perf: improve line handler

handler.go

@@ -1,110 +1,144 @@
 package parser
 
 import (
+	"bytes"
 	"os"
-	"strconv"
 	"strings"
 
 	"github.com/mattn/go-isatty"
 )
 
+const size = 2024
+
 // JSONLineHandler serializes log lines into JSON (NDJSON) format. It keywords the line number if specified.
 // Labels and values are combined into key-value pairs, and the result is a single JSON object.
-func JSONLineHandler(labels []string, values []string, _ bool) (string, error) {
-	b := &strings.Builder{}
-	b.WriteString("{")
+func JSONLineHandler(labels, values []string, _ bool) (string, error) {
+	buf := &bytes.Buffer{}
+	buf.Grow(size)
+	buf.WriteByte('{')
 	for i, value := range values {
 		if i < len(labels) {
 			if i > 0 {
-				b.WriteString(",")
+				buf.WriteByte(',')
 			}
-			b.WriteString("\"")
-			b.WriteString(labels[i])
-			b.WriteString("\":")
-			b.WriteString(strconv.Quote(value))
+			buf.WriteByte('"')
+			buf.WriteString(labels[i])
+			buf.WriteString("\":")
+			buf.WriteByte('"')
+			writeEscapedString(buf, value)
+			buf.WriteByte('"')
 		}
 	}
-	b.WriteString("}")
-	return b.String(), nil
+	buf.WriteByte('}')
+	return buf.String(), nil
 }
 
 // PrettyJSONLineHandler enhances JSONLineHandler by formatting the output for readability. It uses indentation and new lines.
-func PrettyJSONLineHandler(labels []string, values []string, _ bool) (string, error) {
-	b := &strings.Builder{}
-	b.WriteString("{\n")
+func PrettyJSONLineHandler(labels, values []string, _ bool) (string, error) {
+	buf := &bytes.Buffer{}
+	buf.Grow(size)
+	buf.WriteString("{\n")
 	for i, value := range values {
 		if i < len(labels) {
 			if i > 0 {
-				b.WriteString(",\n")
+				buf.WriteString(",\n")
 			}
-			b.WriteString("  \"")
-			b.WriteString(labels[i])
-			b.WriteString("\": ")
-			b.WriteString(strconv.Quote(value))
+			buf.WriteString("  \"")
+			buf.WriteString(labels[i])
+			buf.WriteString("\": ")
+			buf.WriteByte('"')
+			writeEscapedString(buf, value)
+			buf.WriteByte('"')
 		}
 	}
-	b.WriteString("\n}")
-	return b.String(), nil
+	buf.WriteString("\n}")
+	return buf.String(), nil
 }
 
 // KeyValuePairLineHandler converts log lines into a space-separated string of key-value pairs.
-func KeyValuePairLineHandler(labels []string, values []string, _ bool) (string, error) {
-	b := &strings.Builder{}
+func KeyValuePairLineHandler(labels, values []string, _ bool) (string, error) {
+	buf := &bytes.Buffer{}
+	buf.Grow(size)
 	for i, value := range values {
 		if i < len(labels) {
 			if i > 0 {
-				b.WriteString(" ")
+				buf.WriteByte(' ')
 			}
-			b.WriteString(labels[i])
-			b.WriteString("=")
-			b.WriteString(strconv.Quote(value))
+			buf.WriteString(labels[i])
+			buf.WriteByte('=')
+			buf.WriteByte('"')
+			writeEscapedString(buf, value)
+			buf.WriteByte('"')
 		}
 	}
-	return b.String(), nil
+	return buf.String(), nil
 }
 
 // LTSVLineHandler formats log lines as LTSV (Labeled Tab-separated Values).
-func LTSVLineHandler(labels []string, values []string, _ bool) (string, error) {
-	b := &strings.Builder{}
+func LTSVLineHandler(labels, values []string, _ bool) (string, error) {
+	buf := &bytes.Buffer{}
+	buf.Grow(size)
 	for i, value := range values {
 		if i < len(labels) {
 			if i > 0 {
-				b.WriteString("\t")
+				buf.WriteByte('\t')
 			}
-			b.WriteString(labels[i])
-			b.WriteString(":")
+			buf.WriteString(labels[i])
+			buf.WriteByte(':')
 			if value == "" {
-				b.WriteString("-")
+				buf.WriteByte('-')
 			} else {
-				b.WriteString(value)
+				buf.WriteString(value)
 			}
 		}
 	}
-	return b.String(), nil
+	return buf.String(), nil
 }
 
 // TSVLineHandler formats log lines as TSV (Tab-separated Values).
-func TSVLineHandler(labels []string, values []string, isFirst bool) (string, error) {
-	b := &strings.Builder{}
+func TSVLineHandler(labels, values []string, isFirst bool) (string, error) {
+	buf := &bytes.Buffer{}
+	buf.Grow(size)
 	if isFirst {
 		header := strings.Join(labels, "\t")
 		if isatty.IsTerminal(os.Stdout.Fd()) {
 			header = "\033[1;37m" + header + "\033[0m"
 		}
-		b.WriteString(header)
-		b.WriteString("\n")
+		buf.WriteString(header)
+		buf.WriteByte('\n')
 	}
 	for i, value := range values {
 		if i < len(labels) {
 			if i > 0 {
-				b.WriteString("\t")
+				buf.WriteByte('\t')
 			}
 			if value == "" {
-				b.WriteString("-")
+				buf.WriteByte('-')
 			} else {
-				b.WriteString(value)
+				buf.WriteString(value)
 			}
 		}
 	}
-	return b.String(), nil
+	return buf.String(), nil
+}
+
+// EscapedString writes the string s to the given bytes.Buffer while properly escaping
+// special characters (backslash, double quote, newline, carriage return, tab).
+func writeEscapedString(buf *bytes.Buffer, s string) {
+	for _, r := range s {
+		switch r {
+		case '\\':
+			buf.WriteString("\\\\")
+		case '"':
+			buf.WriteString("\\\"")
+		case '\n':
+			buf.WriteString("\\n")
+		case '\r':
+			buf.WriteString("\\r")
+		case '\t':
+			buf.WriteString("\\t")
+		default:
+			buf.WriteRune(r)
+		}
+	}
 }