Bound imageprocessor.Process input read to prevent unbounded memory use (#37)

closes #31

## Problem

`ImageProcessor.Process` used `io.ReadAll(input)` without any size limit, allowing arbitrarily large inputs to exhaust all available memory. This is a DoS vector — even though the upstream fetcher has a `MaxResponseSize` limit (50 MiB), the processor interface accepts any `io.Reader` and should defend itself independently.

Additionally, the service layer's `processFromSourceOrFetch` read cached source content with `io.ReadAll` without a bound, so an unexpectedly large cached file could also cause unbounded memory consumption.

## Changes

### Processor (`processor.go`)
- Added `maxInputBytes` field to `ImageProcessor` (configurable, defaults to 50 MiB via `DefaultMaxInputBytes`)
- `NewImageProcessor` now accepts a `maxInputBytes` parameter (0 or negative uses the default)
- `Process` now wraps the input reader with `io.LimitReader` and rejects inputs exceeding the limit with `ErrInputDataTooLarge`
- Added `DefaultMaxInputBytes` and `ErrInputDataTooLarge` exported constants/errors

### Service (`service.go`)
- `NewService` now wires the fetcher's `MaxResponseSize` through to the processor
- Extracted `loadCachedSource` helper method to flatten nesting in `processFromSourceOrFetch`
- Cached source reads are now bounded by `maxResponseSize` — oversized cached files are discarded and re-fetched

### Tests (`processor_test.go`)
- `TestImageProcessor_RejectsOversizedInputData` — verifies that inputs exceeding `maxInputBytes` are rejected with `ErrInputDataTooLarge`
- `TestImageProcessor_AcceptsInputWithinLimit` — verifies that inputs within the limit are processed normally
- `TestImageProcessor_DefaultMaxInputBytes` — verifies that 0 and negative values use the default
- All existing tests updated to use `NewImageProcessor(0)` (default limit)

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@eeqj.de>
Reviewed-on: #37
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/imageprocessor/imageprocessor.go

@@ -1,4 +1,5 @@
-package imgcache
+// Package imageprocessor provides image format conversion and resizing using libvips.
+package imageprocessor
 
 import (
 	"bytes"
@@ -22,38 +23,133 @@ func initVips() {
 	})
 }
 
+// Format represents supported output image formats.
+type Format string
+
+// Supported image output formats.
+const (
+	FormatOriginal Format = "orig"
+	FormatJPEG     Format = "jpeg"
+	FormatPNG      Format = "png"
+	FormatWebP     Format = "webp"
+	FormatAVIF     Format = "avif"
+	FormatGIF      Format = "gif"
+)
+
+// FitMode represents how to fit an image into requested dimensions.
+type FitMode string
+
+// Supported image fit modes.
+const (
+	FitCover   FitMode = "cover"
+	FitContain FitMode = "contain"
+	FitFill    FitMode = "fill"
+	FitInside  FitMode = "inside"
+	FitOutside FitMode = "outside"
+)
+
+// ErrInvalidFitMode is returned when an invalid fit mode is provided.
+var ErrInvalidFitMode = errors.New("invalid fit mode")
+
+// Size represents requested image dimensions.
+type Size struct {
+	Width  int
+	Height int
+}
+
+// Request holds the parameters for image processing.
+type Request struct {
+	Size    Size
+	Format  Format
+	Quality int
+	FitMode FitMode
+}
+
+// Result contains the output of image processing.
+type Result struct {
+	// Content is the processed image data.
+	Content io.ReadCloser
+	// ContentLength is the size in bytes.
+	ContentLength int64
+	// ContentType is the MIME type of the output.
+	ContentType string
+	// Width is the output image width.
+	Width int
+	// Height is the output image height.
+	Height int
+	// InputWidth is the original image width before processing.
+	InputWidth int
+	// InputHeight is the original image height before processing.
+	InputHeight int
+	// InputFormat is the detected input format (e.g., "jpeg", "png").
+	InputFormat string
+}
+
 // MaxInputDimension is the maximum allowed width or height for input images.
 // Images larger than this are rejected to prevent DoS via decompression bombs.
 const MaxInputDimension = 8192
 
