conn.go

package pgx

import (
	"context"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/v5/internal/anynil"
	"github.com/jackc/pgx/v5/internal/sanitize"
	"github.com/jackc/pgx/v5/internal/stmtcache"
	"github.com/jackc/pgx/v5/pgconn"
	"github.com/jackc/pgx/v5/pgtype"
)

// ConnConfig contains all the options used to establish a connection. It must be created by ParseConfig and
// then it can be modified. A manually initialized ConnConfig will cause ConnectConfig to panic.
type ConnConfig struct {
	pgconn.Config

	Tracer QueryTracer

	// Original connection string that was parsed into config.
	connString string

	// StatementCacheCapacity is maximum size of the statement cache used when executing a query with "cache_statement"
	// query exec mode.
	StatementCacheCapacity int

	// DescriptionCacheCapacity is the maximum size of the description cache used when executing a query with
	// "cache_describe" query exec mode.
	DescriptionCacheCapacity int

	// DefaultQueryExecMode controls the default mode for executing queries. By default pgx uses the extended protocol
	// and automatically prepares and caches prepared statements. However, this may be incompatible with proxies such as
	// PGBouncer. In this case it may be preferrable to use QueryExecModeExec or QueryExecModeSimpleProtocol. The same
	// functionality can be controlled on a per query basis by passing a QueryExecMode as the first query argument.
	DefaultQueryExecMode QueryExecMode

	createdByParseConfig bool // Used to enforce created by ParseConfig rule.
}

// Copy returns a deep copy of the config that is safe to use and modify.
// The only exception is the tls.Config:
// according to the tls.Config docs it must not be modified after creation.
func (cc *ConnConfig) Copy() *ConnConfig {
	newConfig := new(ConnConfig)
	*newConfig = *cc
	newConfig.Config = *newConfig.Config.Copy()
	return newConfig
}

// ConnString returns the connection string as parsed by pgx.ParseConfig into pgx.ConnConfig.
func (cc *ConnConfig) ConnString() string { return cc.connString }

// Conn is a PostgreSQL connection handle. It is not safe for concurrent usage. Use a connection pool to manage access
// to multiple database connections from multiple goroutines.
type Conn struct {
	pgConn             *pgconn.PgConn
	config             *ConnConfig // config used when establishing this connection
	preparedStatements map[string]*pgconn.StatementDescription
	statementCache     stmtcache.Cache
	descriptionCache   stmtcache.Cache

	queryTracer    QueryTracer
	batchTracer    BatchTracer
	copyFromTracer CopyFromTracer
	prepareTracer  PrepareTracer

	notifications []*pgconn.Notification

	doneChan   chan struct{}
	closedChan chan error

	typeMap *pgtype.Map

	wbuf []byte
	eqb  ExtendedQueryBuilder
}

// Identifier a PostgreSQL identifier or name. Identifiers can be composed of
// multiple parts such as ["schema", "table"] or ["table", "column"].
type Identifier []string

// Sanitize returns a sanitized string safe for SQL interpolation.
func (ident Identifier) Sanitize() string {
	parts := make([]string, len(ident))
	for i := range ident {
		s := strings.ReplaceAll(ident[i], string([]byte{0}), "")
		parts[i] = `"` + strings.ReplaceAll(s, `"`, `""`) + `"`
	}
	return strings.Join(parts, ".")
}

// ErrNoRows occurs when rows are expected but none are returned.
var ErrNoRows = errors.New("no rows in result set")

var errDisabledStatementCache = fmt.Errorf("cannot use QueryExecModeCacheStatement with disabled statement cache")
var errDisabledDescriptionCache = fmt.Errorf("cannot use QueryExecModeCacheDescribe with disabled description cache")

// Connect establishes a connection with a PostgreSQL server with a connection string. See
// pgconn.Connect for details.
func Connect(ctx context.Context, connString string) (*Conn, error) {
	connConfig, err := ParseConfig(connString)
	if err != nil {
		return nil, err
	}
	return connect(ctx, connConfig)
}

