git-p4: add Git LFS backend for large file system

Add example implementation including test cases for the large file
system using Git LFS.

Pushing files to the Git LFS server is not tested.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -1038,6 +1038,78 @@ class MockLFS(LargeFileSystem):
             os.makedirs(remotePath)
         shutil.copyfile(localLargeFile, os.path.join(remotePath, os.path.basename(localLargeFile)))
 
+class GitLFS(LargeFileSystem):
+    """Git LFS as backend for the git-p4 large file system.
+       See https://git-lfs.github.com/ for details."""
+
+    def __init__(self, *args):
+        LargeFileSystem.__init__(self, *args)
+        self.baseGitAttributes = []
+
+    def generatePointer(self, contentFile):
+        """Generate a Git LFS pointer for the content. Return LFS Pointer file
+           mode and content which is stored in the Git repository instead of
+           the actual content. Return also the new location of the actual
+           content.
+           """
+        pointerProcess = subprocess.Popen(
+            ['git', 'lfs', 'pointer', '--file=' + contentFile],
+            stdout=subprocess.PIPE
+        )
+        pointerFile = pointerProcess.stdout.read()
+        if pointerProcess.wait():
+            os.remove(contentFile)
+            die('git-lfs pointer command failed. Did you install the extension?')
+        pointerContents = [i+'\n' for i in pointerFile.split('\n')[2:][:-1]]
+        oid = pointerContents[1].split(' ')[1].split(':')[1][:-1]
+        localLargeFile = os.path.join(
+            os.getcwd(),
+            '.git', 'lfs', 'objects', oid[:2], oid[2:4],
+            oid,
+        )
+        # LFS Spec states that pointer files should not have the executable bit set.
+        gitMode = '100644'
+        return (gitMode, pointerContents, localLargeFile)
+
+    def pushFile(self, localLargeFile):
+        uploadProcess = subprocess.Popen(
+            ['git', 'lfs', 'push', '--object-id', 'origin', os.path.basename(localLargeFile)]
+        )
+        if uploadProcess.wait():
+            die('git-lfs push command failed. Did you define a remote?')
+
+    def generateGitAttributes(self):
+        return (
+            self.baseGitAttributes +
+            [
+                '\n',
+                '#\n',
+                '# Git LFS (see https://git-lfs.github.com/)\n',
+                '#\n',
+            ] +
+            ['*.' + f.replace(' ', '[[:space:]]') + ' filter=lfs -text\n'
+                for f in sorted(gitConfigList('git-p4.largeFileExtensions'))
+            ] +
+            ['/' + f.replace(' ', '[[:space:]]') + ' filter=lfs -text\n'
+                for f in sorted(self.largeFiles) if not self.hasLargeFileExtension(f)
+            ]
+        )
+
+    def addLargeFile(self, relPath):
+        LargeFileSystem.addLargeFile(self, relPath)
+        self.writeToGitStream('100644', '.gitattributes', self.generateGitAttributes())
+
+    def removeLargeFile(self, relPath):
+        LargeFileSystem.removeLargeFile(self, relPath)
+        self.writeToGitStream('100644', '.gitattributes', self.generateGitAttributes())
+
+    def processContent(self, git_mode, relPath, contents):
+        if relPath == '.gitattributes':
+            self.baseGitAttributes = contents
+            return (git_mode, self.generateGitAttributes())
+        else:
+            return LargeFileSystem.processContent(self, git_mode, relPath, contents)
+
 class Command:
     def __init__(self):
         self.usage = "usage: %prog [options]"