some improvments

internal/pdf/contentstream/contentstream.go

@@ -3,6 +3,7 @@ package contentstream
 import (
 	"bytes"
 	"fmt"
+	"strings"
 
 	"gitea.tecamino.com/paadi/pdfmerge/internal/pdf/core"
 )
@@ -111,7 +112,7 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 	}
 	inText := false
 	xPos, yPos := float64(-1), float64(-1)
-	txt := ""
+	var txt strings.Builder
 	for _, op := range *operations {
 		switch op.Operand {
 		case "BT":
@@ -122,7 +123,7 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 
 		if op.Operand == "Td" || op.Operand == "TD" || op.Operand == "T*" {
 			// Move to next line...
-			txt += "\n"
+			txt.WriteString("\n")
 		}
 		if op.Operand == "Tm" {
 			if len(op.Params) != 6 {
@@ -147,7 +148,7 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 			if yPos == -1 {
 				yPos = float64(*yfloat)
 			} else if yPos > float64(*yfloat) {
-				txt += "\n"
+				txt.WriteString("\n")
 				xPos = float64(*xfloat)
 				yPos = float64(*yfloat)
 				continue
@@ -155,7 +156,7 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 			if xPos == -1 {
 				xPos = float64(*xfloat)
 			} else if xPos < float64(*xfloat) {
-				txt += "\t"
+				txt.WriteString("\t")
 				xPos = float64(*xfloat)
 			}
 		}
@@ -170,14 +171,14 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 			for _, obj := range *paramList {
 				switch v := obj.(type) {
 				case *core.PdfObjectString:
-					txt += string(*v)
+					txt.WriteString(string(*v))
 				case *core.PdfObjectFloat:
 					if *v < -100 {
-						txt += " "
+						txt.WriteString(" ")
 					}
 				case *core.PdfObjectInteger:
 					if *v < -100 {
-						txt += " "
+						txt.WriteString(" ")
 					}
 				}
 			}
@@ -189,9 +190,9 @@ func (s *ContentStreamParser) ExtractText() (string, error) {
 			if !ok {
 				return "", fmt.Errorf("invalid parameter type, not string (%T)", op.Params[0])
 			}
-			txt += string(*param)
+			txt.WriteString(string(*param))
 		}
 	}
 
-	return txt, nil
+	return txt.String(), nil
 }