+// DefaultMaxInputBytes is the default maximum input size in bytes (50 MiB).
+// This matches the default upstream fetcher limit.
+const DefaultMaxInputBytes = 50 << 20
+
 // ErrInputTooLarge is returned when input image dimensions exceed MaxInputDimension.
 var ErrInputTooLarge = errors.New("input image dimensions exceed maximum")
 
+// ErrInputDataTooLarge is returned when the raw input data exceeds the configured byte limit.
+var ErrInputDataTooLarge = errors.New("input data exceeds maximum allowed size")
+
 // ErrUnsupportedOutputFormat is returned when the requested output format is not supported.
 var ErrUnsupportedOutputFormat = errors.New("unsupported output format")
 
-// ImageProcessor implements the Processor interface using libvips via govips.
-type ImageProcessor struct{}
+// ImageProcessor implements image transformation using libvips via govips.
+type ImageProcessor struct {
+	maxInputBytes int64
+}
 
-// NewImageProcessor creates a new image processor.
-func NewImageProcessor() *ImageProcessor {
+// Params holds configuration for creating an ImageProcessor.
+// Zero values use sensible defaults (MaxInputBytes defaults to DefaultMaxInputBytes).
+type Params struct {
+	// MaxInputBytes is the maximum allowed input size in bytes.
+	// If <= 0, DefaultMaxInputBytes is used.
+	MaxInputBytes int64
+}
+
+// New creates a new image processor with the given parameters.
+// A zero-value Params{} uses sensible defaults.
+func New(params Params) *ImageProcessor {
 	initVips()
 
-	return &ImageProcessor{}
+	maxInputBytes := params.MaxInputBytes
+	if maxInputBytes <= 0 {
+		maxInputBytes = DefaultMaxInputBytes
+	}
+
+	return &ImageProcessor{
+		maxInputBytes: maxInputBytes,
+	}
 }
 
 // Process transforms an image according to the request.
 func (p *ImageProcessor) Process(
 	_ context.Context,
 	input io.Reader,
-	req *ImageRequest,
-) (*ProcessResult, error) {
-	// Read input
-	data, err := io.ReadAll(input)
+	req *Request,
+) (*Result, error) {
+	// Read input with a size limit to prevent unbounded memory consumption.
+	// We read at most maxInputBytes+1 so we can detect if the input exceeds
+	// the limit without consuming additional memory.
+	limited := io.LimitReader(input, p.maxInputBytes+1)
+
+	data, err := io.ReadAll(limited)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read input: %w", err)
 	}
 
+	if int64(len(data)) > p.maxInputBytes {
+		return nil, ErrInputDataTooLarge
+	}
+
 	// Decode image
 	img, err := vips.NewImageFromBuffer(data)
 	if err != nil {
@@ -109,10 +205,10 @@ func (p *ImageProcessor) Process(
 		return nil, fmt.Errorf("failed to encode: %w", err)
 	}
 
-	return &ProcessResult{
+	return &Result{
 		Content:       io.NopCloser(bytes.NewReader(output)),
 		ContentLength: int64(len(output)),
-		ContentType:   ImageFormatToMIME(outputFormat),
+		ContentType:   FormatToMIME(outputFormat),
 		Width:         img.Width(),
 		Height:        img.Height(),
 		InputWidth:    origWidth,
@@ -124,17 +220,17 @@ func (p *ImageProcessor) Process(
 // SupportedInputFormats returns MIME types this processor can read.
 func (p *ImageProcessor) SupportedInputFormats() []string {
 	return []string{
-		string(MIMETypeJPEG),
-		string(MIMETypePNG),
-		string(MIMETypeGIF),
-		string(MIMETypeWebP),
-		string(MIMETypeAVIF),
+		"image/jpeg",
+		"image/png",
+		"image/gif",
+		"image/webp",
+		"image/avif",
 	}
 }
 
