{$mode objfpc}
{$h+}

unit netdb;

Interface

{$i hsh.inc} // disappears if part of resolve.pp !!

Const
  DNSPort        = 53;
  MaxServers     = 4;
  MaxResolveAddr = 10;
  SResolveFile   = '/etc/resolv.conf';
  SServicesFile  = '/etc/services'; 
  SHostsFile     = '/etc/hosts';
  SNetworksFile  = '/etc/networks';
  
Type
  TDNSServerArray = Array[1..MaxServers] of THostAddr;
  TServiceEntry = record
    Name     : String;
    Protocol : String;
    Port     : Word;
    Aliases  : String;
  end;
     
  THostEntry = record
    Name : String;
    Addr : THostAddr;
    Aliases : String;
  end;  
  
  TNetworkEntry = Record
    Name : String;
    Addr : TNetAddr;
    Aliases : String;
  end;  
  
Var  
  DNSServers            : TDNSServerArray;
  DNSServerCount        : Integer;
  DefaultDomainList     : String;
  CheckResolveFileAge   : Boolean; 
  TimeOutS,TimeOutMS    : Longint;
  
  
Function GetDNSServers(FN : String) : Integer;

Function ResolveName(HostName : String; Var Addresses : Array of THostAddr) : Integer;
Function ResolveAddress(HostAddr : THostAddr; Var Addresses : Array of String) : Integer;

Function ResolveHostByName(HostName : String; Var H : THostEntry) : Boolean;
Function ResolveHostByAddr(HostAddr : THostAddr; Var H : THostEntry) : Boolean;

Function GetHostByName(HostName: String;  Var H : THostEntry) : boolean;
Function GetHostByAddr(Addr: THostAddr;  Var H : THostEntry) : boolean;

Function GetNetworkByName(NetName: String; Var N : TNetworkEntry) : boolean;
Function GetNetworkByAddr(Addr: THostAddr; Var N : TNetworkEntry) : boolean;

Function GetServiceByName(Const Name,Proto : String; Var E : TServiceEntry) : Boolean;
Function GetServiceByPort(Port : Word;Const Proto : String; Var E : TServiceEntry) : Boolean;

Implementation

uses 
{$ifdef VER1_0}
   Linux,
{$else}
   Unix,
{$endif}
   sockets,sysutils;

{$i hs.inc}

const
  DNSQRY_A     = 1;                     // name to IP address 
  DNSQRY_AAAA  = 28;                    // name to IP6 address
  DNSQRY_PTR   = 12;                    // IP address to name 
  DNSQRY_MX    = 15;                    // name to MX 
  DNSQRY_TXT   = 16;                    // name to TXT

  // Flags 1
  QF_QR     = $80;
  QF_OPCODE = $78;
  QF_AA     = $04;
  QF_TC     = $02;  // Truncated.
  QF_RD     = $01;

  // Flags 2
  QF_RA     = $80;
  QF_Z      = $70;
  QF_RCODE  = $0F;


   
Type 
  TPayLoad  = Array[0..511] of char;
  TQueryData = packed Record
    id      : Array[0..1] of Byte;
    flags1  : Byte;
    flags2  : Byte; 
    qdcount : word;
    ancount : word;
    nscount : word;
    arcount : word;
    Payload : TPayLoad;
  end;
  
  TRRData = Packed record       // RR record
    Atype    : Word;            // Answer type
    AClass   : Word;
    TTL      : Cardinal;
    RDLength : Word;
  end;

Var
  ResolveFileAge  : Longint;
  ResolveFileName : String;

{ ---------------------------------------------------------------------
    Auxiliary functions.
  ---------------------------------------------------------------------}

Function htons(var W : Word) : word;

begin
  w:=Swap(w);
  Result:=W;
end;

Function ntohs(var W : Word) : Word;

begin
  w:=Swap(w);
  Result:=W;
end;


{ ---------------------------------------------------------------------
   Resolve.conf handling
  ---------------------------------------------------------------------}
  
Function GetDNSServers(Fn : String) : Integer;

Var
  R : Text;
  L : String;
  I : Integer;
  H : THostAddr;

