Usually, HTTP/2 can be used transparently and offers a performance boost over the simpler HTTP/1.1.

But some legacy scripts which output full HTTP/1.1 replies are not compatible with HTTP/2. Such script are called NPH (for Non-Parsed Headers) and are hopefully very rare these today.

Configuring the HTTP/1.1 Required table

If you still have NPH scripts, it is recommended to configure Abyss Web Server to not serve them over HTTP/2. This is controlled by the HTTP/1.1 Required table.

By default, the HTTP/1.1 Required table is already populated with the pattern */nph-* which matches with any file which name starts with nph-. This was the defacto naming convention for NPH scripts.

If your script names do not follow that naming scheme, you will have to declare their virtual paths and/or patterns inside the HTTP/1.1 Required table:

• Open the console
• Press Configure associated with the host which contains NPH scripts
• Click on the General icon
• Press Edit next to Advanced Configuration
• Press Edit next to HTTP/2 Parameters
• Press Add in the HTTP/1.1 Required table
• Enter a virtual path pattern matching with your NPH scripts in the Virtual Path field
• Press OK
• Press OK
• Press OK
• Press Restart

How does HTTP/1.1 downgrading works?

On a HTTP/2 connection, when a script which virtual path matches with one of the HTTP/1.1 Required table entries, a special HTTP/1.1 Required signal is reported to the visitors's browser. The browser will then retry the same request using HTTP/1.1 on a freshly established new connection.

Most browsers will retain the downgrading information in their caches. They will continue to make HTTP/1.1-only connections to the Web site.

What to do if most of a site is using NPH?

If most of a site is based on NPH scripts, it is recommended to avoid wasting a round-trip with the HTTP/2-to-HTTP/1.1 downgrading: Disabling HTTP/2 for the whole site is a netter solution for such use cases.

See also

• Changes introduced by HTTP/2 supportArticle
• Disabling HTTP/2Article