W3C Sample Code Library libwww HTNet Class

# The Net Class

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

The Net class manages information related to a "thread" in libwww. As libwww threads are not really threads but a notion of using interleaved, non-blocking I/O for accessing data objects from the network (or local file system), they can be used on any platform with or without support for native threads. In the case where you have an application using real threads the Net class is simply a object maintaining links to all other objects involved in serving the request. If you are using the libwww pseudo threads then the Net object contains enough information to stop and start a request based on which BSD sockets are ready. In practise this is of course transparent to the application - this is just to explain the difference.

When a Request object is passed to the Library , the core creates a new HTNet object per channel used by the request. In many cases a request only uses a single channel object but, for example, FTP requests use at least two - one for the control connection and one for the data connection.

You can find more information about the libwww pseudo thread model in the Multithread Specifications.

This module is implemented by HTNet.c, and it is a part of the W3C Sample Code Library.

    #ifndef HTNET_H
    #define HTNET_H

The `HTNet` object is the core of the request queue management. This object contains information about the socket descriptor, the input read buffer etc. required to identify and service a request.

    typedef struct _HTNet HTNet;

    #include "HTEvent.h"
    #include "HTReq.h"
    #include "HTResponse.h"
    #include "HTTrans.h"
    #include "HTHost.h"
    #include "HTProt.h"
    #include "HTChannl.h"
    #include "HTDNS.h"

## Generic BEFORE and AFTER Filter Management

Filter functions can be registered to be called before and after a request has either been started or has terminated. The conditions for BEFORE and AFTER filters are not the same, and so we maintain them independently. Filters can be registered globally or locally. The global filters are registered directly by the Net Object (this module) and the local filters are registered by the HTRequest Object. However, both local and global filters use the same regisration mechanism which we provide here.

### Filter Ordering

Filters can be registered by anyone and as they are an often used mechanism for introducing extensions in libwww, they are videly used to handle authentication, redirection, etc. Many filters can be registered at once and not all of the filters may know about the other filters. Therefore, it is difficult to specify an absolute ordering by which the filters should be called. Instead you can decide a relative order by which the filters should be called. The order works pretty much like the Unix priority mechanism running from `HT_FILTER_FIRST` to `HT_FILTER_LAST` having `HT_FILTER_MIDDLE` being the "normal" case.

    typedef enum _HTFilterOrder {
        HT_FILTER_FIRST	= 0x0,		/*     0 */
        HT_FILTER_EARLY	= 0x3FFF,	/* 16383 */
        HT_FILTER_MIDDLE	= 0x7FFF,	/* 32767 */
        HT_FILTER_LATE	= 0xBFFE,	/* 49150 */
        HT_FILTER_LAST	= 0xFFFF	/* 65535 */
    } HTFilterOrder;

In case multiple filters are registered with the same order then they are called in the inverse order they were registered.

### Filter URL Templates

Both BEFORE and AFTER filters can be registered with a URL template in which case they are only called when the Request URL matches the template. A template is simply a string which is matched against the Request URL. The string can be terminated by a single "`*`" in which case all strings matching the template up til the "*" is considered a match. A template can be as short as the access scheme which enmables a filter for a specific access method only, for example "`http//<star>`".

### BEFORE Filters

A BEFORE filter is called whenever we issue a request and they have been selected by the execution procedure. BEFORE filters are registered with a context and a filter order by which they are to be called and a URL template which may be NULL. In this case, the filter is called on every request. The mode can be used by anybody to pass an extra parameter to a filter. This is not really OO thinking - but hey - this is C ;-)

    typedef int HTNetBefore (HTRequest * request, void * param, int mode);

You can add a BEFORE filter in the list provided by the caller. Several filters can be registered in which case they are called with the filter ordering in mind.

    extern BOOL HTNetCall_addBefore (HTList * list, HTNetBefore * before,
    				 const char * tmplate, void * param,
                                     HTFilterOrder order);

You can also unregister all instances of a BEFORE filter from a list using the following function

    extern BOOL HTNetCall_deleteBefore (HTList * list, HTNetBefore * before);

You get rid of all BEFORE filters using this function

    extern BOOL HTNetCall_deleteBeforeAll (HTList * list);

The BEFORE filters are expected and called if appropriate every time we issue a new request. Libwww calls the BEFORE filters in the order specified at registration time. If a filter returns other than HT_OK then stop and return immediately. Otherwise return what the last filter returns.

    extern int HTNetCall_executeBefore (HTList * list, HTRequest * request);

### AFTER Filters

An AFTER filter is called whenever we have terminated a request. That is, on the way out from the protocol module and back to the application. AFTER filters are registered with a context, a status, a filter order by which they are to be called and a URL template which may be NULL. The status of the request may determine which filter to call. The set of possible values are given below. An AFTER filter can be registered to handle one or more of the codes.