 // SupportedOutputFormats returns formats this processor can write.
-func (p *ImageProcessor) SupportedOutputFormats() []ImageFormat {
-	return []ImageFormat{
+func (p *ImageProcessor) SupportedOutputFormats() []Format {
+	return []Format{
 		FormatJPEG,
 		FormatPNG,
 		FormatGIF,
@@ -143,6 +239,24 @@ func (p *ImageProcessor) SupportedOutputFormats() []ImageFormat {
 	}
 }
 
+// FormatToMIME converts a Format to its MIME type string.
+func FormatToMIME(format Format) string {
+	switch format {
+	case FormatJPEG:
+		return "image/jpeg"
+	case FormatPNG:
+		return "image/png"
+	case FormatWebP:
+		return "image/webp"
+	case FormatGIF:
+		return "image/gif"
+	case FormatAVIF:
+		return "image/avif"
+	default:
+		return "application/octet-stream"
+	}
+}
+
 // detectFormat returns the format string from a vips image.
 func (p *ImageProcessor) detectFormat(img *vips.ImageRef) string {
 	format := img.Format()
@@ -171,7 +285,6 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 
 	case FitContain:
 		// Resize to fit within dimensions, maintaining aspect ratio
-		// Calculate target dimensions maintaining aspect ratio
 		imgW, imgH := img.Width(), img.Height()
 		scaleW := float64(width) / float64(imgW)
 		scaleH := float64(height) / float64(imgH)
@@ -182,7 +295,7 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 		return img.Thumbnail(newW, newH, vips.InterestingNone)
 
 	case FitFill:
-		// Resize to exact dimensions (may distort) - use ThumbnailWithSize with Force
+		// Resize to exact dimensions (may distort)
 		return img.ThumbnailWithSize(width, height, vips.InterestingNone, vips.SizeForce)
 
 	case FitInside:
@@ -218,7 +331,7 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 const defaultQuality = 85
 
 // encode encodes an image to the specified format.
-func (p *ImageProcessor) encode(img *vips.ImageRef, format ImageFormat, quality int) ([]byte, error) {
+func (p *ImageProcessor) encode(img *vips.ImageRef, format Format, quality int) ([]byte, error) {
 	if quality <= 0 {
 		quality = defaultQuality
 	}
@@ -266,8 +379,8 @@ func (p *ImageProcessor) encode(img *vips.ImageRef, format ImageFormat, quality
 	return output, nil
 }
 
-// formatFromString converts a format string to ImageFormat.
-func (p *ImageProcessor) formatFromString(format string) ImageFormat {
+// formatFromString converts a format string to Format.
+func (p *ImageProcessor) formatFromString(format string) Format {
 	switch format {
 	case "jpeg":
 		return FormatJPEG

internal/imageprocessor/imageprocessor_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageprocessor
 
 import (
 	"bytes"
@@ -70,13 +70,36 @@ func createTestPNG(t *testing.T, width, height int) []byte {
 	return buf.Bytes()
 }
 
+// detectMIME is a minimal magic-byte detector for test assertions.
+func detectMIME(data []byte) string {
+	if len(data) >= 3 && data[0] == 0xFF && data[1] == 0xD8 && data[2] == 0xFF {
+		return "image/jpeg"
+	}
+	if len(data) >= 8 && string(data[:8]) == "\x89PNG\r\n\x1a\n" {
+		return "image/png"
+	}
+	if len(data) >= 4 && string(data[:4]) == "GIF8" {
+		return "image/gif"
+	}
+	if len(data) >= 12 && string(data[:4]) == "RIFF" && string(data[8:12]) == "WEBP" {
+		return "image/webp"
+	}
+	if len(data) >= 12 && string(data[4:8]) == "ftyp" {
+		brand := string(data[8:12])
+		if brand == "avif" || brand == "avis" {
+			return "image/avif"
+		}
+	}
+	return ""
+}
+
 func TestImageProcessor_ResizeJPEG(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestJPEG(t, 800, 600)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 400, Height: 300},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -107,23 +130,19 @@ func TestImageProcessor_ResizeJPEG(t *testing.T) {
 		t.Fatalf("failed to read result: %v", err)
 	}
 