  Function CheckDirective(Dir : String) : Boolean;
  
  Var
    P : Integer;
  
  begin
    P:=Pos(Dir,L);
    Result:=(P<>0);
    If Result then
      begin
      Delete(L,1,P+Length(Dir));
      Trim(L);
      end;
  end;
   
begin
  Result:=0;
  ResolveFileName:=Fn;
  ResolveFileAge:=FileAge(FN);
  {$i-}
  Assign(R,FN);
  Reset(R);
  {$i+}
  If (IOResult<>0) then 
    exit;
  Try  
    While not EOF(R) do
      begin
      Readln(R,L);
      I:=Pos('#',L);
      If (I<>0) then
        L:=Copy(L,1,I-1);
      If CheckDirective('nameserver') then
        begin
        H:=HostToNet(StrToHostAddr(L));
        If (H[1]<>0) then
          begin
          Inc(Result);
          DNSServers[Result]:=H;
          end;
        end
      else if CheckDirective('domain') then
        DefaultDomainList:=L
      else if CheckDirective('search') then
        DefaultDomainList:=L;
      end;
  Finally
    Close(R);
  end;    
  DNSServerCount:=Result;
end;

Procedure CheckResolveFile;

Var
  F : Integer;

begin
  If CheckResolveFileAge then
    begin
    F:=FileAge(ResolveFileName);
    If ResolveFileAge<F then
      GetDnsServers(ResolveFileName);
    end;  
end;

{ ---------------------------------------------------------------------
    Payload handling functions.
  ---------------------------------------------------------------------}
  

Procedure DumpPayLoad(Q : TQueryData; L : Integer);

Var 
  i : Integer;

begin
  Writeln('Payload : ',l);
  For I:=0 to L-1 do
    Write(Byte(Q.Payload[i]),' ');
  Writeln;  
end;
  
Function BuildPayLoad(Var Q : TQueryData; Name : String; RR : Word; QClass : Word) : Integer;

Var
  P : PByte;
  l,S : Integer;
  
begin
  Result:=-1;
  If length(Name)>506 then
    Exit;
  Result:=0;  
  P:=@Q.Payload;
  Repeat
    L:=Pos('.',Name);
    If (L=0) then
      S:=Length(Name)
    else
      S:=L-1;
    P[Result]:=S;
    Move(Name[1],P[Result+1],S);
    Inc(Result,S+1);
    If (L>0) then
      Delete(Name,1,L);
  Until (L=0);
  P[Result]:=0;
  htons(rr);
  Move(rr,P[Result+1],2);
  Inc(Result,3);
  htons(QClass);
  Move(qclass,P[Result],2);
  Inc(Result,2);
end;



Function NextRR(Const PayLoad : TPayLoad;Var Start : LongInt; AnsLen : LongInt; Var RR : TRRData) : Boolean;

Var
  I : Integer;
  HaveName : Boolean;
  PA : ^TRRData;
  RClass,RType : Word;
  
begin
  Result:=False;
  I:=Start;
  // Skip labels and pointers. At least 1 label or pointer is present.
  Repeat
    HaveName:=True;
    If (Payload[i]>#63) then // Pointer, skip
      Inc(I,2)
    else If Payload[i]=#0 then // Null termination of label, skip.
      Inc(i)
    else  
      begin
      Inc(I,Ord(Payload[i])+1); // Label, continue scan.
      HaveName:=False;
      end;
  Until HaveName or (I>(AnsLen-SizeOf(TRRData)));
  Result:=(I<=(AnsLen-SizeOf(TRRData)));
  // Check RR record.
  PA:=@Payload[i];
  RR:=PA^;
  Start:=I+SizeOf(TRRData);
end;


Function BuildName (Const PayLoad : TPayLoad; Start,len : Integer) : String;

Const
  FIREDNS_POINTER_VALUE = $C000;
  