HT_ERROR
  An error occured
HT_LOADED
  The document was loaded
HT_NO_DATA
  OK, but no data
HT_NO_ACCESS
  The request could not be succeeded due to lack of credentials
HT_NO_PROXY_ACCESS
  The request could not be succeeded due to lack of credentials for accessing an intermediate proxy
HT_RETRY
  Retry request after at a later time
HT_PERM_REDIRECT
  The request has been permanently redirected and we send back the new URL
HT_TEMP_REDIRECT
  The request has been temporarily redirected and we send back the new URL
HT_ALL
  All of above

A Protocol module can also, in certain cases, return a `HT_IGNORE` in which case no filters are called

    typedef int HTNetAfter (HTRequest * request, HTResponse * response,
                            void * param, int status);

You can register a AFTER filter in the list provided by the caller. Several filters can be registered in which case they are called with the filter ordering in mind.

    extern BOOL HTNetCall_addAfter (HTList * list, HTNetAfter * after,
    				const char * tmplate, void * param,
    				int status, HTFilterOrder order);

You can either unregister all filters registered for a given status using this function or the filter for all status codes.

    extern BOOL HTNetCall_deleteAfter (HTList * list, HTNetAfter * after);
    extern BOOL HTNetCall_deleteAfterStatus (HTList * list, int status);

You can also delete all AFTER filters in list

    extern BOOL HTNetCall_deleteAfterAll (HTList * list);

This function calls all the AFTER filters in the order specified at registration time and if it has the right status code and it's not `HT_IGNORE`. We also check for any template and whether it matches or not. If a filter returns other than HT_OK then stop and return immediately. Otherwise return what the last filter returns.

    extern int HTNetCall_executeAfter (HTList * list, HTRequest * request,
    				   int status);

## Global BEFORE and AFTER Filter Management

Global filters are inspected on every request (they do not have to be called - only if the conditions match). You can also register filters locally in the Request object.

#### Global BEFORE Filters

These are the methods to handle global BEFORE Filters.

    extern BOOL HTNet_setBefore (HTList * list);

    extern HTList * HTNet_before (void);

    extern BOOL HTNet_addBefore (HTNetBefore * before, const char * tmplate,
    			     void * param, HTFilterOrder order);

    extern BOOL HTNet_deleteBefore (HTNetBefore * before);

You can call both the local and the global BEFORE filters (if any)

    extern int HTNet_executeBeforeAll (HTRequest * request);

#### Global AFTER Filters

These are the methods to handle global AFTER Filters.

    extern BOOL HTNet_setAfter (HTList * list);

    extern HTList * HTNet_after (void);

    extern BOOL HTNet_addAfter (HTNetAfter * after, const char * tmplate,
    			    void * param, int status,
                                HTFilterOrder order);

    extern BOOL HTNet_deleteAfter (HTNetAfter * after);

    extern BOOL HTNet_deleteAfterStatus (int status);

You can call both the local and the global AFTER filters (if any)

    extern int HTNet_executeAfterAll (HTRequest * request, int status);

## Socket Resource Management

The request queue ensures that no more than a fixed number of TCP connections are open at the same time. If more requests are handed to the Library, they are put into the pending queue and initiated when sockets become free.

### Number of Simultanous open TCP connections

Set the max number of simultanous sockets. The default value is HT_MAX_SOCKETS which is 6. The number of persistent connections depend on this value as a deadlock can occur if all available sockets a persistent (see the DNS Manager for more information on setting the number of persistent connections). The number of persistent connections can never be more than the max number of sockets-2, so letting newmax=2 prevents persistent sockets.

    extern BOOL HTNet_setMaxSocket (int newmax);
    extern int  HTNet_maxSocket (void);

### Socket Counters

    extern void HTNet_increaseSocket (void);
    extern void HTNet_decreaseSocket (void);

    extern int HTNet_availableSockets (void);

