Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/common/data_locator.py

@@ -0,0 +1,154 @@
+import os
+import tempfile
+import fsspec
+from datetime import datetime
+import boto3
+import botocore
+from urllib.parse import urlparse
+
+
+class DataLocator:
+    """
+    DataLocator is a simple wrapper around fsspec functionality, and provides a
+    set of functions to encapsulate a data location (URI or path), interogate
+    metadata about the object at that location (size, existance, etc) and
+    access the underlying data.
+
+    https://filesystem-spec.readthedocs.io/en/latest/index.html
+
+    Example:
+        dl = DataLocator("/tmp/foo.h5ad")
+        if dl.exists():
+            print(dl.size())
+            with dl.open() as f:
+                thecontents = f.read()
+
+    DataLocator will accept a URI or native path.  Error handling is as defined
+    in fsspec.
+
+    """
+
+    def __init__(self, uri_or_path, region_name=None):
+        if isinstance(uri_or_path, DataLocator):
+            locator = uri_or_path
+            self.uri_or_path = locator.uri_or_path
+            self.protocol = locator.protocol
+            self.path = locator.path
+            self.cname = locator.cname
+        else:
+            self.uri_or_path = uri_or_path
+            self.protocol, self.path = DataLocator._get_protocol_and_path(uri_or_path)
+            # work-around for LocalFileSystem not treating file: and None as the same scheme/protocol
+            self.cname = self.path if self.protocol == "file" else self.uri_or_path
+
+        # fsspec.filesystem will throw RuntimeError if the protocol is unsupported
+        if self.protocol == "s3":
+            if region_name:
+                config_kwargs = dict(region_name=region_name)
+                self.fs = fsspec.filesystem(self.protocol, listings_expiry_time=30, config_kwargs=config_kwargs)
+            else:
+                self.fs = fsspec.filesystem(self.protocol, listings_expiry_time=30)
+        else:
+            self.fs = fsspec.filesystem(self.protocol)
+
+    def __repr__(self):
+        return f"DataLocator(protocol={self.protocol}, cname={self.cname}, "
+        f"path={self.path}, uri_or_path={self.uri_or_path})"
+
+    @staticmethod
+    def _get_protocol_and_path(uri_or_path):
+        if "://" in uri_or_path:
+            protocol, path = uri_or_path.split("://", 1)
+            # windows!!!  Ignore single letter drive identifiers,
+            # eg, G:\foo.txt
+            if len(protocol) > 1:
+                return protocol, path
+        return None, uri_or_path
+
+    def exists(self):
+        return self.fs.exists(self.cname)
+
+    def size(self):
+        return self.fs.size(self.cname)
+
+    def lastmodtime(self):
+        """ return datetime object representing last modification time, or None if unavailable """
+        info = self.fs.info(self.cname)
+        if self.islocal() and info is not None:
+            return datetime.fromtimestamp(info["mtime"])
+        else:
+            return getattr(info, "LastModified", None)
+
+    def abspath(self):
+        """
+        return the absolute path for the locator - only really does something
+        for file: protocol, as all others are already absolute
+        """
+        if self.islocal():
+            return os.path.abspath(self.path)
+        else:
+            return self.uri_or_path
+
+    def isfile(self):
+        return self.fs.isfile(self.cname)
+
+    def open(self, *args):
+        return self.fs.open(self.uri_or_path, *args)
+
+    def islocal(self):
+        return self.protocol is None or self.protocol == "file"
+
+    def local_handle(self):
+        if self.islocal():
+            return LocalFilePath(self.path)
+
+        # if not local, create a tmp file system object to contain the data,
+        # and clean it up when done.  If the path has a suffix/extension,
+        # do our best to create a file with the same.
+        ext = os.path.splitext(self.path)
+        suffix = None if ext[1] == "" else ext[1]
+        with self.open() as src, tempfile.NamedTemporaryFile(prefix="cellxgene_", suffix=suffix, delete=False) as tmp:
+            tmp.write(src.read())
+            tmp.close()
+            src.close()
+            tmp_path = tmp.name
+            return LocalFilePath(tmp_path, delete=True)
+
+    def ls(self):
+        paths = self.fs.ls(self.uri_or_path)
+        return [os.path.basename(p) for p in paths]
+
+
+class LocalFilePath:
+    def __init__(self, tmp_path, delete=False):
+        self.tmp_path = tmp_path
+        self.delete = delete
+
+    def __enter__(self):
+        return self.tmp_path
+
+    def __exit__(self, *args):
+        if self.delete:
+            os.unlink(self.tmp_path)
+
+
+def discover_s3_region_name(uri):
+    """If this is an s3 protocol, discover and return the (aws) region name.
+    If a return name could not be discovered, or if the uri is not an s3 protocol, return None."""
+
+    protocol, _ = DataLocator._get_protocol_and_path(uri)
+    if protocol == "s3":
+        bucket = urlparse(uri).netloc
+        client = boto3.client("s3")
+        try:
+            res = client.head_bucket(Bucket=bucket)
+        except botocore.exceptions.ClientError:
+            return None
+
+        region = res.get("ResponseMetadata", {}).get("HTTPHeaders", {}).get("x-amz-bucket-region")
+        if region:
+            return region
+        else:
+            return None
+
+    return None