[performance] use native Go code to probe JPEGs (#3206)

* use native Go code to probe JPEGs

* add note about copying from github.com/disintegration/imaging

* add more code comments

4 files changed, 286 insertions, 3 deletions

diff --git a/internal/media/metadata.go b/internal/media/metadata.go
index e9256f1b1..e8eb32c0d 100644
--- a/internal/media/metadata.go
+++ b/internal/media/metadata.go
@@ -73,7 +73,7 @@ func clearMetadata(ctx context.Context, filepath string) error {
 }
 
 // terminateExif cleans exif data from file at input path, into file
-// at output path, exusing given file extension to determine cleaning.
+// at output path, using given file extension to determine cleaning type.
 func terminateExif(outpath, inpath string, ext string) error {
 	// Open input file at given path.
 	inFile, err := os.Open(inpath)
diff --git a/internal/media/probe.go b/internal/media/probe.go
new file mode 100644
index 000000000..882a2981d
--- /dev/null
+++ b/internal/media/probe.go
@@ -0,0 +1,283 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package media
+
+import (
+	"context"
+	"encoding/binary"
+	"image/jpeg"
+	"io"
+	"os"
+	"strings"
+
+	"codeberg.org/gruf/go-byteutil"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+)
+
+const (
+	// image magic header bytes.
+	magicJPEG = "\xff\xd8\xff"
+)
+
+// probe will first attempt to probe the file at path using native Go code
+// (for performance), but falls back to using ffprobe to retrieve media details.
+func probe(ctx context.Context, filepath string) (*result, error) {
+	// Open input file at given path.
+	file, err := os.Open(filepath)
+	if err != nil {
+		return nil, gtserror.Newf("error opening file %s: %w", filepath, err)
+	}
+
+	// Close on return.
+	defer file.Close()
+
+	// Byte buf to check for
+	// file header magic bytes.
+	buf := make([]byte, 3)
+
+	// Read file header into buffer.
+	_, err = io.ReadFull(file, buf)
+	if err != nil {
+		return nil, gtserror.Newf("error reading file %s: %w", filepath, err)
+	}
+
+	switch {
+	// Attempt to probe JPEG types
+	// separately, to save calls into
+	// WebAssembly for a common image.
+	case string(buf[:len(magicJPEG)]) == magicJPEG:
+		log.Debug(ctx, "probing jpeg")
+		return probeJPEG(file)
+
+	default:
+		// Close BEFORE
+		// pass to ffprobe.
+		_ = file.Close()
+
+		// For everything else, fall back
+		// to calling ffprobe on input file.
+		log.Debug(ctx, "ffprobing file")
+		return ffprobe(ctx, filepath)
+	}
+}
+
+// probeJPEG decodes the given file as JPEG and determines
+// image details from the decoded JPEG using native Go code.
+func probeJPEG(file *os.File) (*result, error) {
+	// Attempt to decode JPEG, adding back hdr magic.
+	cfg, err := jpeg.DecodeConfig(io.MultiReader(
+		strings.NewReader(magicJPEG),
+		file,
+	))
+	if err != nil {
+		return nil, gtserror.Newf("error decoding file %s: %w", file.Name(), err)
+	}
+
+	// Jump back to file start.
+	_, err = file.Seek(0, 0)
+	if err != nil {
+		return nil, gtserror.Newf("error seeking in file %s: %w", file.Name(), err)
+	}
+
+	// Read orientation data from EXIF.
+	orientation := readOrientation(file)
+
+	// Setup result as if
+	// ffprobe'd resulting in
+	// JPEG file container.
+	var res result
+	res.format = "image2"
+
+	// Set image orientation data.
+	res.orientation = orientation
+
+	// Extract image details.
+	res.video = []videoStream{{
+		stream: stream{codec: "mjpeg"},
+		width:  cfg.Width,
+		height: cfg.Height,
+
+		// setting a pixel color format
+		// doesn't matter for JPEG, as we
+		// don't bother even using it.
+		pixfmt: "",
+	}}
+
+	return &res, nil
+}
+
+// readOrientation reads orientation EXIF
+// data (if it even exists) from image file.
+//
+// copied from github.com/disintegration/imaging
+// but modified to optimize discard operations.
+func readOrientation(r *os.File) int {
+	const (
+		markerAPP1     = 0xffe1
+		exifHeader     = 0x45786966
+		byteOrderBE    = 0x4d4d
+		byteOrderLE    = 0x4949
+		orientationTag = 0x0112
+	)
+
+	// Setup a discard read buffer.
