FLOW_CONTROL_ERROR
FLOW_CONTROL_ERROR (0x3) is sent when an endpoint receives more data than its flow control window allows. HTTP/2 flow control prevents fast senders from overwhelming slow receivers. Each stream and the connection itself have separate flow control windows. Sending data beyond the window limit triggers this error.
Code
0x3
Decimal
3
Standard
RFC 9113 §7
Description
HTTP/2 flow control (RFC 9113 §5.2) uses a credit-based system. Both the connection and each individual stream have a flow control window starting at 65,535 bytes. The receiver sends WINDOW_UPDATE frames to grant additional credits. If a sender ignores the window limit and sends more DATA than the window allows, the receiver sends a connection-level FLOW_CONTROL_ERROR GOAWAY. This is a connection-level-only error – it always requires closing the entire connection because the flow control state is unrecoverable.
Common Causes
- –Sender transmitted DATA frames exceeding the flow control window
- –WINDOW_UPDATE increments not processed correctly by sender
- –Implementation bug in flow control accounting
- –Integer overflow in window size calculation