SETTINGS_TIMEOUT
SETTINGS_TIMEOUT (0x4) is sent when a SETTINGS frame has been sent and the sender does not receive a SETTINGS acknowledgment within an acceptable time. HTTP/2 requires that SETTINGS frames be acknowledged with a SETTINGS frame with the ACK flag set. If the peer goes silent after receiving SETTINGS, the connection is closed with SETTINGS_TIMEOUT.
Code
0x4
Decimal
4
Standard
RFC 9113 §7
Description
HTTP/2 requires SETTINGS acknowledgment: after sending a SETTINGS frame, the sender must receive a corresponding SETTINGS ACK. RFC 9113 §6.5 specifies that receipt of a SETTINGS ACK is required. If an implementation never sends the SETTINGS ACK (or the ACK is lost), the sender closes the connection with SETTINGS_TIMEOUT after a reasonable timeout. This is primarily a connection setup issue – most SETTINGS_TIMEOUT errors occur during connection establishment rather than steady-state operation.
Common Causes
- –Peer never sent SETTINGS ACK after receiving SETTINGS frame
- –Network partition dropped the SETTINGS ACK
- –Peer TLS/TCP handshake completed but HTTP/2 handshake stalled
- –Proxy intercepting HTTP/2 but not processing SETTINGS frames