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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
#if 0
How do we use this API(?), I hear you say. Well, here is a self-contained
example complete with tedious comments:
-------------------------------------------------------------------------------
1 | void functy_the_function(void)
2 | {
3 | struct tlv tlv_packet; /* A packet made of tlv's */
4 | struct tlv text; /* Actually useful data */
5 | char *packet; /* Raw bytes to be pushed via UDP */
6 | size_t packet_size; /* Raw packet size */
7 | char message[] = "Get jacked!"; /* Duh! */
9 |
10 | tlv_init(&tlv_packet, REGURAL); /* Initialise tlv_packet to regular */
11 | tlv_init(&text, TEXT); /* Initialise text packet */
12 | tlv_push_data(&text, message, sizeof(message)); /* Push text to appropriate tlv */
13 | tlv_push_tlv(&tlv_packet, &text); /* Push the tlv into tlv packet */
14 |
15 | packet_size = tlv_raw_size(&tlv_packet); /* Get raw size required to push entire tlv_packet as bytes */
16 | packet = (char *)malloc(packet_size); /* Allocate buffer for outgoing packet */
17 | tlv_get_raw(&tlv_packet, packet); /* Flash tlv_packet to buffer */
19 | udp_push(packet, packet_size); /* Push packet via UDP */
20 | udp_flush(); /* Flush to the other side*/
21 |
22 | tlv_destroy(&text); /* Free text tlv */
23 | tlv_destroy(&tlv_packet); /* Free tlv_packet */
24 | free(packet); /* Free packet itself */
25 | return; /* GTFO and save stack space */
26 | }
-------------------------------------------------------------------------------
#endif
#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)
/**
* 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,
/* Data of the following types are other tlv's! */
/**
* Just a TLV container.
*/
REGURAL,
/**
* Says "I'm not dead yet.".
*/
HEARTBEAT,
/**
* Says "Bring out yer dead!".
*/
DISCOVERY
};
/**
* 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 tlv_get(struct tlv_parser *parser, struct tlv *ret);
/**
* Initialises tlv to sane values.
*/
void tlv_init(struct tlv *t, enum tlv_type type);
/**
* 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(const 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_data(struct tlv *t, const char *data, size_t size);
/**
* Pushes a sub-tlv into the packet. 't' can only be REGURAL, HEARTBEAT or
* DISCOVERY.
*/
int tlv_push_tlv(struct tlv *t, const struct tlv *other);
#endif /* USURPATION_PROTOCOL_H_INCLUDED */
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