// ConnectConfig establishes a connection with a PostgreSQL server with a configuration struct.
// connConfig must have been created by ParseConfig.
func ConnectConfig(ctx context.Context, connConfig *ConnConfig) (*Conn, error) {
	// In general this improves safety. In particular avoid the config.Config.OnNotification mutation from affecting other
	// connections with the same config. See https://github.com/jackc/pgx/issues/618.
	connConfig = connConfig.Copy()

	return connect(ctx, connConfig)
}

// ParseConfig creates a ConnConfig from a connection string. ParseConfig handles all options that pgconn.ParseConfig
// does. In addition, it accepts the following options:
//
//	default_query_exec_mode
//		Possible values: "cache_statement", "cache_describe", "describe_exec", "exec", and "simple_protocol". See
//		QueryExecMode constant documentation for the meaning of these values. Default: "cache_statement".
//
//	statement_cache_capacity
//		The maximum size of the statement cache used when executing a query with "cache_statement" query exec mode.
//		Default: 512.
//
//	description_cache_capacity
//		The maximum size of the description cache used when executing a query with "cache_describe" query exec mode.
//		Default: 512.
func ParseConfig(connString string) (*ConnConfig, error) {
	config, err := pgconn.ParseConfig(connString)
	if err != nil {
		return nil, err
	}

	statementCacheCapacity := 512
	if s, ok := config.RuntimeParams["statement_cache_capacity"]; ok {
		delete(config.RuntimeParams, "statement_cache_capacity")
		n, err := strconv.ParseInt(s, 10, 32)
		if err != nil {
			return nil, fmt.Errorf("cannot parse statement_cache_capacity: %w", err)
		}
		statementCacheCapacity = int(n)
	}

	descriptionCacheCapacity := 512
	if s, ok := config.RuntimeParams["description_cache_capacity"]; ok {
		delete(config.RuntimeParams, "description_cache_capacity")
		n, err := strconv.ParseInt(s, 10, 32)
		if err != nil {
			return nil, fmt.Errorf("cannot parse description_cache_capacity: %w", err)
		}
		descriptionCacheCapacity = int(n)
	}

	defaultQueryExecMode := QueryExecModeCacheStatement
	if s, ok := config.RuntimeParams["default_query_exec_mode"]; ok {
		delete(config.RuntimeParams, "default_query_exec_mode")
		switch s {
		case "cache_statement":
			defaultQueryExecMode = QueryExecModeCacheStatement
		case "cache_describe":
			defaultQueryExecMode = QueryExecModeCacheDescribe
		case "describe_exec":
			defaultQueryExecMode = QueryExecModeDescribeExec
		case "exec":
			defaultQueryExecMode = QueryExecModeExec
		case "simple_protocol":
			defaultQueryExecMode = QueryExecModeSimpleProtocol
		default:
			return nil, fmt.Errorf("invalid default_query_exec_mode: %v", err)
		}
	}

	connConfig := &ConnConfig{
		Config:                   *config,
		createdByParseConfig:     true,
		StatementCacheCapacity:   statementCacheCapacity,
		DescriptionCacheCapacity: descriptionCacheCapacity,
		DefaultQueryExecMode:     defaultQueryExecMode,
		connString:               connString,
	}

	return connConfig, nil
}

// connect connects to a database. connect takes ownership of config. The caller must not use or access it again.
func connect(ctx context.Context, config *ConnConfig) (c *Conn, err error) {
	if connectTracer, ok := config.Tracer.(ConnectTracer); ok {
		ctx = connectTracer.TraceConnectStart(ctx, TraceConnectStartData{ConnConfig: config})
		defer func() {
			connectTracer.TraceConnectEnd(ctx, TraceConnectEndData{Conn: c, Err: err})
		}()
	}

	// Default values are set in ParseConfig. Enforce initial creation by ParseConfig rather than setting defaults from
	// zero values.
	if !config.createdByParseConfig {
		panic("config must be created by ParseConfig")
	}

	c = &Conn{
		config:      config,
		typeMap:     pgtype.NewMap(),
		queryTracer: config.Tracer,
	}

	if t, ok := c.queryTracer.(BatchTracer); ok {
		c.batchTracer = t
	}
	if t, ok := c.queryTracer.(CopyFromTracer); ok {
		c.copyFromTracer = t
	}
	if t, ok := c.queryTracer.(PrepareTracer); ok {
		c.prepareTracer = t
	}

