refactor(thumbnails): thread context.Context through the preprocessor Convert interface

The Tika preview extractor does a network call; it was using context.Background().
Pass the request context from the gRPC handler through Convert so the unpack call
respects cancellation and deadlines. Non-I/O decoders ignore the context.

services/thumbnails/pkg/preprocessor/preprocessor.go

@@ -4,6 +4,7 @@ import (
 	"archive/zip"
 	"bufio"
 	"bytes"
+	"context"
 	"encoding/base64"
 	"encoding/json"
 	"image"
@@ -26,14 +27,14 @@ import (
 
 // FileConverter is the interface for the file converter
 type FileConverter interface {
-	Convert(r io.Reader) (any, error)
+	Convert(ctx context.Context, r io.Reader) (any, error)
 }
 
 // GifDecoder is a converter for the gif file
 type GifDecoder struct{}
 
 // Convert reads the gif file and returns the thumbnail image
-func (i GifDecoder) Convert(r io.Reader) (any, error) {
+func (i GifDecoder) Convert(_ context.Context, r io.Reader) (any, error) {
 	img, err := gif.DecodeAll(r)
 	if err != nil {
 		return nil, errors.Wrap(err, `could not decode the image`)
@@ -45,7 +46,7 @@ func (i GifDecoder) Convert(r io.Reader) (any, error) {
 type GgsDecoder struct{ thumbnailpath string }
 
 // Convert reads the ggs file and returns the thumbnail image
-func (g GgsDecoder) Convert(r io.Reader) (any, error) {
+func (g GgsDecoder) Convert(ctx context.Context, r io.Reader) (any, error) {
 	var buf bytes.Buffer
 	_, err := io.Copy(&buf, r)
 	if err != nil {
@@ -65,7 +66,7 @@ func (g GgsDecoder) Convert(r io.Reader) (any, error) {
 			if converter == nil {
 				return nil, thumbnailerErrors.ErrNoConverterForExtractedImageFromGgsFile
 			}
-			img, err := converter.Convert(thumbnail)
+			img, err := converter.Convert(ctx, thumbnail)
 			if err != nil {
 				return nil, errors.Wrap(err, `could not decode the image`)
 			}
@@ -79,7 +80,7 @@ func (g GgsDecoder) Convert(r io.Reader) (any, error) {
 type AudioDecoder struct{}
 
 // Convert reads the audio file and extracts the thumbnail image from the id3 tag
-func (i AudioDecoder) Convert(r io.Reader) (any, error) {
+func (i AudioDecoder) Convert(ctx context.Context, r io.Reader) (any, error) {
 	b, err := io.ReadAll(r)
 	if err != nil {
 		return nil, err
@@ -99,7 +100,7 @@ func (i AudioDecoder) Convert(r io.Reader) (any, error) {
 		return nil, thumbnailerErrors.ErrNoConverterForExtractedImageFromAudioFile
 	}
 
-	return converter.Convert(bytes.NewReader(picture.Data))
+	return converter.Convert(ctx, bytes.NewReader(picture.Data))
 }
 
 // TxtToImageConverter is a converter for the text file
@@ -108,7 +109,7 @@ type TxtToImageConverter struct {
 }
 
 // Convert reads the text file and renders it into a thumbnail image
-func (t TxtToImageConverter) Convert(r io.Reader) (any, error) {
+func (t TxtToImageConverter) Convert(_ context.Context, r io.Reader) (any, error) {
 	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
 
 	imgBounds := img.Bounds()
@@ -203,7 +204,7 @@ type GGPStruct struct {
 type GgpDecoder struct{}
 
 // Convert reads the ggp file and returns the first thumbnail image
-func (j GgpDecoder) Convert(r io.Reader) (any, error) {
+func (j GgpDecoder) Convert(_ context.Context, r io.Reader) (any, error) {
 	ggp := &GGPStruct{}
 	err := json.NewDecoder(r).Decode(ggp)
 	if err != nil {