Explain the internal working of Caddy's config adapter?

A config adapter is the component that translates some input format into Caddy's native JSON structure before the server loads it. The Caddyfile is the most-used example, but the same mechanism supports other adapters too.

When you run caddy run --config Caddyfile or caddy reload, Caddy first detects (or is told) which adapter applies, parses the input text into an abstract syntax tree of tokens, then walks that tree to build the equivalent JSON config object - site addresses become server and route entries, directives become handler objects, matchers become matcher objects, and so on.

You can run this translation step by itself with caddy adapt --config Caddyfile --pretty, which prints the resulting JSON without starting the server - a useful way to see exactly what a Caddyfile expands into, or to debug why a directive isn't behaving as expected. Because the adapter step is isolated from the runtime, Caddy only ever actually executes JSON internally, regardless of which format an operator wrote.