	// Only install pgx notification system if no other callback handler is present.
	if config.Config.OnNotification == nil {
		config.Config.OnNotification = c.bufferNotifications
	}

	c.pgConn, err = pgconn.ConnectConfig(ctx, &config.Config)
	if err != nil {
		return nil, err
	}

	c.preparedStatements = make(map[string]*pgconn.StatementDescription)
	c.doneChan = make(chan struct{})
	c.closedChan = make(chan error)
	c.wbuf = make([]byte, 0, 1024)

	if c.config.StatementCacheCapacity > 0 {
		c.statementCache = stmtcache.NewLRUCache(c.config.StatementCacheCapacity)
	}

	if c.config.DescriptionCacheCapacity > 0 {
		c.descriptionCache = stmtcache.NewLRUCache(c.config.DescriptionCacheCapacity)
	}

	return c, nil
}

// Close closes a connection. It is safe to call Close on a already closed
// connection.
func (c *Conn) Close(ctx context.Context) error {
	if c.IsClosed() {
		return nil
	}

	err := c.pgConn.Close(ctx)
	return err
}

// Prepare creates a prepared statement with name and sql. sql can contain placeholders
// for bound parameters. These placeholders are referenced positional as $1, $2, etc.
//
// Prepare is idempotent; i.e. it is safe to call Prepare multiple times with the same
// name and sql arguments. This allows a code path to Prepare and Query/Exec without
// concern for if the statement has already been prepared.
func (c *Conn) Prepare(ctx context.Context, name, sql string) (sd *pgconn.StatementDescription, err error) {
	if c.prepareTracer != nil {
		ctx = c.prepareTracer.TracePrepareStart(ctx, c, TracePrepareStartData{Name: name, SQL: sql})
	}

	if name != "" {
		var ok bool
		if sd, ok = c.preparedStatements[name]; ok && sd.SQL == sql {
			if c.prepareTracer != nil {
				c.prepareTracer.TracePrepareEnd(ctx, c, TracePrepareEndData{AlreadyPrepared: true})
			}
			return sd, nil
		}
	}

	if c.prepareTracer != nil {
		defer func() {
			c.prepareTracer.TracePrepareEnd(ctx, c, TracePrepareEndData{Err: err})
		}()
	}

	sd, err = c.pgConn.Prepare(ctx, name, sql, nil)
	if err != nil {
		return nil, err
	}

	if name != "" {
		c.preparedStatements[name] = sd
	}

	return sd, nil
}

// Deallocate released a prepared statement
func (c *Conn) Deallocate(ctx context.Context, name string) error {
	delete(c.preparedStatements, name)
	_, err := c.pgConn.Exec(ctx, "deallocate "+quoteIdentifier(name)).ReadAll()
	return err
}

func (c *Conn) bufferNotifications(_ *pgconn.PgConn, n *pgconn.Notification) {
	c.notifications = append(c.notifications, n)
}

// WaitForNotification waits for a PostgreSQL notification. It wraps the underlying pgconn notification system in a
// slightly more convenient form.
func (c *Conn) WaitForNotification(ctx context.Context) (*pgconn.Notification, error) {
	var n *pgconn.Notification

	// Return already received notification immediately
	if len(c.notifications) > 0 {
		n = c.notifications[0]
		c.notifications = c.notifications[1:]
		return n, nil
	}

	err := c.pgConn.WaitForNotification(ctx)
	if len(c.notifications) > 0 {
		n = c.notifications[0]
		c.notifications = c.notifications[1:]
	}
	return n, err
}

// IsClosed reports if the connection has been closed.
func (c *Conn) IsClosed() bool {
	return c.pgConn.IsClosed()
}

func (c *Conn) die(err error) {
	if c.IsClosed() {
		return
	}

	ctx, cancel := context.WithCancel(context.Background())
	cancel() // force immediate hard cancel
	c.pgConn.Close(ctx)
}

func quoteIdentifier(s string) string {
	return `"` + strings.ReplaceAll(s, `"`, `""`) + `"`
}

