+/*
+ * Acess2 Networking Toolkit
+ * By John Hodge (thePowersGang)
+ *
+ * dns.c
+ * - Hostname<->Address resolution
+ */
+#include <stddef.h> // size_t / NULL
+#include <stdint.h> // uint*_t
+#include <string.h> // memcpy, strchrnul
+#include <assert.h>
+#include <net.h>
+#include "include/dns.h"
+
+// === PROTOTYPES ===
+size_t DNS_EncodeName(void *buf, const char *dotted_name);
+int DNS_DecodeName(char dotted_name[256], const void *buf, size_t space);
+int DNS_int_ParseRR(const void *buf, size_t space, char* name_p, enum eTypes* type_p, enum eClass* class_p, uint32_t* ttl_p, size_t* rdlength_p);
+static uint16_t get16(const void *buf);
+static size_t put16(void *buf, uint16_t val);
+
+
+// === CODE ===
+int DNS_Query(int ServerAType, const void *ServerAddr, const char *name, enum eTypes type, enum eClass class, handle_record_t* handle_record, void *info)
+{
+ int namelen = DNS_EncodeName(NULL, name);
+ assert(namelen < 256);
+ size_t pos = 0;
+ char packet[ 512 ];
+ assert( (6*2) + (namelen + 2*2) < 512 );
+ // - Header
+ pos += put16(packet + pos, 0xAC00); // Identifier (arbitary)
+ pos += put16(packet + pos, (0 << 0) | (0 << 1) ); // Op : Query, Standard, no other flags
+ pos += put16(packet + pos, 1); // QDCount
+ pos += put16(packet + pos, 0); // ANCount
+ pos += put16(packet + pos, 0); // NSCount
+ pos += put16(packet + pos, 0); // ARCount
+ // - Question
+ pos += DNS_EncodeName(packet + pos, name);
+ pos += put16(packet + pos, type); // QType
+ pos += put16(packet + pos, class); // QClass
+
+ assert(pos <= sizeof(packet));
+
+ // Send and wait for reply
+ // - Lock
+ // > TODO: Lock DNS queries
+ // - Send
+ int sock = Net_OpenSocket_UDP(ServerAType, ServerAddr, 53, 0);
+ if( sock < 0 ) {
+ // Connection failed
+ // TODO: Correctly report this failure with a useful error code
+ return 1;
+ }
+ int rv = _SysWrite(sock, packet, pos);
+ if( rv != pos ) {
+ // TODO: Error reporting
+ _SysClose(sock);
+ return 1;
+ }
+ // - Wait
+ int return_len = 0;
+ do {
+ return_len = _SysRead(sock, packet, sizeof(packet));
+ } while( return_len == 0 );
+ if( return_len < 0 ) {
+ // TODO: Error reporting
+ _SysClose(sock);
+ return 1;
+ }
+ _SysClose(sock);
+ // - Release
+ // > TODO: Lock DNS queries
+
+ // For each response in the answer (and additional) sections, call the passed callback
+ char rr_name[256];
+ unsigned int qd_count = get16(packet + 4);
+ unsigned int an_count = get16(packet + 6);
+ unsigned int ns_count = get16(packet + 8);
+ unsigned int ar_count = get16(packet + 10);
+ pos = 6*2;
+ // TODO: Can I safely assert / fail if qd_count is non-zero?
