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<LI>DWORD dwContext  The context identifier for the operation. For synchronous
sessions, this is not an important parameter.
<P>
<LI>DWORD dwAccessType  The access type: INTERNET_OPEN_TYPE_PRECONFIG (default),
INTERNET_OPEN_TYPE_DIRECT, or INTERNET_OPEN_TYPE_PROXY.
<P>
<LI>LPCTSTR pstrProxyName  The name of your proxy, if access is INTERNET_OPEN_TYPE_PROXY.
<P>
<LI>LPCTSTR pstrProxyBypass  A list of addresses to be connected directly
rather than through the proxy server, if access is INTERNET_OPEN_TYPE_PROXY.
<P>
<LI>DWORD dwFlags  Options that can be OR'ed together. The available options
are INTERNET_FLAG_DONT_CACHE, INTERNET_FLAG_ASYNC, and INTERNET_FLAG_OFFLINE.
</UL>
<P>dwAccessType<B> </B>defaults to using the value in the Registry. Obviously, an
application that insists on direct Internet access or proxy Internet access is less
useful than one that enables users to configure that information. Making users set
their Internet access type outside this program might be confusing, though. To set
your default Internet access, double-click the My Computer icon on your desktop,
then on the Control Panel, and then on the Internet tool in the Control Panel. Choose
the Connection tab (the version for Internet Explorer under Windows 95 is shown in
Figure 19.7) and complete the dialog box as appropriate for your setup. If you are
using NT or Windows 98, or if your browser version is different, you might see a
slightly different dialog, but you should still be able to choose your connection
type.</P>
<P><A HREF="javascript:popUp('19uvc07.gif')"><B>FIG. 19.7</B></A><B> </B><I>Set your
Internet connection settings once, and all applications can retrieve them from the
Registry.</I></P>
<P>
<UL>
<LI>If you dial up to the Internet, select the Dial check box and fill in the parameters
in the top half of the page.
<P>
<LI>If you connect to the Internet through a proxy server, select the Proxy check
box and click the Settings button to identify your proxy addresses and ports.
<P>
<LI>If you are connected directly to the Internet, leave both check boxes unselected.
</UL>
<P>If you want to set up an <I>asynchronous</I> (nonblocking) session, for the reasons
discussed in the "Using Windows Sockets" section of Chapter 18, your options
in dwFlags must include INTERNET_FLAG_ASYNC. In addition, you must call the member
function EnableStatusCallback() to set up the callback function. When a request is
made through the session--such as the call to OpenURL() that occurs later in TryURL()--and
the response will not be immediate, a nonblocking session returns a pseudo error
code, ERROR_IO_PENDING. When the response is ready, these sessions automatically
invoke the callback function.</P>
<P>For this simple application, there is no need to allow the user to do other work
or interact with the user interface while waiting for the session to respond, so
the session is constructed as a blocking session and all the other default parameters
are also used:</P>
<P>
<PRE> CInternetSession session;
</PRE>
<P>Having constructed the session, TryURL() goes on to add a line to m_out that echoes
the URL passed in as a parameter. The "\r\n" characters are <I>return</I>
and <I>newline</I>, and they separate the lines added to m_out. UpdateData(FALSE)
gets that onscreen:</P>
<P>
<PRE> m_out += "Trying " + URL + "\r\n";
UpdateData(FALSE);
</PRE>
<P>Next is a call to the session's OpenURL() member function. This function returns
a pointer to one of several file types because the URL might have been to one of
four protocols:</P>
<UL>
<LI>file:// opens a file. The function constructs a CStdioFile and returns a pointer
to it.
<P>
<LI>ftp:// goes to an FTP site and returns a pointer to a CInternetFile object.
<P>
<LI>gopher:// goes to a Gopher site and returns a pointer to a CGopherFile object.
<P>
<LI>http:// goes to a World Wide Web site and returns a pointer to a CHttpFile object.
</UL>
<P>Because CGopherFile and CHttpFile both inherit from CInternetFile and because
you can be sure that TryURL() will not be passed a file:// URL, it is safe to cast
the returned pointer to a CInternetFile.</P>
<BLOCKQUOTE>
<P>
<HR>
<strong>TIP:</strong> There is some confusion in Microsoft's online documentation whenever
sample URLs are shown. A backslash (\) character will never appear in an URL. In
any Microsoft example that includes backslashes, use forward slashes (/) instead.
<HR>
</BLOCKQUOTE>
<P>If the URL would not open, file will be NULL, or OpenURL()_ will throw an exception.
(For background on exceptions, see Chapter 26, "Exceptions and Templates.")