// Ping executes an empty sql statement against the *Conn
// If the sql returns without error, the database Ping is considered successful, otherwise, the error is returned.
func (c *Conn) Ping(ctx context.Context) error {
	_, err := c.Exec(ctx, ";")
	return err
}

// PgConn returns the underlying *pgconn.PgConn. This is an escape hatch method that allows lower level access to the
// PostgreSQL connection than pgx exposes.
//
// It is strongly recommended that the connection be idle (no in-progress queries) before the underlying *pgconn.PgConn
// is used and the connection must be returned to the same state before any *pgx.Conn methods are again used.
func (c *Conn) PgConn() *pgconn.PgConn { return c.pgConn }

// TypeMap returns the connection info used for this connection.
func (c *Conn) TypeMap() *pgtype.Map { return c.typeMap }

// Config returns a copy of config that was used to establish this connection.
func (c *Conn) Config() *ConnConfig { return c.config.Copy() }

// Exec executes sql. sql can be either a prepared statement name or an SQL string. arguments should be referenced
// positionally from the sql string as $1, $2, etc.
func (c *Conn) Exec(ctx context.Context, sql string, arguments ...any) (pgconn.CommandTag, error) {
	if c.queryTracer != nil {
		ctx = c.queryTracer.TraceQueryStart(ctx, c, TraceQueryStartData{SQL: sql, Args: arguments})
	}

	if err := c.deallocateInvalidatedCachedStatements(ctx); err != nil {
		return pgconn.CommandTag{}, err
	}

	commandTag, err := c.exec(ctx, sql, arguments...)

	if c.queryTracer != nil {
		c.queryTracer.TraceQueryEnd(ctx, c, TraceQueryEndData{CommandTag: commandTag, Err: err})
	}

	return commandTag, err
}

func (c *Conn) exec(ctx context.Context, sql string, arguments ...any) (commandTag pgconn.CommandTag, err error) {
	mode := c.config.DefaultQueryExecMode
	var queryRewriter QueryRewriter

optionLoop:
	for len(arguments) > 0 {
		switch arg := arguments[0].(type) {
		case QueryExecMode:
			mode = arg
			arguments = arguments[1:]
		case QueryRewriter:
			queryRewriter = arg
			arguments = arguments[1:]
		default:
			break optionLoop
		}
	}

	if queryRewriter != nil {
		sql, arguments = queryRewriter.RewriteQuery(ctx, c, sql, arguments)
	}

	// Always use simple protocol when there are no arguments.
	if len(arguments) == 0 {
		mode = QueryExecModeSimpleProtocol
	}

	if sd, ok := c.preparedStatements[sql]; ok {
		return c.execPrepared(ctx, sd, arguments)
	}

	switch mode {
	case QueryExecModeCacheStatement:
		if c.statementCache == nil {
			return pgconn.CommandTag{}, errDisabledStatementCache
		}
		sd := c.statementCache.Get(sql)
		if sd == nil {
			sd, err = c.Prepare(ctx, stmtcache.NextStatementName(), sql)
			if err != nil {
				return pgconn.CommandTag{}, err
			}
			c.statementCache.Put(sd)
		}

		return c.execPrepared(ctx, sd, arguments)
	case QueryExecModeCacheDescribe:
		if c.descriptionCache == nil {
			return pgconn.CommandTag{}, errDisabledDescriptionCache
		}
		sd := c.descriptionCache.Get(sql)
		if sd == nil {
			sd, err = c.Prepare(ctx, "", sql)
			if err != nil {
				return pgconn.CommandTag{}, err
			}
		}

		return c.execParams(ctx, sd, arguments)
	case QueryExecModeDescribeExec:
		sd, err := c.Prepare(ctx, "", sql)
		if err != nil {
			return pgconn.CommandTag{}, err
		}
		return c.execPrepared(ctx, sd, arguments)
	case QueryExecModeExec:
		return c.execSQLParams(ctx, sql, arguments)
	case QueryExecModeSimpleProtocol:
		return c.execSimpleProtocol(ctx, sql, arguments)
	default:
		return pgconn.CommandTag{}, fmt.Errorf("unknown QueryExecMode: %v", mode)
	}
}

