Avoid allocating strings in common message types

conn.go

@@ -959,7 +959,7 @@ func (c *Conn) rxReadyForQuery(msg *pgproto3.ReadyForQuery) {
 func (c *Conn) rxRowDescription(msg *pgproto3.RowDescription) []FieldDescription {
 	fields := make([]FieldDescription, len(msg.Fields))
 	for i := 0; i < len(fields); i++ {
-		fields[i].Name = msg.Fields[i].Name
+		fields[i].Name = string(msg.Fields[i].Name)
 		fields[i].Table = pgtype.OID(msg.Fields[i].TableOID)
 		fields[i].AttributeNumber = msg.Fields[i].TableAttributeNumber
 		fields[i].DataType = pgtype.OID(msg.Fields[i].DataTypeOID)

pgconn/pgconn.go

@@ -199,25 +199,7 @@ func connect(ctx context.Context, config *Config, fallbackConfig *FallbackConfig
 			// handled by ReceiveMessage
 		case *pgproto3.ErrorResponse:
 			pgConn.conn.Close()
-			return nil, &PgError{
+			return nil, errorResponseToPgError(msg)
-				Severity:         msg.Severity,
-				Code:             msg.Code,
-				Message:          msg.Message,
-				Detail:           msg.Detail,
-				Hint:             msg.Hint,
-				Position:         msg.Position,
-				InternalPosition: msg.InternalPosition,
-				InternalQuery:    msg.InternalQuery,
-				Where:            msg.Where,
-				SchemaName:       msg.SchemaName,
-				TableName:        msg.TableName,
-				ColumnName:       msg.ColumnName,
-				DataTypeName:     msg.DataTypeName,
-				ConstraintName:   msg.ConstraintName,
-				File:             msg.File,
-				Line:             msg.Line,
-				Routine:          msg.Routine,
-			}
 		default:
 			pgConn.conn.Close()
 			return nil, errors.New("unexpected message")
@@ -348,7 +330,7 @@ func (pgConn *PgConn) ParameterStatus(key string) string {
 }
 
 // CommandTag is the result of an Exec function
-type CommandTag string
+type CommandTag []byte
 
 // RowsAffected returns the number of rows affected. If the CommandTag was not
 // for a row affecting command (e.g. "CREATE TABLE") then it returns 0.
@@ -362,6 +344,10 @@ func (ct CommandTag) RowsAffected() int64 {
 	return n
 }
 
+func (ct CommandTag) String() string {
+	return string(ct)
+}
+
 // SendExec enqueues the execution of sql via the PostgreSQL simple query protocol. sql may contain multiple queries.
 // Execution is implicitly wrapped in a transactions unless a transaction is already in progress or sql contains
 // transaction control statements. It is only sent to the PostgreSQL server when Flush is called.
@@ -511,6 +497,7 @@ func (pgConn *PgConn) SendExecParams(sql string, paramValues [][]byte, paramOIDs
 	}
 
 	pgConn.batchBuf = appendParse(pgConn.batchBuf, "", sql, paramOIDs)
+	pgConn.batchBuf = appendDescribe(pgConn.batchBuf, 'S', "")
 	pgConn.batchBuf = appendBind(pgConn.batchBuf, "", "", paramFormats, paramValues, resultFormats)
 	pgConn.batchBuf = appendExecute(pgConn.batchBuf, "", 0)
 	pgConn.batchBuf = appendSync(pgConn.batchBuf)
@@ -530,6 +517,7 @@ func (pgConn *PgConn) SendExecParams(sql string, paramValues [][]byte, paramOIDs
 //
 // Query is only sent to the PostgreSQL server when Flush is called.
 func (pgConn *PgConn) SendExecPrepared(stmtName string, paramValues [][]byte, paramFormats []int16, resultFormats []int16) {
+	pgConn.batchBuf = appendDescribe(pgConn.batchBuf, 'S', stmtName)
 	pgConn.batchBuf = appendBind(pgConn.batchBuf, "", stmtName, paramFormats, paramValues, resultFormats)
 	pgConn.batchBuf = appendExecute(pgConn.batchBuf, "", 0)
 	pgConn.batchBuf = appendSync(pgConn.batchBuf)
@@ -616,6 +604,12 @@ func (rr *PgResultReader) NextRow() bool {
 	}
 }
 