Whereas in a normal application it would be a serious error if an URL didn't open,
in this application you are making up URLs to see whether they work, and it's expected
that some won't. As a result, you should catch these exceptions yourself and do just
enough to prevent runtime errors. In this case, it's enough to make sure that file
is NULL when an exception is thrown. To delete the exception and prevent memory leaks,
call CException::Delete(), which safely deletes the exception. The block of code
containing the call to OpenURL() is in Listing 19.3.</P>
<P>
<H4>Listing 19.3  QueryDlg.cpp--CQueryDlg::TryURL()</H4>
<PRE> CInternetFile* file = NULL;
try
{
//We know for sure this is an Internet file,
//so the cast is safe
file = (CInternetFile*) session.OpenURL(URL);
}
catch (CInternetException* pEx)
{
//if anything went wrong, just set file to NULL
file = NULL;
pEx->Delete();
</PRE>
<PRE> }
</PRE>
<P>If file is not NULL, this routine will display some of the Web page that was found.
It first echoes another line to m_out. Then, in a for loop, the routine calls CInternetFile::ReadString()
to fill the CString line with the characters in file up to the first \r\n, which
are stripped off. This code simply tacks line (and another \r\n) onto m_out. If you
would like to see more or less than the first 20 lines of the page, adjust the number
in this for loop. When the first few lines have been read, TryURL() closes and deletes
the file. That block of code is shown in Listing 19.4.</P>
<P>
<H4>Listing 19.4  QueryDlg.cpp--CQueryDlg::TryURL()</H4>
<PRE> if (file)
{
m_out += "Connection established. \r\n";
CString line;
for (int i=0; i < 20 && file->ReadString(line); i++)
{
m_out += line + "\r\n";
}
file->Close();
delete file;
</PRE>
<PRE> }
</PRE>
<P>If the file could not be opened, a message to that effect is added to m_out:</P>
<P>
<PRE> else
{
m_out += "No server found there. \r\n";
}
</PRE>
<P>Then, whether the file existed or not, a line of dashes is tacked on m_out to
indicate the end of this attempt, and one last call to UpdateData(FALSE) puts the
new m_out onscreen:</P>
<P>
<PRE> m_out += "------------------------\r\n";
UpdateData(FALSE);
}
</PRE>
<P>You can now build and run this application. If you enter <B>microsoft.com</B>
in the text box and click Query, you'll discover that there are Web pages at both
<B>http://microsoft.com</B> and <B>http://www.microsoft.com</B>. Figure 19.8 shows
the results of that query.</P>
<P><A HREF="javascript:popUp('19uvc08.gif')"><B>FIG. 19.8</B></A><B> </B><I>Query
can find Microsoft's Web sites.</I></P>
<P>If Query doesn't find Web pages at either the domain name you provided or <B>www.</B>
plus the domain name, it doesn't mean that the domain doesn't exist or even that
the organization that owns the domain name doesn't have a Web page. It does make
it less likely, however, that the organization both exists and has a Web page. If
you see a stream of HTML, you know for certain that the organization exists and has
a Web page. You might be able to read the HTML yourself, but even if you can't, you
can now connect to the site with a Web browser such as Microsoft's Internet Explorer.</P>
<P>
<H2><A NAME="Heading4"></A>Querying FTP Sites</H2>
<P>As part of a site name investigation, you should check whether there is an FTP
site, too. Most FTP sites have names like <B>ftp.company.com</B>, though some older
sites don't have names of that form. Checking for these sites isn't as simple as
just calling TryURL() again because TryURL() assumes that the URL leads to a file,
and URLs like <B>ftp.greatidea.org</B> lead to a list of files that cannot simply
be opened and read. Rather than make TryURL() even more complicated, add a protected
function to the class called TryFTPSite(CString host). (Right-click CQueryDlg in
the ClassView and choose Add Member Function to add the function. It can return void.)</P>
<P>TryFTPSite() has to establish a connection within the session, and if the connection
is established, it has to get some information that can be added to m_out to show
the user that the connection has been made. Getting a list of files is reasonably
complex; because this is just an illustrative application, the simpler task of getting
the name of the default FTP directory is the way to go. The code is in Listing 19.5.</P>
<P>
<H4>Listing 19.5  QueryDlg.cpp--CQueryDlg::TryFTPSite()</H4>
<PRE>void CQueryDlg::TryFTPSite(CString host)
{
CInternetSession session;
m_out += "Trying FTP site " + host + "\r\n";