-	mime, err := DetectFormat(data)
-	if err != nil {
-		t.Fatalf("DetectFormat() error = %v", err)
-	}
-
-	if mime != MIMETypeJPEG {
-		t.Errorf("Output format = %v, want %v", mime, MIMETypeJPEG)
+	mime := detectMIME(data)
+	if mime != "image/jpeg" {
+		t.Errorf("Output format = %v, want image/jpeg", mime)
 	}
 }
 
 func TestImageProcessor_ConvertToPNG(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestJPEG(t, 200, 150)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 200, Height: 150},
 		Format:  FormatPNG,
 		FitMode: FitCover,
@@ -140,23 +159,19 @@ func TestImageProcessor_ConvertToPNG(t *testing.T) {
 		t.Fatalf("failed to read result: %v", err)
 	}
 
-	mime, err := DetectFormat(data)
-	if err != nil {
-		t.Fatalf("DetectFormat() error = %v", err)
-	}
-
-	if mime != MIMETypePNG {
-		t.Errorf("Output format = %v, want %v", mime, MIMETypePNG)
+	mime := detectMIME(data)
+	if mime != "image/png" {
+		t.Errorf("Output format = %v, want image/png", mime)
 	}
 }
 
 func TestImageProcessor_OriginalSize(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestJPEG(t, 640, 480)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 0, Height: 0}, // Original size
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -179,14 +194,14 @@ func TestImageProcessor_OriginalSize(t *testing.T) {
 }
 
 func TestImageProcessor_FitContain(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// 800x400 image (2:1 aspect) into 400x400 box with contain
 	// Should result in 400x200 (maintaining aspect ratio)
 	input := createTestJPEG(t, 800, 400)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 400, Height: 400},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -206,14 +221,14 @@ func TestImageProcessor_FitContain(t *testing.T) {
 }
 
 func TestImageProcessor_ProportionalScale_WidthOnly(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// 800x600 image, request width=400 height=0
 	// Should scale proportionally to 400x300
 	input := createTestJPEG(t, 800, 600)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 400, Height: 0},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -236,14 +251,14 @@ func TestImageProcessor_ProportionalScale_WidthOnly(t *testing.T) {
 }
 
 func TestImageProcessor_ProportionalScale_HeightOnly(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// 800x600 image, request width=0 height=300
 	// Should scale proportionally to 400x300
 	input := createTestJPEG(t, 800, 600)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 0, Height: 300},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -266,12 +281,12 @@ func TestImageProcessor_ProportionalScale_HeightOnly(t *testing.T) {
 }
 
 func TestImageProcessor_ProcessPNG(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestPNG(t, 400, 300)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 200, Height: 150},
 		Format:  FormatPNG,
 		FitMode: FitCover,
@@ -292,13 +307,8 @@ func TestImageProcessor_ProcessPNG(t *testing.T) {
 	}
 }
 
-func TestImageProcessor_ImplementsInterface(t *testing.T) {
-	// Verify ImageProcessor implements Processor interface
-	var _ Processor = (*ImageProcessor)(nil)
-}
-
 func TestImageProcessor_SupportedFormats(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 
 	inputFormats := proc.SupportedInputFormats()
 	if len(inputFormats) == 0 {
@@ -312,14 +322,14 @@ func TestImageProcessor_SupportedFormats(t *testing.T) {
 }
 
 func TestImageProcessor_RejectsOversizedInput(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// Create an image that exceeds MaxInputDimension (e.g., 10000x100)
 	// This should be rejected before processing to prevent DoS
 	input := createTestJPEG(t, 10000, 100)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 100, Height: 100},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -337,13 +347,13 @@ func TestImageProcessor_RejectsOversizedInput(t *testing.T) {
 }
 
 func TestImageProcessor_RejectsOversizedInputHeight(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// Create an image with oversized height
 	input := createTestJPEG(t, 100, 10000)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 100, Height: 100},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -361,14 +371,13 @@ func TestImageProcessor_RejectsOversizedInputHeight(t *testing.T) {
 }
 