### Persistent Socket Counters

    extern void HTNet_increasePersistentSocket (void);
    extern void HTNet_decreasePersistentSocket (void);

    extern int HTNet_availablePersistentSockets (void);

### Any Ongoing Connections?

Returns whether there are active requests. Idle persistent sockets do not count as active.

    extern BOOL HTNet_isIdle (void);

### List Active Queue

Returns the list of active requests that are currently having an open connection. Returns list of HTNet objects or NULL if error.

    extern HTList *HTNet_activeQueue (void);
    extern BOOL HTNet_idle (void);

### Are we Active?

We have some small functions that tell whether there are registered requests in the Net manager. There are tree queues: The active, the pending, and the persistent. The active queue is the set of requests that are actively sending or receiving data. The pending is the requests that we have registered but which are waiting for a free socket. The Persistent queue are requets that are waiting to use the same socket in order to save network resoures (if the server understands persistent connections).

#### Active Requests?

Returns whether there are requests in the active queue or not

    extern BOOL HTNet_idle (void);

#### Registered Requests?

Returns whether there are requests registered in any of the lists or not

    extern BOOL HTNet_isEmpty (void);
    extern int HTNet_count (void);

### List Pending Queue

Returns the list of pending requests that are waiting to become active. Returns list of HTNet objects or NULL if error

    extern HTList *HTNet_pendingQueue (void);

## Creation and Deletion Methods

The Net object is intended to live as long as the request is still active. In that regard it is very similar to the Request Object . However, the main difference is that a Net object represents a "thread" in the Library and a request may have multiple "threads" - an example is a FTP request which has a thread to handle the control connection and one to handle the data connections.

### Create a new Object

If we have more than HTMaxActive connections already then put this into the pending queue, else start the request by calling the call back function registered with this access method. Returns YES if OK, else NO

    extern BOOL HTNet_newClient (HTRequest * request);

You can create a new HTNet object as a new request to be handled. If we have more than HTMaxActive connections already then return NO. Returns YES if OK, else NO

    extern BOOL HTNet_newServer (HTRequest * request);

And you can create a plain new HTNet object using the following method:

    extern HTNet * HTNet_new (HTHost * host);

### Duplicate an existing Object

Creates a new HTNet object as a duplicate of the same request. Returns YES if OK, else NO.

    extern HTNet * HTNet_dup (HTNet * src);
    extern BOOL HTNet_deleteDup (HTNet * dup);

### Launch a Net Object

Start a Net obejct by calling the protocol module.

    extern BOOL HTNet_start (HTNet * net);

### Call a Net Event Handler

This functions lets the caller play event manager as it can calls any event handler with the event type and context passed to the function

    extern BOOL HTNet_execute (HTNet * net, HTEventType type);

    extern HTEvent * HTNet_event (HTNet * net);
    extern BOOL HTNet_setEventParam (HTNet * net, void * eventParam);
    extern void * HTNet_eventParam (HTNet * net);
    extern BOOL HTNet_setEventCallback(HTNet * net, HTEventCallback * cbf);
    extern HTEventCallback * HTNet_eventCallback(HTNet * net);

### Delete an Object

Deletes the HTNet object from the list of active requests and calls any registered call back functions IF not the status is HT_IGNORE. This is used if we have internal requests that the app doesn't know about. We also see if we have pending requests that can be started up now when we have a socket free. The filters are called in the reverse order of which they were registered (last one first);

    extern BOOL HTNet_delete (HTNet * me, int status);

### Delete ALL HTNet Objects

Deletes all HTNet object that might either be active or pending We DO NOT call the call back functions - A crude way of saying goodbye!

    extern BOOL HTNet_deleteAll (void);

## Net Class Methods

### Make an Object Wait

Let a net object wait for a persistent socket. It will be launched from the HTNet_delete() function when the socket gets free.

    extern BOOL HTNet_wait (HTNet *net);

### Priority Management

Each HTNet object is created with a priority which it inherits from the Request manager. However, in some stuations it is useful to be to change the current priority after the request has been started. These two functions allow you to do this. The effect will show up the first time (which might be imidiately) the socket blocks and control returns to the event loop. Also have a look at how you can do this before the request is issued in the request manager.

    extern HTPriority HTNet_priority (HTNet * net);
    extern BOOL HTNet_setPriority (HTNet * net, HTPriority priority);