UpdateData(FALSE);
CFtpConnection* connection = NULL;
try
{
connection = session.GetFtpConnection(host);
}
catch (CInternetException* pEx)
{
//if anything went wrong, just set connection to NULL
connection = NULL;
pEx->Delete();
}
if (connection)
{
m_out += "Connection established. \r\n";
CString line;
connection->GetCurrentDirectory(line);
m_out += "default directory is " + line + "\r\n";
connection->Close();
delete connection;
}
else
{
m_out += "No server found there. \r\n";
}
m_out += "------------------------\r\n";
UpdateData(FALSE);
</PRE>
<PRE>}
</PRE>
<P>This code is very much like TryURL(), except that rather than open a file with
session.OpenURL(), it opens an FTP connection with session.GetFtpConnection(). Again,
exceptions are caught and essentially ignored, with the routine just making sure
that the connection pointer won't be used. The call to GetCurrentDirectory() returns
the directory on the remote site in which sessions start. The rest of the routine
is just like TryURL().</P>
<P>Add two lines at the end of OnQuery() to call this new function:</P>
<P>
<PRE> TryFTPSite(m_host);
TryFTPSite("ftp." + m_host);
</PRE>
<P>Build the application and try it: Figure 19.9 shows Query finding no FTP site
at <B>microsoft.com</B> and finding one at <B>ftp.microsoft.com</B>. The delay before
results start to appear might be a little disconcerting. You can correct this by
using asynchronous sockets, or <I>threading,</I> so that early results can be added
to the edit box while later results are still coming in over the wire. However, for
a simple demonstration application like this, just wait patiently until the results
appear. It might take several minutes, depending on network traffic between your
site and Microsoft's, your line speed, and so on.</P>
<P><A HREF="javascript:popUp('19uvc09.gif')"><B>FIG. 19.9</B></A><B> </B><I>Query
finds one Microsoft FTP site.</I></P>
<P>If Query doesn't find Web pages or FTP sites, perhaps this domain doesn't exist
at all or doesn't have any Internet services other than email, but there are a few
more investigative tricks available. The results of these investigations will definitely
add to your knowledge of existing sites.</P>
<P>
<H2><A NAME="Heading5"></A>Querying Gopher Sites</H2>
<P>As with FTP, TryURL() won't work when querying a Gopher site like <B>gopher.company.com</B>
because this returns a list of filenames instead of a single file. The solution is
to write a protected member function called TryGopherSite() that is almost identical
to TryFTPSite(), except that it opens a CGopherConnection. Also, rather than echo
a single line describing the default directory, it echoes a single line describing
the Gopher locator associated with the site. Add TryGopherSite to CQueryDlg by right-clicking
the classname in ClassView and choosing Add Member Function, as you did for TryFTPSite().
The code for TryGopherSite() is in Listing 19.6.</P>
<P>
<H4>Listing 19.6  QueryDlg.cpp--CQueryDlg::TryGopherSite()</H4>
<PRE>void CQueryDlg::TryGopherSite(CString host)
{
CInternetSession session;
m_out += "Trying Gopher site " + host + "\r\n";
UpdateData(FALSE);
CGopherConnection* connection = NULL;
try
{
connection = session.GetGopherConnection(host);
}
catch (CInternetException* pEx)
{
//if anything went wrong, just set connection to NULL
connection = NULL;
pEx->Delete();
}
if (connection)
{
m_out += "Connection established. \r\n";
CString line;
CGopherLocator locator = connection->CreateLocator(NULL, NULL,
GOPHER_TYPE_DIRECTORY);
line = locator;
m_out += "first locator is " + line + "\r\n";
connection->Close();
delete connection;
}
else
{
m_out += "No server found there. \r\n";
}
m_out += "------------------------\r\n";
UpdateData(FALSE);
</PRE>
<PRE>}
</PRE>
<P>The call to CreateLocator() takes three parameters. The first is the filename,
which might include wild cards. NULL means any file. The second parameter is a selector
that can be NULL. The third is one of the following types:</P>
<P>GOPHER_TYPE_TEXT_FILE</P>
<P>GOPHER_TYPE_DIRECTORY</P>
<P>GOPHER_TYPE_CSO</P>
<P>GOPHER_TYPE_ERROR</P>
<P>GOPHER_TYPE_MAC_BINHEX</P>
<P>GOPHER_TYPE_DOS_ARCHIVE</P>
<P>GOPHER_TYPE_UNIX_UUENCODED</P>
<P>GOPHER_TYPE_INDEX_SERVER</P>
<P>GOPHER_TYPE_TELNET</P>
<P>GOPHER_TYPE_BINARY</P>
<P>GOPHER_TYPE_REDUNDANT</P>
<P>GOPHER_TYPE_TN3270</P>
<P>GOPHER_TYPE_GIF</P>
<P>GOPHER_TYPE_IMAGE</P>
<P>GOPHER_TYPE_BITMAP</P>
<P>GOPHER_TYPE_MOVIE</P>
<P>GOPHER_TYPE_SOUND</P>
<P>GOPHER_TYPE_HTML</P>
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