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, 49 insertions, 25 deletions

diff --git a/caddy.go b/caddy.go
index d8609d2..9dcd883 100644
--- a/caddy.go
+++ b/caddy.go
@@ -32,23 +32,44 @@ import (
 	"github.com/mholt/certmagic"
 )
 
-// Config represents a Caddy configuration. It is the
-// top of the module structure: all Caddy modules will
-// be loaded, starting with this struct. In order to
-// be loaded and run successfully, a Config and all its
-// modules must be JSON-encodable; i.e. when filling a
-// Config struct manually, its JSON-encodable fields
-// (the ones with JSON struct tags, usually ending with
-// "Raw" if they decode into a separate field) must be
-// set so that they can be unmarshaled and provisioned.
-// Setting the fields for the decoded values instead
-// will result in those values being overwritten at
-// unmarshaling/provisioning.
+// Config is the top (or beginning) of the Caddy configuration structure.
+// Caddy config is expressed natively as a JSON document. If you prefer
+// not to work with JSON directly, there are [many config adapters](/docs/config-adapters)
+// available that can convert various inputs into Caddy JSON.
+//
+// Many parts of this config are extensible through the use of Caddy modules.
+// Fields which have a json.RawMessage type and which appear as dots (•••) in
+// the online docs can be fulfilled by modules in a certain module
+// namespace. The docs show which modules can be used in a given place.
+//
+// Whenever a module is used, its name must be given either inline as part of
+// the module, or as the key to the module's value. The docs will make it clear
+// which to use.
+//
+// Generally, all config settings are optional, as it is Caddy convention to
+// have good, documented default values. If a parameter is required, the docs
+// should say so.
+//
+// Go programs which are directly building a Config struct value should take
+// care to populate the JSON-encodable fields of the struct (i.e. the fields
+// with `json` struct tags) if employing the module lifecycle (e.g. Provision
+// method calls).
 type Config struct {
-	Admin      *AdminConfig               `json:"admin,omitempty"`
-	Logging    *Logging                   `json:"logging,omitempty"`
-	StorageRaw json.RawMessage            `json:"storage,omitempty"`
-	AppsRaw    map[string]json.RawMessage `json:"apps,omitempty"`
+	Admin   *AdminConfig `json:"admin,omitempty"`
+	Logging *Logging     `json:"logging,omitempty"`
+
+	// StorageRaw is a storage module that defines how/where Caddy
+	// stores assets (such as TLS certificates). By default, this is
+	// the local file system (`caddy.storage.file_system` module).
+	// If the `XDG_DATA_HOME` environment variable is set, then
+	// `$XDG_DATA_HOME/caddy` is the default folder. Otherwise,
+	// `$HOME/.local/share/caddy` is the default folder.
+	StorageRaw json.RawMessage `json:"storage,omitempty" caddy:"namespace=caddy.storage inline_key=module"`
+
+	// AppsRaw are the apps that Caddy will load and run. The
+	// app module name is the key, and the app's config is the
+	// associated value.
+	AppsRaw ModuleMap `json:"apps,omitempty" caddy:"namespace="`
 
 	apps    map[string]App
 	storage certmagic.Storage
@@ -322,7 +343,7 @@ func run(newCfg *Config, start bool) error {
 	// set up global storage and make it CertMagic's default storage, too
 	err = func() error {
 		if newCfg.StorageRaw != nil {
-			val, err := ctx.LoadModuleInline("module", "caddy.storage", newCfg.StorageRaw)
+			val, err := ctx.LoadModule(newCfg, "StorageRaw")
 			if err != nil {
 				return fmt.Errorf("loading storage module: %v", err)
 			}
@@ -331,8 +352,8 @@ func run(newCfg *Config, start bool) error {
 				return fmt.Errorf("creating storage value: %v", err)
 			}
 			newCfg.storage = stor
-			newCfg.StorageRaw = nil // allow GC to deallocate
 		}
+
 		if newCfg.storage == nil {
 			newCfg.storage = &certmagic.FileStorage{Path: dataDir()}
 		}
@@ -346,12 +367,12 @@ func run(newCfg *Config, start bool) error {
 
 	// Load, Provision, Validate each app and their submodules
 	err = func() error {
-		for modName, rawMsg := range newCfg.AppsRaw {
-			val, err := ctx.LoadModule(modName, rawMsg)
-			if err != nil {
-				return fmt.Errorf("loading app module '%s': %v", modName, err)
-			}
-			newCfg.apps[modName] = val.(App)
+		appsIface, err := ctx.LoadModule(newCfg, "AppsRaw")
+		if err != nil {
+			return fmt.Errorf("loading app modules: %v", err)
+		}
+		for appName, appIface := range appsIface.(map[string]interface{}) {
+			newCfg.apps[appName] = appIface.(App)
 		}
 		return nil
 	}()
@@ -447,7 +468,10 @@ func Validate(cfg *Config) error {
 	return err
 }
 
-// Duration is a JSON-string-unmarshable duration type.
+// Duration can be an integer or a string. An integer is
+// interpreted as nanoseconds. If a string, it is a Go
+// time.Duration value such as `300ms`, `1.5h`, or `2h45m`;
+// valid units are `ns`, `us`/`µs`, `ms`, `s`, `m`, and `h`.
 type Duration time.Duration
 
 // UnmarshalJSON satisfies json.Unmarshaler.