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/*
* Usurpataion --- client-server protocol interface.
*
* Copyright (C) 2019 Ramūnas Mažeikis
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; version 2.1
* of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
*/
#ifndef USURPATION_PROTOCOL_H_INCLUDED
#define USURPATION_PROTOCOL_H_INCLUDED
#include <errno.h>
#define E_TLV_OVERFLOW (1 << 0)
#define E_UNKNOWN_TYPE (1 << 1)
#define END_OF_PACKET (1 << 2)
#define TLV_SZ_MAX_RAW (MTU - 64)
/**
* Regular packets contain tlv's defined by tlv_type.
*
* Hearbeat packet tell daemon that device is still alive and listening.
*
* Discovery packets are used for what they say.
*/
enum packet_type {
REGURAL,
HEARTBEAT,
DISCOVERY
};
/**
* Message sequence number since beggining of sesssion.
*
* Mainly used for identifying lost messages.
*/
typedef unsigned int msg_idx_t;
enum tlv_type {
/**
* NULL-terminated string. To be put in a queue to display on the
* screen.
*/
TEXT,
/** Fixed point. 1 decimal digit of precision. */
FPI1,
/** Literally time_t */
TIMESTAMP,
/** Represents a request for lost message. Data is unsigned integer
* that uniquely identifies the message.
*/
REQUEST,
/**
* Response to request. Begins with unsigned integer that represents
* which message is being repeated and the actual null-terminated
* message after that.
*/
REPLY,
/**
* UUID that represents a particular device.
*/
UUID
};
/**
* Packet data itself is a special type of tlv. A packet is either regular,
* hearbeat or discovery.
*
* May be used to send data.
*/
struct tlv_packet {
enum packet_type type;
size_t size;
size_t offset;
char *data; /* Bytes representing tlv's */
};
/**
* Literally type-length-value
* */
struct tlv {
enum tlv_type type;
size_t length;
void *data;
};
/**
* Keeps state of the parsing process.
*
* Related functions return one tlv at a time.
*/
struct tlv_parser {
char *data;
size_t offset;
size_t size;
};
/**
* Fills tlv structure to represent the next tlv in the packet.
*
* Returns END_OF_PACKET if all tlv's were read of E_TLV_OVERFLOW, if the last
* tlv, according to its declared size should not fit in a packet.
*/
int get_tlv(struct tlv_parser *parser, struct tlv *ret);
/**
* Appends data to the next packet to be sent. Type of data is determined by
* enum tlv_type.
*
* In case of overflow return E_TLV_OVERFLOW.
*
* On next call after retreiving last packet returns END_OF_PACKET.
*
* Overflow can be detected after forming tlv header. This means that the
* packet may have changes.
* */
int push_data(struct tlv_packet *packet, enum tlv_type type, char *data);
/**
* Resets offset to 0 and set entire buffer to 0.
*/
void clear_data(struct tlv_packet *packet);
/**
* Initialises tlv to sane values.
*/
void tlv_init(struct tlv *t);
/**
* Frees data held in the tlv structure. The structure itself shall be freed as
* needed by calling code.
*/
void tlv_destroy(struct tlv *t);
/**
* Tells amount of bytes needed to push tlv to a buffer
*/
size_t tlv_raw_size(struct tlv *t);
/**
* Pushes tlv to buffer as contiguous data. Check tlv size with tlv_raw_size
* beforehand. If you don't do that and overflow --- tough tiddy.
*/
int tlv_get_raw(struct tlv *t, char *buf);
/**
* Pushes data to tlv. Returns E_TLV_OVERFLOW if pushing data would cause the
* final size to be greater than TLV_SZ_MAX_RAW. In case of such error the data is left
* untouched.
*/
int tlv_push(struct tlv *t, const char *data, size_t size);
#endif /* USURPATION_PROTOCOL_H_INCLUDED */
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