func (c *Conn) execSimpleProtocol(ctx context.Context, sql string, arguments []any) (commandTag pgconn.CommandTag, err error) {
	if len(arguments) > 0 {
		sql, err = c.sanitizeForSimpleQuery(sql, arguments...)
		if err != nil {
			return pgconn.CommandTag{}, err
		}
	}

	mrr := c.pgConn.Exec(ctx, sql)
	for mrr.NextResult() {
		commandTag, err = mrr.ResultReader().Close()
	}
	err = mrr.Close()
	return commandTag, err
}

func (c *Conn) execParams(ctx context.Context, sd *pgconn.StatementDescription, arguments []any) (pgconn.CommandTag, error) {
	err := c.eqb.Build(c.typeMap, sd, arguments)
	if err != nil {
		return pgconn.CommandTag{}, err
	}

	result := c.pgConn.ExecParams(ctx, sd.SQL, c.eqb.ParamValues, sd.ParamOIDs, c.eqb.ParamFormats, c.eqb.ResultFormats).Read()
	c.eqb.reset() // Allow c.eqb internal memory to be GC'ed as soon as possible.
	return result.CommandTag, result.Err
}

func (c *Conn) execPrepared(ctx context.Context, sd *pgconn.StatementDescription, arguments []any) (pgconn.CommandTag, error) {
	err := c.eqb.Build(c.typeMap, sd, arguments)
	if err != nil {
		return pgconn.CommandTag{}, err
	}

	result := c.pgConn.ExecPrepared(ctx, sd.Name, c.eqb.ParamValues, c.eqb.ParamFormats, c.eqb.ResultFormats).Read()
	c.eqb.reset() // Allow c.eqb internal memory to be GC'ed as soon as possible.
	return result.CommandTag, result.Err
}

type unknownArgumentTypeQueryExecModeExecError struct {
	arg any
}

func (e *unknownArgumentTypeQueryExecModeExecError) Error() string {
	return fmt.Sprintf("cannot use unregistered type %T as query argument in QueryExecModeExec", e.arg)
}

func (c *Conn) execSQLParams(ctx context.Context, sql string, args []any) (pgconn.CommandTag, error) {
	err := c.eqb.Build(c.typeMap, nil, args)
	if err != nil {
		return pgconn.CommandTag{}, err
	}

	result := c.pgConn.ExecParams(ctx, sql, c.eqb.ParamValues, nil, c.eqb.ParamFormats, c.eqb.ResultFormats).Read()
	c.eqb.reset() // Allow c.eqb internal memory to be GC'ed as soon as possible.
	return result.CommandTag, result.Err
}

func (c *Conn) getRows(ctx context.Context, sql string, args []any) *baseRows {
	r := &baseRows{}

	r.ctx = ctx
	r.queryTracer = c.queryTracer
	r.typeMap = c.typeMap
	r.startTime = time.Now()
	r.sql = sql
	r.args = args
	r.conn = c

	return r
}

type QueryExecMode int32

const (
	_ QueryExecMode = iota

	// Automatically prepare and cache statements. This uses the extended protocol. Queries are executed in a single
	// round trip after the statement is cached. This is the default.
	QueryExecModeCacheStatement

	// Cache statement descriptions (i.e. argument and result types) and assume they do not change. This uses the
	// extended protocol. Queries are executed in a single round trip after the description is cached. If the database
	// schema is modified or the search_path is changed this may result in undetected result decoding errors.
	QueryExecModeCacheDescribe

	// Get the statement description on every execution. This uses the extended protocol. Queries require two round trips
	// to execute. It does not use prepared statements (allowing usage with most connection poolers) and is safe even
	// when the the database schema is modified concurrently.
	QueryExecModeDescribeExec

	// Assume the PostgreSQL query parameter types based on the Go type of the arguments. This uses the extended protocol
	// with text formatted parameters and results. Queries are executed in a single round trip. Type mappings can be
	// registered with pgtype.Map.RegisterDefaultPgType. Queries will be rejected that have arguments that are
	// unregistered or ambigious. e.g. A map[string]string may have the PostgreSQL type json or hstore. Modes that know
	// the PostgreSQL type can use a map[string]string directly as an argument. This mode cannot.
	QueryExecModeExec

