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Wed Nov 22 23:32:40 1995 UTC (28 years, 6 months ago) by frystyk
Branches: MAIN
CVS tags: v4/0D, v4/0C, v4/0B, v4/0, autoconf, HEAD
Integration of server START

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<TITLE>Domain Name Service Manager</TITLE>
<!-- Changed by: Henrik Frystyk Nielsen, 15-Nov-1995 -->
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<H1>Domain Name Service Manager</H1>

<PRE>
/*
**	(c) COPYRIGHT MIT 1995.
**	Please first read the full copyright statement in the file COPYRIGH.
*/
</PRE>

This module has the common code for handling DNS access. It maintains
a cache of all visited hosts so that subsequent connects to the same
host doesn't imply a new request to the DNS every time. <P>

Multihomed hosts are treated specially in that the time spend on every
connect is measured and kept in the cache. On the next request to the
same host, the IP-address with the lowest average connect time is
chosen. If one IP-address fails completely, e.g. <EM>connection
refused</EM> then it disabled and HTDoConnect tries one of the other
IP-addresses to the same host.<P>

If the connect fails in the case of at single-homed host then the
entry is removed from the cache and HTDoConnect tries again asking the
DNS. <P>

This module is implemented by <A HREF="HTDNS.c">HTDNS.c</A>, and it is
a part of the <A HREF="http://www.w3.org/pub/WWW/Library/"> W3C
Reference Library</A>.

<PRE>
#ifndef HTDNS_H
#define HTDNS_H
#include "tcp.h"
#include "HTEvntrg.h"
</PRE>

<H2>The DNS Object</H2>

The DNS object contains information obtained from the DNS system but
in addition it stores known information about the remote server, for
example the type (HTTP/1.0, HTTP/1.1, FT etc.) along with information
on how the connections can be used (if it supports persistent TCP
connections, interleaved access etc.)

<PRE>
typedef struct _HTdns HTdns;
</PRE>

<H2>Cache Timeouts</H2>

When to remove an entry in the cache. The default value is 48h.

<PRE>
extern void HTDNS_setTimeout (time_t timeout);
extern time_t HTDNS_timeout  (time_t timeout);
</PRE>

<H2>Object Methods</H2>

<H3>Persistent Sockets</H3>

<PRE>
extern SOCKET HTDNS_socket	(HTdns *dns);
extern BOOL   HTDNS_setSocket	(HTdns *dns, SOCKET socket);
extern void   HTDNS_clearActive	(HTdns *dns);
extern int    HTDNS_socketCount (void);
</PRE>

<H3>Persistent Connection Timeouts</H3>

When should we drop a socket. The default value is 1h

<PRE>
extern time_t HTDNS_sockTimeout (time_t timeout);
extern void HTDNS_setSockTimeout (time_t timeout);
</PRE>

<H3>Persistent Connection Expiration</H3>

Absolute value of when this socket will expire. Default value can be
set with the function HTDNS_setSockTimeout and is normally 1 h.

<PRE>
extern HTEventCallback HTDNS_closeSocket;

extern void HTDNS_setSockExpires (HTdns * dns, time_t expires);
extern time_t HTDNS_sockExpires (HTdns * dns);
</PRE>

<H3>Set the Server Class and Type</H3>

Define the <EM>server class</EM> of the server at the other end. A
class is a generic description of the protocol which is exactly like
the access method in a URL, for example "http" etc. The <EM>server
version</EM> is a finer distinction (sub-class) between various
versions of the server class, for example HTTP/0.9, HTTP/1.1 etc. The
server version is a bit flag that the protocol module can define on
its own. That way we don't have to change this module when registering
a new protocol module. The <EM>server type</EM> is a description of
whether we can keep the connection persistent or not.

<PRE>
extern char * HTDNS_serverClass		(HTdns * dns);
extern void HTDNS_setServerClass	(HTdns * dns, char * s_class);

extern int  HTDNS_serverVersion		(HTdns * dns);
extern void HTDNS_setServerVersion	(HTdns * dns, int version);

typedef enum _HTTCPType {
    HT_TCP_PLAIN	= 0x0,			    /* One request at a time */
    HT_TCP_BATCH	= 0x1,			       /* Use batch requests */
    HT_TCP_INTERLEAVE	= 0x2	  	      /* Can we interleave requests? */
} HTTCPType;

extern HTTCPType HTDNS_connection	(HTdns * dns);
extern void HTDNS_setConnection		(HTdns * dns, HTTCPType type);
</PRE>

<H3>Recalculating the Time-Weights on Multihomed Hosts</H3>

On every connect to a multihomed host, the average connect time is updated
exponentially for all the entries.

<PRE>
extern BOOL HTDNS_updateWeigths (HTdns *dns, int cur, time_t deltatime);
</PRE>

<H3>Delete a host element from Cache</H3>

This function deletes a single cache entry.

<PRE>
extern BOOL HTDNS_delete (CONST char * host);
</PRE>

<H3>Delete ALL host elements from Cache</H3>

This function is called from <A HREF="HTAccess.html#Library">
HTLibTerminate</A>. It can be called at any point in time if the DNS
cache is going to be flushed.

<PRE>
extern BOOL HTDNS_deleteAll (void);
</PRE>

<H2>Resolver Functions</H2>

These are the functions that resolve a host name 

<H3>Get Host By Socket</H3>

This function should have been called HTGetHostByAddr but for
historical reasons this is not the case. <P>

<PRE>
extern char * HTGetHostBySock (int soc);
</PRE>

<H3>Get Host By Name</H3>

This function gets the address of the host and puts it in to the
socket structure. It maintains its own cache of connections so that
the communication to the Domain Name Server is minimized. Returns the
number of homes or -1 if error.

<PRE>
extern int HTGetHostByName (struct _HTNet *net, char *host);
</PRE>

<PRE>
#endif
</PRE>

End of declaration file
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