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dsc.c
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dsc.c
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/******************************************************************************
*
* FILENAME:
* dsc.c
*
* DESCRIPTION:
* Define APIs for datagram socket communication(UDP).
*
* REVISION(MM/DD/YYYY):
* 07/30/2014 Shengkui Leng (lengshengkui@outlook.com)
* - Initial version
*
******************************************************************************/
#include <unistd.h>
#include "dsc.h"
/******************************************************************************
* NAME:
* compute_checksum
*
* DESCRIPTION:
* Compute 16-bit One's Complement sum of data. (The algorithm comes from
* RFC-1071)
* NOTES: Before call this function, please set the checksum field to 0.
*
* PARAMETERS:
* buf - The data buffer
* len - The length of data(bytes).
*
* RETURN:
* Checksum
******************************************************************************/
static uint16_t compute_checksum(void *buf, ssize_t len)
{
uint16_t *word;
uint8_t *byte;
ssize_t i;
unsigned long sum = 0;
if (!buf) {
return 0;
}
word = (uint16_t *)buf;
for (i = 0; i < len/2; i++) {
sum += word[i];
}
/* If the length(bytes) of data buffer is an odd number, add the last byte. */
if (len & 1) {
byte = (uint8_t *)buf;
sum += byte[len-1];
}
/* Take only 16 bits out of the sum and add up the carries */
while (sum>>16) {
sum = (sum>>16) + (sum&0xFFFF);
}
return (uint16_t)(~sum);
}
/******************************************************************************
* NAME:
* verify_command_packet
*
* DESCRIPTION:
* Verify the data integrity of the command packet.
*
* PARAMETERS:
* buf - The data of command packet
* len - The length of data
*
* RETURN:
* 1 - OK, 0 - FAIL
******************************************************************************/
static int verify_command_packet(void *buf, size_t len)
{
dsc_command_t *pkt;
if (buf == NULL) {
return 0;
}
pkt = (dsc_command_t *)buf;
if (pkt->signature != DSC_SIGNATURE) {
printf("Error: invalid signature of packet (0x%08X)\n", pkt->signature);
return 0;
}
if (pkt->data_len + sizeof(dsc_command_t) != len) {
printf("Error: invalid length of packet (%ld:%ld)\n",
pkt->data_len + sizeof(dsc_command_t), len);
return 0;
}
if (compute_checksum(buf, len) != 0) {
printf("Error: invalid checksum of packet\n");
return 0;
}
return 1;
}
/******************************************************************************
* NAME:
* server_init
*
* DESCRIPTION:
* Do some initialzation work for server.
*
* PARAMETERS:
* req_handler - The function pointer of a user-defined request handler.
* port - The port number of server
*
* RETURN:
* A pointer of server info.
******************************************************************************/
dsc_server_t *server_init(request_handler_t req_handler, int port)
{
dsc_server_t *s;
int rc;
if (req_handler == NULL) {
printf("Error: invalid parameter!\n");
return NULL;
}
s = (dsc_server_t *)malloc(sizeof(dsc_server_t));
if (s == NULL) {
perror("malloc error");
return NULL;
}
memset(s, 0, sizeof(dsc_server_t));
/* Setup request handler */
s->request_handler = req_handler;
memset(&s->addr, 0, sizeof(s->addr));
s->addr.sin_family = AF_INET;
s->addr.sin_port = htons(port);
s->addr.sin_addr.s_addr = htonl(INADDR_ANY);
s->sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (s->sockfd < 0) {
perror("socket error");
free(s);
return NULL;
}
/* Avoid "Address already in use" error in bind() */
int val = 1;
if (setsockopt(s->sockfd, SOL_SOCKET, SO_REUSEADDR, &val,
sizeof(val)) == -1) {
perror("setsockopt error");
free(s);
return NULL;
}
rc = bind(s->sockfd, (struct sockaddr *)&s->addr, sizeof(s->addr));
if (rc != 0) {
perror("bind error");
close(s->sockfd);
free(s);
return NULL;
}
return s;
}
/******************************************************************************
* NAME:
* server_accept_request
*
* DESCRIPTION:
* Accept a request from client and process it.