Var
  I,O : Integer;
  P : Word;
  
begin
  SetLength(Result,512);
  I:=Start;
  O:=1;
  // Copy labels and pointers. At least 1 label or pointer is present.
  Repeat
    If (Payload[i]>#63) then // Pointer, move.
      begin
      Move(Payload[i],P,2);
      I:=ntohs(p)-FIREDNS_POINTER_VALUE-12;
      end
    else if Payload[i]<>#0 then // Label, copy
      begin
      If O<>1 then
        begin
        Result[O]:='.';
        Inc(O);
        end;
      P:=Ord(Payload[i]);  
      Move(Payload[i+1],Result[o],P);
      Inc(I,P+1);
      Inc(O,P);
      end;
   Until (Payload[I]=#0);    
end;


{ ---------------------------------------------------------------------
    QueryData handling functions
  ---------------------------------------------------------------------}
  
Function CheckAnswer(Const Qry : TQueryData; Var Ans : TQueryData) : Boolean;

begin
  Result:=False;
  With Ans do
    begin
    // Check ID.
    If (ID[1]<>QRY.ID[1]) or (ID[0]<>Qry.ID[0]) then
      exit;  
    // Flags ?
    If (Flags1 and QF_QR)=0 then
      exit;
    if (Flags1 and QF_OPCODE)<>0 then 
      exit;  
    if (Flags2 and QF_RCODE)<>0 then
      exit;  
    // Number of answers ?  
    htons(Ancount);
    If Ancount<1 then
      Exit;
    Result:=True;
    end;
end;

Function SkipAnsQueries(Var Ans : TQueryData; L : Integer) : integer;

Var
  Q,I : Integer;

begin
  Result:=0;
  With Ans do
    begin
    htons(qdcount);
    i:=0;
    q:=0;
    While (Q<qdcount) and (i<l) do  
      begin
      If Ord(Payload[i])>63 then
        begin
        Inc(I,6);
        Inc(Q);
        end
      else
        begin
        If Payload[i]=#0 then
          begin
          inc(q);
          Inc(I,5);
          end
        else
          Inc(I,Ord(Payload[i])+1);  
        end;  
      end;
    Result:=I;  
    end;  
end;

{ ---------------------------------------------------------------------
    DNS Query functions.
  ---------------------------------------------------------------------}
  

Function Query(Resolver : Integer; Var Qry,Ans : TQueryData; QryLen : Integer; Var AnsLen : Integer) : Boolean;

Var
  BA,SA : TInetSockAddr;
  Sock,L,I : Longint;
  Al,RTO : Longint;
  ReadFDS : FDSet;
  
begin
  Result:=False;
  With Qry do
    begin
    ID[0]:=Random(256);
    ID[1]:=Random(256);
    Flags1:=QF_RD;
    Flags2:=0;
    qdcount:=1 shl 8;
    ancount:=0;
    nscount:=0;
    arcount:=0;
    end;
  Sock:=Socket(PF_INET,SOCK_DGRAM,0);
  If Sock=-1 then 
    exit;
  With SA do
    begin
    family:=AF_INET;
    port:=DNSport;
    htons(port);
    addr:=cardinal(HostToNet(DNSServers[Resolver]));
    end;
  sendto(sock,qry,qrylen+12,0,SA,SizeOf(SA));
  // Wait for answer.
  RTO:=TimeOutS*1000+TimeOutMS;
  FD_ZERO(ReadFDS);
  FD_Set(Sock,readfds);
  if Select(Sock+1,@readfds,Nil,Nil,RTO)<=0 then
    begin
    fdclose(Sock);
    exit;
    end;
  AL:=SizeOf(SA);
  L:=recvfrom(Sock,ans,SizeOf(Ans),0,SA,AL);
  fdclose(Sock);
  // Check lenght answer and fields in header data.
  If (L<12) or not CheckAnswer(Qry,Ans) Then
    exit;
  // Return Payload length.  
  Anslen:=L-12;  
  Result:=True;  
end;

Function ResolveNameAt(Resolver : Integer; HostName : String; Var Addresses : Array of THostAddr) : Integer;

