Using If-Unmodified-Since with POST request

#1

I’ve been working on updating our services to improve caching but also to deal with stale data updates. I’ve implemented Last-Modified/ETag on GET requests, but I’m a little bit stuck on POST.

We would have data fetched with a GET, and that Last-Modified in the response is what’s required as the date to pass in the If-Unmodified-Since header to specific POST request. I don’t see any cache extensions for this header.

I’m also wondering if there are best practices for this in SS or any direction on best approach.

#2

ServiceStack’s HTTP Caching is only applied to GET requests, there is no explicit support for If-Unmodified-Since Header which is primarily used for optimistic concurrency control not caching.

So you could access it like any other HTTP Header, e.g:

var checkUnmodifiedSince = base.Request.GetHeader("If-Unmodified-Since");
#3

Right, so optimistic concurrency control is what I was referring to when I said stale data update. Regardless, correct, it’s not caching and probably shouldn’t have been labeled as such. I just added some simple extensions to check it exactly that way, and one for creating an exception with 412 response.

 public static class HttpAdditionalExtensions
{
    public static bool UnModifiedSince(this IRequest req, DateTime? lastModified)
    {
        if (lastModified.HasValue)
        {
            string header = req.Headers[HttpHeaders.IfUnmodifiedSince];
            DateTime result;
            if (header == null) 
                  return false;

            if (header != null && DateTime.TryParse(header, new DateTimeFormatInfo(), DateTimeStyles.RoundtripKind, out result))
            {
                DateTime universalTime = lastModified.Value.Truncate(TimeSpan.FromSeconds(1.0)).ToUniversalTime();
                return result >= universalTime;
            }
        }
        return false;
    }

    public static Exception NotModified(string description = null)
    {
         return (Exception)new HttpError(HttpStatusCode.PreconditionFailed, description);
    }
}

Sometimes just writing a post and asking a question makes it more clear. Added my code above if anyone is doing the same.

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