Use higher pgconn.FieldDescription with string Name

Instead of using pgproto3.FieldDescription through pgconn and pgx. This
lets the lowest level pgproto3 still be as memory efficient as possible.

https://github.com/jackc/pgx/pull/1281

pgconn/pgconn.go

@@ -83,6 +83,7 @@ type PgConn struct {
 	multiResultReader MultiResultReader
 	pipeline          Pipeline
 	contextWatcher    *ctxwatch.ContextWatcher
+	fieldDescriptions [16]FieldDescription
 
 	cleanupDone chan struct{}
 }
@@ -526,9 +527,10 @@ func (pgConn *PgConn) PID() uint32 {
 // TxStatus returns the current TxStatus as reported by the server in the ReadyForQuery message.
 //
 // Possible return values:
-//   'I' - idle / not in transaction
+//
-//   'T' - in a transaction
+//	'I' - idle / not in transaction
-//   'E' - in a failed transaction
+//	'T' - in a transaction
+//	'E' - in a failed transaction
 //
 // See https://www.postgresql.org/docs/current/protocol-message-formats.html.
 func (pgConn *PgConn) TxStatus() byte {
@@ -714,11 +716,41 @@ func (ct CommandTag) Select() bool {
 	return strings.HasPrefix(ct.s, "SELECT")
 }
 
+type FieldDescription struct {
+	Name                 string
+	TableOID             uint32
+	TableAttributeNumber uint16
+	DataTypeOID          uint32
+	DataTypeSize         int16
+	TypeModifier         int32
+	Format               int16
+}
+
+func (pgConn *PgConn) convertRowDescription(dst []FieldDescription, rd *pgproto3.RowDescription) []FieldDescription {
+	if cap(dst) >= len(rd.Fields) {
+		dst = dst[:len(rd.Fields):len(rd.Fields)]
+	} else {
+		dst = make([]FieldDescription, len(rd.Fields))
+	}
+
+	for i := range rd.Fields {
+		dst[i].Name = string(rd.Fields[i].Name)
+		dst[i].TableOID = rd.Fields[i].TableOID
+		dst[i].TableAttributeNumber = rd.Fields[i].TableAttributeNumber
+		dst[i].DataTypeOID = rd.Fields[i].DataTypeOID
+		dst[i].DataTypeSize = rd.Fields[i].DataTypeSize
+		dst[i].TypeModifier = rd.Fields[i].TypeModifier
+		dst[i].Format = rd.Fields[i].Format
+	}
+
+	return dst
+}
+
 type StatementDescription struct {
 	Name      string
 	SQL       string
 	ParamOIDs []uint32
-	Fields    []pgproto3.FieldDescription
+	Fields    []FieldDescription
 }
 
 // Prepare creates a prepared statement. If the name is empty, the anonymous prepared statement will be used. This
@@ -765,8 +797,7 @@ readloop:
 			psd.ParamOIDs = make([]uint32, len(msg.ParameterOIDs))
 			copy(psd.ParamOIDs, msg.ParameterOIDs)
 		case *pgproto3.RowDescription:
-			psd.Fields = make([]pgproto3.FieldDescription, len(msg.Fields))
+			psd.Fields = pgConn.convertRowDescription(nil, msg)
-			copy(psd.Fields, msg.Fields)
 		case *pgproto3.ErrorResponse:
 			parseErr = ErrorResponseToPgError(msg)
 		case *pgproto3.ReadyForQuery:
@@ -1281,8 +1312,9 @@ func (mrr *MultiResultReader) NextResult() bool {
 				pgConn:            mrr.pgConn,
 				multiResultReader: mrr,
 				ctx:               mrr.ctx,
-				fieldDescriptions: msg.Fields,
+				fieldDescriptions: mrr.pgConn.convertRowDescription(mrr.pgConn.fieldDescriptions[:], msg),
 			}
+
 			mrr.rr = &mrr.pgConn.resultReader
 			return true
 		case *pgproto3.CommandComplete:
@@ -1325,7 +1357,7 @@ type ResultReader struct {
 	pipeline          *Pipeline
 	ctx               context.Context
 
-	fieldDescriptions []pgproto3.FieldDescription
+	fieldDescriptions []FieldDescription
 	rowValues         [][]byte
 	commandTag        CommandTag
 	commandConcluded  bool
@@ -1335,7 +1367,7 @@ type ResultReader struct {
 
 // Result is the saved query response that is returned by calling Read on a ResultReader.
 type Result struct {
-	FieldDescriptions []pgproto3.FieldDescription
+	FieldDescriptions []FieldDescription
 	Rows              [][][]byte
 	CommandTag        CommandTag
 	Err               error
@@ -1347,7 +1379,7 @@ func (rr *ResultReader) Read() *Result {
 
 	for rr.NextRow() {
 		if br.FieldDescriptions == nil {
-			br.FieldDescriptions = make([]pgproto3.FieldDescription, len(rr.FieldDescriptions()))
+			br.FieldDescriptions = make([]FieldDescription, len(rr.FieldDescriptions()))
 			copy(br.FieldDescriptions, rr.FieldDescriptions())
 		}
 