*
* PARAMETERS:
* s - A pointer of server info
*
* RETURN:
* 0 - OK, Others - Error
******************************************************************************/
int server_accept_request(dsc_server_t *s)
{
dsc_command_t *req;
dsc_command_t *resp;
uint8_t buf[DSC_BUF_SIZE];
ssize_t bytes, req_len, resp_len;
struct sockaddr_in client_addr;
socklen_t client_addrlen = sizeof(struct sockaddr);
if (s == NULL) {
printf("Error: invalid parameter!\n");
return -1;
}
/* Receive request from client */
memset(buf, 0, sizeof(buf));
req_len = recvfrom(s->sockfd, &buf, sizeof(buf), 0,
(struct sockaddr *)&client_addr, &client_addrlen);
if (req_len < 0) {
perror("recvform error");
return -1;
} else if (req_len == 0) {
return -1;
}
/* Check the integrity of the request packet */
if (!verify_command_packet(buf, req_len)) {
/* Discard invaid packet */
return -1;
}
/* Process the request */
req = (dsc_command_t *)buf;
resp = s->request_handler(req);
if (resp == NULL) {
resp = (dsc_command_t *)buf; /* Use a local buffer */
resp->status = STATUS_ERROR;
resp->data_len = 0;
}
resp_len = sizeof(dsc_command_t) + resp->data_len;
resp->signature = req->signature;
resp->checksum = 0;
resp->checksum = compute_checksum(resp, resp_len);
int rc = 0;
/* Send response */
bytes = sendto(s->sockfd, resp, resp_len, 0, (struct sockaddr *)&client_addr,
sizeof(struct sockaddr));
if (bytes != resp_len) {
perror("sendto error");
rc = -1;
}
if (resp != (dsc_command_t *)buf) { /* If NOT local buffer, free it */
free(resp);
}
return rc;
}
/******************************************************************************
* NAME:
* server_close
*
* DESCRIPTION:
* Close the socket fd and free memory.
*
* PARAMETERS:
* s - A pointer of server info
*
* RETURN:
* None
******************************************************************************/
void server_close(dsc_server_t *s)
{
if (s == NULL) {
return;
}
close(s->sockfd);
free(s);
}
/******************************************************************************
* NAME:
* client_init
*
* DESCRIPTION:
* Do some initialzation work for client.
*
* PARAMETERS:
* server_ip - The IP address of server
* server_port - The port number of server
*
* RETURN:
* A pointer of client info.
******************************************************************************/
dsc_client_t *client_init(const char *server_ip, int server_port)
{
dsc_client_t *c;
int fd;
c = (dsc_client_t *)malloc(sizeof(dsc_client_t));
if (c == NULL) {
perror("malloc error");
return NULL;
}
memset(c, 0, sizeof(dsc_client_t));
memset(&c->serv_addr, 0, sizeof(c->serv_addr));
c->serv_addr.sin_family = AF_INET;
c->serv_addr.sin_port = htons(server_port);
c->serv_addr.sin_addr.s_addr = inet_addr(server_ip);
fd = socket(AF_INET, SOCK_DGRAM, 0);
if (fd < 0) {
perror("socket error");
free(c);
return NULL;
}
c->sockfd = fd;
struct timeval tv;
tv.tv_sec = 1;
tv.tv_usec = 0;
if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) < 0) {
perror("Set recv timeout Error");
free(c);
close(fd);
return NULL;
}
return c;
}
/******************************************************************************
* NAME:
* client_send_request
*
* DESCRIPTION:
* Send a request to server, and get the response.
*
* PARAMETERS:
* c - A pointer of client info
* req - The request to send
*
* RETURN:
* The response for the request. The caller need to free the memory.
******************************************************************************/
dsc_command_t *client_send_request(dsc_client_t *c, dsc_command_t *req)
{
uint8_t buf[DSC_BUF_SIZE];
ssize_t bytes, req_len;
struct sockaddr_in server_addr;
socklen_t server_addrlen = sizeof(struct sockaddr);
if ((c == NULL) || (req == NULL)) {
printf("Error: invalid parameter!\n");
return NULL;
}
/* Send request */
req_len = sizeof(dsc_command_t) + req->data_len;
req->signature = DSC_SIGNATURE;
req->checksum = 0;
req->checksum = compute_checksum(req, req_len);
bytes = sendto(c->sockfd, req, req_len, 0, (struct sockaddr *)&c->serv_addr,
sizeof(struct sockaddr));
if (bytes != req_len) {
perror("sendto error");
return NULL;
}
/* Get response */
memset(buf, 0, sizeof(buf));
bytes = recvfrom(c->sockfd, &buf, sizeof(buf), 0,
(struct sockaddr *)&server_addr, &server_addrlen);
if (bytes < 0) {
perror("recvform error");
return NULL;
} else if (bytes == 0) {
return NULL;
}
/* Check the integrity of the response packet */
if (verify_command_packet(buf, bytes)) {
dsc_command_t *resp = (dsc_command_t *)malloc(bytes);
if (resp) {
memcpy(resp, buf, bytes);
} else {
perror("malloc error");
}
return resp;
}
return NULL;
}
/******************************************************************************
* NAME:
* client_close
*
* DESCRIPTION:
* Close the client socket fd and free memory.
*
* PARAMETERS:
* c - The pointer of client info
*
* RETURN:
* None
******************************************************************************/
void client_close(dsc_client_t *c)
{
if (c == NULL) {
return;
}
close(c->sockfd);
free(c);
}