Permit SendBatch with Simple Protocol

This commit adds support for sending batches of queries via the Simple
protocol with SendBatch. The result appears identically to how it would
if it were created with the extended protocol.

conn.go

@@ -708,6 +708,29 @@ func (c *Conn) QueryRow(ctx context.Context, sql string, args ...interface{}) Ro
 // explicit transaction control statements are executed. The returned BatchResults must be closed before the connection
 // is used again.
 func (c *Conn) SendBatch(ctx context.Context, b *Batch) BatchResults {
+	simpleProtocol := c.config.PreferSimpleProtocol
+	var sb strings.Builder
+	if simpleProtocol {
+		for i, bi := range b.items {
+			if i > 0 {
+				sb.WriteByte(';')
+			}
+			sql, err := c.sanitizeForSimpleQuery(bi.query, bi.arguments...)
+			if err != nil {
+				return &batchResults{ctx: ctx, conn: c, err: err}
+			}
+			sb.WriteString(sql)
+		}
+		mrr := c.pgConn.Exec(ctx, sb.String())
+		return &batchResults{
+			ctx:  ctx,
+			conn: c,
+			mrr:  mrr,
+			b:    b,
+			ix:   0,
+		}
+	}
+
 	distinctUnpreparedQueries := map[string]struct{}{}
 
 	for _, bi := range b.items {

conn_test.go

@@ -360,6 +360,48 @@ func TestExecPerQuerySimpleProtocol(t *testing.T) {
 
 }
 
+func TestSendBatchSimpleProtocol(t *testing.T) {
+	t.Parallel()
+
+	config := mustParseConfig(t, os.Getenv("PGX_TEST_DATABASE"))
+	config.PreferSimpleProtocol = true
+
+	conn := mustConnect(t, config)
+	defer closeConn(t, conn)
+
+	ctx, cancelFunc := context.WithCancel(context.Background())
+	defer cancelFunc()
+
+
+	var batch pgx.Batch
+	batch.Queue("SELECT 1::int")
+	batch.Queue("SELECT 2::int; SELECT $1::int", 3)
+	results := conn.SendBatch(ctx, &batch)
+	rows, err := results.Query()
+	assert.NoError(t, err)
+	assert.True(t, rows.Next())
+	values, err := rows.Values()
+	assert.NoError(t, err)
+	assert.Equal(t, int32(1), values[0])
+	assert.False(t, rows.Next())
+
+	rows, err = results.Query()
+	assert.NoError(t, err)
+	assert.True(t, rows.Next())
+	values, err = rows.Values()
+	assert.NoError(t, err)
+	assert.Equal(t, int32(2), values[0])
+	assert.False(t, rows.Next())
+
+	rows, err = results.Query()
+	assert.NoError(t, err)
+	assert.True(t, rows.Next())
+	values, err = rows.Values()
+	assert.NoError(t, err)
+	assert.Equal(t, int32(3), values[0])
+	assert.False(t, rows.Next())
+}
+
 func TestPrepare(t *testing.T) {
 	t.Parallel()