@@ -1385,7 +1417,7 @@ func (rr *ResultReader) NextRow() bool {
 
 // FieldDescriptions returns the field descriptions for the current result set. The returned slice is only valid until
 // the ResultReader is closed.
-func (rr *ResultReader) FieldDescriptions() []pgproto3.FieldDescription {
+func (rr *ResultReader) FieldDescriptions() []FieldDescription {
 	return rr.fieldDescriptions
 }
 
@@ -1473,7 +1505,7 @@ func (rr *ResultReader) receiveMessage() (msg pgproto3.BackendMessage, err error
 
 	switch msg := msg.(type) {
 	case *pgproto3.RowDescription:
-		rr.fieldDescriptions = msg.Fields
+		rr.fieldDescriptions = rr.pgConn.convertRowDescription(rr.pgConn.fieldDescriptions[:], msg)
 	case *pgproto3.CommandComplete:
 		rr.concludeCommand(rr.pgConn.makeCommandTag(msg.CommandTag), nil)
 	case *pgproto3.EmptyQueryResponse:
@@ -1825,7 +1857,7 @@ func (p *Pipeline) GetResults() (results any, err error) {
 				pgConn:            p.conn,
 				pipeline:          p,
 				ctx:               p.ctx,
-				fieldDescriptions: msg.Fields,
+				fieldDescriptions: p.conn.convertRowDescription(p.conn.fieldDescriptions[:], msg),
 			}
 			return &p.conn.resultReader, nil
 		case *pgproto3.CommandComplete:
@@ -1872,8 +1904,7 @@ func (p *Pipeline) getResultsPrepare() (*StatementDescription, error) {
 			psd.ParamOIDs = make([]uint32, len(msg.ParameterOIDs))
 			copy(psd.ParamOIDs, msg.ParameterOIDs)
 		case *pgproto3.RowDescription:
-			psd.Fields = make([]pgproto3.FieldDescription, len(msg.Fields))
+			psd.Fields = p.conn.convertRowDescription(nil, msg)
-			copy(psd.Fields, msg.Fields)
 			return psd, nil
 
 		// NoData is returned instead of RowDescription when there is no expected result. e.g. An INSERT without a RETURNING

pgconn/pgconn_test.go

@@ -642,13 +642,13 @@ func TestConnExecMultipleQueriesEagerFieldDescriptions(t *testing.T) {
 
 	require.True(t, mrr.NextResult())
 	require.Len(t, mrr.ResultReader().FieldDescriptions(), 1)
-	assert.Equal(t, []byte("msg"), mrr.ResultReader().FieldDescriptions()[0].Name)
+	assert.Equal(t, "msg", mrr.ResultReader().FieldDescriptions()[0].Name)
 	_, err = mrr.ResultReader().Close()
 	require.NoError(t, err)
 
 	require.True(t, mrr.NextResult())
 	require.Len(t, mrr.ResultReader().FieldDescriptions(), 1)
-	assert.Equal(t, []byte("num"), mrr.ResultReader().FieldDescriptions()[0].Name)
+	assert.Equal(t, "num", mrr.ResultReader().FieldDescriptions()[0].Name)
 	_, err = mrr.ResultReader().Close()
 	require.NoError(t, err)
 
@@ -772,7 +772,7 @@ func TestConnExecParams(t *testing.T) {
 
 	result := pgConn.ExecParams(context.Background(), "select $1::text as msg", [][]byte{[]byte("Hello, world")}, nil, nil, nil)
 	require.Len(t, result.FieldDescriptions(), 1)
-	assert.Equal(t, []byte("msg"), result.FieldDescriptions()[0].Name)
+	assert.Equal(t, "msg", result.FieldDescriptions()[0].Name)
 
 	rowCount := 0
 	for result.NextRow() {
@@ -937,7 +937,7 @@ func TestResultReaderValuesHaveSameCapacityAsLength(t *testing.T) {
 
 	result := pgConn.ExecParams(context.Background(), "select $1::text as msg", [][]byte{[]byte("Hello, world")}, nil, nil, nil)
 	require.Len(t, result.FieldDescriptions(), 1)
-	assert.Equal(t, []byte("msg"), result.FieldDescriptions()[0].Name)
+	assert.Equal(t, "msg", result.FieldDescriptions()[0].Name)
 
 	rowCount := 0
 	for result.NextRow() {
@@ -968,7 +968,7 @@ func TestConnExecPrepared(t *testing.T) {
 