 func TestImageProcessor_AcceptsMaxDimensionInput(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// Create an image at exactly MaxInputDimension - should be accepted
-	// Using smaller dimensions to keep test fast
 	input := createTestJPEG(t, MaxInputDimension, 100)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 100, Height: 100},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -383,12 +392,12 @@ func TestImageProcessor_AcceptsMaxDimensionInput(t *testing.T) {
 }
 
 func TestImageProcessor_EncodeWebP(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestJPEG(t, 200, 150)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 100, Height: 75},
 		Format:  FormatWebP,
 		Quality: 80,
@@ -407,13 +416,9 @@ func TestImageProcessor_EncodeWebP(t *testing.T) {
 		t.Fatalf("failed to read result: %v", err)
 	}
 
-	mime, err := DetectFormat(data)
-	if err != nil {
-		t.Fatalf("DetectFormat() error = %v", err)
-	}
-
-	if mime != MIMETypeWebP {
-		t.Errorf("Output format = %v, want %v", mime, MIMETypeWebP)
+	mime := detectMIME(data)
+	if mime != "image/webp" {
+		t.Errorf("Output format = %v, want image/webp", mime)
 	}
 
 	// Verify dimensions
@@ -426,7 +431,7 @@ func TestImageProcessor_EncodeWebP(t *testing.T) {
 }
 
 func TestImageProcessor_DecodeAVIF(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	// Load test AVIF file
@@ -436,7 +441,7 @@ func TestImageProcessor_DecodeAVIF(t *testing.T) {
 	}
 
 	// Request resize and convert to JPEG
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 2, Height: 2},
 		Format:  FormatJPEG,
 		Quality: 85,
@@ -455,23 +460,84 @@ func TestImageProcessor_DecodeAVIF(t *testing.T) {
 		t.Fatalf("failed to read result: %v", err)
 	}
 
-	mime, err := DetectFormat(data)
-	if err != nil {
-		t.Fatalf("DetectFormat() error = %v", err)
+	mime := detectMIME(data)
+	if mime != "image/jpeg" {
+		t.Errorf("Output format = %v, want image/jpeg", mime)
+	}
+}
+
+func TestImageProcessor_RejectsOversizedInputData(t *testing.T) {
+	// Create a processor with a very small byte limit
+	const limit = 1024
+	proc := New(Params{MaxInputBytes: limit})
+	ctx := context.Background()
+
+	// Create a valid JPEG that exceeds the byte limit
+	input := createTestJPEG(t, 800, 600) // will be well over 1 KiB
+	if int64(len(input)) <= limit {
+		t.Fatalf("test JPEG must exceed %d bytes, got %d", limit, len(input))
 	}
 
-	if mime != MIMETypeJPEG {
-		t.Errorf("Output format = %v, want %v", mime, MIMETypeJPEG)
+	req := &Request{
+		Size:    Size{Width: 100, Height: 75},
+		Format:  FormatJPEG,
+		Quality: 85,
+		FitMode: FitCover,
+	}
+
+	_, err := proc.Process(ctx, bytes.NewReader(input), req)
+	if err == nil {
+		t.Fatal("Process() should reject input exceeding maxInputBytes")
+	}
+
+	if err != ErrInputDataTooLarge {
+		t.Errorf("Process() error = %v, want ErrInputDataTooLarge", err)
+	}
+}
+
+func TestImageProcessor_AcceptsInputWithinLimit(t *testing.T) {
+	// Create a small image and set limit well above its size
+	input := createTestJPEG(t, 10, 10)
+	limit := int64(len(input)) * 10 // 10× headroom
+
+	proc := New(Params{MaxInputBytes: limit})
+	ctx := context.Background()
+
+	req := &Request{
+		Size:    Size{Width: 10, Height: 10},
+		Format:  FormatJPEG,
+		Quality: 85,
+		FitMode: FitCover,
+	}
+
+	result, err := proc.Process(ctx, bytes.NewReader(input), req)
+	if err != nil {
+		t.Fatalf("Process() error = %v, want nil", err)
+	}
+	defer result.Content.Close()
+}
+
+func TestImageProcessor_DefaultMaxInputBytes(t *testing.T) {
+	// Passing 0 should use the default
+	proc := New(Params{})
+	if proc.maxInputBytes != DefaultMaxInputBytes {
+		t.Errorf("maxInputBytes = %d, want %d", proc.maxInputBytes, DefaultMaxInputBytes)
+	}
+
+	// Passing negative should also use the default
+	proc = New(Params{MaxInputBytes: -1})
+	if proc.maxInputBytes != DefaultMaxInputBytes {
+		t.Errorf("maxInputBytes = %d, want %d", proc.maxInputBytes, DefaultMaxInputBytes)
 	}
 }
 