Var
  Qry, Ans            : TQueryData;
  MaxAnswer,I,QryLen,
  AnsLen,AnsStart     : Longint;
  RR                  : TRRData;
  
begin
  Result:=0;
  QryLen:=BuildPayLoad(Qry,HostName,DNSQRY_A,1);
  If Not Query(Resolver,Qry,Ans,QryLen,AnsLen) then
    Result:=-1
  else  
    begin
    AnsStart:=SkipAnsQueries(Ans,AnsLen);
    MaxAnswer:=Ans.AnCount-1;
    If MaxAnswer>High(Addresses) then
      MaxAnswer:=High(Addresses);
    I:=0;
    While (I<=MaxAnswer) and NextRR(Ans.Payload,AnsStart,AnsLen,RR) do
      begin
      if (Ntohs(RR.AType)=DNSQRY_A) and (1=NtoHS(RR.AClass)) then
        begin
        Move(Ans.PayLoad[AnsStart],Addresses[i],SizeOf(THostAddr));
        inc(Result);
        Inc(AnsStart,RR.RDLength);
        end;
      Inc(I);
      end;  
    end;
end;

Function ResolveName(HostName : String; Var Addresses : Array of THostAddr) : Integer;

Var
  I : Integer;

begin
  CheckResolveFile;
  I:=1;
  Result:=0;
  While (Result=0) and (I<=DNSServerCount) do
    begin
    Result:=ResolveNameAt(I,HostName,Addresses);
    Inc(I);
    end;
end;

Function ResolveAddressAt(Resolver : Integer; Address : String; Var Names : Array of String) : Integer;


Var
  Qry, Ans            : TQueryData;
  MaxAnswer,I,QryLen,
  AnsLen,AnsStart     : Longint;
  RR                  : TRRData;
  S                   : String;
begin
  Result:=0;
  QryLen:=BuildPayLoad(Qry,Address,DNSQRY_PTR,1);
  If Not Query(Resolver,Qry,Ans,QryLen,AnsLen) then
    Result:=-1
  else  
    begin
    AnsStart:=SkipAnsQueries(Ans,AnsLen);
    MaxAnswer:=Ans.AnCount-1;
    If MaxAnswer>High(Names) then
      MaxAnswer:=High(Names);
    I:=0;
    While (I<=MaxAnswer) and NextRR(Ans.Payload,AnsStart,AnsLen,RR) do
      begin
      if (Ntohs(RR.AType)=DNSQRY_PTR) and (1=NtoHS(RR.AClass)) then
        begin
        Names[i]:=BuildName(Ans.Payload,AnsStart,AnsLen);
        inc(Result);
        Inc(AnsStart,RR.RDLength);
        end;
      Inc(I);
      end;  
    end;
end;


Function ResolveAddress(HostAddr : THostAddr; Var Addresses : Array of String) : Integer;

Var
  I : Integer;
  S : String;
  
begin
  CheckResolveFile;
  I:=1;
  Result:=0;
  S:=Format('%d.%d.%d.%d.in-addr.arpa',[HostAddr[4],HostAddr[3],HostAddr[2],HostAddr[1]]);
  While (Result=0) and (I<=DNSServerCount) do
    begin
    Result:=ResolveAddressAt(I,S,Addresses);
    Inc(I);
    end;
end;

Function ResolveHostByName(HostName : String; Var H : THostEntry) : Boolean;

Var
  Address : Array[1..MaxResolveAddr] of THostAddr;
  L : Integer;
  
begin
  L:=ResolveName(HostName,Address);
  Result:=(L>0);
  If Result then
    begin
    // We could add a reverse call here to get the real name and aliases.
    H.Name:=HostName;
    H.Addr:=Address[1];
    H.aliases:='';
    end;
end;

Function ResolveHostByAddr(HostAddr : THostAddr; Var H : THostEntry) : Boolean;

Var
  Names : Array[1..MaxResolveAddr] of String;
  I,L : Integer;
  
begin
  L:=ResolveAddress(HostAddr,Names);
  Result:=(L>0);
  If Result then
    begin
    H.Name:=Names[1];
    H.Addr:=HostAddr;
    H.Aliases:='';
    If (L>1) then
      For I:=2 to L do
        If (I=2) then
          H.Aliases:=Names[i]
        else  
          H.Aliases:=H.Aliases+','+Names[i];
    end;
end;

{ ---------------------------------------------------------------------
    Some Parsing routines
  ---------------------------------------------------------------------}

Const 
  Whitespace = [' ',#9];

