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. pixad's fx graph provides them with
providers.Constructors(), 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/imageprocessor/max_concurrent_processing_internal_test.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"errors"
 	"io"
-	"runtime"
 	"strings"
 	"sync"
 	"testing"
@@ -117,47 +116,15 @@ func waitForEntries(t *testing.T, entered <-chan struct{}, count int) {
 	}
 }
 
-func TestNewDefaultsMaxConcurrentProcessingToHalfTheCPUs(t *testing.T) {
+func TestNewMakesMaxConcurrentProcessingSlots(t *testing.T) {
 	t.Parallel()
 
-	for _, limit := range []int{0, -1} {
-		proc := New(Params{MaxConcurrentProcessing: limit})
-		if got := cap(proc.processingSemaphore); got != max(runtime.GOMAXPROCS(0)/2, 1) {
-			t.Errorf("MaxConcurrentProcessing %d: %d slots, want %d, half the CPUs",
-				limit, got, max(runtime.GOMAXPROCS(0)/2, 1))
-		}
-	}
-
-	proc := New(Params{MaxConcurrentProcessing: 3})
+	proc := New(Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 3})
 	if got := cap(proc.processingSemaphore); got != 3 {
 		t.Errorf("MaxConcurrentProcessing 3: %d slots, want 3", got)
 	}
 }
 
-// TestNewDefaultIsHalfTheCPUsAndAtLeastOne checks that New, given no
-// MaxConcurrentProcessing, makes one slot for every two CPUs Go uses,
-// rounded down, and one slot when Go uses one CPU.
-//
-//nolint:paralleltest // it sets GOMAXPROCS, which other tests read
-func TestNewDefaultIsHalfTheCPUsAndAtLeastOne(t *testing.T) {
-	cpusBefore := runtime.GOMAXPROCS(0)
-
-	t.Cleanup(func() { runtime.GOMAXPROCS(cpusBefore) })
-
-	for _, tc := range []struct{ cpus, want int }{
-		{1, 1}, {2, 1}, {3, 1}, {8, 4},
-	} {
-		runtime.GOMAXPROCS(tc.cpus)
-
-		got := cap(New(Params{}).processingSemaphore)
-		t.Logf("GOMAXPROCS %d: %d slots", tc.cpus, got)
-
-		if got != tc.want {
-			t.Errorf("GOMAXPROCS %d: %d slots, want %d", tc.cpus, got, tc.want)
-		}
-	}
-}
-
 // TestProcessNeverExceedsMaxConcurrentProcessing starts more Process calls
 // than MaxConcurrentProcessing allows and holds the first ones inside
 // Process until the test lets them go. No more than the limit may be
@@ -171,7 +138,7 @@ func TestProcessNeverExceedsMaxConcurrentProcessing(t *testing.T) {
 		calls = 6
 	)
 
-	proc := New(Params{MaxConcurrentProcessing: limit})
+	proc := New(Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: limit})
 	input := createTestJPEG(t, 50, 50)
 
 	counter := &readingCounter{}
@@ -218,7 +185,7 @@ func TestProcessNeverExceedsMaxConcurrentProcessing(t *testing.T) {
 func TestProcessWaitsThenFailsWhenNoSlotFrees(t *testing.T) {
 	t.Parallel()
 
-	proc := New(Params{MaxConcurrentProcessing: 1})
+	proc := New(Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 1})
 	proc.processingWaitTimeout = 100 * time.Millisecond
 
 	input := createTestJPEG(t, 10, 10)
@@ -334,7 +301,7 @@ func TestProcessReleasesSlotOnError(t *testing.T) {
 func TestWaitForProcessing(t *testing.T) {
 	t.Parallel()
 
-	proc := New(Params{MaxConcurrentProcessing: 2})
+	proc := New(Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 2})
 
 	gate := make(chan struct{})
 	entered := make(chan struct{}, 1)