FIX: Fix live client upgrading buffer shift

threecgreen · threecgreen · commit 104f7023700f · 2025-07-14T13:19:28.000Z
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Bug fixes
 - Removed `Intraday` variant from `DatasetCondition` enum
+- Fixed potential corrupted records when upgrading DBN versions in live clients
 
 ## 0.38.2 - 2025-07-01
 
diff --git a/src/live_blocking.cpp b/src/live_blocking.cpp
@@ -189,10 +189,12 @@ const databento::Record* LiveBlocking::NextRecord(
     }
   }
   current_record_ = Record{BufferRecordHeader()};
-  buffer_.Consume(current_record_.Size());
+  const auto bytes_to_consume = current_record_.Size();
   current_record_ =
       DbnDecoder::DecodeRecordCompat(version_, upgrade_policy_, send_ts_out_,
                                      &compat_buffer_, current_record_);
+  // Can't consume til after upgrade as Consume may shift
+  buffer_.Consume(bytes_to_consume);
   return &current_record_;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -189,10 +189,12 @@ const databento::Record* LiveBlocking::NextRecord(`
`189`	`189`	`}`
`190`	`190`	`}`
`191`	`191`	`current_record_ = Record{BufferRecordHeader()};`
`192`		`- buffer_.Consume(current_record_.Size());`
	`192`	`+ const auto bytes_to_consume = current_record_.Size();`
`193`	`193`	`current_record_ =`
`194`	`194`	`DbnDecoder::DecodeRecordCompat(version_, upgrade_policy_, send_ts_out_,`
`195`	`195`	`&compat_buffer_, current_record_);`
	`196`	`+ // Can't consume til after upgrade as Consume may shift`
	`197`	`+ buffer_.Consume(bytes_to_consume);`
`196`	`198`	`return &current_record_;`
`197`	`199`	`}`
`198`	`200`