Function NextWord(Var Line : String) : String;

Var 
  I,J : Integer;

begin
  I:=1;
  While (I<=Length(Line)) and (Line[i] in Whitespace) do
    inc(I);
  J:=I;
  While (J<=Length(Line)) and Not (Line[J] in WhiteSpace) do
    inc(j);
  Result:=Copy(Line,I,J-1);  
  Delete(Line,1,J);  
end;
  
Procedure StripComment(Var line : String);

Var
  P : Integer;

begin
  P:=Pos('#',Line);
  If (P<>0) then
    Line:=Trim(Copy(Line,1,P-1));
end;

Function MatchNameOrAlias(Const Entry,Name: String; Aliases : String) : Boolean;

Var
  P : Integer;
  A : String;

begin
  Result:=CompareText(Entry,Name)=0;
  If Not Result then
    While (Not Result) and (Length(Aliases)>0) do
      begin
      P:=Pos(',',Aliases);
      If (P=0) then
        P:=Length(Aliases)+1;
      A:=Copy(Aliases,1,P-1);
      Delete(Aliases,1,P);
      Result:=CompareText(A,Entry)=0;
      end;
end;

{ ---------------------------------------------------------------------
    /etc/hosts handling.
  ---------------------------------------------------------------------}

Function GetNextHostEntry(var F : Text; Var H : THostEntry): boolean;

Var
  Line,S : String;
  P : Integer;
  
begin
  Result:=False;
  Repeat
    ReadLn(F,Line);
    StripComment(Line);
    S:=NextWord(Line);
    If (S<>'') then
      begin
      H.Addr:=StrToHostAddr(S);
      if (H.Addr[1]<>0) then
        begin
        S:=NextWord(Line);
        If (S<>'') then
          begin
          H.Name:=S;
          Result:=True;
          H.Aliases:='';
          Repeat
            S:=NextWord(line);
            If (S<>'') then
              If (H.Aliases='') then
                H.Aliases:=S
              else
                H.Aliases:=H.Aliases+','+S;  
          until (S='');
          end;
        end;      
      end;
  until Result or EOF(F);
end;  

Function FindHostEntryInHostsFile(N: String; Addr: THostAddr; Var H : THostEntry) : boolean;

Var
  F : Text;
  HE : THostEntry;
  
begin
  Result:=False;
  If FileExists(SHostsFile) then
    begin
    Assign(F,SHostsFile);
    {$i-}
    Reset(F);
    {$i+}
    If (IOResult=0) then
      begin
      While Not Result and GetNextHostEntry(F,HE) do
        begin
        If (N<>'') then
          Result:=MatchNameOrAlias(N,HE.Name,HE.Aliases)
        else
          Result:=Cardinal(Addr)=Cardinal(HE.Addr);
        end; 
      Close(f);
      If Result then
        begin
        H.Name:=HE.Name;
        H.Addr:=HE.Addr;
        H.Aliases:=HE.Aliases;
        end;
      end;  
    end;
end;

Function GetHostByName(HostName: String;  Var H : THostEntry) : boolean;

begin
  Result:=FindHostEntryInHostsFile(HostName,NoAddress,H);
end;


Function GetHostByAddr(Addr: THostAddr;  Var H : THostEntry) : boolean;

begin
  Result:=FindHostEntryInHostsFile('',Addr,H);
end;

{ ---------------------------------------------------------------------
    /etc/networks handling
  ---------------------------------------------------------------------}

Function GetNextNetworkEntry(var F : Text; Var N : TNetworkEntry): boolean;

Var
  NN,Line,S : String;
  P : Integer;
  A : TNetAddr;
  
begin
  Result:=False;
  Repeat
    ReadLn(F,Line);
    StripComment(Line);
    S:=NextWord(Line);
    If (S<>'') then
      begin
      NN:=S;
      A:=StrToHostAddr(NextWord(Line));
      Result:=(NN<>'') and (A[1]<>0); // Valid addr.
      If result then
        begin
        N.Addr:=A;
        N.Name:=NN;
        N.Aliases:='';
        end;      
      end;
  until Result or EOF(F);
end;  

