Remove BaseDendrite (#3023)

Removes `BaseDendrite` to, hopefully, make testing and composing of
components easier in the future.

internal/sqlutil/connection_manager.go

@@ -19,15 +19,21 @@ import (
 	"fmt"
 
 	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/setup/process"
 )
 
 type Connections struct {
-	db     *sql.DB
-	writer Writer
+	db             *sql.DB
+	writer         Writer
+	globalConfig   config.DatabaseOptions
+	processContext *process.ProcessContext
 }
 
-func NewConnectionManager() Connections {
-	return Connections{}
+func NewConnectionManager(processCtx *process.ProcessContext, globalConfig config.DatabaseOptions) Connections {
+	return Connections{
+		globalConfig:   globalConfig,
+		processContext: processCtx,
+	}
 }
 
 func (c *Connections) Connection(dbProperties *config.DatabaseOptions) (*sql.DB, Writer, error) {
@@ -35,14 +41,29 @@ func (c *Connections) Connection(dbProperties *config.DatabaseOptions) (*sql.DB,
 	if dbProperties.ConnectionString.IsSQLite() {
 		writer = NewExclusiveWriter()
 	}
+	var err error
+	if dbProperties.ConnectionString == "" {
+		// if no connectionString was provided, try the global one
+		dbProperties = &c.globalConfig
+	}
 	if dbProperties.ConnectionString != "" || c.db == nil {
-		var err error
 		// Open a new database connection using the supplied config.
 		c.db, err = Open(dbProperties, writer)
 		if err != nil {
 			return nil, nil, err
 		}
 		c.writer = writer
+		go func() {
+			if c.processContext == nil {
+				return
+			}
+			// If we have a ProcessContext, start a component and wait for
+			// Dendrite to shut down to cleanly close the database connection.
+			c.processContext.ComponentStarted()
+			<-c.processContext.WaitForShutdown()
+			_ = c.db.Close()
+			c.processContext.ComponentFinished()
+		}()
 		return c.db, c.writer, nil
 	}
 	if c.db != nil && c.writer != nil {