Reduce string allocations in mimetype code

internal/repository/mime/mime.go

@@ -0,0 +1,16 @@
+package mime
+
+import "strings"
+
+// Split spits the mimetype into its main type and subtype.
+func Split(mimeTypeFull string) (mimeType, mimeSubType string) {
+	// Replace with strings.Cut() when Go 1.18 is our new base version.
+	separatorIndex := strings.IndexByte(mimeTypeFull, '/')
+	if separatorIndex == -1 || mimeTypeFull[separatorIndex+1:] == "" {
+		return "", "" // Empty or only one part. Ignore.
+	}
+
+	mimeType = mimeTypeFull[:separatorIndex]
+	mimeSubType = mimeTypeFull[separatorIndex+1:]
+	return
+}

internal/repository/mime/mime_test.go

@@ -0,0 +1,21 @@
+package mime
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSplitMimeType(t *testing.T) {
+	main, sub := Split("text/plain")
+	assert.Equal(t, "text", main)
+	assert.Equal(t, "plain", sub)
+
+	main, sub = Split("text/")
+	assert.Empty(t, main)
+	assert.Empty(t, sub)
+
+	main, sub = Split("")
+	assert.Empty(t, main)
+	assert.Empty(t, sub)
+}

storage/filter.go

@@ -4,6 +4,7 @@ import (
 	"strings"
 
 	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/internal/repository/mime"
 )
 
 // FileFilter is an interface that can be implemented to provide a filter to a file dialog.
@@ -42,18 +43,21 @@ func NewExtensionFileFilter(extensions []string) FileFilter {
 
 // Matches returns true if a file URI has one of the filtered mimetypes.
 func (mt *MimeTypeFileFilter) Matches(uri fyne.URI) bool {
-	mimeType, mimeSubType := splitMimeType(uri)
+	mimeType, mimeSubType := mime.Split(uri.MimeType())
 	for _, mimeTypeFull := range mt.MimeTypes {
-		mimeTypeSplit := strings.Split(mimeTypeFull, "/")
-		if len(mimeTypeSplit) <= 1 {
+		mType, mSubType := mime.Split(mimeTypeFull)
+		if mType == "" || mSubType == "" {
 			continue
 		}
-		mType := mimeTypeSplit[0]
-		mSubType := strings.Split(mimeTypeSplit[1], ";")[0]
-		if mType == mimeType {
-			if mSubType == mimeSubType || mSubType == "*" {
-				return true
-			}
+
+		// Replace with strings.Cut() when Go 1.18 is our new base version.
+		subTypeSeparatorIndex := strings.IndexByte(mSubType, ';')
+		if subTypeSeparatorIndex != -1 {
+			mSubType = mSubType[:subTypeSeparatorIndex]
+		}
+
+		if mType == mimeType && (mSubType == mimeSubType || mSubType == "*") {
+			return true
 		}
 	}
 	return false
@@ -64,16 +68,3 @@ func (mt *MimeTypeFileFilter) Matches(uri fyne.URI) bool {
 func NewMimeTypeFileFilter(mimeTypes []string) FileFilter {
 	return &MimeTypeFileFilter{MimeTypes: mimeTypes}
 }
-
-func splitMimeType(uri fyne.URI) (mimeType, mimeSubType string) {
-	mimeTypeFull := uri.MimeType()
-	mimeTypeSplit := strings.Split(mimeTypeFull, "/")
-	if len(mimeTypeSplit) <= 1 {
-		mimeType, mimeSubType = "", ""
-		return
-	}
-	mimeType = mimeTypeSplit[0]
-	mimeSubType = mimeTypeSplit[1]
-
-	return
-}

storage/repository/uri.go

@@ -30,7 +30,6 @@ func (u *uri) Name() string {
 }
 
 func (u *uri) MimeType() string {
-
 	mimeTypeFull := mime.TypeByExtension(u.Extension())
 	if mimeTypeFull == "" {
 		mimeTypeFull = "text/plain"
@@ -50,7 +49,12 @@ func (u *uri) MimeType() string {
 		}
 	}
 
-	return strings.Split(mimeTypeFull, ";")[0]
+	// Replace with strings.Cut() when Go 1.18 is our new base version.
+	semicolonIndex := strings.IndexByte(mimeTypeFull, ';')
+	if semicolonIndex == -1 {
+		return mimeTypeFull
+	}
+	return mimeTypeFull[:semicolonIndex]
 }
 
 func (u *uri) Scheme() string {

widget/fileicon.go

@@ -1,10 +1,9 @@
 package widget
 
 import (
-	"strings"
-
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/canvas"
+	"fyne.io/fyne/v2/internal/repository/mime"
 	"fyne.io/fyne/v2/internal/widget"
 	"fyne.io/fyne/v2/storage"
 	"fyne.io/fyne/v2/theme"
@@ -99,7 +98,8 @@ func (i *FileIcon) lookupIcon(uri fyne.URI) fyne.Resource {
 		return theme.FolderIcon()
 	}
 
-	switch splitMimeType(uri) {
+	mainMimeType, _ := mime.Split(uri.MimeType())
+	switch mainMimeType {
 	case "application":
 		return theme.FileApplicationIcon()
 	case "audio":
@@ -201,11 +201,3 @@ func trimmedExtension(uri fyne.URI) string {
 	}
 	return ext
 }
-
-func splitMimeType(uri fyne.URI) string {
-	mimeTypeSplit := strings.Split(uri.MimeType(), "/")
-	if len(mimeTypeSplit) <= 1 {
-		return ""
-	}
-	return mimeTypeSplit[0]
-}