[C/코드해석] pop_string

코드 원문

https://github.com/strongswan/strongswan/blob/09df86c033d18f89d1b1e463593a4a69ceecd950/src/libcharon/plugins/stroke/stroke_socket.c

/**
 * Helper function which corrects the string pointers
 * in a stroke_msg_t. Strings in a stroke_msg sent over "wire"
 * contains RELATIVE addresses (relative to the beginning of the
 * stroke_msg). They must be corrected if they reach our address
 * space...
 */
static void pop_string(stroke_msg_t *msg, char **string)
{
	if (*string == NULL)
	{
		return;
	}

	/* check for sanity of string pointer and string */
	if (string < (char**)msg ||
		string > (char**)((char*)msg + sizeof(stroke_msg_t)) ||
		(unsigned long)*string < (unsigned long)((char*)msg->buffer - (char*)msg) ||
		(unsigned long)*string > msg->length)
	{
		*string = "(invalid pointer in stroke msg)";
	}
	else
	{
		*string = (char*)msg + (unsigned long)*string;
	}
}

 

사용 예제

 

struct stroke_end_t {
	char *auth;
	char *auth2;
	char *id;
	char *id2;
	char *eap_id;
	char *rsakey;
	char *cert;
	char *cert2;
	char *ca;
	char *ca2;
	char *groups;
	char *groups2;
	char *cert_policy;
	char *updown;
	char *address

 

static void pop_string(stroke_msg_t *msg, char **string)
 * Pop the strings of a stroke_end_t struct and log them for debugging purposes
 */
static void pop_end(stroke_msg_t *msg, const char* label, stroke_end_t *end)
{
	pop_string(msg, &end->address);

 

 

코드 해석

// 
static void pop_string(stroke_msg_t *msg, char **string)
{
	if (*string == NULL)
	{
		return;
	}

	/* check for sanity of string pointer and string */
	if (string < (char**)msg ||
		string > (char**)((char*)msg + sizeof(stroke_msg_t)) ||
		(unsigned long)*string < (unsigned long)((char*)msg->buffer - (char*)msg) ||
		(unsigned long)*string > msg->length)
	{
		*string = "(invalid pointer in stroke msg)";
	}
	else
	{
		*string = (char*)msg + (unsigned long)*string;
	}
}