Prepare returns description

pgconn/benchmark_test.go

@@ -54,7 +54,7 @@ func BenchmarkExecPrepared(b *testing.B) {
 	require.Nil(b, err)
 	defer closeConn(b, conn)
 
-	err = conn.Prepare(context.Background(), "ps1", "select 'hello'::text as a, 42::int4 as b, '2019-01-01'::date", nil)
+	_, err = conn.Prepare(context.Background(), "ps1", "select 'hello'::text as a, 42::int4 as b, '2019-01-01'::date", nil)
 
 	b.ResetTimer()
 
@@ -69,7 +69,7 @@ func BenchmarkSendExecPrepared(b *testing.B) {
 	require.Nil(b, err)
 	defer closeConn(b, conn)
 
-	err = conn.Prepare(context.Background(), "ps1", "select 'hello'::text as a, 42::int4 as b, '2019-01-01'::date", nil)
+	_, err = conn.Prepare(context.Background(), "ps1", "select 'hello'::text as a, 42::int4 as b, '2019-01-01'::date", nil)
 
 	b.ResetTimer()
 

pgconn/pgconn.go

@@ -757,13 +757,42 @@ func (pgConn *PgConn) ExecPrepared(ctx context.Context, stmtName string, paramVa
 	return pgConn.bufferLastResult(ctx)
 }
 
+type FieldDescription struct {
+	Name                 string
+	TableOID             uint32
+	TableAttributeNumber uint16
+	DataTypeOID          uint32
+	DataTypeSize         int16
+	TypeModifier         int32
+	FormatCode           int16
+}
+
+// pgproto3FieldDescriptionToPgconnFieldDescription copies and converts the data from a pgproto3.FieldDescription to a
+// FieldDescription.
+func pgproto3FieldDescriptionToPgconnFieldDescription(src *pgproto3.FieldDescription, dst *FieldDescription) {
+	dst.Name = string(src.Name)
+	dst.TableOID = src.TableOID
+	dst.TableAttributeNumber = src.TableAttributeNumber
+	dst.DataTypeOID = src.DataTypeOID
+	dst.DataTypeSize = src.DataTypeSize
+	dst.TypeModifier = src.TypeModifier
+	dst.FormatCode = src.Format
+}
+
+type PreparedStatementDescription struct {
+	Name      string
+	SQL       string
+	ParamOIDs []uint32
+	Fields    []FieldDescription
+}
+
 // Prepare creates a prepared statement.
-func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs []uint32) error {
+func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs []uint32) (*PreparedStatementDescription, error) {
 	if pgConn.batchCount != 0 {
-		return errors.New("unflushed previous sends")
+		return nil, errors.New("unflushed previous sends")
 	}
 	if pgConn.pendingReadyForQueryCount != 0 {
-		return errors.New("unread previous results")
+		return nil, errors.New("unread previous results")
 	}
 
 	cleanupContext := contextDoneToConnDeadline(ctx, pgConn.conn)
@@ -775,26 +804,32 @@ func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs [
 	pgConn.batchCount += 1
 	err := pgConn.Flush(context.Background())
 	if err != nil {
-		return preferContextOverNetTimeoutError(ctx, err)
+		return nil, preferContextOverNetTimeoutError(ctx, err)
 	}
 
+	psd := &PreparedStatementDescription{Name: name, SQL: sql}
+
 	for pgConn.pendingReadyForQueryCount > 0 {
 		msg, err := pgConn.ReceiveMessage()
 		if err != nil {
-			return preferContextOverNetTimeoutError(ctx, err)
+			return nil, preferContextOverNetTimeoutError(ctx, err)
 		}
 
 		switch msg := msg.(type) {
 		case *pgproto3.ParameterDescription:
-			// TODO
+			psd.ParamOIDs = make([]uint32, len(msg.ParameterOIDs))
+			copy(psd.ParamOIDs, msg.ParameterOIDs)
 		case *pgproto3.RowDescription:
-			// TODO
+			psd.Fields = make([]FieldDescription, len(msg.Fields))
+			for i := range msg.Fields {
+				pgproto3FieldDescriptionToPgconnFieldDescription(&msg.Fields[i], &psd.Fields[i])
+			}
 		case *pgproto3.ErrorResponse:
-			return errorResponseToPgError(msg)
+			return nil, errorResponseToPgError(msg)
 		}
 	}
 
-	return nil
+	return psd, nil
 }
 
 func errorResponseToPgError(msg *pgproto3.ErrorResponse) *PgError {

pgconn/pgconn_test.go

@@ -327,8 +327,11 @@ func TestConnExecPrepared(t *testing.T) {
 	require.Nil(t, err)
 	defer closeConn(t, pgConn)
 
-	err = pgConn.Prepare(context.Background(), "ps1", "select $1::text", nil)
+	psd, err := pgConn.Prepare(context.Background(), "ps1", "select $1::text", nil)
 	require.Nil(t, err)
+	require.NotNil(t, psd)
+	assert.Len(t, psd.ParamOIDs, 1)
+	assert.Len(t, psd.Fields, 1)
 
 	result, err := pgConn.ExecPrepared(context.Background(), "ps1", [][]byte{[]byte("Hello, world")}, nil, nil)
 	require.Nil(t, err)
@@ -343,7 +346,7 @@ func TestConnExecPreparedCanceled(t *testing.T) {
 	require.Nil(t, err)
 	defer closeConn(t, pgConn)
 
-	err = pgConn.Prepare(context.Background(), "ps1", "select current_database(), pg_sleep(1)", nil)
+	_, err = pgConn.Prepare(context.Background(), "ps1", "select current_database(), pg_sleep(1)", nil)
 	require.Nil(t, err)
 
 	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
@@ -362,7 +365,7 @@ func TestConnBatchedQueries(t *testing.T) {
 	require.Nil(t, err)
 	defer closeConn(t, pgConn)
 
-	err = pgConn.Prepare(context.Background(), "ps1", "select $1::text", nil)
+	_, err = pgConn.Prepare(context.Background(), "ps1", "select $1::text", nil)
 	require.Nil(t, err)
 
 	pgConn.SendExec("select 'SendExec 1'")