http: allow empty request bodies in JSON parsing

The JSON decoder returns io.EOF when the request body is empty, which
was previously treated as an error. This prevented API endpoints with
optional request bodies from succeeding when called without a body.

Treat io.EOF as an empty object to support endpoints like DELETE
/sys/rekey/init that accept either a body with parameters or no body
at all.

Signed-off-by: Tero Saarni <[email protected]>

Author: tsaarni

changelog/31650.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+http: allow empty request bodies in JSON parsing
+```

http/handler.go

@@ -896,7 +896,10 @@ func parseJSONRequest(perfStandby bool, r *http.Request, w http.ResponseWriter,
 		reader = io.NopCloser(io.TeeReader(reader, origBody))
 	}
 	err := jsonutil.DecodeJSONFromReader(reader, out)
-	if err != nil && err != io.EOF {
+	if err == io.EOF {
+		// Empty body is not an error.
+		err = nil
+	} else if err != nil {
 		return nil, fmt.Errorf("failed to parse JSON input: %w", err)
 	}
 	if origBody != nil {