DNS Server : bug fix and prettifying (#1011)
* Retrieve some code from what has been done on the ESP8266. Clarify a bit the signification of several bytes in the response. * Add the type and class as members of the DNS class for an eventual future use. * Clarify the sense of a magic number present in DNS server. * A bit of aesthetics for the DNS server. * Add a structure for the DNS question, use it DNS server to store the question data and to create the DNS answer from scratch.
This commit is contained in:
Laurent Louf
Me No Dev
parent
d29cfdb104
commit
694c3a453f
@ -5,9 +5,10 @@
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DNSServer::DNSServer()
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{
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_ttl = htonl(60);
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_ttl = htonl(DNS_DEFAULT_TTL);
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_errorReplyCode = DNSReplyCode::NonExistentDomain;
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_dnsHeader = NULL;
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_dnsHeader = (DNSHeader*) malloc( sizeof(DNSHeader) ) ;
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_dnsQuestion = (DNSQuestion*) malloc( sizeof(DNSQuestion) ) ;
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_buffer = NULL;
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_currentPacketSize = 0;
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_port = 0;
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@ -55,11 +56,37 @@ void DNSServer::processNextRequest()
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_currentPacketSize = _udp.parsePacket();
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if (_currentPacketSize)
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{
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if (_buffer != NULL) free(_buffer);
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// Allocate buffer for the DNS query
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if (_buffer != NULL)
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free(_buffer);
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_buffer = (unsigned char*)malloc(_currentPacketSize * sizeof(char));
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if (_buffer == NULL) return;
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if (_buffer == NULL)
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return;
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// Put the packet received in the buffer and get DNS header (beginning of message)
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// and the question
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_udp.read(_buffer, _currentPacketSize);
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_dnsHeader = (DNSHeader*) _buffer;
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memcpy( _dnsHeader, _buffer, DNS_HEADER_SIZE ) ;
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if ( requestIncludesOnlyOneQuestion() )
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{
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// The QName has a variable length, maximum 255 bytes and is comprised of multiple labels.
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// Each label contains a byte to describe its length and the label itself. The list of
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// labels terminates with a zero-valued byte. In "github.com", we have two labels "github" & "com"
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// Iterate through the labels and copy them as they come into a single buffer (for simplicity's sake)
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_dnsQuestion->QNameLength = 0 ;
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while ( _buffer[ DNS_HEADER_SIZE + _dnsQuestion->QNameLength ] != 0 )
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{
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memcpy( (void*) &_dnsQuestion->QName[_dnsQuestion->QNameLength], (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength], _buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength] + 1 ) ;
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_dnsQuestion->QNameLength += _buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength] + 1 ;
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}
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_dnsQuestion->QName[_dnsQuestion->QNameLength] = 0 ;
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_dnsQuestion->QNameLength++ ;
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// Copy the QType and QClass
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memcpy( &_dnsQuestion->QType, (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength], sizeof(_dnsQuestion->QType) ) ;
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memcpy( &_dnsQuestion->QClass, (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength + sizeof(_dnsQuestion->QType)], sizeof(_dnsQuestion->QClass) ) ;
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}
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if (_dnsHeader->QR == DNS_QR_QUERY &&
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_dnsHeader->OPCode == DNS_OPCODE_QUERY &&
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@ -87,15 +114,21 @@ bool DNSServer::requestIncludesOnlyOneQuestion()
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_dnsHeader->ARCount == 0;
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}
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String DNSServer::getDomainNameWithoutWwwPrefix()
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{
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// Error checking : if the buffer containing the DNS request is a null pointer, return an empty domain
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String parsedDomainName = "";
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if (_buffer == NULL) return parsedDomainName;
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unsigned char *start = _buffer + 12;
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if (_buffer == NULL)
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return parsedDomainName;
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// Set the start of the domain just after the header (12 bytes). If equal to null character, return an empty domain
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unsigned char *start = _buffer + DNS_OFFSET_DOMAIN_NAME;
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if (*start == 0)
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{
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return parsedDomainName;
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}
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int pos = 0;
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while(true)
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{
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@ -121,16 +154,35 @@ String DNSServer::getDomainNameWithoutWwwPrefix()
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void DNSServer::replyWithIP()
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{
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if (_buffer == NULL) return;
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_dnsHeader->QR = DNS_QR_RESPONSE;