+	buf := new(byteutil.Buffer)
+	buf.Guarantee(32)
+
+	// discard simply reads into buf.
+	discard := func(n int) error {
+		buf.Guarantee(n) // ensure big enough
+		_, err := io.ReadFull(r, buf.B[:n])
+		return err
+	}
+
+	// Skip past JPEG SOI marker.
+	if err := discard(2); err != nil {
+		return orientationUnspecified
+	}
+
+	// Find JPEG
+	// APP1 marker.
+	for {
+		var marker, size uint16
+
+		if err := binary.Read(r, binary.BigEndian, &marker); err != nil {
+			return orientationUnspecified
+		}
+
+		if err := binary.Read(r, binary.BigEndian, &size); err != nil {
+			return orientationUnspecified
+		}
+
+		if marker>>8 != 0xff {
+			return orientationUnspecified // Invalid JPEG marker.
+		}
+
+		if marker == markerAPP1 {
+			break
+		}
+
+		if size < 2 {
+			return orientationUnspecified // Invalid block size.
+		}
+
+		if err := discard(int(size - 2)); err != nil {
+			return orientationUnspecified
+		}
+	}
+
+	// Check if EXIF
+	// header is present.
+	var header uint32
+
+	if err := binary.Read(r, binary.BigEndian, &header); err != nil {
+		return orientationUnspecified
+	}
+
+	if header != exifHeader {
+		return orientationUnspecified
+	}
+
+	if err := discard(2); err != nil {
+		return orientationUnspecified
+	}
+
+	// Read byte
+	// order info.
+	var (
+		byteOrderTag uint16
+		byteOrder    binary.ByteOrder
+	)
+
+	if err := binary.Read(r, binary.BigEndian, &byteOrderTag); err != nil {
+		return orientationUnspecified
+	}
+
+	switch byteOrderTag {
+	case byteOrderBE:
+		byteOrder = binary.BigEndian
+	case byteOrderLE:
+		byteOrder = binary.LittleEndian
+	default:
+		return orientationUnspecified // Invalid byte order flag.
+	}
+
+	if err := discard(2); err != nil {
+		return orientationUnspecified
+	}
+
+	// Skip the
+	// EXIF offset.
+	var offset uint32
+
+	if err := binary.Read(r, byteOrder, &offset); err != nil {
+		return orientationUnspecified
+	}
+
+	if offset < 8 {
+		return orientationUnspecified // Invalid offset value.
+	}
+
+	if err := discard(int(offset - 8)); err != nil {
+		return orientationUnspecified
+	}
+
+	// Read the
+	// number of tags.
+	var numTags uint16
+
+	if err := binary.Read(r, byteOrder, &numTags); err != nil {
+		return orientationUnspecified
+	}
+
+	// Find the orientation tag.
+	for i := 0; i < int(numTags); i++ {
+		var tag uint16
+
+		if err := binary.Read(r, byteOrder, &tag); err != nil {
+			return orientationUnspecified
+		}
+
+		if tag != orientationTag {
+			if err := discard(10); err != nil {
+				return orientationUnspecified
+			}
+			continue
+		}
+
+		if err := discard(6); err != nil {
+			return orientationUnspecified
+		}
+
+		var val uint16
+
+		if err := binary.Read(r, byteOrder, &val); err != nil {
+			return orientationUnspecified
+		}
+
+		if val < 1 || val > 8 {
+			return orientationUnspecified // Invalid tag value.
+		}
+
+		return int(val)
+	}
+
+	// Missing orientation tag.
+	return orientationUnspecified
+}
diff --git a/internal/media/processingemoji.go b/internal/media/processingemoji.go
index 696b78ed3..89a1bcc91 100644
--- a/internal/media/processingemoji.go
+++ b/internal/media/processingemoji.go
@@ -154,7 +154,7 @@ func (p *ProcessingEmoji) store(ctx context.Context) error {
 
 	// Pass input file through ffprobe to
 	// parse further metadata information.
-	result, err := ffprobe(ctx, temppath)
+	result, err := probe(ctx, temppath)
 	if err != nil && !isUnsupportedTypeErr(err) {
 		return gtserror.Newf("ffprobe error: %w", err)
 	} else if result == nil {
diff --git a/internal/media/processingmedia.go b/internal/media/processingmedia.go
index b89bbb41d..78c6c61a9 100644
--- a/internal/media/processingmedia.go
+++ b/internal/media/processingmedia.go
@@ -162,7 +162,7 @@ func (p *ProcessingMedia) store(ctx context.Context) error {
 
 	// Pass input file through ffprobe to
 	// parse further metadata information.
-	result, err := ffprobe(ctx, temppath)
+	result, err := probe(ctx, temppath)
 	if err != nil && !isUnsupportedTypeErr(err) {
 		return gtserror.Newf("ffprobe error: %w", err)
 	} else if result == nil {