dns_impl.inl

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#ifndef CYGONCE_NS_DNS_DNS_IMPL_H
#define CYGONCE_NS_DNS_DNS_IMPL_H
//=============================================================================
//
//      dns_impl.inl
//
//      DNS client code implementation.
//
//=============================================================================
//####ECOSGPLCOPYRIGHTBEGIN####
// -------------------------------------------
// This file is part of eCos, the Embedded Configurable Operating System.
// Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.
//
// eCos is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 2 or (at your option) any later version.
//
// eCos 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 General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License along
// with eCos; if not, write to the Free Software Foundation, Inc.,
// 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
//
// As a special exception, if other files instantiate templates or use macros
// or inline functions from this file, or you compile this file and link it
// with other works to produce a work based on this file, this file does not
// by itself cause the resulting work to be covered by the GNU General Public
// License. However the source code for this file must still be made available
// in accordance with section (3) of the GNU General Public License.
//
// This exception does not invalidate any other reasons why a work based on
// this file might be covered by the GNU General Public License.
//
// Alternative licenses for eCos may be arranged by contacting Red Hat, Inc.
// at http://sources.redhat.com/ecos/ecos-license/
// -------------------------------------------
//####ECOSGPLCOPYRIGHTEND####
//=============================================================================
//#####DESCRIPTIONBEGIN####
//
// Author(s):   andrew.lunn
// Contributors:andrew.lunn, jskov
// Date:        2001-09-18
// Description: The code is kept in this separate file to allow it to be
//              used from RedBoot.
//
//####DESCRIPTIONEND####
//
//=============================================================================

#include <cyg/ns/dns/dns_priv.h>

/* Validate a hostname is legal as defined in RFC 1035 */
static int
valid_hostname(const char *hostname)
{
    const char * label;
    const char * label_end;
  
    if (!hostname) {
        return false;
    }
    label = hostname;
    while (*label) {
        if (!isalpha(*label))
            return false;
        label_end = strchr(label, (int)'.') - 1;
        if (label_end == (char *)-1) {
            label_end = strchr(label, (int)'\0') - 1;
        }
        while (label != label_end) {
            if (!isalnum(*label) && (*label != '-')) {
                return false;
            }
            label++;
        }
        label = label_end+1;            /* Move onto the . or the null. */
        if (*label == '.') {            /* Move over the . if there is one */
            label++;
        }
    }
    return true;
}

/* Build a qname structure. The structure consists of pairs of
   <len><label> where <label> is eg ma in tux.ma.tech.ascom.ch. len is
   the length of the label. */
static int 
build_qname(char *ptr, const char *hostname)
{
    const char *label = hostname;
    char *end_label;
    int total_len = 0;
    int len;
  
    while (*label) {
        end_label = strchr(label, (int)'.') - 1;
        if (end_label == (char *)-1) {
            end_label = strchr(label, (int)'\0') - 1;
        }
        len = end_label - label + 1;
        if (len > 63) {
            return -1;
        }
        *ptr++ = (char) len;            /* Put the length of the label */
        memcpy(ptr, label, len);        /* and now the label */
        ptr += len;
    
        total_len += len +1;
        label = end_label+1;            /* Move onto the . or the null. */
        if (*label == '.') {            /* Move over the . if there is one */
            label++;
        }
    }
    *ptr = 0;                           /* Add the last length of zero
                                           to mark the end */
    return (total_len+1);
}

/* Given a pointer to a qname, find the length of the qname. This is
   the number of bytes needed to represent the qname, not the length
   of the name. A qname is terminated by either a 00, or a pointer
   into another qname. This pointer has the top two bits set. */
static int 
qname_len(unsigned char * qname)
{
    unsigned char * ptr = qname;
    
    while ((*ptr != 0) && ((*ptr & 0xc0) != 0xc0)) {
        ptr += *ptr + 1;
    }
    /* Pointers are two bytes */
    if ((*ptr & 0xc0) == 0xc0) {
        ptr++;
    }
    ptr++;                              /* Skip over the trailing byte */

    return (ptr - qname);
}

/* Build a real name from a qname. Alloc the memory needed and return
   it. Return NULL on error */
char *
real_name(char *msg, unsigned char *qname)
{
    unsigned char * ptr = qname;
    char * name;
    char * label;
    int len = 0;
    int offset;

    /* First pass works out the length of the name */
    while (*ptr != 0) {
        if ((*ptr & 0xc0) == 0xc0) {
            /* pointer to somewhere else. Follow the pointer */
            offset = ((*ptr & 0x3f) << 8) | *(ptr+1);
            ptr = msg + offset;
        } else {
            len += *ptr + 1;
            ptr += *ptr + 1;
        }
    }

