struct ofp_header {
    uint8_t version;    /* OFP_VERSION. */
    uint8_t type;       /* One of the OFPT_ constants. */
    uint16_t length;    /* Length including this ofp_header. */
    uint32_t xid;       /* Transaction id associated with this packet.
                           Replies use the same id as was in the request
                           to facilitate pairing. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);

/* OFPT_HELLO.  This message has an empty body, but implementations must
 * ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
    struct ofp_header header;
};

/* Switch configuration. */
struct ofp_switch_config {
    struct ofp_header header;
    uint16_t flags;             /* OFPC_* flags. */
    uint16_t miss_send_len;     /* Max bytes of new flow that datapath should
                                   send to the controller. */
};

/* A physical port has changed in the datapath */
struct ofp_port_status {
    struct ofp_header header;
    uint8_t reason;          /* One of OFPPR_*. */
    uint8_t pad[7];          /* Align to 64-bits. */
    struct ofp_phy_port desc;
};

struct ofp_switch_features {   
  struct ofp_header header;    
  uint64_t datapath_id;   
/* Datapath unique ID.  The lower 48-bits are for a MAC address, while the upper 16-bits are implementer-defined. */     
  uint32_t n_buffers;     /* Max packets buffered at once. */     
  uint8_t n_tables;       /* Number of tables supported by datapath. */    
  uint8_t pad[3];         /* Align to 64-bits. */     /* Features. */    
  uint32_t capabilities;  /* Bitmap of support "ofp_capabilities". */    
  uint32_t actions;       /* Bitmap of supported "ofp_action_type"s. */     /* Port info.*/    

struct ofp_phy_port ports[0];  /* Port definitions.  The number of ports                                      is inferred from the length field in the header. */};
/* Description of a physical port */
struct ofp_phy_port { 
  uint16_t port_no;    
  uint8_t hw_addr[OFP_ETH_ALEN];    
  char name[OFP_MAX_PORT_NAME_LEN]; /* Null-terminated */     
  uint32_t config;        /* Bitmap of OFPPC_* flags. */    
  uint32_t state;         /* Bitmap of OFPPS_* flags. */     
/* Bitmaps of OFPPF_* that describe features.  All bits zeroed if  * unsupported or unavailable. */    
  uint32_t curr;          /* Current features. */    
  uint32_t advertised;    /* Features being advertised by the port. */    
  uint32_t supported;     /* Features supported by the port. */    
  uint32_t peer;          /* Features advertised by peer. */
 };

/* Packet received on port (datapath -> controller). */
struct ofp_packet_in {
    struct ofp_header header;
    uint32_t buffer_id;     /* ID assigned by datapath. */
    uint16_t total_len;     /* Full length of frame. */
    uint16_t in_port;       /* Port on which frame was received. */
    uint8_t reason;         /* Reason packet is being sent (one of OFPR_*) */
    uint8_t pad;
    uint8_t data[0];        /* Ethernet frame, halfway through 32-bit word,
                               so the IP header is 32-bit aligned.  The
                               amount of data is inferred from the length
                               field in the header.  Because of padding,
                               offsetof(struct ofp_packet_in, data) ==
                               sizeof(struct ofp_packet_in) - 2. */
};

/* Flow setup and teardown (controller -> datapath). */
struct ofp_flow_mod {
    struct ofp_header header;
    struct ofp_match match;      /* Fields to match */
    uint64_t cookie;             /* Opaque controller-issued identifier. */

    /* Flow actions. */
    uint16_t command;             /* One of OFPFC_*. */
    uint16_t idle_timeout;        /* Idle time before discarding (seconds). */
    uint16_t hard_timeout;        /* Max time before discarding (seconds). */
    uint16_t priority;            /* Priority level of flow entry. */
    uint32_t buffer_id;           /* Buffered packet to apply to (or -1).
                                     Not meaningful for OFPFC_DELETE*. */
    uint16_t out_port;            /* For OFPFC_DELETE* commands, require
                                     matching entries to include this as an
                                     output port.  A value of OFPP_NONE
                                     indicates no restriction. */
    uint16_t flags;               /* One of OFPFF_*. */
    struct ofp_action_header actions[0]; /* The action length is inferred
                                            from the length field in the
                                            header. */
};

/* Send packet (controller -> datapath). */
struct ofp_packet_out {
    struct ofp_header header;
    uint32_t buffer_id;           /* ID assigned by datapath (-1 if none). */
    uint16_t in_port;             /* Packet's input port (OFPP_NONE if none). */
    uint16_t actions_len;         /* Size of action array in bytes. */
    struct ofp_action_header actions[0]; /* Actions. */
    /* uint8_t data[0]; */        /* Packet data.  The length is inferred
                                     from the length field in the header.
                                     (Only meaningful if buffer_id == -1.) */
};