	// Use the simple protocol. Assume the PostgreSQL query parameter types based on the Go type of the arguments.
	// Queries are executed in a single round trip. Type mappings can be registered with
	// pgtype.Map.RegisterDefaultPgType. Queries will be rejected that have arguments that are unregistered or ambigious.
	// e.g. A map[string]string may have the PostgreSQL type json or hstore. Modes that know the PostgreSQL type can use
	// a map[string]string directly as an argument. This mode cannot.
	//
	// QueryExecModeSimpleProtocol should have the user application visible behavior as QueryExecModeExec with minor
	// exceptions such as behavior when multiple result returning queries are erroneously sent in a single string.
	//
	// QueryExecModeSimpleProtocol uses client side parameter interpolation. All values are quoted and escaped. Prefer
	// QueryExecModeExec over QueryExecModeSimpleProtocol whenever possible. In general QueryExecModeSimpleProtocol
	// should only be used if connecting to a proxy server, connection pool server, or non-PostgreSQL server that does
	// not support the extended protocol.
	QueryExecModeSimpleProtocol
)

func (m QueryExecMode) String() string {
	switch m {
	case QueryExecModeCacheStatement:
		return "cache statement"
	case QueryExecModeCacheDescribe:
		return "cache describe"
	case QueryExecModeDescribeExec:
		return "describe exec"
	case QueryExecModeExec:
		return "exec"
	case QueryExecModeSimpleProtocol:
		return "simple protocol"
	default:
		return "invalid"
	}
}

// QueryResultFormats controls the result format (text=0, binary=1) of a query by result column position.
type QueryResultFormats []int16

// QueryResultFormatsByOID controls the result format (text=0, binary=1) of a query by the result column OID.
type QueryResultFormatsByOID map[uint32]int16

// QueryRewriter rewrites a query when used as the first arguments to a query method.
type QueryRewriter interface {
	RewriteQuery(ctx context.Context, conn *Conn, sql string, args []any) (newSQL string, newArgs []any)
}

// Query sends a query to the server and returns a Rows to read the results. Only errors encountered sending the query
// and initializing Rows will be returned. Err() on the returned Rows must be checked after the Rows is closed to
// determine if the query executed successfully.
//
// The returned Rows must be closed before the connection can be used again. It is safe to attempt to read from the
// returned Rows even if an error is returned. The error will be the available in rows.Err() after rows are closed. It
// is allowed to ignore the error returned from Query and handle it in Rows.
//
// It is possible for a query to return one or more rows before encountering an error. In most cases the rows should be
// collected before processing rather than processed while receiving each row. This avoids the possibility of the
// application processing rows from a query that the server rejected. The CollectRows function is useful here.
//
// An implementor of QueryRewriter may be passed as the first element of args. It can rewrite the sql and change or
// replace args. For example, NamedArgs is QueryRewriter that implements named arguments.
//
// For extra control over how the query is executed, the types QueryExecMode, QueryResultFormats, and
// QueryResultFormatsByOID may be used as the first args to control exactly how the query is executed. This is rarely
// needed. See the documentation for those types for details.
func (c *Conn) Query(ctx context.Context, sql string, args ...any) (Rows, error) {
	if c.queryTracer != nil {
		ctx = c.queryTracer.TraceQueryStart(ctx, c, TraceQueryStartData{SQL: sql, Args: args})
	}

	if err := c.deallocateInvalidatedCachedStatements(ctx); err != nil {
		if c.queryTracer != nil {
			c.queryTracer.TraceQueryEnd(ctx, c, TraceQueryEndData{Err: err})
		}
		return &baseRows{err: err, closed: true}, err
	}

	var resultFormats QueryResultFormats
	var resultFormatsByOID QueryResultFormatsByOID
	mode := c.config.DefaultQueryExecMode
	var queryRewriter QueryRewriter

optionLoop:
	for len(args) > 0 {
		switch arg := args[0].(type) {
		case QueryResultFormats:
			resultFormats = arg
			args = args[1:]
		case QueryResultFormatsByOID:
			resultFormatsByOID = arg
			args = args[1:]
		case QueryExecMode:
			mode = arg
			args = args[1:]
		case QueryRewriter:
			queryRewriter = arg
			args = args[1:]
		default:
			break optionLoop
		}
	}

	if queryRewriter != nil {
		sql, args = queryRewriter.RewriteQuery(ctx, c, sql, args)
	}

