HTTP version selection #987
Description
This API will update HttpClient behavior to enable more useful version selection from users. This will make possible prenegotiated HTTP/2 cleartext, H2C upgrade, prenegotiated HTTP/3, and leave the door open for Alt-Svc to migrate connections in the future.
If accepted, would supersede #988 and allow us to get rid of the current AppContext switch for prenegotiated H2C.
Proposed API
class HttpClient
{
//Version DefaultVersion { get; set; } // Exists today - will be interpreted as Min or Max based on new API below.
public HttpVersionPolicy DefaultVersionPolicy { get; set; } = HttpVersionPolicy.RequestVersionOrLower;
}
class HttpRequestMessage
{
//Version Version { get; set; } // Exists today - will be interpreted as Min or Max based on new API below.
public HttpVersionPolicy VersionPolicy { get; set; } = HttpVersionPolicy.RequestVersionOrLower;
}
public enum HttpVersionPolicy
{
RequestVersionOrLower,
RequestVersionOrHigher,
RequestVersionExact
}Behavior
The default would have identical behavior to what we have today.
RequestVersionOrLower: start as high as possible (HTTP/1.1, or ALPN if available) up toHttpRequestMessage.Version.RequestVersionOrHigher: start as high as possible (at leastHttpRequestMessage.Version, or ALPN if available), and upgrade (via H2C upgrade or Alt-Svc) if possible. Enables prenegotiated H2C.RequestVersionExact: use explicitly the version the user asked for, and if server requires an upgrade/downgrade for a specific request, return an appropriate error. Enables prenegotiated H2C.
Example: User doesn't know, but use whatever server has available.
var msg = new HttpRequestMessage { VersionPolicy = HttpVersionPolicy.RequestVersionOrHigher };
// ...Example: Prenegotiated HTTP/3
var msg = new HttpRequestMessage { Version = HttpVersion.Version30, VersionPolicy = VersionPolicy = HttpVersionPolicy.RequestVersionOrHigher };
// ...Example: H2C upgrade
var msg = new HttpRequestMessage { VersionPolicy = HttpVersionPolicy.RequestVersionOrHigher };Example: Prenegotiated H2C
var msg = new HttpRequestMessage
{
Version = HttpVersion.Version20,
VersionPolicy = HttpVersionPolicy.RequestVersionOrHigher
RequestUri = new Uri("http://unsecure-url.com")
};Example: app depends on Connection: close
var msg = new HttpRequestMessage { }; // default policy just fine.
msg.Headers.ConnectionClose = true;