HTTP/2: require peer SETTINGS as first frame#636
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httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java
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Enforce RFC 9113 connection preface rules by rejecting non-SETTINGS frames received before the peer SETTINGS once the connection handshake is active.
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Enforce RFC 9113 connection preface rules by rejecting non-SETTINGS frames received before the peer SETTINGS once the connection handshake is active.
RFC 9113, Section 3.4: That is, the connection preface starts with the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n". This sequence MUST be followed by a SETTINGS frame (Section 6.5), which MAY be empty. The client sends the client connection preface as the first application data octets of a connection.
RFC 9113, Section 6.5: Receipt of a SETTINGS frame with the ACK flag set and a length field value other than 0 MUST be treated as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR. For more information, see Section 6.5.3 ("Settings Synchronization").