Keep an original by its path and its content, so a second original at one path is not discarded (hq ADR 0100)

internal/apply/hold.go

@@ -22,13 +22,19 @@ import (
 // first copy is the one that was there before the mesh.
 type Keep func(path string, content []byte, mode os.FileMode) (string, error)
 
-// KeepIn keeps originals under dir/kept, each named for the path it came from, readable by root
-// alone — a predecessor's configuration may carry its credentials.
+// KeepIn keeps originals under dir/kept, each named for the path it came from AND for what was in
+// it, readable by root alone — a predecessor's configuration may carry its credentials.
+//
+// **By content as well as path, because a path has more than one original.** A file held, let go
+// when its module was unassigned, rewritten by the predecessor and found again is a second
+// original; named by path alone the second copy was silently discarded while the report said it
+// was kept (novox/hq ADR 0100). The same content at the same path is kept once.
 func KeepIn(dir string) Keep {
 	return func(path string, content []byte, _ os.FileMode) (string, error) {
-		sum := sha256.Sum256([]byte(path))
-		kept := filepath.Join(dir, "kept",
-			hex.EncodeToString(sum[:])[:16]+"-"+filepath.Base(path))
+		where := sha256.Sum256([]byte(path))
+		what := sha256.Sum256(content)
+		kept := filepath.Join(dir, "kept", hex.EncodeToString(where[:])[:12]+"-"+
+			hex.EncodeToString(what[:])[:12]+"-"+filepath.Base(path))
 		if _, err := os.Lstat(kept); err == nil {
 			return kept, nil
 		}

internal/apply/hold_test.go

@@ -382,8 +382,13 @@ func TestAHoldNoLongerDeclaredIsLetGoAndFoundAgainIfItsModuleReturns(t *testing.
 		t.Fatalf("a returning module's found file was not held again: %+v", o)
 	}
 	again, _ := state.HeldAt("hello-web.page")
-	if kept, _ := os.ReadFile(again.Kept); again.Kept != first.Kept || string(kept) != "the predecessor's page\n" {
-		t.Errorf("the first kept original was lost: %s %q", again.Kept, kept)
+	// The predecessor rewrote it while nothing held it, so that is a second original, kept beside
+	// the first rather than in place of it (novox/hq ADR 0100).
+	if kept, _ := os.ReadFile(again.Kept); string(kept) != "the predecessor wrote again\n" {
+		t.Errorf("what is named as kept is %q", kept)
+	}
+	if kept, _ := os.ReadFile(first.Kept); string(kept) != "the predecessor's page\n" {
+		t.Errorf("the first kept original was lost: %q", kept)
 	}
 	if got, _ := os.ReadFile(page); string(got) != "the predecessor wrote again\n" {
 		t.Errorf("the found file was touched: %q", got)
@@ -958,3 +963,60 @@ func TestAPackagedUnitTheMachineUsesIsStillHeld(t *testing.T) {
 		t.Errorf("the predecessor's service was restarted: %v", m.asked)
 	}
 }
+
+func TestASecondOriginalAtTheSamePathIsKeptToo(t *testing.T) {
+	// Held, let go when the module was unassigned, rewritten by the predecessor, found again:
+	// both originals are kept, and the report names the one it kept (novox/hq ADR 0100).
+	dir := t.TempDir()
+	page := filepath.Join(dir, "index.html")
+	keep := KeepIn(dir)
+	first, err := keep(page, []byte("the predecessor's page\n"), 0o640)
+	if err != nil {
+		t.Fatal(err)
+	}
+	same, err := keep(page, []byte("the predecessor's page\n"), 0o640)
+	if err != nil || same != first {
+		t.Errorf("the same original was kept twice: %s %s %v", first, same, err)
+	}
+	second, err := keep(page, []byte("the predecessor wrote again\n"), 0o640)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if second == first {
+		t.Fatal("a second original was kept under the first's name")
+	}
+	if got, _ := os.ReadFile(first); string(got) != "the predecessor's page\n" {
+		t.Errorf("the first original is %q", got)
+	}
+	if got, _ := os.ReadFile(second); string(got) != "the predecessor wrote again\n" {
+		t.Errorf("the second original is %q", got)
+	}
+}
+
+func TestAHoldLetGoAndFoundAgainKeepsBothOriginals(t *testing.T) {
+	dir, page, m := predecessor(t)
+	_, state := applyAdopted(t, adopted(t, untaken("hello-web.page", "hello-web.server"), webResources(page)),
+		store.State{}, m, dir)
+	first, _ := state.HeldAt("hello-web.page")
+
+	// Unassigned, then the predecessor writes again, then assigned once more.
+	_, state = applyAdopted(t, adopted(t, `{"taken":[]}`, withConf(dir)), state, m, dir)
+	if err := os.WriteFile(page, []byte("the predecessor wrote again\n"), 0o640); err != nil {
+		t.Fatal(err)
+	}
+	report, state := applyAdopted(t, adopted(t, untaken("hello-web.page", "hello-web.server"), webResources(page)),
+		state, m, dir)
+	again, _ := state.HeldAt("hello-web.page")
+	if again.Kept == first.Kept {
+		t.Fatalf("the second original was kept under the first's name: %s", again.Kept)
+	}
+	if got, _ := os.ReadFile(again.Kept); string(got) != "the predecessor wrote again\n" {
+		t.Errorf("what the report names as kept is %q", got)
+	}
+	if got, _ := os.ReadFile(first.Kept); string(got) != "the predecessor's page\n" {
+		t.Errorf("the first original was lost: %q", got)
+	}
+	if o := outcomeOf(report, "hello-web.page"); o.Action != "held" {
+		t.Errorf("the file found again was not held: %+v", o)
+	}
+}