    /* Now allocate the memory needed and copy the host name into it */
    name = alloc_string(len+1);
    if (name) {
        label = name;
        ptr = qname;
        while (*ptr != 0) {
            if ((*ptr & 0xc0) == 0xc0) {
                /* pointer to somewhere else. Follow the pointer */
                offset = ((*ptr & 0x3f) << 8) | *(ptr+1);
                ptr = msg + offset;
            } else {
                len = *ptr;
                memcpy(label, (ptr+1), len);
                label += len;
                *label++ = '.';
                ptr += *ptr + 1;
            }
        }
        *label = '\0';
    }
    return name;
}

/* Build a query message which can be sent to the server. If something
   goes wrong return -1, otherwise the length of the query message */
static int 
build_query(char * msg, const char * hostname, short rr_type)
{
    struct dns_header *dns_hdr;
    char *ptr;
    int len;

    /* Fill out the header */
    dns_hdr = (struct dns_header *) msg;
    dns_hdr->id = htons(id++);
    dns_hdr->rd = true;
    dns_hdr->opcode = DNS_QUERY;
    dns_hdr->qdcount = htons(1);
  
    /* Now the question we want to ask */
    ptr = (char *)&dns_hdr[1];

    len = build_qname(ptr, hostname);

    if (len < 0) {
        h_errno = NO_RECOVERY;
        return -1;
    }
    ptr += len;

    /* Set the type and class fields */
    *ptr++ = (rr_type >> 8) & 0xff;
    *ptr++ = rr_type & 0xff;
    *ptr++ = (DNS_CLASS_IN >> 8) & 0xff;
    *ptr++ = DNS_CLASS_IN & 0xff;

    len = ptr - msg;

    return len;
}

/* Check if the hostname is actually of dot format. If so convert it 
   and return host entity structure. If not, return NULL. */
static struct hostent *
dot_hostname(const char *hostname)
{
    struct hostent *hent = NULL;
    struct in_addr addr;

    if (inet_aton(hostname, &addr)) {
        hent = alloc_hent();
        if (hent) {
            memcpy(hent->h_addr_list[0], &addr, sizeof(struct in_addr));
            hent->h_addrtype = AF_INET;
            hent->h_length = sizeof(struct in_addr);
            hent->h_name = alloc_string(strlen(hostname)+1);
            if (!hent->h_name) {
                free_hent(hent);
                return NULL;
            }
            strcpy(hent->h_name, hostname);
        }
    }
    return hent;
}

/* Decode the answer from the server. Returns NULL if failed, or 
   a hostent structure containing different data depending on the
   query type:
    DNS_TYPE_A: 
      h_name:         a pointer to the hostname
      h_addr_list[0]: a pointer to in_addr structure
    DNS_TYPE_PTR:
      h_name:         a pointer to the hostname
      h_addr_list[0]: a pointer to an empty in_addr structure. Caller
                      must fill out!
*/
static struct hostent *
parse_answer(char * msg, short rr_type)
{
    static struct hostent *hent;
    struct dns_header *dns_hdr;
    struct resource_record rr, *rr_p = NULL;
    char *qname = NULL;
    char *ptr;

    dns_hdr = (struct dns_header *)msg;

    if (DNS_REPLY_NAME_ERROR == dns_hdr->rcode) {
        h_errno = HOST_NOT_FOUND;
        return NULL;
    }

    if ((dns_hdr->qr != 1) || 
        (dns_hdr->opcode != DNS_QUERY) ||
        (dns_hdr->rcode != DNS_REPLY_NOERR)) {
        h_errno = NO_RECOVERY;
        return NULL;
    }
  
    dns_hdr->ancount = ntohs(dns_hdr->ancount);
    dns_hdr->qdcount = ntohs(dns_hdr->qdcount);
    ptr = (char *)&dns_hdr[1];

    /* Skip over the query section */
    if (dns_hdr->qdcount > 0) {
        while (dns_hdr->qdcount) {
            ptr += qname_len(ptr);
            ptr += 4;                   /* skip type & class */
            dns_hdr->qdcount--;
        }
    }  
    /* Skip over the answers resource records to find an answer of the
       correct type. */
    while (dns_hdr->ancount) {
        qname = ptr;
        ptr += qname_len(ptr);
        rr_p = (struct resource_record *)ptr;
        memcpy(&rr, ptr, sizeof(rr));
        if ((rr.rr_type == htons(rr_type)) && 
            (rr.class == htons(DNS_CLASS_IN))) {
            break;
        }