Atomic migrations

internal/db/dbutil/dbutil.go

@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"os"
 	"strconv"
+	"strings"
 	"time"
 
 	// Register driver
@@ -110,8 +111,28 @@ func NewDB(dsn, app string) (*sql.DB, error) {
 	return db, nil
 }
 
+// injectVersionUpdate fixes the dirty state (set by golang-migrate) after a
+// successful migration. If the frontend starts a migration that will turn out
+// to be successful but does not stay alive for the duration of the query due to
+// a startup timeout, there will be no chance to set the new version or unset
+// the dirty flag. This function ensures that each successful migration sets the
+// version and dirty flag itself, without requiring the frontend to be alive
+// once the migration is committed.
+//
+// See https://github.com/golang-migrate/migrate/issues/325.
+func injectVersionUpdate(f bindata.AssetFunc) bindata.AssetFunc {
+	return func(name string) ([]byte, error) {
+		oldContents, err := f(name)
+		if err != nil {
+			return nil, err
+		}
+		newContents := strings.Replace(string(oldContents), "COMMIT;", fmt.Sprintf("UPDATE schema_migrations SET dirty=false;\nCOMMIT;"), 1)
+		return []byte(newContents), nil
+	}
+}
+
 func NewMigrationSourceLoader(dataSource string) *bindata.AssetSource {
-	return bindata.Resource(migrations.AssetNames(), migrations.Asset)
+	return bindata.Resource(migrations.AssetNames(), injectVersionUpdate(migrations.Asset))
 }
 
 func NewMigrate(db *sql.DB, dataSource string) (*migrate.Migrate, error) {

internal/db/dbutil/dbutil_test.go

@@ -67,3 +67,15 @@ func TestPostgresDSN(t *testing.T) {
 		})
 	}
 }
+
+func TestInjectVersionUpdate(t *testing.T) {
+	gotContents, err := injectVersionUpdate(func(name string) ([]byte, error) { return []byte("BEGIN;\n-- some statements...\nCOMMIT;"), nil })("migrations/100_dummy.up.sql")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := string(gotContents)
+	want := "BEGIN;\n-- some statements...\nUPDATE schema_migrations SET dirty=false;\nCOMMIT;"
+	if got != want {
+		t.Errorf("incorrect contents: got != want\ngot:  %v\nwant: %v", got, want)
+	}
+}

migrations/migrations_test.go

@@ -1,6 +1,7 @@
 package migrations_test
 
 import (
+	"io/ioutil"
 	"path/filepath"
 	"reflect"
 	"sort"
@@ -39,6 +40,26 @@ func TestIDConstraints(t *testing.T) {
 	}
 }
 
+// Makes sure that every migration contains exactly one `COMMIT;` so that
+// `InjectVersionUpdate` in internal/db/dbutil/dbutil.go is guaranteed to succeed.
+func TestTransactions(t *testing.T) {
+	ups, err := filepath.Glob("*.up.sql")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, name := range ups {
+		contents, err := ioutil.ReadFile(name)
+		if err != nil {
+			t.Fatalf("failed to read migration file %q: %v", name, err)
+		}
+		commitCount := strings.Count(string(contents), "COMMIT;")
+		if commitCount != 1 {
+			t.Fatalf("expected migration %q to contain exactly one COMMIT; but it contains %d", name, commitCount)
+		}
+	}
+}
+
 func TestNeedsGenerate(t *testing.T) {
 	want, err := filepath.Glob("*.sql")
 	if err != nil {