v2: Module documentation; refactor LoadModule(); new caddy struct tags (#2924)

This commit goes a long way toward making automated documentation of
Caddy config and Caddy modules possible. It's a broad, sweeping change,
but mostly internal. It allows us to automatically generate docs for all
Caddy modules (including future third-party ones) and make them viewable
on a web page; it also doubles as godoc comments.

As such, this commit makes significant progress in migrating the docs
from our temporary wiki page toward our new website which is still under
construction.

With this change, all host modules will use ctx.LoadModule() and pass in
both the struct pointer and the field name as a string. This allows the
reflect package to read the struct tag from that field so that it can
get the necessary information like the module namespace and the inline
key.

This has the nice side-effect of unifying the code and documentation. It
also simplifies module loading, and handles several variations on field
types for raw module fields (i.e. variations on json.RawMessage, such as
arrays and maps).

I also renamed ModuleInfo.Name -> ModuleInfo.ID, to make it clear that
the ID is the "full name" which includes both the module namespace and
the name. This clarity is helpful when describing module hierarchy.

As of this change, Caddy modules are no longer an experimental design.
I think the architecture is good enough to go forward.

1 files changed, 27 insertions, 6 deletions

diff --git a/admin.go b/admin.go
index 981f2dc..fcbb62e 100644
--- a/admin.go
+++ b/admin.go
@@ -39,12 +39,33 @@ import (
 
 // TODO: is there a way to make the admin endpoint so that it can be plugged into the HTTP app? see issue #2833
 
-// AdminConfig configures the admin endpoint.
+// AdminConfig configures Caddy's API endpoint, which is used
+// to manage Caddy while it is running.
 type AdminConfig struct {
-	Disabled      bool     `json:"disabled,omitempty"`
-	Listen        string   `json:"listen,omitempty"`
-	EnforceOrigin bool     `json:"enforce_origin,omitempty"`
-	Origins       []string `json:"origins,omitempty"`
+	// If true, the admin endpoint will be completely disabled.
+	// Note that this makes any runtime changes to the config
+	// impossible, since the interface to do so is through the
+	// admin endpoint.
+	Disabled bool `json:"disabled,omitempty"`
+
+	// The address to which the admin endpoint's listener should
+	// bind itself. Can be any single network address that can be
+	// parsed by Caddy.
+	Listen string `json:"listen,omitempty"`
+
+	// If true, CORS headers will be emitted, and requests to the
+	// API will be rejected if their `Host` and `Origin` headers
+	// do not match the expected value(s). Use `origins` to
+	// customize which origins/hosts are allowed.If `origins` is
+	// not set, the listen address is the only value allowed by
+	// default.
+	EnforceOrigin bool `json:"enforce_origin,omitempty"`
+
+	// The list of allowed origins for API requests. Only used if
+	// `enforce_origin` is true. If not set, the listener address
+	// will be the default value. If set but empty, no origins will
+	// be allowed.
+	Origins []string `json:"origins,omitempty"`
 }
 
 // listenAddr extracts a singular listen address from ac.Listen,
@@ -706,7 +727,7 @@ traverseLoop:
 			ptr = v[partInt]
 
 		default:
-			return fmt.Errorf("invalid path: %s", parts[:i+1])
+			return fmt.Errorf("invalid traversal path at: %s", strings.Join(parts[:i+1], "/"))
 		}
 	}