Implement config adapters and beginning of Caddyfile adapter

Along with several other changes, such as renaming caddyhttp.ServerRoute
to caddyhttp.Route, exporting some types that were not exported before,
and tweaking the caddytls TLS values to be more consistent.

Notably, we also now disable automatic cert management for names which
already have a cert (manually) loaded into the cache. These names no
longer need to be specified in the "skip_certificates" field of the
automatic HTTPS config, because they will be skipped automatically.

cmd/main.go

@@ -25,6 +25,7 @@ import (
 	"os"
 
 	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig"
 )
 
 // Main implements the main function of the caddy command.
@@ -62,6 +63,7 @@ var commands = map[string]commandFunc{
 	"version":      cmdVersion,
 	"list-modules": cmdListModules,
 	"environ":      cmdEnviron,
+	"adapt-config": cmdAdaptConfig,
 }
 
 func usageString() string {
@@ -85,3 +87,66 @@ func handlePingbackConn(conn net.Conn, expect []byte) error {
 	}
 	return nil
 }
+
+// loadConfig loads the config from configFile and adapts it
+// using adapterName. If adapterName is specified, configFile
+// must be also. It prints any warnings to stderr, and returns
+// the resulting JSON config bytes.
+func loadConfig(configFile, adapterName string) ([]byte, error) {
+	// specifying an adapter without a config file is ambiguous
+	if configFile == "" && adapterName != "" {
+		return nil, fmt.Errorf("cannot adapt config without config file (use --config)")
+	}
+
+	// load initial config and adapter
+	var config []byte
+	var cfgAdapter caddyconfig.Adapter
+	var err error
+	if configFile != "" {
+		config, err = ioutil.ReadFile(configFile)
+		if err != nil {
+			return nil, fmt.Errorf("reading config file: %v", err)
+		}
+	} else if adapterName == "" {
+		// as a special case when no config file or adapter
+		// is specified, see if the Caddyfile adapter is
+		// plugged in, and if so, try using a default Caddyfile
+		cfgAdapter = caddyconfig.GetAdapter("caddyfile")
+		if cfgAdapter != nil {
+			config, err = ioutil.ReadFile("Caddyfile")
+			if err != nil && !os.IsNotExist(err) {
+				return nil, fmt.Errorf("reading default Caddyfile: %v", err)
+			}
+			configFile = "Caddyfile"
+		}
+	}
+
+	// load config adapter
+	if adapterName != "" {
+		cfgAdapter = caddyconfig.GetAdapter(adapterName)
+		if cfgAdapter == nil {
+			return nil, fmt.Errorf("unrecognized config adapter: %s", adapterName)
+		}
+	}
+
+	// adapt config
+	if cfgAdapter != nil {
+		adaptedConfig, warnings, err := cfgAdapter.Adapt(config, map[string]string{
+			"filename": configFile,
+			// TODO: all other options... (http-port, etc...)
+		})
+		if err != nil {
+			return nil, fmt.Errorf("adapting config using %s: %v", adapterName, err)
+		}
+		for _, warn := range warnings {
+			msg := warn.Message
+			if warn.Directive != "" {
+				msg = fmt.Sprintf("%s: %s", warn.Directive, warn.Message)
+			}
+			fmt.Printf("[WARNING][%s] %s:%d: %s", adapterName, warn.File, warn.Line, msg)
+		}
+		config = adaptedConfig
+	}
+
+	return config, nil
+}