Have slo tell the object-server that it wants whole manifests

Otherwise, we waste a request on some 416/206 response that won't be
helpful.

To do this, add a new X-Backend-Ignore-Range-If-Metadata-Present header
whose value is a comma-separated list of header names. Middlewares may
include this header to tell object-servers to send the whole object
(rather than a 206 or 416) if *any* of the metadata are present.

Have dlo and symlink use it, too; it won't save us any round-trips, but
it should clean up some object-server logging.

Change-Id: I4ff2a178d0456e7e37d561109ef57dd0d92cbd4e

1 files changed, 18 insertions, 0 deletions

diff --git a/swift/common/request_helpers.py b/swift/common/request_helpers.py
index bdc234c9e..876b8d809 100644
--- a/swift/common/request_helpers.py
+++ b/swift/common/request_helpers.py
@@ -808,3 +808,21 @@ def resolve_etag_is_at_header(req, metadata):
                 alternate_etag = metadata[name]
                 break
     return alternate_etag
+
+
+def update_ignore_range_header(req, name):
+    """
+    Helper function to update an X-Backend-Ignore-Range-If-Metadata-Present
+    header whose value is a list of header names which, if any are present
+    on an object, mean the object server should respond with a 200 instead
+    of a 206 or 416.
+
+    :param req: a swob Request
+    :param name: name of a header which, if found, indicates the proxy will
+                 want the whole object
+    """
+    if ',' in name:
+        # HTTP header names should not have commas but we'll check anyway
+        raise ValueError('Header name must not contain commas')
+    hdr = 'X-Backend-Ignore-Range-If-Metadata-Present'
+    req.headers[hdr] = csv_append(req.headers.get(hdr), name)