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_dnsHeader->ANCount = _dnsHeader->QDCount;
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_dnsHeader->QDCount = 0;
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_udp.beginPacket(_udp.remoteIP(), _udp.remotePort());
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_udp.write(_buffer, _currentPacketSize);
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_udp.write((unsigned char*)&_ttl, 4);
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_udp.write((uint8_t)0);
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_udp.write((uint8_t)4);
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_udp.write(_resolvedIP, 4);
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// Change the type of message to a response and set the number of answers equal to
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// the number of questions in the header
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_dnsHeader->QR = DNS_QR_RESPONSE;
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_dnsHeader->ANCount = _dnsHeader->QDCount;
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_udp.write( (unsigned char*) _dnsHeader, DNS_HEADER_SIZE ) ;
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// Write the question
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_udp.write(_dnsQuestion->QName, _dnsQuestion->QNameLength) ;
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_udp.write( (unsigned char*) &_dnsQuestion->QType, 2 ) ;
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_udp.write( (unsigned char*) &_dnsQuestion->QClass, 2 ) ;
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// Write the answer
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// Use DNS name compression : instead of repeating the name in this RNAME occurence,
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// set the two MSB of the byte corresponding normally to the length to 1. The following
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// 14 bits must be used to specify the offset of the domain name in the message
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// (<255 here so the first byte has the 6 LSB at 0)
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_udp.write((uint8_t) 0xC0);
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_udp.write((uint8_t) DNS_OFFSET_DOMAIN_NAME);
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// DNS type A : host address, DNS class IN for INternet, returning an IPv4 address
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uint16_t answerType = htons(DNS_TYPE_A), answerClass = htons(DNS_CLASS_IN), answerIPv4 = htons(DNS_RDLENGTH_IPV4) ;
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_udp.write((unsigned char*) &answerType, 2 );
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_udp.write((unsigned char*) &answerClass, 2 );
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_udp.write((unsigned char*) &_ttl, 4); // DNS Time To Live
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_udp.write((unsigned char*) &answerIPv4, 2 );
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_udp.write(_resolvedIP, sizeof(_resolvedIP)); // The IP address to return
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_udp.endPacket();
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}
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@ -5,6 +5,9 @@
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#define DNS_QR_QUERY 0
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#define DNS_QR_RESPONSE 1
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#define DNS_OPCODE_QUERY 0
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#define DNS_DEFAULT_TTL 60 // Default Time To Live : time interval in seconds that the resource record should be cached before being discarded
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#define DNS_OFFSET_DOMAIN_NAME 12 // Offset in bytes to reach the domain name in the DNS message
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#define DNS_HEADER_SIZE 12
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enum class DNSReplyCode
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{
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@ -19,6 +22,26 @@ enum class DNSReplyCode
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NXRRSet = 8
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};
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enum DNSType
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{
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DNS_TYPE_A = 1, // Host Address
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DNS_TYPE_AAAA = 28, // IPv6 Address
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DNS_TYPE_SOA = 6, // Start Of a zone of Authority
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DNS_TYPE_PTR = 12, // Domain name PoinTeR
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DNS_TYPE_DNAME = 39 // Delegation Name
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} ;
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enum DNSClass
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{
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DNS_CLASS_IN = 1, // INternet
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DNS_CLASS_CH = 3 // CHaos
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} ;
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enum DNSRDLength
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{
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DNS_RDLENGTH_IPV4 = 4 // 4 bytes for an IPv4 address
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} ;
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struct DNSHeader
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{
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uint16_t ID; // identification number
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@ -41,6 +64,14 @@ struct DNSHeader
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uint16_t ARCount; // number of resource entries
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};
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struct DNSQuestion
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{
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uint8_t QName[255] ;
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int8_t QNameLength ;
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uint16_t QType ;
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uint16_t QClass ;
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} ;
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class DNSServer
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{
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public:
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@ -66,6 +97,8 @@ class DNSServer
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DNSHeader* _dnsHeader;
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uint32_t _ttl;
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DNSReplyCode _errorReplyCode;
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DNSQuestion* _dnsQuestion ;
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void downcaseAndRemoveWwwPrefix(String &domainName);
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String getDomainNameWithoutWwwPrefix();
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