Handle default or non-existing branch name

- Added requirements.txt file
- Added venv/ folder to .gitignore
- The application now resolves for the default branch of a repository
if the branch name is not given. It will also return an error if the
branch name given does not exist in the repository.

Resolves : #159

.gitignore

@@ -13,6 +13,7 @@ data8assets/
 .autopull_list
 summer/
 test-repo/
+venv/
 
 .ipynb_checkpoints
 docs/_build

nbgitpuller/handlers.py

@@ -149,7 +149,7 @@ def get(self):
         app_env = os.getenv('NBGITPULLER_APP', default='notebook')
 
         repo = self.get_argument('repo')
-        branch = self.get_argument('branch', 'master')
+        branch = self.get_argument('branch', None)
         depth = self.get_argument('depth', None)
         urlPath = self.get_argument('urlpath', None) or \
                   self.get_argument('urlPath', None)

nbgitpuller/pull.py

@@ -70,11 +70,60 @@ def __init__(self, git_url, branch_name, repo_dir, **kwargs):
         assert git_url and branch_name
 
         self.git_url = git_url
-        self.branch_name = branch_name
+
+        if branch_name == "None":
+            self.branch_name = self.resolve_default_branch()
+        elif not self.branch_exists(branch_name):
+            raise ValueError(f"{branch_name}: branch not found in {self.git_url}")
+        else:
+            self.branch_name = branch_name
+
         self.repo_dir = repo_dir
         newargs = {k: v for k, v in kwargs.items() if v is not None}
         super(GitPuller, self).__init__(**newargs)
 
+    def branch_exists(self, branch):
+        """
+        This checks to make sure the branch we are told to access
+        exists in the repo
+        """
+        p_heads = subprocess.run(
+            ["git", "ls-remote", "--heads", self.git_url],
+            capture_output=True,
+            text=True,
+        )
+        p_tags = subprocess.run(
+            ["git", "ls-remote", "--tags", self.git_url],
+            capture_output=True,
+            text=True,
+        )
+        lines = p_heads.stdout.splitlines() + p_tags.stdout.splitlines()
+        branches = []
+        for line in lines:
+            _, ref = line.split()
+            refs, heads, branch_name = ref.split("/", 2)
+            branches.append(branch_name)
+        return branch in branches
+
+    def resolve_default_branch(self):
+        """
+        This will resolve the default branch of the repo in
+        the case where the branch given does not exist
+        """
+        p = subprocess.run(
+            ["git", "ls-remote", "--symref", self.git_url, "HEAD"],
+            capture_output=True,
+            text=True,
+        )
+
+        for line in p.stdout.splitlines():
+            if line.startswith("ref:"):
+                # line resembles --> ref: refs/heads/main HEAD
+                _, ref, head = line.split()
+                refs, heads, branch_name = ref.split("/", 2)
+                return branch_name
+        raise ValueError(f"default branch not found in {self.git_url}")
+
     def pull(self):
         """
         Pull selected repo from a remote git repository,

requirements.txt

@@ -0,0 +1,3 @@
+traitlets
+pytest
+-e .

tests/test_gitpuller.py

@@ -61,10 +61,10 @@ def push_file(self, path, content):
 
 
 class Puller(Repository):
-    def __init__(self, remote, path='puller', *args, **kwargs):
+    def __init__(self, remote, path='puller', branch="master", *args, **kwargs):
         super().__init__(path)
         remotepath = "file://%s" % os.path.abspath(remote.path)
-        self.gp = GitPuller(remotepath, 'master', path, *args, **kwargs)
+        self.gp = GitPuller(remotepath, branch, path, *args, **kwargs)
 
     def pull_all(self):
         for line in self.gp.pull():
@@ -96,6 +96,20 @@ def test_initialize():
             assert puller.git('rev-parse', 'HEAD') == pusher.git('rev-parse', 'HEAD')
 
 
+def test_branch_exists():
+    with Remote() as remote,  Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            assert not puller.gp.branch_exists("wrong")
+
+
+def test_resolve_default_branch():
+    with Remote() as remote,  Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            assert puller.gp.resolve_default_branch() == "master"
+
+
 def test_simple_push_pull():
     """
     Test the 'happy path' push/pull interaction