Function FindNetworkEntryInNetworksFile(Net: String; Addr: TNetAddr; Var N : TNetworkEntry) : boolean;

Var
  F : Text;
  NE : TNetworkEntry;
  
begin
  Result:=False;
  If FileExists(SNetworksFile) then
    begin
    Assign(F,SNetworksFile);
    {$i-}
    Reset(F);
    {$i+}
    If (IOResult=0) then
      begin
      While Not Result and GetNextNetworkEntry(F,NE) do
        begin
        If (Net<>'') then
          Result:=MatchNameOrAlias(Net,NE.Name,NE.Aliases)
        else
          Result:=Cardinal(Addr)=Cardinal(NE.Addr);
        end; 
      Close(f);
      If Result then
        begin
        N.Name:=NE.Name;
        N.Addr:=NE.Addr;
        N.Aliases:=NE.Aliases;
        end;
      end;  
    end;
end;
  
Function GetNetworkByName(NetName: String; Var N : TNetworkEntry) : boolean;

begin
  Result:=FindNetworkEntryInNetworksFile(NetName,NoNet,N);
end;

Function GetNetworkByAddr(Addr: THostAddr; Var N : TNetworkEntry) : boolean;

begin
  Result:=FindNetworkEntryInNetworksFile('',Addr,N);
end;

{ ---------------------------------------------------------------------
    /etc/services section
  ---------------------------------------------------------------------}

Function GetNextServiceEntry(Var F : Text; Var E : TServiceEntry) : Boolean;


Var
  Line,S : String;
  P : INteger;
  
begin
  Result:=False;
  Repeat
    ReadLn(F,Line);
    StripComment(Line);
    S:=NextWord(Line);
    If (S<>'') then
      begin
      E.Name:=S;
      S:=NextWord(Line);
      P:=Pos('/',S);
      If (P<>0) then
        begin
        E.Port:=StrToIntDef(Copy(S,1,P-1),0);
        If (E.Port<>0) then
          begin
          E.Protocol:=Copy(S,P+1,Length(S)-P);
          Result:=length(E.Protocol)>0;
          E.Aliases:='';
          Repeat
            S:=NextWord(Line);
            If (S<>'') then
              If (Length(E.Aliases)=0) then
                E.aliases:=S
              else  
                E.Aliases:=E.Aliases+','+S;
          until (S='');
          end;
        end;
      end;
  until Result or EOF(F);
end;


Function FindServiceEntryInFile(Const Name,Proto : String; Port : Integer; Var E : TServiceEntry) : Boolean;

Var
  F : Text;
  TE : TServiceEntry;
  
begin
  Result:=False;
  If FileExists(SServicesFile) then
    begin
    Assign(F,SServicesFile);
    {$i-}
    Reset(F);
    {$i+}
    If (IOResult=0) then
      begin
      While Not Result and GetNextServiceEntry(F,TE) do
        begin
        If (Port=-1) then
          Result:=MatchNameOrAlias(Name,TE.Name,TE.Aliases)
        else 
          Result:=(Port=TE.Port);
        If Result and (Proto<>'') then
          Result:=(Proto=TE.Protocol);
        end; 
      Close(f);
      If Result then
        begin
        E.Name:=TE.Name;
        E.Port:=TE.Port;
        E.Protocol:=TE.Protocol;
        E.Aliases:=TE.Aliases;
        end;
      end;  
    end;
end;

Function GetServiceByName(Const Name,Proto : String; Var E : TServiceEntry) : Boolean;

begin
  Result:=FindServiceEntryInFile(Name,Proto,-1,E);  
end;

Function GetServiceByPort(Port : Word;Const Proto : String; Var E : TServiceEntry) : Boolean;

begin
  Result:=FindServiceEntryInFile('',Proto,Port,E);  
end;

{ ---------------------------------------------------------------------
    Initialization section
  ---------------------------------------------------------------------}

Procedure InitResolver;

Var
  I : Integer;

begin
  TimeOutS :=5;
  TimeOutMS:=0;
  CheckResolveFileAge:=False;
  If FileExists(SResolveFile) then
    GetDNsservers(SResolveFile);
end;

begin
  InitResolver;
end.