Build the image pipeline in pixad's fx graph (closes #313)

The new package internal/providers builds the cache, the fetcher, the
processor, the image service, the session manager and the encrypted URL
generator from the config. providers.Option gives them to pixad's fx
graph, and handlers.New receives them built. The server tests build the
same graph, with only the fetcher's dial function replaced. database.New
opens the database, so these parts can read it while fx builds them; the
cache's stop hook still runs before the database's.

Each setting's default is declared in internal/config, and
internal/providers works out the default cache_max_bytes. The cache's
MaxBytes is the one value for the disk cache limit, and 0 turns the disk
cache off. The fetcher and the processor take explicit values.

Model: opus-5-5

internal/imgcache/service.go

@@ -43,18 +43,20 @@ type Service struct {
 type ServiceConfig struct {
 	// Cache is the cache instance
 	Cache *Cache
-	// FetcherConfig configures the upstream fetcher built when Fetcher is
-	// not set. Its AllowHTTP and MaxResponseSize are used either way.
-	FetcherConfig *httpfetcher.Config
-	// Fetcher is an optional custom fetcher (for testing)
+	// Fetcher fetches source images from upstream hosts
 	Fetcher httpfetcher.Fetcher
+	// Processor converts and resizes the images
+	Processor *imageprocessor.ImageProcessor
 	// SigningKey is the HMAC signing key (empty disables signing)
 	SigningKey string
 	// Allowlist is the list of hosts that don't require signatures
 	Allowlist []string
-	// MaxConcurrentProcessing is the most images processed at once; zero
-	// uses the image processor's default, half the CPUs
-	MaxConcurrentProcessing int
+	// AllowHTTP makes the service fetch sources over http instead of
+	// https (testing only), so the fetcher must allow http too
+	AllowHTTP bool
+	// MaxResponseSize is the largest source accepted, in bytes; a cached
+	// source larger than this is fetched again
+	MaxResponseSize int64
 	// Logger for logging
 	Logger *slog.Logger
 }
@@ -75,32 +77,11 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		return nil, errSigningKeyRequired
 	}
 
-	// Resolve fetcher config for defaults
-	fetcherCfg := cfg.FetcherConfig
-	if fetcherCfg == nil {
-		fetcherCfg = httpfetcher.DefaultConfig()
-	}
-
-	// Use custom fetcher if provided, otherwise create HTTP fetcher
-	var fetcher httpfetcher.Fetcher
-	if cfg.Fetcher != nil {
-		fetcher = cfg.Fetcher
-	} else {
-		fetcher = httpfetcher.New(fetcherCfg)
-	}
-
-	signer := signature.New(cfg.SigningKey)
-
 	log := cfg.Logger
 	if log == nil {
 		log = slog.Default()
 	}
 
-	allowHTTP := false
-	if cfg.FetcherConfig != nil {
-		allowHTTP = cfg.FetcherConfig.AllowHTTP
-	}
-
 	// JPEG XL is the default output format, so pixad does not start
 	// without it.
 	err := imageprocessor.CheckJPEGXLSupport()
@@ -108,21 +89,15 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		return nil, err
 	}
 
-	maxResponseSize := fetcherCfg.MaxResponseSize
-	processor := imageprocessor.New(imageprocessor.Params{
-		MaxInputBytes:           maxResponseSize,
-		MaxConcurrentProcessing: cfg.MaxConcurrentProcessing,
-	})
-
 	return &Service{
 		cache:           cfg.Cache,
-		fetcher:         fetcher,
-		processor:       processor,
-		signer:          signer,
+		fetcher:         cfg.Fetcher,
+		processor:       cfg.Processor,
+		signer:          signature.New(cfg.SigningKey),
 		allowlist:       allowlist.New(cfg.Allowlist),
 		log:             log,
-		allowHTTP:       allowHTTP,
-		maxResponseSize: maxResponseSize,
+		allowHTTP:       cfg.AllowHTTP,
+		maxResponseSize: cfg.MaxResponseSize,
 	}, nil
 }