One image request type instead of five (closes #307)

The new package internal/imagerequest holds the request type, its two
parts Source and Transform, the Format and Fit types, the dimension and
fit checks, the /v1/image/ path parsing and the variant key; it imports
no other package of pixa. imgcache.ParsedURL, imgcache.ImageRequest,
signature.Request, imageprocessor.Request, the second Size, format and
fit types and the conversions between them are gone. The image
processor takes a Transform only. encurl keeps a private struct with the
token's short CBOR field names. VariantKey moves with the function that
makes it. Tests follow the moved and renamed code; the tests of the
removed conversions go with them.

Model: opus-5-5

internal/imgcache/storage.go

@@ -10,8 +10,9 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
-	"strings"
 	"time"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
 // Storage constants.
@@ -32,9 +33,6 @@ var (
 // ContentHash is a SHA256 hash of file content (hex-encoded).
 type ContentHash string
 
-// VariantKey is a SHA256 hash identifying a specific image variant (hex-encoded).
-type VariantKey string
-
 // PathHash is a SHA256 hash of a URL path (hex-encoded).
 type PathHash string
 
@@ -403,34 +401,6 @@ func HashPath(path string) PathHash {
 	return PathHash(hex.EncodeToString(h[:]))
 }
 
-// CacheKey generates a unique key for a request variant.
-// Format: sha256(host:path:query:width:height:format:quality:fit_mode)
-// The path and query go through escapePercentAndColon, so that a ":" in
-// either cannot be taken for the one between them.
-func CacheKey(req *ImageRequest) VariantKey {
-	data := fmt.Sprintf("%s:%s:%s:%d:%d:%s:%d:%s",
-		req.SourceHost,
-		escapePercentAndColon(req.SourcePath),
-		escapePercentAndColon(req.SourceQuery),
-		req.Size.Width,
-		req.Size.Height,
-		req.Format,
-		req.Quality,
-		req.FitMode,
-	)
-	h := sha256.Sum256([]byte(data))
-
-	return VariantKey(hex.EncodeToString(h[:]))
-}
-
-// escapePercentAndColon returns s with each "%" written as "%25" and each
-// ":" as "%3A", so that the result holds no ":".
-func escapePercentAndColon(s string) string {
-	s = strings.ReplaceAll(s, "%", "%25")
-
-	return strings.ReplaceAll(s, ":", "%3A")
-}
-
 // VariantStorage handles key-based file storage for processed image variants.
 // Files are stored at: <basedir>/<ab>/<cd>/<cache_key>
 // Metadata is stored at: <basedir>/<ab>/<cd>/<cache_key>.meta
@@ -464,7 +434,7 @@ func NewVariantStorage(baseDir string, log *slog.Logger) (*VariantStorage, error
 // with writeFileSynced. The .meta file is written first, so that a crash
 // cannot leave the content in place without it.
 func (s *VariantStorage) Store(
-	key VariantKey, r io.Reader, contentType string,
+	key imagerequest.VariantKey, r io.Reader, contentType string,
 ) (int64, error) {
 	data, err := io.ReadAll(r)
 	if err != nil {
@@ -508,7 +478,7 @@ func (s *VariantStorage) Store(
 }
 
 // Load returns a reader for the content at the given key.
-func (s *VariantStorage) Load(key VariantKey) (io.ReadCloser, error) {
+func (s *VariantStorage) Load(key imagerequest.VariantKey) (io.ReadCloser, error) {
 	path := s.keyToPath(key)
 
 	f, err := os.Open(path) //nolint:gosec // path derived from cache key
@@ -525,7 +495,9 @@ func (s *VariantStorage) Load(key VariantKey) (io.ReadCloser, error) {
 
 // LoadWithSize returns a reader and file size for the content at the
 // given key.
-func (s *VariantStorage) LoadWithSize(key VariantKey) (io.ReadCloser, int64, error) {
+func (s *VariantStorage) LoadWithSize(
+	key imagerequest.VariantKey,
+) (io.ReadCloser, int64, error) {
 	path := s.keyToPath(key)
 
 	f, err := os.Open(path) //nolint:gosec // path derived from cache key
@@ -551,7 +523,7 @@ func (s *VariantStorage) LoadWithSize(key VariantKey) (io.ReadCloser, int64, err
 // the given key. The content type is read from the .meta file, and is
 // empty when that file is missing or unreadable.
 func (s *VariantStorage) LoadWithMeta(
-	key VariantKey,
+	key imagerequest.VariantKey,
 ) (io.ReadCloser, int64, string, error) {
 	f, size, err := s.LoadWithSize(key)
 	if err != nil {
@@ -574,7 +546,7 @@ func (s *VariantStorage) LoadWithMeta(
 }
 
 // Exists checks if content exists at the given key.
-func (s *VariantStorage) Exists(key VariantKey) bool {
+func (s *VariantStorage) Exists(key imagerequest.VariantKey) bool {
 	path := s.keyToPath(key)
 	_, err := os.Stat(path)
 
@@ -583,7 +555,7 @@ func (s *VariantStorage) Exists(key VariantKey) bool {
 
 // Delete removes the content at the given key together with its .meta
 // sidecar file. A missing file is not an error.
-func (s *VariantStorage) Delete(key VariantKey) error {
+func (s *VariantStorage) Delete(key imagerequest.VariantKey) error {
 	path := s.keyToPath(key)
 
 	err := os.Remove(path)
@@ -602,7 +574,7 @@ func (s *VariantStorage) Delete(key VariantKey) error {
 }
 
 // keyToPath converts a key to a file path: <basedir>/<ab>/<cd>/<key>
-func (s *VariantStorage) keyToPath(key VariantKey) string {
+func (s *VariantStorage) keyToPath(key imagerequest.VariantKey) string {
 	k := string(key)
 	if len(k) < MinHashLength {
 		return filepath.Join(s.baseDir, k)