 	result := pgConn.ExecPrepared(context.Background(), "ps1", [][]byte{[]byte("Hello, world")}, nil, nil)
 	require.Len(t, result.FieldDescriptions(), 1)
-	assert.Equal(t, []byte("msg"), result.FieldDescriptions()[0].Name)
+	assert.Equal(t, "msg", result.FieldDescriptions()[0].Name)
 
 	rowCount := 0
 	for result.NextRow() {

pgxpool/rows.go

@@ -3,22 +3,21 @@ package pgxpool
 import (
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgconn"
-	"github.com/jackc/pgx/v5/pgproto3"
 )
 
 type errRows struct {
 	err error
 }
 
-func (errRows) Close()                                         {}
+func (errRows) Close()                                       {}
-func (e errRows) Err() error                                   { return e.err }
+func (e errRows) Err() error                                 { return e.err }
-func (errRows) CommandTag() pgconn.CommandTag                  { return pgconn.CommandTag{} }
+func (errRows) CommandTag() pgconn.CommandTag                { return pgconn.CommandTag{} }
-func (errRows) FieldDescriptions() []pgproto3.FieldDescription { return nil }
+func (errRows) FieldDescriptions() []pgconn.FieldDescription { return nil }
-func (errRows) Next() bool                                     { return false }
+func (errRows) Next() bool                                   { return false }
-func (e errRows) Scan(dest ...any) error                       { return e.err }
+func (e errRows) Scan(dest ...any) error                     { return e.err }
-func (e errRows) Values() ([]any, error)                       { return nil, e.err }
+func (e errRows) Values() ([]any, error)                     { return nil, e.err }
-func (e errRows) RawValues() [][]byte                          { return nil }
+func (e errRows) RawValues() [][]byte                        { return nil }
-func (e errRows) Conn() *pgx.Conn                              { return nil }
+func (e errRows) Conn() *pgx.Conn                            { return nil }
 
 type errRow struct {
 	err error
@@ -51,7 +50,7 @@ func (rows *poolRows) CommandTag() pgconn.CommandTag {
 	return rows.r.CommandTag()
 }
 
-func (rows *poolRows) FieldDescriptions() []pgproto3.FieldDescription {
+func (rows *poolRows) FieldDescriptions() []pgconn.FieldDescription {
 	return rows.r.FieldDescriptions()
 }
 

query_test.go

@@ -66,7 +66,7 @@ func TestConnQueryRowsFieldDescriptionsBeforeNext(t *testing.T) {
 	defer rows.Close()
 
 	require.Len(t, rows.FieldDescriptions(), 1)
-	assert.Equal(t, []byte("msg"), rows.FieldDescriptions()[0].Name)
+	assert.Equal(t, "msg", rows.FieldDescriptions()[0].Name)
 }
 
 func TestConnQueryWithoutResultSetCommandTag(t *testing.T) {

rows.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/jackc/pgx/v5/internal/stmtcache"
 	"github.com/jackc/pgx/v5/pgconn"
-	"github.com/jackc/pgx/v5/pgproto3"
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
@@ -34,7 +33,7 @@ type Rows interface {
 	// CommandTag returns the command tag from this query. It is only available after Rows is closed.
 	CommandTag() pgconn.CommandTag
 
-	FieldDescriptions() []pgproto3.FieldDescription
+	FieldDescriptions() []pgconn.FieldDescription
 
 	// Next prepares the next row for reading. It returns true if there is another
 	// row and false if no more rows are available. It automatically closes rows
@@ -135,7 +134,7 @@ type baseRows struct {
 	rowCount    int
 }
 
-func (rows *baseRows) FieldDescriptions() []pgproto3.FieldDescription {
+func (rows *baseRows) FieldDescriptions() []pgconn.FieldDescription {
 	return rows.resultReader.FieldDescriptions()
 }
 
@@ -337,7 +336,7 @@ func (e ScanArgError) Unwrap() error {
 // fieldDescriptions - OID and format of values
 // values - the raw data as returned from the PostgreSQL server
 // dest - the destination that values will be decoded into
-func ScanRow(typeMap *pgtype.Map, fieldDescriptions []pgproto3.FieldDescription, values [][]byte, dest ...any) error {
+func ScanRow(typeMap *pgtype.Map, fieldDescriptions []pgconn.FieldDescription, values [][]byte, dest ...any) error {
 	if len(fieldDescriptions) != len(values) {
 		return fmt.Errorf("number of field descriptions must equal number of values, got %d and %d", len(fieldDescriptions), len(values))
 	}
@@ -395,7 +394,7 @@ func ForEachRow(rows Rows, scans []any, fn func() error) (pgconn.CommandTag, err
 
 // CollectableRow is the subset of Rows methods that a RowToFunc is allowed to call.
 type CollectableRow interface {
-	FieldDescriptions() []pgproto3.FieldDescription
+	FieldDescriptions() []pgconn.FieldDescription
 	Scan(dest ...any) error
 	Values() ([]any, error)
 	RawValues() [][]byte