Merge pull request #2151 from dolthub/zachmu/empty-message

Correctly support empty messages

Author: zachmu

server/connection_handler.go

@@ -453,6 +453,11 @@ func (h *ConnectionHandler) handleQuery(message *pgproto3.Query) (endOfMessages
 		return endOfMessages, err
 	}
 
+	// empty query special case
+	if query.AST == nil {
+		return true, h.send(&pgproto3.EmptyQueryResponse{})
+	}
+
 	return true, h.query(query)
 }
 

testing/go/framework.go

@@ -129,6 +129,9 @@ type ScriptTestAssertion struct {
 	CopyFromStdInFile string
 }
 
+// EmptyCommandTag is special command tag placeholder to check for the empty string
+const EmptyCommandTag = "EMPTY_COMMAND_TAG"
+
 // Connection contains the default and current connections.
 type Connection struct {
 	Default  *pgx.Conn
@@ -249,10 +252,14 @@ func runScript(t *testing.T, ctx context.Context, script ScriptTest, conn *Conne
 					require.NoError(t, err)
 				}
 			} else if assertion.ExpectedTag != "" {
-				// check for command tag
 				commandTag, err := conn.Exec(ctx, assertion.Query)
 				require.NoError(t, err)
-				assert.Equal(t, assertion.ExpectedTag, commandTag.String())
+				tag := assertion.ExpectedTag
+				if tag == EmptyCommandTag {
+					tag = ""
+				}
+
+				assert.Equal(t, tag, commandTag.String())
 			} else {
 				rows, err := conn.Query(ctx, assertion.Query, assertion.BindVars...)
 				require.NoError(t, err)

testing/go/smoke_test.go

@@ -823,3 +823,25 @@ func TestSmokeTests(t *testing.T) {
 		},
 	})
 }
+
+func TestEmptyQuery(t *testing.T) {
+	RunScripts(t, []ScriptTest{
+		{
+			// TODO: we want to be able to assert that the empty query returns a specific postgres backend message,
+			//  EmptyQueryResponse. The pg library automatically converts this response to an empty-string CommandTag,
+			//  which we can't tell apart from other empty CommandTag responses. We do assert that the command tag is empty,
+			//  but it would nice to be able to assert a particular message type.
+			Name: "Empty query test",
+			Assertions: []ScriptTestAssertion{
+				{
+					Query:       ";",
+					ExpectedTag: EmptyCommandTag,
+				},
+				{
+					Query:       " ",
+					ExpectedTag: EmptyCommandTag,
+				},
+			},
+		},
+	})
+}