+// FieldDescriptions returns the field descriptions for the current result set. The returned slice is only valid until
+// the PgResultReader is closed.
+func (rr *PgResultReader) FieldDescriptions() []pgproto3.FieldDescription {
+	return rr.fieldDescriptions
+}
+
 // Values returns the current row data. NextRow must have been previously been called. The returned [][]byte is only
 // valid until the next NextRow call or the PgResultReader is closed. However, the underlying byte data is safe to
 // retain a reference to and mutate.
@@ -914,23 +908,23 @@ func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs [
 
 func errorResponseToPgError(msg *pgproto3.ErrorResponse) *PgError {
 	return &PgError{
-		Severity:         msg.Severity,
+		Severity:         string(msg.Severity),
-		Code:             msg.Code,
+		Code:             string(msg.Code),
-		Message:          msg.Message,
+		Message:          string(msg.Message),
-		Detail:           msg.Detail,
+		Detail:           string(msg.Detail),
-		Hint:             msg.Hint,
+		Hint:             string(msg.Hint),
 		Position:         msg.Position,
 		InternalPosition: msg.InternalPosition,
-		InternalQuery:    msg.InternalQuery,
+		InternalQuery:    string(msg.InternalQuery),
-		Where:            msg.Where,
+		Where:            string(msg.Where),
-		SchemaName:       msg.SchemaName,
+		SchemaName:       string(msg.SchemaName),
-		TableName:        msg.TableName,
+		TableName:        string(msg.TableName),
-		ColumnName:       msg.ColumnName,
+		ColumnName:       string(msg.ColumnName),
-		DataTypeName:     msg.DataTypeName,
+		DataTypeName:     string(msg.DataTypeName),
-		ConstraintName:   msg.ConstraintName,
+		ConstraintName:   string(msg.ConstraintName),
-		File:             msg.File,
+		File:             string(msg.File),
 		Line:             msg.Line,
-		Routine:          msg.Routine,
+		Routine:          string(msg.Routine),
 	}
 }
 

pgmock/pgmock.go

@@ -224,7 +224,7 @@ where (
 		SendMessage(&pgproto3.ParameterDescription{}),
 		SendMessage(&pgproto3.RowDescription{
 			Fields: []pgproto3.FieldDescription{
-				{Name: "oid",
+				{Name: []byte("oid"),
 					TableOID:             1247,
 					TableAttributeNumber: 65534,
 					DataTypeOID:          26,
@@ -232,7 +232,7 @@ where (
 					TypeModifier:         -1,
 					Format:               0,
 				},
-				{Name: "typname",
+				{Name: []byte("typname"),
 					TableOID:             1247,
 					TableAttributeNumber: 1,
 					DataTypeOID:          19,
@@ -435,7 +435,7 @@ where (
 		steps = append(steps, step)
 	}
 
-	steps = append(steps, SendMessage(&pgproto3.CommandComplete{CommandTag: "SELECT 163"}))
+	steps = append(steps, SendMessage(&pgproto3.CommandComplete{CommandTag: []byte("SELECT 163")}))
 	steps = append(steps, SendMessage(&pgproto3.ReadyForQuery{TxStatus: 'I'}))
 
 	steps = append(steps, []Step{
@@ -450,7 +450,7 @@ where (
 		SendMessage(&pgproto3.ParameterDescription{}),
 		SendMessage(&pgproto3.RowDescription{
 			Fields: []pgproto3.FieldDescription{
-				{Name: "oid",
+				{Name: []byte("oid"),
 					TableOID:             1247,
 					TableAttributeNumber: 65534,
 					DataTypeOID:          26,
@@ -458,7 +458,7 @@ where (
 					TypeModifier:         -1,
 					Format:               0,
 				},
-				{Name: "typname",
+				{Name: []byte("typname"),
 					TableOID:             1247,
 					TableAttributeNumber: 1,
 					DataTypeOID:          19,
@@ -475,7 +475,7 @@ where (
 		ExpectMessage(&pgproto3.Execute{}),
 		ExpectMessage(&pgproto3.Sync{}),
 		SendMessage(&pgproto3.BindComplete{}),
-		SendMessage(&pgproto3.CommandComplete{CommandTag: "SELECT 0"}),
+		SendMessage(&pgproto3.CommandComplete{CommandTag: []byte("SELECT 0")}),
 		SendMessage(&pgproto3.ReadyForQuery{TxStatus: 'I'}),
 	}...)
 
