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.

5 files changed, 24 insertions, 28 deletions

diff --git a/modules/caddyhttp/encode/brotli/brotli.go b/modules/caddyhttp/encode/brotli/brotli.go
index cf055aa..52bb205 100644
--- a/modules/caddyhttp/encode/brotli/brotli.go
+++ b/modules/caddyhttp/encode/brotli/brotli.go
@@ -37,8 +37,8 @@ type Brotli struct {
 // CaddyModule returns the Caddy module information.
 func (Brotli) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "http.encoders.brotli",
-		New:  func() caddy.Module { return new(Brotli) },
+		ID:  "http.encoders.brotli",
+		New: func() caddy.Module { return new(Brotli) },
 	}
 }
 
diff --git a/modules/caddyhttp/encode/caddyfile.go b/modules/caddyhttp/encode/caddyfile.go
index 4764e9b..dd12de2 100644
--- a/modules/caddyhttp/encode/caddyfile.go
+++ b/modules/caddyhttp/encode/caddyfile.go
@@ -15,7 +15,6 @@
 package encode
 
 import (
-	"encoding/json"
 	"fmt"
 
 	"github.com/caddyserver/caddy/v2"
@@ -52,14 +51,14 @@ func (enc *Encode) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 		for _, arg := range d.RemainingArgs() {
 			mod, err := caddy.GetModule("http.encoders." + arg)
 			if err != nil {
-				return fmt.Errorf("finding encoder module '%s': %v", mod.Name, err)
+				return fmt.Errorf("finding encoder module '%s': %v", mod, err)
 			}
 			encoding, ok := mod.New().(Encoding)
 			if !ok {
-				return fmt.Errorf("module %s is not an HTTP encoding", mod.Name)
+				return fmt.Errorf("module %s is not an HTTP encoding", mod)
 			}
 			if enc.EncodingsRaw == nil {
-				enc.EncodingsRaw = make(map[string]json.RawMessage)
+				enc.EncodingsRaw = make(caddy.ModuleMap)
 			}
 			enc.EncodingsRaw[arg] = caddyconfig.JSON(encoding, nil)
 		}
@@ -72,7 +71,7 @@ func (enc *Encode) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 			}
 			unm, ok := mod.New().(caddyfile.Unmarshaler)
 			if !ok {
-				return fmt.Errorf("encoder module '%s' is not a Caddyfile unmarshaler", mod.Name)
+				return fmt.Errorf("encoder module '%s' is not a Caddyfile unmarshaler", mod)
 			}
 			err = unm.UnmarshalCaddyfile(d.NewFromNextTokens())
 			if err != nil {
@@ -80,10 +79,10 @@ func (enc *Encode) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 			}
 			encoding, ok := unm.(Encoding)
 			if !ok {
-				return fmt.Errorf("module %s is not an HTTP encoding", mod.Name)
+				return fmt.Errorf("module %s is not an HTTP encoding", mod)
 			}
 			if enc.EncodingsRaw == nil {
-				enc.EncodingsRaw = make(map[string]json.RawMessage)
+				enc.EncodingsRaw = make(caddy.ModuleMap)
 			}
 			enc.EncodingsRaw[name] = caddyconfig.JSON(encoding, nil)
 		}
diff --git a/modules/caddyhttp/encode/encode.go b/modules/caddyhttp/encode/encode.go
index 3716fc6..c68f507 100644
--- a/modules/caddyhttp/encode/encode.go
+++ b/modules/caddyhttp/encode/encode.go
@@ -21,7 +21,6 @@ package encode
 
 import (
 	"bytes"
-	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
@@ -40,9 +39,9 @@ func init() {
 
 // Encode is a middleware which can encode responses.
 type Encode struct {
-	EncodingsRaw map[string]json.RawMessage `json:"encodings,omitempty"`
-	Prefer       []string                   `json:"prefer,omitempty"`
-	MinLength    int                        `json:"minimum_length,omitempty"`
+	EncodingsRaw caddy.ModuleMap `json:"encodings,omitempty" caddy:"namespace=http.encoders"`
+	Prefer       []string        `json:"prefer,omitempty"`
+	MinLength    int             `json:"minimum_length,omitempty"`
 
 	writerPools map[string]*sync.Pool // TODO: these pools do not get reused through config reloads...
 }
@@ -50,25 +49,23 @@ type Encode struct {
 // CaddyModule returns the Caddy module information.
 func (Encode) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "http.handlers.encode",
-		New:  func() caddy.Module { return new(Encode) },
+		ID:  "http.handlers.encode",
+		New: func() caddy.Module { return new(Encode) },
 	}
 }
 
 // Provision provisions enc.
 func (enc *Encode) Provision(ctx caddy.Context) error {
-	for modName, rawMsg := range enc.EncodingsRaw {
-		val, err := ctx.LoadModule("http.encoders."+modName, rawMsg)
-		if err != nil {
-			return fmt.Errorf("loading encoder module '%s': %v", modName, err)
-		}
-		encoding := val.(Encoding)
-		err = enc.addEncoding(encoding)
+	mods, err := ctx.LoadModule(enc, "EncodingsRaw")
+	if err != nil {
+		return fmt.Errorf("loading encoder modules: %v", err)
+	}
+	for modName, modIface := range mods.(map[string]interface{}) {
+		err = enc.addEncoding(modIface.(Encoding))
 		if err != nil {
-			return err
+			return fmt.Errorf("adding encoding %s: %v", modName, err)
 		}
 	}
-	enc.EncodingsRaw = nil // allow GC to deallocate
 
 	if enc.MinLength == 0 {
 		enc.MinLength = defaultMinLength
diff --git a/modules/caddyhttp/encode/gzip/gzip.go b/modules/caddyhttp/encode/gzip/gzip.go
index d6d67f7..590f708 100644
--- a/modules/caddyhttp/encode/gzip/gzip.go
+++ b/modules/caddyhttp/encode/gzip/gzip.go
@@ -37,8 +37,8 @@ type Gzip struct {
 // CaddyModule returns the Caddy module information.
 func (Gzip) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "http.encoders.gzip",
-		New:  func() caddy.Module { return new(Gzip) },
+		ID:  "http.encoders.gzip",
+		New: func() caddy.Module { return new(Gzip) },
 	}
 }
 
diff --git a/modules/caddyhttp/encode/zstd/zstd.go b/modules/caddyhttp/encode/zstd/zstd.go
index f2b4e85..5182fc4 100644
--- a/modules/caddyhttp/encode/zstd/zstd.go
+++ b/modules/caddyhttp/encode/zstd/zstd.go
@@ -31,8 +31,8 @@ type Zstd struct{}
 // CaddyModule returns the Caddy module information.
 func (Zstd) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "http.encoders.zstd",
-		New:  func() caddy.Module { return new(Zstd) },
+		ID:  "http.encoders.zstd",
+		New: func() caddy.Module { return new(Zstd) },
 	}
 }