pkg/index: redo indexing of a blob when CAMLI_REDO_INDEX_ON_RECEIVE is set

So an upcoming HEIC reindexing tool.

Updates #969

Change-Id: If194904d770bb670fa581c4e5e09c303806bc784

doc/environment-vars.md

@@ -222,6 +222,12 @@ files to be ignored by [pkg/client](/pkg/client) when uploading.
 : If true, no thumbnail caching is done, and URLs even have cache
   buster components, to force browsers to reload a lot.
 
+`CAMLI_REDO_INDEX_ON_RECEIVE` (bool)
+: If true, the indexer will always index any blob it receives, regardless of
+  whether it thinks it's done it in the past. This is generally only useful when
+  working on the indexing code and retroactively indexing a subset of content
+  without forcing a global reindexing.
+
 `CAMLI_VAR_DIR` (string)
 : Path used by [pkg/osutil](/pkg/osutil) to override operating system specific
   application storage directory. Generally unused.

pkg/index/receive.go

@@ -220,9 +220,17 @@ func (ix *Index) ReceiveBlob(ctx context.Context, blobRef blob.Ref, source io.Re
 		}
 	}()
 
-	if haveVal, haveErr := ix.s.Get("have:" + blobRef.String()); haveErr == nil {
-		if strings.HasSuffix(haveVal, "|indexed") {
-			return sbr, nil
+	// By default, return immediately if it looks like we already
+	// have indexed this blob before.  But if the user has
+	// CAMLI_REDO_INDEX_ON_RECEIVE set in their environment,
+	// always index it. This is generally only useful when working
+	// on the indexing code and retroactively indexing a subset of
+	// content without forcing a global reindexing.
+	if allowReindex, _ := strconv.ParseBool(os.Getenv("CAMLI_REDO_INDEX_ON_RECEIVE")); !allowReindex {
+		if haveVal, haveErr := ix.s.Get("have:" + blobRef.String()); haveErr == nil {
+			if strings.HasSuffix(haveVal, "|indexed") {
+				return sbr, nil
+			}
 		}
 	}