cmd: Adjust config load logs/errors (#6032)

* cmd: Adjust config load logs/errors

* Update cmd/main.go

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

---------

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

cmd/main.go

@@ -17,6 +17,7 @@ package caddycmd
 import (
 	"bufio"
 	"bytes"
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -107,6 +108,12 @@ func LoadConfig(configFile, adapterName string) ([]byte, string, error) {
 }
 
 func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([]byte, string, error) {
+	// if no logger is provided, use a nop logger
+	// just so we don't have to check for nil
+	if logger == nil {
+		logger = zap.NewNop()
+	}
+
 	// specifying an adapter without a config file is ambiguous
 	if adapterName != "" && configFile == "" {
 		return nil, "", fmt.Errorf("cannot adapt config without config file (use --config)")
@@ -119,16 +126,16 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 	if configFile != "" {
 		if configFile == "-" {
 			config, err = io.ReadAll(os.Stdin)
+			if err != nil {
+				return nil, "", fmt.Errorf("reading config from stdin: %v", err)
+			}
+			logger.Info("using config from stdin")
 		} else {
 			config, err = os.ReadFile(configFile)
-		}
-		if err != nil {
-			return nil, "", fmt.Errorf("reading config file: %v", err)
-		}
-		if logger != nil {
-			logger.Info("using provided configuration",
-				zap.String("config_file", configFile),
-				zap.String("config_adapter", adapterName))
+			if err != nil {
+				return nil, "", fmt.Errorf("reading config from file: %v", err)
+			}
+			logger.Info("using config from file", zap.String("file", configFile))
 		}
 	} else if adapterName == "" {
 		// if the Caddyfile adapter is plugged in, we can try using an
@@ -145,9 +152,7 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 			} else {
 				// success reading default Caddyfile
 				configFile = "Caddyfile"
-				if logger != nil {
-					logger.Info("using adjacent Caddyfile")
-				}
+				logger.Info("using adjacent Caddyfile")
 			}
 		}
 	}
@@ -177,16 +182,24 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 		if err != nil {
 			return nil, "", fmt.Errorf("adapting config using %s: %v", adapterName, err)
 		}
+		logger.Info("adapted config to JSON", zap.String("adapter", adapterName))
 		for _, warn := range warnings {
 			msg := warn.Message
 			if warn.Directive != "" {
 				msg = fmt.Sprintf("%s: %s", warn.Directive, warn.Message)
 			}
-			if logger != nil {
-				logger.Warn(msg, zap.String("adapter", adapterName), zap.String("file", warn.File), zap.Int("line", warn.Line))
-			}
+			logger.Warn(msg,
+				zap.String("adapter", adapterName),
+				zap.String("file", warn.File),
+				zap.Int("line", warn.Line))
 		}
 		config = adaptedConfig
+	} else {
+		// validate that the config is at least valid JSON
+		err = json.Unmarshal(config, new(any))
+		if err != nil {
+			return nil, "", fmt.Errorf("config is not valid JSON: %v; did you mean to use a config adapter (the --adapter flag)?", err)
+		}
 	}
 
 	return config, configFile, nil