control.h

#ifndef H3_CONTROL_H
#define H3_CONTROL_H
 
#include "common/platform/sys/syscall.h"
 
/* RFC 9114 6.2.1/7.2.4/5.2: the HTTP/3 control stream, SETTINGS ordering, and
 * GOAWAY graceful shutdown. A peer opens at most one control stream which is
 * never closed; its first frame must be SETTINGS (once); GOAWAY ids are
 * monotonically non-increasing and forbid new requests at or above the
 * limit. Any violation latches a connection error (terminal). */

typedef enum {
  H3_ERR_NONE = 0,
  H3_ERR_STREAM_CREATION,  /* 2nd control stream */
  H3_ERR_CLOSED_CRITICAL,  /* control stream closed */
  H3_ERR_MISSING_SETTINGS, /* first control frame not SETTINGS */
  H3_ERR_FRAME_UNEXPECTED, /* a second SETTINGS */
  H3_ERR_ID                /* GOAWAY id increased */
} h3_error;

typedef struct {
  u8       control_open;  
  u8       settings_seen; 
  u8       goaway_seen;   
  u64      goaway_limit; 
  h3_error error;        
} h3_control;
 
void h3_control_init(h3_control* c);
 
/* A peer opened its control stream. The second one is a STREAM_CREATION error.
 */
void h3_control_open(h3_control* c);
 
/* The control stream closed: a CLOSED_CRITICAL_STREAM error. */
void h3_control_closed(h3_control* c);
 
/* A control-stream frame arrived; is_settings marks the SETTINGS type. The
 * first frame must be SETTINGS (else MISSING_SETTINGS); a later SETTINGS is
 * FRAME_UNEXPECTED. */
void h3_control_frame(h3_control* c, int is_settings);
 
/* A GOAWAY with `id` arrived. Accepted if not greater than a prior GOAWAY id;
 * an increase is an ID error. */
void h3_control_goaway(h3_control* c, u64 id);
 
/* Whether a new request with `id` may be accepted: not after a GOAWAY whose
 * limit it reaches (RFC 9114 5.2). Existing requests are unaffected. */
int h3_control_accept_request(const h3_control* c, u64 id);
 
#endif