Thank you, this resolves the problem with the Content-Type being sent when the script is NPH and using the CGI method. However, it does not appear to resolve the Connection: Keep-Alive issue, the connection is still being closed when the script finishes.

My script is calculating the body length and sending the Content-Length header, aswell as any other headers that are specified in the rfc.

304 Example using:
print header(-status => '304 Not Modified', -nph => 1, -type => '', -connection => 'Keep-Alive', 'Keep-Alive' => 'timeout=15, max=100');

Here is the connection closing after issueing the 304:

GET /nph-test.pl HTTP/1.1
Host: www.xyz.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.7
+) Gecko/2009021910 Firefox/3.0.7 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.
+8,text/vnd.wap.wml;q=0.6
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP/1.1 304 Not Modified
Server: Apache/1.3.26 (Unix)  (Red-Hat/Linux) FrontPage/5.0.2.2510
Status: 304 Not Modified
Date: Tue, 24 Mar 2009 14:40:18 GMT
keep-alive: timeout=15, max=100
connection: Keep-Alive

Connection closed by foreign host.
[download]

And here after serving a page:

GET /nph-servefiles.pl HTTP/1.1
Host: www.xyz.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.7
+) Gecko/2009021910 Firefox/3.0.7 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.
+8,text/vnd.wap.wml;q=0.6
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP/1.1 200 OK
Accept-Ranges: none
Expires: Sun, 20 Mar 2011 18:56:47 GMT
Server: Apache/1.3.26 (Unix)  (Red-Hat/Linux) FrontPage/5.0.2.2510
Vary: Accept,Accept-Encoding,User-Agent
Content-Length: 20
Etag: "06f0001f16dfd8b9632cc9640d62e5e0-gzip"
Cache-Control: s-maxage=1209600,proxy-revalidate,must-revalidate, max-
+age=62741536
Content-Encoding: gzip
Last-Modified: Tue, 24 Mar 2009 02:04:17 GMT
Date: Tue, 24 Mar 2009 14:56:01 GMT
Connection: Keep-Alive
Content-Type: application/xhtml+xml, charset=utf-8
Keep-Alive: timeout=15,max=100

Connection closed by foreign host.
[download]

And here 2 requests not using a script:

GET /images/validate.gif HTTP/1.1
Host: www.xyz.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.7
+) Gecko/2009021910 Firefox/3.0.7 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.
+8,text/vnd.wap.wml;q=0.6
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP/1.1 200 OK
Date: Tue, 24 Mar 2009 14:44:31 GMT
Server: Apache/1.3.26 (Unix)  (Red-Hat/Linux) FrontPage/5.0.2.2510
Cache-Control: s-maxage=1209600,proxy-revalidate,must-revalidate, max-
+age=62741536
Expires: Sun, 20 Mar 2011 18:56:47 GMT
Last-Modified: Fri, 20 Mar 2009 18:56:47 GMT
ETag: "92042c-1bd8-49c3e6ef"
Accept-Ranges: bytes
Content-Length: 7128
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Content-Type: image/gif

GET /images/validate.gif HTTP/1.1
Host: www.xyz.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.7
+) Gecko/2009021910 Firefox/3.0.7 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.
+8,text/vnd.wap.wml;q=0.6
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP/1.1 200 OK
Date: Tue, 24 Mar 2009 14:44:48 GMT
Server: Apache/1.3.26 (Unix)  (Red-Hat/Linux) FrontPage/5.0.2.2510
Cache-Control: s-maxage=1209600,proxy-revalidate,must-revalidate, max-
+age=62741519
Expires: Sun, 20 Mar 2011 18:56:47 GMT
Last-Modified: Fri, 20 Mar 2009 18:56:47 GMT
ETag: "92042c-1bd8-49c3e6ef"
Accept-Ranges: bytes
Content-Length: 7128
Keep-Alive: timeout=15, max=99
Connection: Keep-Alive
Content-Type: image/gif
[download]

Any further information appreciated

I'm not experienced in this area. I'll have to get back to you later today after having time to do some testing.

Here are 2 snippets that you can try to see the effect.

hello.pl


#!/usr/bin/perl -w
use CGI::Carp qw(fatalsToBrowser);
use strict;
use warnings;
use CGI qw(:standard );

my $http_body_length = 0;
my $http_body = "<html>\n<head>\n</head>\n<body>\n<p>Hello World</p>\n
+</body>\n</html>\n";
{
    use bytes;
    $http_body_length = length($http_body);
}
print header(-type => 'text/html',
                -content_length => $http_body_length );
print $http_body;
[download]

You will see that hello.pl sends keep-alives as expected as the headers are parsed by Apache and the connection remains open

nph-hello.pl


#!/usr/bin/perl -w
use CGI::Carp qw(fatalsToBrowser);
use strict;
use warnings;
use CGI qw(:standard );

my $http_body_length = 0;
my $http_body = "<html>\n<head>\n</head>\n<body>\n<p>Hello World</p>\n
+</body>\n</html>\n";
{
    use bytes;
    $http_body_length = length($http_body);
}
print header(-type => 'text/html',
                -content_length => $http_body_length,
                -nph => 1);
print $http_body;
[download]

You will see that nph-hello.pl does not send keep-alives as the headers are not parsed by Apache and the connection closes upon exit

I have tried adding the 'Connection' and 'Keep-Alive' headers to nph-hello.pl and of course they are sent but Apache does not keep the connection open. Example:


print header(-type => 'text/html',
                -content_length => $http_body_length,
                -connection => 'Keep-Alive',
                -nph => 1);
[download]

This is what I am trying to accomplish.

The issue with the Content-Type being sent with the 304 response has been resolved. It appears that the issue was with the configuration of the host providers Apache setup. They moved the website onto a different server and the problem went away. I have not had confirmation but I think it was because they had a DefaultType set in the httpd.conf but also the new server is running a newer version of Apache so I can't be sure but it also may have been a bug in Apache 1.3. So I have moved away from using NPH and no longer have to worry about the Keep-Alive issue as that functions correctly in non NPH mode. Many thanks for your help.