### Persistent Connections

You can set a Net object to handle persistent connections for example using HTTP, NNTP, or FTP. You can control whether a Net object supports persistent connections or not using this function.

    extern BOOL HTNet_persistent (HTNet * net);

You can set or disable a Net object supporting persistent connections using this function:

    extern BOOL HTNet_setPersistent (HTNet *           net,
                                     BOOL              persistent,
                                     HTTransportMode   mode);

### Kill one or more Requests

#### Kill this request and all requests in the Pipeline

When pipelining, it is not possible to kill a single request as we then loose track of where we are in the pipe. It is therefore necessary to kill the whole pipeline.

    extern BOOL HTNet_killPipe (HTNet * net);

#### Kill a single Request

This is not often used anymore, consider using the pipeline version above. Kill the request by calling the call back function with a request for closing the connection. Does not remove the object. This is done by HTNet_delete() function which is called by the load routine. Returns OK if success, NO on error.

    extern BOOL HTNet_kill (HTNet * me);

#### Kill ALL Requests

Kills all registered (active as well as pending) requests by calling the call back function with a request for closing the connection. We do not remove the HTNet object as it is done by HTNet_delete(). Returns OK if success, NO on error

    extern BOOL HTNet_killAll (void);

### Create Input and Output Streams

You create the input stream and bind it to the channel using the following methods. Please read the description in the HTIOStream module on the parameters target, param, and mode. Both methods return YES if OK, else NO.

    #if 0
    extern HTInputStream * HTNet_getInput (HTNet * net, HTStream * target,
    				       void * param, int mode);
    #endif
    extern HTOutputStream * HTNet_getOutput (HTNet * me, void * param, int mode);

### Net Context Descriptor

Just like the request object, a net object can be assigned a context which keeps track of context dependent information. The Library does not use this information nor does it depend on it but it allows the application to customize a net object to specific uses.

    extern BOOL HTNet_setContext (HTNet * net, void * context);
    extern void * HTNet_context (HTNet * net);

### Socket Descriptor

    extern BOOL HTNet_setSocket (HTNet * net, SOCKET sockfd);
    extern SOCKET HTNet_socket (HTNet * net);

### Preemptive or Non-preemptive Access

A access scheme is defined with a default for using either preemptive (blocking I/O) or non-premitve (non-blocking I/O). This is basically a result of the implementation of the protocol module itself. However, if non-blocking I/O is the default then some times it is nice to be able to set the mode to blocking instead. For example when loading the first document (the home page) then blocking can be used instead of non-blocking.

    extern BOOL HTNet_preemptive (HTNet * net);

### The Request Object

The Request object is normally set up automatically but can be changed at a later time.

    extern BOOL HTNet_setRequest (HTNet * net, HTRequest * request);
    extern HTRequest * HTNet_request (HTNet * net);

### The Protocol Object

    extern BOOL HTNet_setProtocol (HTNet * net, HTProtocol * protocol);
    extern HTProtocol * HTNet_protocol (HTNet * net);

### The Transport Object

The transport object is normally set up automatically but can be changed at a later time.

    extern BOOL HTNet_setTransport (HTNet * net, HTTransport * tp);
    extern HTTransport * HTNet_transport (HTNet * net);

### The Channel Object

    extern BOOL HTNet_setChannel (HTNet * net, HTChannel * channel);
    extern HTChannel * HTNet_channel (HTNet * net);

### The Host Object

    extern BOOL HTNet_setHost (HTNet * net, HTHost * host);
    extern HTHost * HTNet_host (HTNet * net);

### The DNS Object

The DNS object keeps track of the DNS entries that we have already checked out.

    extern BOOL HTNet_setDns (HTNet * net, HTdns * dns);
    extern HTdns * HTNet_dns (HTNet * net);

### Target for Input Read Stream

    extern HTStream * HTNet_readStream(HTNet * net);
    extern BOOL HTNet_setReadStream (HTNet * net, HTStream * stream);

### Should we count Raw bytes?

This functions can be used to determine whether bytes count should be managed at the low level read stream or at a higher level. If the data transfer equals the lifetime of a single document like for example in FTP or HTTP/1.0 then this may be a reasonable thing to do.

    extern BOOL HTNet_setRawBytesCount (HTNet * net, BOOL mode);
    extern BOOL HTNet_rawBytesCount (HTNet * net);

    #endif /* HTNET_H */