From 9c3fb2db360f3ad33e1ab7695fd672657788bb89 Mon Sep 17 00:00:00 2001
From: John Kerl <kerl.john.r@gmail.com>
Date: Tue, 19 Jul 2022 09:53:54 -0400
Subject: [PATCH] More REST-server call-avoidance (#223)

* temp

* narrow exception-type handling
---
 apis/python/src/tiledbsc/tiledb_group.py | 59 ++++++++++++++----------
 1 file changed, 35 insertions(+), 24 deletions(-)

diff --git a/apis/python/src/tiledbsc/tiledb_group.py b/apis/python/src/tiledbsc/tiledb_group.py
index fdcc4321ea..e377b842e7 100644
--- a/apis/python/src/tiledbsc/tiledb_group.py
+++ b/apis/python/src/tiledbsc/tiledb_group.py
@@ -88,9 +88,8 @@ def _open(self, mode: str = "r") -> tiledb.Group:
         It works asa `with self._open() as G:` as well as `G = self._open(); ...; G.close()`.
         """
         assert mode in ("r", "w")
-        if mode == "r" and not self.exists():
-            raise Exception(f"Does not exist: {self.uri}")
         # This works in with-open-as contexts because tiledb.Group has __enter__ and __exit__ methods.
+        # Raises an exception, as desired, if the group does not exist (or, doesn't exist _yet_).
         return tiledb.Group(self.uri, mode=mode, ctx=self._ctx)
 
     def _get_child_uris(self, member_names: Sequence[str]) -> Dict[str, str]:
@@ -100,31 +99,43 @@ def _get_child_uris(self, member_names: Sequence[str]) -> Dict[str, str]:
         is reduced when we ask for all group-element name-to-URI mappings in a single
         request to the REST server.
         """
-        if not self.exists():
-            # Group not constructed yet. Here, appending "/" and name is appropriate in all
-            # cases: even for tiledb://... URIs, pre-construction URIs are of the form
-            # tiledb://namespace/s3://something/something/soma/membername.
-            return {
-                member_name: self.uri + "/" + member_name
-                for member_name in member_names
-            }
 
-        answer = {}
+        try:
+            # If the group exists, get URIs for elements. In local disk, S3, etc this is just
+            # concatenating a slash and the member name to the self URI; for TileDB Cloud,
+            # the member URIs involve UUIDs which are known to the server.
+            answer = {}
 
-        mapping = self._get_member_names_to_uris()
-        for member_name in member_names:
-            if member_name in mapping:
-                answer[member_name] = mapping[member_name]
-            else:
-                # Truly a slash, not os.path.join:
-                # * If the client is Linux/Un*x/Mac, it's the same of course
-                # * On Windows, os.path.sep is a backslash but backslashes are _not_ accepted for S3 or
-                #   tiledb-cloud URIs, whereas in Windows versions for years now forward slashes _are_
-                #   accepted for local-disk paths.
-                # This means forward slash is acceptable in all cases.
-                answer[member_name] = self.uri + "/" + member_name
+            mapping = self._get_member_names_to_uris()
+            for member_name in member_names:
+                if member_name in mapping:
+                    answer[member_name] = mapping[member_name]
+                else:
+                    # Truly a slash, not os.path.join:
+                    # * If the client is Linux/Un*x/Mac, it's the same of course
+                    # * On Windows, os.path.sep is a backslash but backslashes are _not_ accepted for S3 or
+                    #   tiledb-cloud URIs, whereas in Windows versions for years now forward slashes _are_
+                    #   accepted for local-disk paths.
+                    # This means forward slash is acceptable in all cases.
+                    answer[member_name] = self.uri + "/" + member_name
+
+            return answer
 
-        return answer
+        except tiledb.cc.TileDBError as e:
+            stre = str(e)
+            # Local-disk/S3 does-not-exist exceptions say 'Group does not exist'; TileDB Cloud
+            # does-not-exist exceptions are worded less clearly.
+            if "Group does not exist" in stre or "HTTP code 401" in stre:
+                # Group not constructed yet, but we must return pre-creation URIs. Here, appending
+                # "/" and name is appropriate in all cases: even for tiledb://... URIs,
+                # pre-construction URIs are of the form
+                # tiledb://namespace/s3://something/something/soma/membername.
+                return {
+                    member_name: self.uri + "/" + member_name
+                    for member_name in member_names
+                }
+            else:
+                raise e
 
     def _get_child_uri(self, member_name: str) -> str:
         """