+ // - Questions, ignored
+ for( unsigned int i = 0; i < qd_count; i ++ ) {
+ pos += DNS_DecodeName(NULL, packet + pos, return_len - pos);
+ pos += 2*2;
+ }
+ // - Answers, pass on to handler
+ for( unsigned int i = 0; i < an_count; i ++ )
+ {
+ enum eTypes type;
+ enum eClass class;
+ uint32_t ttl;
+ size_t rdlength;
+ int rv = DNS_int_ParseRR(packet + pos, return_len - pos, rr_name, &type, &class, &ttl, &rdlength);
+ if( rv < 0 ) {
+ return 1;
+ }
+ pos += rv;
+
+ handle_record(info, rr_name, type, class, ttl, rdlength, packet + pos);
+ }
+ // Authority Records (should all be NS records)
+ for( unsigned int i = 0; i < ns_count; i ++ )
+ {
+ size_t rdlength;
+ int rv = DNS_int_ParseRR(packet + pos, return_len - pos, rr_name, NULL, NULL, NULL, &rdlength);
+ if( rv < 0 ) {
+ return 1;
+ }
+ pos += rv;
+ }
+ // - Additional records, pass to handler
+ for( unsigned int i = 0; i < ar_count; i ++ )
+ {
+ enum eTypes type;
+ enum eClass class;
+ uint32_t ttl;
+ size_t rdlength;
+ int rv = DNS_int_ParseRR(packet + pos, return_len - pos, rr_name, &type, &class, &ttl, &rdlength);
+ if( rv < 0 ) {
+ return 1;
+ }
+ pos += rv;
+
+ handle_record(info, rr_name, type, class, ttl, rdlength, packet + pos);
+ }
+
+ return 0;
+}
+
+/// Encode a dotted name as a DNS name
+size_t DNS_EncodeName(void *buf, const char *dotted_name)
+{
+ size_t ret = 0;
+ const char *str = dotted_name;
+ uint8_t *buf8 = buf;
+ while( *str )
+ {
+ const char *next = strchr(str, '.');
+ size_t seg_len = (next ? next - str : strlen(str));
+ if( seg_len > 63 ) {
+ // Oops, too long (truncate)
+ seg_len = 63;
+ }
+ if( seg_len == 0 && next != NULL ) {
+ // '..' encountered, invalid (skip)
+ str = next+1;
+ continue ;
+ }
+
+ if( buf8 )
+ {
+ buf8[ret] = seg_len;
+ memcpy(buf8+ret+1, str, seg_len);
+ }
+ ret += 1 + seg_len;
+
+ if( next == NULL ) {
+ // No trailing '.', assume it's there? Yes, need to be NUL terminated
+ if(buf8) buf8[ret] = 0;
+ ret ++;
+ break;
+ }
+ else {
+ str = next + 1;
+ }
+ }
+ return ret;
+}
+
+// Decode a name (including trailing . for root)
+int DNS_DecodeName(char dotted_name[256], const void *buf, size_t space)
+{
+ int consumed = 0;
+ int out_pos = 0;
+ const uint8_t *buf8 = buf;
+ while( *buf8 && space > 0 )
+ {
+ if( consumed + 1 > space ) return -1;
+ uint8_t seg_len = *buf8;
+ buf8 ++;
+ consumed ++;
+ // Protocol violation (overflowed end of buffer)
+ if( consumed + seg_len > space )
+ return -1;
+ // Protocol violation (segment too long)
+ if( seg_len >= 64 )
+ return -1;
+ // Protocol violation (name was too long)
+ if( out_pos + seg_len + 1 > sizeof(dotted_name)-1 )
+ return -1;
+
+ // Read segment
+ memcpy(dotted_name + out_pos, buf8, seg_len);
+ buf8 += seg_len;
+ consumed += seg_len;
+
+ // Place '.'
+ dotted_name[out_pos+seg_len+1] = '.';
+ // Increment output counter
+ out_pos += seg_len + 1;
+ }
+
+ dotted_name[out_pos] = '\0';
+ return consumed;
+}
+
+// Parse a Resource Record
+int DNS_int_ParseRR(const void *buf, size_t space, char* name_p, enum eTypes* type_p, enum eClass* class_p, uint32_t* ttl_p, size_t* rdlength_p)
+{
+ const uint8_t *buf8 = buf;
+ size_t consumed = 0;
+
+ // 1. Name
+ int rv = DNS_DecodeName(name_p, buf8, space);
+ if(rv < 0) return -1;
+
+ buf8 += rv, consumed += rv;
+
+ if( type_p )
+ *type_p = get16(buf8);
+ buf8 += 2, consumed += 2;
+
+ if( class_p )
+ *class_p = get16(buf8);
+ buf8 += 2, consumed += 2;
+
+ return consumed;
+}
+
+static uint16_t get16(const void *buf) {
+ const uint8_t* buf8 = buf;
+ uint16_t rv = 0;
+ rv |= buf8[0];
+ rv |= (uint16_t)buf8[1] << 8;
+ return rv;
+}
+static size_t put16(void *buf, uint16_t val) {
+ uint8_t* buf8 = buf;
+ buf8[0] = val & 0xFF;
+ buf8[1] = val >> 8;
+ return 2;
+}
+
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