Detect a fetched image's format from its bytes once (closes #319)

magic.DetectFormat returns an imagerequest.Format. ValidateMagicBytes
returns the format it checked against the upstream Content-Type. The
cache reads a cached source's format from its file's first bytes, as it
reads a variant's. The proxy hands the format to Process. Process
refuses a format that is not a source format, and input libvips would
load with another loader, such as an SVG passing as AVIF.
Format.MIMEType declares each MIME string once, and the fetcher, the
cache's variant read and the Accept matching use it. magic.MIMEType,
magic.ImageFormat, MIMEToImageFormat, magic's SVG detection,
detectFormat, formatFromString, FormatToMIME and Result.InputFormat are
gone.

Model: opus-5-5

internal/imageprocessor/encoder_settings_internal_test.go

@@ -11,17 +11,18 @@ import (
 	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
-// processedSize runs input through Process and returns the output's size in
-// bytes.
+// processedSize runs input, an image in sourceFormat, through Process and
+// returns the output's size in bytes.
 func processedSize(
-	t *testing.T, input []byte, transform *imagerequest.Transform,
+	t *testing.T, input []byte, sourceFormat imagerequest.Format,
+	transform *imagerequest.Transform,
 ) int64 {
 	t.Helper()
 
 	result, err := New(Params{
 		MaxInputBytes:           50 << 20,
 		MaxConcurrentProcessing: 1,
-	}).Process(t.Context(), bytes.NewReader(input), transform)
+	}).Process(t.Context(), bytes.NewReader(input), sourceFormat, transform)
 	if err != nil {
 		t.Fatalf("Process() error = %v", err)
 	}
@@ -74,7 +75,7 @@ func TestImageProcessor_PNGIsCompressed(t *testing.T) {
 		}
 	}
 
-	size := processedSize(t, encodePNG(t, flat),
+	size := processedSize(t, encodePNG(t, flat), imagerequest.FormatPNG,
 		&imagerequest.Transform{Format: imagerequest.FormatPNG})
 
 	const rawBytes = width * height * 3
@@ -92,7 +93,7 @@ func TestImageProcessor_WebPAtEffort2(t *testing.T) {
 
 	input := createTestJPEG(t, 200, 150)
 
-	size := processedSize(t, input,
+	size := processedSize(t, input, imagerequest.FormatJPEG,
 		&imagerequest.Transform{Format: imagerequest.FormatWebP, Quality: 85})
 
 	want, _, err := decode(t, input).ExportWebp(&vips.WebpExportParams{
@@ -134,7 +135,7 @@ func TestImageProcessor_AVIFAtEffort1(t *testing.T) {
 
 	input := encodePNG(t, source)
 
-	size := processedSize(t, input,
+	size := processedSize(t, input, imagerequest.FormatPNG,
 		&imagerequest.Transform{Format: imagerequest.FormatAVIF, Quality: 85})
 
 	want, _, err := decode(t, input).ExportAvif(&vips.AvifExportParams{
@@ -161,7 +162,7 @@ func TestImageProcessor_JPEGXLAtEffort4(t *testing.T) {
 
 	input := createTestJPEG(t, 200, 150)
 
-	size := processedSize(t, input,
+	size := processedSize(t, input, imagerequest.FormatJPEG,
 		&imagerequest.Transform{Format: imagerequest.FormatJXL, Quality: 85})
 
 	params := vips.NewJxlExportParams()