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DNS Server : bug fix and prettifying (#1011)

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* 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 2018-03-04 20:17:40 +01:00 committed by Me No Dev
parent d29cfdb104
commit 694c3a453f
2 changed files with 109 additions and 24 deletions
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86
libraries/DNSServer/src/DNSServer.cpp
View File

@ -5,10 +5,11 @@
DNSServer::DNSServer()
{
_ttl = htonl(60);
_ttl = htonl(DNS_DEFAULT_TTL);
_errorReplyCode = DNSReplyCode::NonExistentDomain;
_dnsHeader = NULL;
_buffer = NULL;
_dnsHeader = (DNSHeader*) malloc( sizeof(DNSHeader) ) ;
_dnsQuestion = (DNSQuestion*) malloc( sizeof(DNSQuestion) ) ;
_buffer = NULL;
_currentPacketSize = 0;
_port = 0;
}
@ -55,11 +56,37 @@ void DNSServer::processNextRequest()
_currentPacketSize = _udp.parsePacket();
if (_currentPacketSize)
{
if (_buffer != NULL) free(_buffer);
// Allocate buffer for the DNS query
if (_buffer != NULL)
free(_buffer);
_buffer = (unsigned char*)malloc(_currentPacketSize * sizeof(char));
if (_buffer == NULL) return;
if (_buffer == NULL)
return;
// Put the packet received in the buffer and get DNS header (beginning of message)
// and the question
_udp.read(_buffer, _currentPacketSize);
_dnsHeader = (DNSHeader*) _buffer;
memcpy( _dnsHeader, _buffer, DNS_HEADER_SIZE ) ;
if ( requestIncludesOnlyOneQuestion() )
{
// The QName has a variable length, maximum 255 bytes and is comprised of multiple labels.
// Each label contains a byte to describe its length and the label itself. The list of
// labels terminates with a zero-valued byte. In "github.com", we have two labels "github" & "com"
// Iterate through the labels and copy them as they come into a single buffer (for simplicity's sake)
_dnsQuestion->QNameLength = 0 ;
while ( _buffer[ DNS_HEADER_SIZE + _dnsQuestion->QNameLength ] != 0 )
{
memcpy( (void*) &_dnsQuestion->QName[_dnsQuestion->QNameLength], (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength], _buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength] + 1 ) ;
_dnsQuestion->QNameLength += _buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength] + 1 ;
}
_dnsQuestion->QName[_dnsQuestion->QNameLength] = 0 ;
_dnsQuestion->QNameLength++ ;
// Copy the QType and QClass
memcpy( &_dnsQuestion->QType, (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength], sizeof(_dnsQuestion->QType) ) ;
memcpy( &_dnsQuestion->QClass, (void*) &_buffer[DNS_HEADER_SIZE + _dnsQuestion->QNameLength + sizeof(_dnsQuestion->QType)], sizeof(_dnsQuestion->QClass) ) ;
}
if (_dnsHeader->QR == DNS_QR_QUERY &&
_dnsHeader->OPCode == DNS_OPCODE_QUERY &&
@ -87,15 +114,21 @@ bool DNSServer::requestIncludesOnlyOneQuestion()
_dnsHeader->ARCount == 0;
}
String DNSServer::getDomainNameWithoutWwwPrefix()
{
// Error checking : if the buffer containing the DNS request is a null pointer, return an empty domain
String parsedDomainName = "";
if (_buffer == NULL) return parsedDomainName;
unsigned char *start = _buffer + 12;
if (_buffer == NULL)
return parsedDomainName;
// Set the start of the domain just after the header (12 bytes). If equal to null character, return an empty domain
unsigned char *start = _buffer + DNS_OFFSET_DOMAIN_NAME;
if (*start == 0)
{
return parsedDomainName;
}
int pos = 0;
while(true)
{
@ -121,16 +154,35 @@ String DNSServer::getDomainNameWithoutWwwPrefix()
void DNSServer::replyWithIP()
{
if (_buffer == NULL) return;
_dnsHeader->QR = DNS_QR_RESPONSE;
_dnsHeader->ANCount = _dnsHeader->QDCount;
_dnsHeader->QDCount = 0;
_udp.beginPacket(_udp.remoteIP(), _udp.remotePort());
_udp.write(_buffer, _currentPacketSize);
_udp.write((unsigned char*)&_ttl, 4);
_udp.write((uint8_t)0);
_udp.write((uint8_t)4);
_udp.write(_resolvedIP, 4);
// Change the type of message to a response and set the number of answers equal to
// the number of questions in the header
_dnsHeader->QR = DNS_QR_RESPONSE;
_dnsHeader->ANCount = _dnsHeader->QDCount;
_udp.write( (unsigned char*) _dnsHeader, DNS_HEADER_SIZE ) ;
// Write the question
_udp.write(_dnsQuestion->QName, _dnsQuestion->QNameLength) ;
_udp.write( (unsigned char*) &_dnsQuestion->QType, 2 ) ;
_udp.write( (unsigned char*) &_dnsQuestion->QClass, 2 ) ;
// Write the answer
// Use DNS name compression : instead of repeating the name in this RNAME occurence,
// set the two MSB of the byte corresponding normally to the length to 1. The following
// 14 bits must be used to specify the offset of the domain name in the message
// (<255 here so the first byte has the 6 LSB at 0)
_udp.write((uint8_t) 0xC0);
_udp.write((uint8_t) DNS_OFFSET_DOMAIN_NAME);
// DNS type A : host address, DNS class IN for INternet, returning an IPv4 address
uint16_t answerType = htons(DNS_TYPE_A), answerClass = htons(DNS_CLASS_IN), answerIPv4 = htons(DNS_RDLENGTH_IPV4) ;
_udp.write((unsigned char*) &answerType, 2 );
_udp.write((unsigned char*) &answerClass, 2 );
_udp.write((unsigned char*) &_ttl, 4); // DNS Time To Live
_udp.write((unsigned char*) &answerIPv4, 2 );
_udp.write(_resolvedIP, sizeof(_resolvedIP)); // The IP address to return
_udp.endPacket();
}