@@ -491,7 +491,7 @@ where (
 		SendMessage(&pgproto3.ParameterDescription{}),
 		SendMessage(&pgproto3.RowDescription{
 			Fields: []pgproto3.FieldDescription{
-				{Name: "oid",
+				{Name: []byte("oid"),
 					TableOID:             1247,
 					TableAttributeNumber: 65534,
 					DataTypeOID:          26,
@@ -499,7 +499,7 @@ where (
 					TypeModifier:         -1,
 					Format:               0,
 				},
-				{Name: "typname",
+				{Name: []byte("typname"),
 					TableOID:             1247,
 					TableAttributeNumber: 1,
 					DataTypeOID:          19,
@@ -507,7 +507,7 @@ where (
 					TypeModifier:         -1,
 					Format:               0,
 				},
-				{Name: "typbasetype",
+				{Name: []byte("typbasetype"),
 					TableOID:             1247,
 					TableAttributeNumber: 65534,
 					DataTypeOID:          26,
@@ -524,7 +524,7 @@ where (
 		ExpectMessage(&pgproto3.Execute{}),
 		ExpectMessage(&pgproto3.Sync{}),
 		SendMessage(&pgproto3.BindComplete{}),
-		SendMessage(&pgproto3.CommandComplete{CommandTag: "SELECT 0"}),
+		SendMessage(&pgproto3.CommandComplete{CommandTag: []byte("SELECT 0")}),
 		SendMessage(&pgproto3.ReadyForQuery{TxStatus: 'I'}),
 	}...)
 

pgproto3/command_complete.go

@@ -8,7 +8,7 @@ import (
 )
 
 type CommandComplete struct {
-	CommandTag string
+	CommandTag []byte
 }
 
 func (*CommandComplete) Backend() {}
@@ -19,7 +19,7 @@ func (dst *CommandComplete) Decode(src []byte) error {
 		return &invalidMessageFormatErr{messageType: "CommandComplete"}
 	}
 
-	dst.CommandTag = string(src[:idx])
+	dst.CommandTag = src[:idx]
 
 	return nil
 }
@@ -43,6 +43,6 @@ func (src *CommandComplete) MarshalJSON() ([]byte, error) {
 		CommandTag string
 	}{
 		Type:       "CommandComplete",
-		CommandTag: src.CommandTag,
+		CommandTag: string(src.CommandTag),
 	})
 }

pgproto3/row_description.go

@@ -14,7 +14,7 @@ const (
 )
 
 type FieldDescription struct {
-	Name                 string
+	Name                 []byte
 	TableOID             uint32
 	TableAttributeNumber uint16
 	DataTypeOID          uint32
@@ -45,7 +45,7 @@ func (dst *RowDescription) Decode(src []byte) error {
 		if err != nil {
 			return err
 		}
-		fd.Name = string(bName[:len(bName)-1])
+		fd.Name = bName[:len(bName)-1]
 
 		// Since buf.Next() doesn't return an error if we hit the end of the buffer
 		// check Len ahead of time

tx_test.go

@@ -289,7 +289,7 @@ func TestTxCommitExCancel(t *testing.T) {
 	script.Steps = append(script.Steps, pgmock.PgxInitSteps()...)
 	script.Steps = append(script.Steps,
 		pgmock.ExpectMessage(&pgproto3.Query{String: "begin"}),
-		pgmock.SendMessage(&pgproto3.CommandComplete{CommandTag: "BEGIN"}),
+		pgmock.SendMessage(&pgproto3.CommandComplete{CommandTag: []byte("BEGIN")}),
 		pgmock.SendMessage(&pgproto3.ReadyForQuery{TxStatus: 'T'}),
 		pgmock.WaitForClose(),
 	)