Store a source the way a variant is stored, one row and one file per source URL (closes #308)

A source is now one source_content row and one file named by its
SourceKey, the SHA-256 of its host, path and query, made as the variant
key is. A store writes the file, then upserts the row, and removes the
file when the row cannot be written; an eviction deletes the row, then
the file, with no lock. source_metadata, the JSON files under
cache/metadata/, MetadataStorage, the content lock, the eviction
transaction and its test hook are gone. Two source URLs serving the same
bytes store them twice. Reconciliation still drops a source row whose
file is missing, as TestReconciliationReadsAPageAtATime counts those
reads. The tests of the removed sharing, lock and hook go with them.

Model: opus-5-5

internal/server/image_proxy_internal_test.go

@@ -3,9 +3,7 @@ package server
 import (
 	"bytes"
 	"context"
-	"crypto/sha256"
 	"database/sql"
-	"encoding/hex"
 	"image"
 	"image/color"
 	"image/jpeg"
@@ -43,8 +41,8 @@ const upstreamHost = "192.0.2.10"
 // upstream fetcher, image processor, disk cache and database, with only the
 // upstream origin replaced by a local test server. The first request for a URL
 // is fetched and converted; the second is served from the cache without
-// another upstream request. The source and the converted image are then on
-// disk, with their rows in the database.
+// another upstream request. The converted image is then on disk, with its row
+// in the database.
 func TestImageProxyFlow(t *testing.T) {
 	t.Parallel()
 
@@ -113,7 +111,6 @@ func TestImageProxyFlow(t *testing.T) {
 				t.Errorf("upstream received %d requests, want 1", got)
 			}
 
-			checkSourceCached(t, db, stateDir, source)
 			checkVariantCached(t, db, stateDir, first.Body.Bytes(), tt.contentType)
 		})
 	}
@@ -254,41 +251,6 @@ func getImage(t *testing.T, s *Server, target string) *httptest.ResponseRecorder
 	return rec
 }
 
-// checkSourceCached checks that source is stored under its SHA-256 in
-// cache/sources, recorded in source_content, and that the source URL's row in
-// source_metadata points at it.
-func checkSourceCached(t *testing.T, db *sql.DB, stateDir string, source []byte) {
-	t.Helper()
-
-	sum := sha256.Sum256(source)
-	hash := hex.EncodeToString(sum[:])
-
-	checkFile(t, filepath.Join(stateDir, "cache", "sources", hash[0:2], hash[2:4], hash),
-		source)
-
-	var rows int
-
-	err := db.QueryRowContext(t.Context(),
-		"SELECT COUNT(*) FROM source_content WHERE content_hash = ?", hash,
-	).Scan(&rows)
-	if err != nil || rows != 1 {
-		t.Errorf("source_content rows for the source = %d (error %v), want 1",
-			rows, err)
-	}
-
-	var metadataHash string
-
-	err = db.QueryRowContext(t.Context(),
-		`SELECT content_hash FROM source_metadata
-			WHERE source_host = ? AND source_path = ?`,
-		upstreamHost, "/photo.png",
-	).Scan(&metadataHash)
-	if err != nil || metadataHash != hash {
-		t.Errorf("source_metadata content_hash = %q (error %v), want %q",
-			metadataHash, err, hash)
-	}
-}
-
 // checkVariantCached checks that the converted image served is recorded in
 // variant_content with contentType, and stored under its cache key in
 // cache/variants.