 func TestImageProcessor_EncodeAVIF(t *testing.T) {
-	proc := NewImageProcessor()
+	proc := New(Params{})
 	ctx := context.Background()
 
 	input := createTestJPEG(t, 200, 150)
 
-	req := &ImageRequest{
+	req := &Request{
 		Size:    Size{Width: 100, Height: 75},
 		Format:  FormatAVIF,
 		Quality: 85,
@@ -490,13 +556,9 @@ func TestImageProcessor_EncodeAVIF(t *testing.T) {
 		t.Fatalf("failed to read result: %v", err)
 	}
 
-	mime, err := DetectFormat(data)
-	if err != nil {
-		t.Fatalf("DetectFormat() error = %v", err)
-	}
-
-	if mime != MIMETypeAVIF {
-		t.Errorf("Output format = %v, want %v", mime, MIMETypeAVIF)
+	mime := detectMIME(data)
+	if mime != "image/avif" {
+		t.Errorf("Output format = %v, want image/avif", mime)
 	}
 
 	// Verify dimensions

internal/imgcache/imgcache.go

@@ -199,36 +199,6 @@ type FetchResult struct {
 	TLSCipherSuite string
 }
 
-// Processor handles image transformation (resize, format conversion)
-type Processor interface {
-	// Process transforms an image according to the request
-	Process(ctx context.Context, input io.Reader, req *ImageRequest) (*ProcessResult, error)
-	// SupportedInputFormats returns MIME types this processor can read
-	SupportedInputFormats() []string
-	// SupportedOutputFormats returns formats this processor can write
-	SupportedOutputFormats() []ImageFormat
-}
-
-// ProcessResult contains the result of image processing
-type ProcessResult struct {
-	// Content is the processed image data
-	Content io.ReadCloser
-	// ContentLength is the size in bytes
-	ContentLength int64
-	// ContentType is the MIME type of the output
-	ContentType string
-	// Width is the output image width
-	Width int
-	// Height is the output image height
-	Height int
-	// InputWidth is the original image width before processing
-	InputWidth int
-	// InputHeight is the original image height before processing
-	InputHeight int
-	// InputFormat is the detected input format (e.g., "jpeg", "png")
-	InputFormat string
-}
-
 // Storage handles persistent storage of cached content
 type Storage interface {
 	// Store saves content and returns its hash

internal/imgcache/service.go

@@ -11,17 +11,19 @@ import (
 	"time"
 
 	"github.com/dustin/go-humanize"
+	"sneak.berlin/go/pixa/internal/imageprocessor"
 )
 
 // Service implements the ImageCache interface, orchestrating cache, fetcher, and processor.
 type Service struct {
 	cache           *Cache
 	fetcher         Fetcher
-	processor Processor
+	processor       *imageprocessor.ImageProcessor
 	signer          *Signer
 	whitelist       *HostWhitelist
 	log             *slog.Logger
 	allowHTTP       bool
+	maxResponseSize int64
 }
 
 // ServiceConfig holds configuration for the image service.
@@ -50,15 +52,17 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		return nil, errors.New("signing key is required")
 	}
 
