As
you've seen in previous examples, we are not limited to dealing
just with HTML text (defined by the MIME type text/html)
but we can also output documents formatted in numerous ways, like
plain text, GIF or JPEG images, and even AIFF sound clips. Here
is a program that returns a GIF image:
#!/usr/local/bin/perl
$gif_image = join ("/", $ENV{'DOCUMENT_ROOT'}, "icons/tiger.gif");
if (open (IMAGE, "<" . $gif_image)) {
$no_bytes = (stat ($gif_image))[7];
print "Content-type: image/gif", "\n";
print "Content-length: $no_bytes", "\n\n";
The first thing to notice is that the content type is image/gif.
This signals the browser that a GIF image will be sent, so the browser
knows how to display it.
The next thing to notice
is the Content-length header. The Content-length
header notifies the server of the size of the data that you intend
to send. This prevents unexpected end-of-data errors from the server
when dealing with binary data, because the server will read the
specified number of bytes from the data stream regardless of any
spurious end-of-data characters.
To get the content length, we use the stat command, which returns a 13-element
array containing the statistics for a given file, to determine the
size of the file. The eighth element of this array (index number
7, because arrays are zero-based in Perl) represents the size of
the file in bytes. The remainder of the script follows:
print <IMAGE>;
} else {
print "Content-type: text/plain", "\n\n";
print "Sorry! I cannot open the file $gif_image!", "\n";
}
exit (0);
As is the case with binary files, one read on the file handle
will retrieve the entire file. Compare that to text files where
one read will return only a single line. As a result, this example
is fine when dealing with small graphic files, but is not very efficient
with larger files. Now, we'll look at an example that reads and
displays the graphic file in small pieces:
#!/usr/local/bin/perl
$gif_image = join ("/", $ENV{'DOCUMENT_ROOT'}, "icons/tiger.gif");
if (open (IMAGE, "<" . $gif_image)) {
$no_bytes = (stat ($gif_image))[7];
$piece_size = $no_bytes / 10;
print "Content-type: image/gif", "\n";
print "Content-length: $no_bytes", "\n\n";
for ($loop=0; $loop <= $no_bytes; $loop += $piece_size) {
read (IMAGE, $data, $piece_size);
print $data;
}
close (IMAGE);
} else {
print "Content-type: text/plain", "\n\n";
print "Sorry! I cannot open the file $gif_image!", "\n";
}
exit (0);
The loop iterates through the file reading and displaying
pieces of data that are one-tenth the size of the entire binary
file.
As you will see in the following section, you can use server
redirection to return existing files much more quickly and easily
than with CGI programs like the ones described earlier.
