1,26 +1,54 @@
 """
 Base classes for repo2docker ContentProviders
 
-ContentProviders accept a `spec` of various kinds, and 
+ContentProviders accept a `spec` of various kinds, and
 provide the contents from the spec to a given output directory.
 """
+import os
+
+
 class ContentProviderException(Exception):
-    """Exception raised when a ContentProvider can not provide content
-    """
+    """Exception raised when a ContentProvider can not provide content."""
     pass
 
+
 class ContentProvider:
-    kind = ""
+    def __init__(self, logger):
+        self.log = logger
 
-    def provide(self, spec, output_dir, yield_output=False):
-        """Provide the contents of given spec to output_dir
+    def detect(self, repo, ref=None, extra_args=None):
+        """Determine compatibility between source and this provider.
 
-        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.
+        If the provider knows how to fetch this source it will return a
+        `spec` that can be passed to `fetch`. The arguments are the `repo`
+        string passed on the command-line, the value of the --ref parameter,
+        if provided and any provider specific arguments provided on the
+        command-line.
+
+        If the provider does not know how to fetch this source it will return
+        `None`.
         """
         raise NotImplementedError()
 
+    def fetch(self, spec, output_dir, yield_output=False):
+        """Provide the contents of given spec to output_dir
+
+        This generator yields logging information if `yield_output=True`,
+        otherwise log output is printed to stdout.
+
+        Arguments:
+            spec -- Dict 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()
+
+
+class Local(ContentProvider):
+    def detect(self, source, ref=None, extra_args=None):
+        if os.path.exists(source):
+            return {'path': source}
+
+    def fetch(self, spec, output_dir, yield_output=False):
+        pass

repo2docker/contentproviders/git.py

@@ -1,28 +1,46 @@
 import subprocess
+import sys
 
 from .base import ContentProvider, ContentProviderException
-from ..utils import execute_cmd
+from ..utils import execute_cmd, check_ref
 
-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']
+class Git(ContentProvider):
+    """Provide contents of a remote git repository."""
+
+    def detect(self, source, ref=None, extra_args=None):
+        # Git is our content provider of last resort. This is to maintain the
+        # old behaviour when git and local directories were the only supported
+        # content providers. This means that this content provider will always
+        # match. The downside is that the call to `fetch()` later on might fail
+        return {'repo': source, 'ref': ref}
+
+    def fetch(self, spec, output_dir, yield_output=False):
+        repo = spec['repo']
         ref = spec.get('ref', None)
+
+        # make a, possibly shallow, clone of the remote repository
         try:
-            for line in execute_cmd(['git', 'clone', url, output_dir],
+            cmd = ['git', 'clone', '--recursive']
+            if ref is None:
+                cmd.extend(['--depth', '1'])
+            cmd.extend([repo, output_dir])
+            for line in execute_cmd(cmd, capture=yield_output):
+                yield line
+
+        except subprocess.CalledProcessError as e:
+            msg = "Failed to clone repository from {repo}.".format(repo=repo)
+            raise ContentProviderException(msg) from e
+
+        # check out the specific ref given by the user
+        if ref is not None:
+            hash = check_ref(ref, output_dir)
+            if hash is None:
+                self.log.error('Failed to check out ref %s', ref,
+                               extra=dict(phase='failed'))
+                sys.exit(1)
+            # If the hash is resolved above, we should be able to reset to it
+            for line in execute_cmd(['git', 'reset', '--hard', hash],
+                                    cwd=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