cmd/zon: Peek at first byte

(In order to decide on what decoder to pick)

Author: peterhellberg

cmd/zon/main.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"bufio"
+	"bytes"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -23,16 +25,29 @@ func run(r io.Reader, w io.Writer) error {
 
 	flag.Parse()
 
+	b := bufio.NewReader(r)
+
+	var dec Decoder = json.NewDecoder(b)
+	{
+		first, err := b.Peek(1)
+		if err != nil {
+			return err
+		}
+
+		if probablyZON := bytes.Equal([]byte("."), first); probablyZON {
+			dec = zon.NewDecoder(b)
+		}
+	}
+
 	if *j {
-		dec := zon.NewDecoder(r)
 		enc := json.NewEncoder(w)
 
 		enc.SetIndent("", *i)
 
 		return convert(dec, enc)
 	}
 
-	return convert(json.NewDecoder(r), zon.NewEncoder(w, zon.Indent(*i)))
+	return convert(dec, zon.NewEncoder(w, zon.Indent(*i)))
 }
 
 type Decoder interface{ Decode(v any) error }