47
libraries/DNSServer/src/DNSServer.h
View File

@ -5,20 +5,43 @@
#define DNS_QR_QUERY 0
#define DNS_QR_RESPONSE 1
#define DNS_OPCODE_QUERY 0
#define DNS_DEFAULT_TTL 60 // Default Time To Live : time interval in seconds that the resource record should be cached before being discarded
#define DNS_OFFSET_DOMAIN_NAME 12 // Offset in bytes to reach the domain name in the DNS message
#define DNS_HEADER_SIZE 12
enum class DNSReplyCode
{
NoError = 0,
NoError = 0,
FormError = 1,
ServerFailure = 2,
ServerFailure = 2,
NonExistentDomain = 3,
NotImplemented = 4,
Refused = 5,
YXDomain = 6,
YXRRSet = 7,
NXRRSet = 8
NotImplemented = 4,
Refused = 5,
YXDomain = 6,
YXRRSet = 7,
NXRRSet = 8
};
enum DNSType
{
DNS_TYPE_A = 1, // Host Address
DNS_TYPE_AAAA = 28, // IPv6 Address
DNS_TYPE_SOA = 6, // Start Of a zone of Authority
DNS_TYPE_PTR = 12, // Domain name PoinTeR
DNS_TYPE_DNAME = 39 // Delegation Name
} ;
enum DNSClass
{
DNS_CLASS_IN = 1, // INternet
DNS_CLASS_CH = 3 // CHaos
} ;
enum DNSRDLength
{
DNS_RDLENGTH_IPV4 = 4 // 4 bytes for an IPv4 address
} ;
struct DNSHeader
{
uint16_t ID; // identification number
@ -41,6 +64,14 @@ struct DNSHeader
uint16_t ARCount; // number of resource entries
};
struct DNSQuestion
{
uint8_t QName[255] ;
int8_t QNameLength ;
uint16_t QType ;
uint16_t QClass ;
} ;
class DNSServer
{
public:
@ -66,6 +97,8 @@ class DNSServer
DNSHeader* _dnsHeader;
uint32_t _ttl;
DNSReplyCode _errorReplyCode;
DNSQuestion* _dnsQuestion ;
void downcaseAndRemoveWwwPrefix(String &domainName);
String getDomainNameWithoutWwwPrefix();