dns.c
来自「mcf5307实验源代码」· C语言 代码 · 共 1,215 行 · 第 1/5 页
C
1,215 行
break;
case DNS_TYPE_PTR :
/* The answer has the correct type and class. Get the name. */
name_size = DNS_Unpack_Domain_Name (data,
rr_ptr->dns_rdata,
(CHAR *)pkt);
break;
default :
return -1;
}
/* Get the time to live for this RR. */
*ttl = longswap (rr_ptr->dns_ttl);
/* Indicate an answer was found. */
answer_received = 1;
break;
}
/* Copy the length of this answer. */
memcpy (&length, &rr_ptr->dns_rdlength, 2);
/* Point to the next answer, if any. The rdlength field is the
length of the data section of the RR. Add 10 for the sizes of
the type, class, ttl, and rdlength.
*/
p_ptr += (10 + intswap ((int16)length));
}
}
NU_Deallocate_Memory(name);
if (answer_received)
return (NU_SUCCESS);
else
return (-1);
} /* DNS_Extract_Data */
/******************************************************************************/
/* FUNCTION */
/* */
/* DNS_Add_Host */
/* */
/* DESCRIPTION */
/* */
/* This function adds a new host to the "hosts file". */
/* A block of memory is alocated each time we want to add a new host. */
/* This can be wasteful of memory because Nucleus PLUS has a minimum */
/* allocation size of 50 bytes. The alternative would have been to */
/* allocate enough memory for several of these at one time. The problem */
/* with that is the RFC defines the maximum size of a name at 255 bytes. */
/* We would have to assume that a maximum sized name would have to be */
/* stored and allocate memory accordingly. Since most names are nowhere */
/* close to 255 bytes this method would have been even more wasteful. */
/* */
/* AUTHOR */
/* */
/* Glen Johnson, Accelerated Technology Inc. */
/* */
/* CALLED BY */
/* */
/* DNS_Find_Host_By_Addr Find a host by address. */
/* DNS_Find_Host_By_Name Find a host by name. */
/* */
/* CALLS */
/* */
/* dll_enqueue Add an item to a list. */
/* NU_Allocate_Memory Allocate memory. */
/* NU_Retrieve_Clock Get the current clock tick. */
/* */
/* INPUTS */
/* */
/* name The name of the host to add. */
/* ip_addr The IP address of the host to add. */
/* ttl The Time To Live for this entry. */
/* */
/* OUTPUTS */
/* */
/* NULL is returned if the host can not be added, otherwise a host pointer.*/
/* */
/* HISTORY */
/* */
/* NAME DATE REMARKS */
/* */
/* Glen Johnson 06/17/97 Created initial version for NET 3.1 */
/* */
/******************************************************************************/
DNS_HOST *DNS_Add_Host(CHAR *name, CHAR *ip_addr, UNSIGNED ttl)
{
INT size;
DNS_HOST *dns_host;
UNSIGNED time;
/* Get the size of the name. */
size = strlen(name) + 1;
/* Retrieve the current time. */
time = NU_Retrieve_Clock();
/* Before allocating memory for a new entry, check to see if the TTL of an
old entry has expired. If so re-use that entry. */
for ( dns_host = DNS_Hosts.dns_head;
dns_host;
dns_host = dns_host->dns_next )
{
/* First check to see if this entry has a ttl. A ttl of 0 is used to
indicate permanent entries.
*/
if (dns_host->dns_ttl)
/* Check to see if the ttl has expired. */
if (INT32_CMP(dns_host->dns_ttl, time) <= 0)
/* Good so far. Check to see if the name will fit in this
entry. */
if (dns_host->dns_name_size >= size)
break;
}
/* Did we find an entry that can be re-used. */
if (!dns_host)
{
/* A new host structure must be created. */
/* We need to compute the size of the block of memory to allocate. The
size will include the size of a host structure + length of the name +
1 (for the null terminator). We may want to reuse this entry later
for other hosts. So allocate a minimum number of bytes for the name.
This will make it more likely that this entry can be reused.
*/
/* If the size is less than the minimum, then bump it up. */
if (size < DNS_MIN_NAME_ALLOC)
size = DNS_MIN_NAME_ALLOC;
/* Allocate a block of memory for the new DNS host structure and for the
name. */
if (NU_Allocate_Memory (&System_Memory, (VOID **)&dns_host,
size + sizeof(DNS_HOST),
NU_NO_SUSPEND) != NU_SUCCESS)
{
return (NU_NULL);
}
/* The name will be stored immediately after the structure. */
dns_host->dns_name = (CHAR *)(dns_host + 1);
/* Add this host to the list. */
dll_enqueue((tqe_t *) &DNS_Hosts, (tqe_t *) dns_host);
}
/* Copy the name and IP address. */
strcpy(dns_host->dns_name, name);
memcpy(dns_host->dns_ipaddr, ip_addr, 4);
/* TTL is specified in seconds. So multiply by the number ticks per
second. */
ttl *= TICKSPERSEC;
/* Initialize ttl. */
dns_host->dns_ttl = ttl + NU_Retrieve_Clock();
/* TTL value of 0 is used to indicate that the entry is permanent. So if by
some chance the value computed is 0, add 1. */
if (!dns_host->dns_ttl)
dns_host->dns_ttl++;
/* Initialize the size of the name of this host. */
dns_host->dns_name_size = size;
return (dns_host);
} /* DNS_Add_Host */
/******************************************************************************/
/* FUNCTION */
/* */
/* DNS_Addr_To_String */
/* */
/* DESCRIPTION */
/* */
/* This function takes an IP address and converts it to a character string.*/
/* */
/* AUTHOR */
/* */
/* Glen Johnson, Accelerated Technology Inc. */
/* */
/* CALLED BY */
/* */
/* DNS_Build_Query Create a DNS query packet. */
/* */
/* CALLS */
/* */
/* itoa Convert an intger to a ascii string. */
/* */
/* INPUTS */
/* */
/* addr The address of to convert. */
/* new_name The address in ascii format. */
/* */
/* OUTPUTS */
/* */
/* NU_SUCCESS Indicates success. */
/* */
/* HISTORY */
/* */
/* NAME DATE REMARKS */
/* */
/* Glen Johnson 06/17/97 Created initial version for NET 3.1 */
/* */
/******************************************************************************/
STATUS DNS_Addr_To_String(CHAR *addr, CHAR *new_name)
{
INT i;
CHAR *ptr = new_name;
uchar *a = (uchar *)addr;
/* We need to add each octet of the address to the name in reverse order. */
for (i = 3; i >= 0; i--)
{
/* Convert the octet to a character string. */
itoa(a[i], ptr, 10);
/* Move past the string just added. */
ptr += strlen(ptr);
/* Add the dot. */
*ptr++ = '.';
}
strcpy(ptr, "IN-ADDR.ARPA");
return NU_SUCCESS;
} /* DNS_Addr_To_String */
#endif /* DNS_INCLUDED */
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