GO-1322 Fix stacktrace decoder

cmd/logdecode/main.go

@@ -5,37 +5,57 @@ import (
 	"bytes"
 	"compress/gzip"
 	"encoding/base64"
+	"errors"
 	"fmt"
+	"io"
 	"os"
 )
 
 func main() {
-	scanner := bufio.NewScanner(os.Stdin)
-	fmt.Print("Enter base64 encoded string: ")
+	var (
+		err    error
+		reader io.Reader
+		file   = os.Stdin
+	)
+	if len(os.Args) == 2 {
+		if file, err = os.Open(os.Args[1]); err != nil {
+			fmt.Println("Error opening file:", err)
+			return
+		}
+	} else {
+		fmt.Print("Enter base64 encoded string: ")
+	}
+	scanner := bufio.NewScanner(file)
 	scanner.Scan()
 	base64Str := scanner.Text()
 
 	gzipBytes, err := base64.StdEncoding.DecodeString(base64Str)
 	if err != nil {
 		fmt.Println("Error decoding base64:", err)
+		// On some OS stdin is limited with 4092 bytes
+		if errors.Is(err, base64.CorruptInputError(4092)) {
+			fmt.Println("Try to pass base64 in a file. Filename should be the argument of the program")
+		}
 		return
 	}
 
-	reader, err := gzip.NewReader(bytes.NewReader(gzipBytes))
+	br := bytes.NewReader(gzipBytes)
+	zr, err := gzip.NewReader(br)
 	if err != nil {
-		fmt.Println("Error creating gzip reader:", err)
-		return
+		reader = br
+	} else {
+		reader = zr
+		defer zr.Close()
 	}
-	defer reader.Close()
 
 	result := ""
 	buf := make([]byte, 1024)
 	for {
 		n, err := reader.Read(buf)
+		result += string(buf[:n])
 		if err != nil {
 			break
 		}
-		result += string(buf[:n])
 	}
 
 	fmt.Println(result)