+	// Resolve fetcher config for defaults
+	fetcherCfg := cfg.FetcherConfig
+	if fetcherCfg == nil {
+		fetcherCfg = DefaultFetcherConfig()
+	}
+
 	// Use custom fetcher if provided, otherwise create HTTP fetcher
 	var fetcher Fetcher
 	if cfg.Fetcher != nil {
 		fetcher = cfg.Fetcher
 	} else {
-		fetcherCfg := cfg.FetcherConfig
-		if fetcherCfg == nil {
-			fetcherCfg = DefaultFetcherConfig()
-		}
 		fetcher = NewHTTPFetcher(fetcherCfg)
 	}
 
@@ -74,14 +78,17 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		allowHTTP = cfg.FetcherConfig.AllowHTTP
 	}
 
+	maxResponseSize := fetcherCfg.MaxResponseSize
+
 	return &Service{
 		cache:           cfg.Cache,
 		fetcher:         fetcher,
-		processor: NewImageProcessor(),
+		processor:       imageprocessor.New(imageprocessor.Params{MaxInputBytes: maxResponseSize}),
 		signer:          signer,
 		whitelist:       NewHostWhitelist(cfg.Whitelist),
 		log:             log,
 		allowHTTP:       allowHTTP,
+		maxResponseSize: maxResponseSize,
 	}, nil
 }
 
@@ -146,6 +153,40 @@ func (s *Service) Get(ctx context.Context, req *ImageRequest) (*ImageResponse, e
 	return response, nil
 }
 
+// loadCachedSource attempts to load source content from cache, returning nil
+// if the cached data is unavailable or exceeds maxResponseSize.
+func (s *Service) loadCachedSource(contentHash ContentHash) []byte {
+	reader, err := s.cache.GetSourceContent(contentHash)
+	if err != nil {
+		s.log.Warn("failed to load cached source, fetching", "error", err)
+
+		return nil
+	}
+
+	// Bound the read to maxResponseSize to prevent unbounded memory use
+	// from unexpectedly large cached files.
+	limited := io.LimitReader(reader, s.maxResponseSize+1)
+	data, err := io.ReadAll(limited)
+	_ = reader.Close()
+
+	if err != nil {
+		s.log.Warn("failed to read cached source, fetching", "error", err)
+
+		return nil
+	}
+
+	if int64(len(data)) > s.maxResponseSize {
+		s.log.Warn("cached source exceeds max response size, discarding",
+			"hash", contentHash,
+			"max_bytes", s.maxResponseSize,
+		)
+
+		return nil
+	}
+
+	return data
+}
+
 // processFromSourceOrFetch processes an image, using cached source content if available.
 func (s *Service) processFromSourceOrFetch(
 	ctx context.Context,
@@ -162,22 +203,8 @@ func (s *Service) processFromSourceOrFetch(
 	var fetchBytes int64
 
 	if contentHash != "" {
-		// We have cached source - load it
 		s.log.Debug("using cached source", "hash", contentHash)
-
-		reader, err := s.cache.GetSourceContent(contentHash)
-		if err != nil {
-			s.log.Warn("failed to load cached source, fetching", "error", err)
-			// Fall through to fetch
-		} else {
-			sourceData, err = io.ReadAll(reader)
-			_ = reader.Close()
-
-			if err != nil {
-				s.log.Warn("failed to read cached source, fetching", "error", err)
-				// Fall through to fetch
-			}
-		}
+		sourceData = s.loadCachedSource(contentHash)
 	}
 
 	// Fetch from upstream if we don't have source data or it's empty
@@ -274,7 +301,14 @@ func (s *Service) processAndStore(
 	// Process the image
 	processStart := time.Now()
 
-	processResult, err := s.processor.Process(ctx, bytes.NewReader(sourceData), req)
+	processReq := &imageprocessor.Request{
+		Size:    imageprocessor.Size{Width: req.Size.Width, Height: req.Size.Height},
+		Format:  imageprocessor.Format(req.Format),
+		Quality: req.Quality,
+		FitMode: imageprocessor.FitMode(req.FitMode),
+	}
+
+	processResult, err := s.processor.Process(ctx, bytes.NewReader(sourceData), processReq)
 	if err != nil {
 		return nil, fmt.Errorf("image processing failed: %w", err)
 	}