perf(filter): Speed up expression String methods

Use the StringBuilder for a more efficient
string concatenation.

Author: rabbitstack

pkg/filter/ql/expr.go

@@ -18,7 +18,9 @@
 
 package ql
 
-import "fmt"
+import (
+	"strings"
+)
 
 // Node represents a node in the abstract syntax tree.
 type Node interface {
@@ -36,7 +38,14 @@ type ParenExpr struct {
 }
 
 // String returns a string representation of the parenthesized expression.
-func (e *ParenExpr) String() string { return fmt.Sprintf("(%s)", e.Expr.String()) }
+func (e *ParenExpr) String() string {
+	var b strings.Builder
+	b.Grow(len(e.Expr.String()) + 2)
+	b.WriteString("(")
+	b.WriteString(e.Expr.String())
+	b.WriteString(")")
+	return b.String()
+}
 
 // BinaryExpr represents an operation between two expressions.
 type BinaryExpr struct {
@@ -47,7 +56,20 @@ type BinaryExpr struct {
 
 // String returns a string representation of the binary expression.
 func (e *BinaryExpr) String() string {
-	return fmt.Sprintf("%s %s %s", e.LHS.String(), e.Op.String(), e.RHS.String())
+	var b strings.Builder
+
+	lhs := e.LHS.String()
+	op := e.Op.String()
+	rhs := e.RHS.String()
+
+	b.Grow(len(lhs) + len(op) + len(rhs) + 2)
+	b.WriteString(lhs)
+	b.WriteString(" ")
+	b.WriteString(op)
+	b.WriteString(" ")
+	b.WriteString(rhs)
+
+	return b.String()
 }
 
 // NotExpr represents an unary not expression.
@@ -56,4 +78,11 @@ type NotExpr struct {
 }
 
 // String returns a string representation of the not expression.
-func (e *NotExpr) String() string { return fmt.Sprintf("(%s)", e.Expr.String()) }
+func (e *NotExpr) String() string {
+	var b strings.Builder
+	b.Grow(len(e.Expr.String()) + 2)
+	b.WriteString("(")
+	b.WriteString(e.Expr.String())
+	b.WriteString(")")
+	return b.String()
+}

pkg/filter/ql/literal.go

@@ -19,7 +19,6 @@
 package ql
 
 import (
-	"bytes"
 	"fmt"
 	"github.com/rabbitstack/fibratus/pkg/filter/fields"
 	"github.com/rabbitstack/fibratus/pkg/kevent"
@@ -129,16 +128,23 @@ type ListLiteral struct {
 
 // String returns a string representation of the literal.
 func (s *ListLiteral) String() string {
-	var buf bytes.Buffer
-	_, _ = buf.WriteString("(")
-	for idx, tagKey := range s.Values {
+	var n int
+	for _, elem := range s.Values {
+		n += len(elem) + 2
+	}
+
+	var b strings.Builder
+	b.Grow(n + 2)
+	b.WriteString("(")
+	for idx, elem := range s.Values {
 		if idx != 0 {
-			_, _ = buf.WriteString(", ")
+			b.WriteString(", ")
 		}
-		_, _ = buf.WriteString(tagKey)
+		b.WriteString(elem)
 	}
-	_, _ = buf.WriteString(")")
-	return buf.String()
+	b.WriteString(")")
+
+	return b.String()
 }
 
 // Function represents a function call.