Get Response Headers (ASP.NET) | Tech Off

sbc
GW R/Me

I am attempting to get the response headers (specifically the Last-Modified one). However, all I get is Connection and Host.

WebRequest request = WebRequest.Create("http://channel9.msdn.com/rss.aspx?forumid=15);
request.Method = "HEAD";
try
{
    request.GetResponse();
    Response.Write(request.Headers);
    Response.End();
}
catch(WebException ex)
{
    Response.Write(ex.ToString());
}

Results in:

Connection: Keep-Alive Host: channel9.msdn.com

Maurits
AKA Matthew van Eerde

WebRequest req = ...
WebResponse resp = req.GetResponse()

foo(resp.Headers)

sbc
GW R/Me

Maurits wrote:

WebRequest req = ...
WebResponse resp = req.GetResponse()

foo(resp.Headers)

Thanks. Is req.Headers the headers sent to the server? In that case, how do I supply a user agent - to make the server think I am using IE for instance.

However, when I try resp.Headers["Last-Modified"] I get prompted for a download of a 0 byte text file. The Last-Modified header does not seem to be sent. How can you make sure you are not getting the same thing as before (i.e. load from cache if nothing has changed)?

Maurits
AKA Matthew van Eerde

Yes, req.Headers is the headers sent to the remote server

I imagine you could do something like

req.Headers.Item("User-Agent") = "SBCBot/1.0";

to change the user agent.

WebRequest objects don't use a cache... you'll have to build your own. You should set "If-Modified-Since" on the request -- if you get back a "Not Modifed" response instead of data, the data wasn't modified.

Make sure your If-Modified-Since header is an HTTP-standard date format.

EDIT: I'm guessing, though, that Channel 9's RSS feed doesn't honor the If-Modified-Since header.

Maurits
AKA Matthew van Eerde

WebRequest objects have an IfModifiedSince property that handles setting the If-Modified-Since header for you.

EDIT: BTW, the example on that page makes absolutely no sense to me.
EDIT2: There's a UserAgent property too. Here's the list of HttpWebRequest.Headers properties.
EDIT3: And here's the HttpWebResponse.Headers properties. Note LastModified is there.

EDIT4:
So you can do...

req.UserAgent = strIEUserAgent;
req.IfModifiedSince = dateLastModificationIKnowAbout;

...

dateLastModificationIKnowAbout = resp.LastModified;

EDIT5:

For completeness...

Suppose you set IfModifiedSince.

If the content has not been modified, the server should send back a response with Status Code 304 Not Modified.

Otherwise you can assume either Angel

the content was modified or (b) the server doesn't support If-Modified-Since for that page.

EDIT6:

To wit:

if (resp.StatusCode = HttpStatusCode.NotModified)
{
// no changes since If-Modified-Since
}
else
{
// new content... pull from resp
}

EDIT7: Emailed a proposed new example skeleton to the feedback link on the page referenced in the first edit

sbc
GW R/Me

Thanks for the feedback. I never knew there was a HttpWebRequest class (I am using WebRequest). It has the kind of things I am looking for.

That is the problem with the MSDN documentation - some parts are verbose (don't give a very good example of usage) others lack any kind of example code. Also, has it ever been updated since .NET 1.1 came out? It should be kept up to date. I find it is an OK reference, but for anything useful, Google is a much better solution (to look up code and help).

If I actually bought .NET I would expect the documentation to be a lot better that it is now (in a way we do, as Windows is not free). Is the SDK documentation the same as what you get with VS.NET?

Sven Groot
You can't have everything; after all, where would you put it?

sbc wrote:

Also, has it ever been updated since .NET 1.1 came out?

Yes, there was the October 2003 update for the .Net 1.1 SDK and MSDN for VS2003.

sbc
GW R/Me

Sven Groot wrote:

sbc wrote: Also, has it ever been updated since .NET 1.1 came out?

Yes, there was the October 2003 update for the .Net 1.1 SDK and MSDN for VS2003.

What was in the update?

Sven Groot
You can't have everything; after all, where would you put it?

sbc wrote:

Sven Groot wrote:

sbc wrote: Also, has it ever been updated since .NET 1.1 came out?

Yes, there was the October 2003 update for the .Net 1.1 SDK and MSDN for VS2003.

What was in the update?

According to the download page:
"

Over 5,000 additional code examples for Visual Basic, Visual C#, and Visual C++.

Bug fixes.

Content improvements and clarifications.
"

sbc
GW R/Me

Sven Groot wrote:

sbc wrote:

Sven Groot wrote:

sbc wrote: Also, has it ever been updated since .NET 1.1 came out?

Yes, there was the October 2003 update for the .Net 1.1 SDK and MSDN for VS2003.

What was in the update?

According to the download page:
"
Over 5,000 additional code examples for Visual Basic, Visual C#, and Visual C++.

Bug fixes.

Content improvements and clarifications.
"

No updates since then? My ideal help system would be one that could update in the background (no need to go to a site to download an exe, just go Tools > Update (or something similar) and it updates the documentation while you were still using it). Integrated community feedback (like with the PHP docs) as well.