[bugfix] Allow processing of .png files where checksum is not correct (#487)

* add png stripping code from google/wuffs

* experiment with stripping data from pngs

* add test images

* use StrippedPngDecode for pngs

* add StrippedPngDecode func

* update tests for (no)alphachannel pngs

* nolint on copied function

1 files changed, 144 insertions, 0 deletions

diff --git a/internal/media/manager_test.go b/internal/media/manager_test.go
index 95cefe1db..75e706ba7 100644
--- a/internal/media/manager_test.go
+++ b/internal/media/manager_test.go
@@ -111,6 +111,150 @@ func (suite *ManagerTestSuite) TestSimpleJpegProcessBlocking() {
 	suite.Equal(processedThumbnailBytesExpected, processedThumbnailBytes)
 }
 
+func (suite *ManagerTestSuite) TestPngNoAlphaChannelProcessBlocking() {
+	ctx := context.Background()
+
+	data := func(_ context.Context) (io.Reader, int, error) {
+		// load bytes from a test image
+		b, err := os.ReadFile("./test/test-png-noalphachannel.png")
+		if err != nil {
+			panic(err)
+		}
+		return bytes.NewBuffer(b), len(b), nil
+	}
+
+	accountID := "01FS1X72SK9ZPW0J1QQ68BD264"
+
+	// process the media with no additional info provided
+	processingMedia, err := suite.manager.ProcessMedia(ctx, data, nil, accountID, nil)
+	suite.NoError(err)
+	// fetch the attachment id from the processing media
+	attachmentID := processingMedia.AttachmentID()
+
+	// do a blocking call to fetch the attachment
+	attachment, err := processingMedia.LoadAttachment(ctx)
+	suite.NoError(err)
+	suite.NotNil(attachment)
+
+	// make sure it's got the stuff set on it that we expect
+	// the attachment ID and accountID we expect
+	suite.Equal(attachmentID, attachment.ID)
+	suite.Equal(accountID, attachment.AccountID)
+
+	// file meta should be correctly derived from the image
+	suite.EqualValues(gtsmodel.Original{
+		Width: 186, Height: 187, Size: 34782, Aspect: 0.9946524064171123,
+	}, attachment.FileMeta.Original)
+	suite.EqualValues(gtsmodel.Small{
+		Width: 186, Height: 187, Size: 34782, Aspect: 0.9946524064171123,
+	}, attachment.FileMeta.Small)
+	suite.Equal("image/png", attachment.File.ContentType)
+	suite.Equal("image/jpeg", attachment.Thumbnail.ContentType)
+	suite.Equal(17471, attachment.File.FileSize)
+	suite.Equal("LFP?{^.A-?xd.9o#RVRQ~oj:_0xW", attachment.Blurhash)
+
+	// now make sure the attachment is in the database
+	dbAttachment, err := suite.db.GetAttachmentByID(ctx, attachmentID)
+	suite.NoError(err)
+	suite.NotNil(dbAttachment)
+
+	// make sure the processed file is in storage
+	processedFullBytes, err := suite.storage.Get(attachment.File.Path)
+	suite.NoError(err)
+	suite.NotEmpty(processedFullBytes)
+
+	// load the processed bytes from our test folder, to compare
+	processedFullBytesExpected, err := os.ReadFile("./test/test-png-noalphachannel-processed.png")
+	suite.NoError(err)
+	suite.NotEmpty(processedFullBytesExpected)
+
+	// the bytes in storage should be what we expected
+	suite.Equal(processedFullBytesExpected, processedFullBytes)
+
+	// now do the same for the thumbnail and make sure it's what we expected
+	processedThumbnailBytes, err := suite.storage.Get(attachment.Thumbnail.Path)
+	suite.NoError(err)
+	suite.NotEmpty(processedThumbnailBytes)
+
+	processedThumbnailBytesExpected, err := os.ReadFile("./test/test-png-noalphachannel-thumbnail.jpg")
+	suite.NoError(err)
+	suite.NotEmpty(processedThumbnailBytesExpected)
+
+	suite.Equal(processedThumbnailBytesExpected, processedThumbnailBytes)
+}
+
+func (suite *ManagerTestSuite) TestPngAlphaChannelProcessBlocking() {
+	ctx := context.Background()
+
+	data := func(_ context.Context) (io.Reader, int, error) {
+		// load bytes from a test image
+		b, err := os.ReadFile("./test/test-png-alphachannel.png")
+		if err != nil {
+			panic(err)
+		}
+		return bytes.NewBuffer(b), len(b), nil
+	}
+
+	accountID := "01FS1X72SK9ZPW0J1QQ68BD264"
+
+	// process the media with no additional info provided
+	processingMedia, err := suite.manager.ProcessMedia(ctx, data, nil, accountID, nil)
+	suite.NoError(err)
+	// fetch the attachment id from the processing media
+	attachmentID := processingMedia.AttachmentID()
+
+	// do a blocking call to fetch the attachment
+	attachment, err := processingMedia.LoadAttachment(ctx)
+	suite.NoError(err)
+	suite.NotNil(attachment)
+
+	// make sure it's got the stuff set on it that we expect
+	// the attachment ID and accountID we expect
+	suite.Equal(attachmentID, attachment.ID)
+	suite.Equal(accountID, attachment.AccountID)
+
+	// file meta should be correctly derived from the image
+	suite.EqualValues(gtsmodel.Original{
+		Width: 186, Height: 187, Size: 34782, Aspect: 0.9946524064171123,
+	}, attachment.FileMeta.Original)
+	suite.EqualValues(gtsmodel.Small{
+		Width: 186, Height: 187, Size: 34782, Aspect: 0.9946524064171123,
+	}, attachment.FileMeta.Small)
+	suite.Equal("image/png", attachment.File.ContentType)
+	suite.Equal("image/jpeg", attachment.Thumbnail.ContentType)
+	suite.Equal(18904, attachment.File.FileSize)
+	suite.Equal("LFP?{^.A-?xd.9o#RVRQ~oj:_0xW", attachment.Blurhash)
+
+	// now make sure the attachment is in the database
+	dbAttachment, err := suite.db.GetAttachmentByID(ctx, attachmentID)
+	suite.NoError(err)
+	suite.NotNil(dbAttachment)
+
+	// make sure the processed file is in storage
+	processedFullBytes, err := suite.storage.Get(attachment.File.Path)
+	suite.NoError(err)
+	suite.NotEmpty(processedFullBytes)
+
+	// load the processed bytes from our test folder, to compare
+	processedFullBytesExpected, err := os.ReadFile("./test/test-png-alphachannel-processed.png")
+	suite.NoError(err)
+	suite.NotEmpty(processedFullBytesExpected)
+
+	// the bytes in storage should be what we expected
+	suite.Equal(processedFullBytesExpected, processedFullBytes)
+
+	// now do the same for the thumbnail and make sure it's what we expected
+	processedThumbnailBytes, err := suite.storage.Get(attachment.Thumbnail.Path)
+	suite.NoError(err)
+	suite.NotEmpty(processedThumbnailBytes)
+
+	processedThumbnailBytesExpected, err := os.ReadFile("./test/test-png-alphachannel-thumbnail.jpg")
+	suite.NoError(err)
+	suite.NotEmpty(processedThumbnailBytesExpected)
+
+	suite.Equal(processedThumbnailBytesExpected, processedThumbnailBytes)
+}
+
 func (suite *ManagerTestSuite) TestSimpleJpegProcessBlockingWithCallback() {
 	ctx := context.Background()