	// Bypass any statement caching.
	if sql == "" {
		mode = QueryExecModeSimpleProtocol
	}

	c.eqb.reset()
	anynil.NormalizeSlice(args)
	rows := c.getRows(ctx, sql, args)

	var err error
	sd, explicitPreparedStatement := c.preparedStatements[sql]
	if sd != nil || mode == QueryExecModeCacheStatement || mode == QueryExecModeCacheDescribe || mode == QueryExecModeDescribeExec {
		if sd == nil {
			switch mode {
			case QueryExecModeCacheStatement:
				if c.statementCache == nil {
					err = errDisabledStatementCache
					rows.fatal(err)
					return rows, err
				}
				sd = c.statementCache.Get(sql)
				if sd == nil {
					sd, err = c.Prepare(ctx, stmtcache.NextStatementName(), sql)
					if err != nil {
						rows.fatal(err)
						return rows, err
					}
					c.statementCache.Put(sd)
				}
			case QueryExecModeCacheDescribe:
				if c.descriptionCache == nil {
					err = errDisabledDescriptionCache
					rows.fatal(err)
					return rows, err
				}
				sd = c.descriptionCache.Get(sql)
				if sd == nil {
					sd, err = c.Prepare(ctx, "", sql)
					if err != nil {
						rows.fatal(err)
						return rows, err
					}
					c.descriptionCache.Put(sd)
				}
			case QueryExecModeDescribeExec:
				sd, err = c.Prepare(ctx, "", sql)
				if err != nil {
					rows.fatal(err)
					return rows, err
				}
			}
		}

		if len(sd.ParamOIDs) != len(args) {
			rows.fatal(fmt.Errorf("expected %d arguments, got %d", len(sd.ParamOIDs), len(args)))
			return rows, rows.err
		}

		rows.sql = sd.SQL

		err = c.eqb.Build(c.typeMap, sd, args)
		if err != nil {
			rows.fatal(err)
			return rows, rows.err
		}

		if resultFormatsByOID != nil {
			resultFormats = make([]int16, len(sd.Fields))
			for i := range resultFormats {
				resultFormats[i] = resultFormatsByOID[uint32(sd.Fields[i].DataTypeOID)]
			}
		}

		if resultFormats == nil {
			resultFormats = c.eqb.ResultFormats
		}

		if !explicitPreparedStatement && mode == QueryExecModeCacheDescribe {
			rows.resultReader = c.pgConn.ExecParams(ctx, sql, c.eqb.ParamValues, sd.ParamOIDs, c.eqb.ParamFormats, resultFormats)
		} else {
			rows.resultReader = c.pgConn.ExecPrepared(ctx, sd.Name, c.eqb.ParamValues, c.eqb.ParamFormats, resultFormats)
		}
	} else if mode == QueryExecModeExec {
		err := c.eqb.Build(c.typeMap, nil, args)
		if err != nil {
			rows.fatal(err)
			return rows, rows.err
		}

		rows.resultReader = c.pgConn.ExecParams(ctx, sql, c.eqb.ParamValues, nil, c.eqb.ParamFormats, c.eqb.ResultFormats)
	} else if mode == QueryExecModeSimpleProtocol {
		sql, err = c.sanitizeForSimpleQuery(sql, args...)
		if err != nil {
			rows.fatal(err)
			return rows, err
		}

		mrr := c.pgConn.Exec(ctx, sql)
		if mrr.NextResult() {
			rows.resultReader = mrr.ResultReader()
			rows.multiResultReader = mrr
		} else {
			err = mrr.Close()
			rows.fatal(err)
			return rows, err
		}

		return rows, nil
	} else {
		err = fmt.Errorf("unknown QueryExecMode: %v", mode)
		rows.fatal(err)
		return rows, rows.err
	}

	c.eqb.reset() // Allow c.eqb internal memory to be GC'ed as soon as possible.

	return rows, rows.err
}

// QueryRow is a convenience wrapper over Query. Any error that occurs while
// querying is deferred until calling Scan on the returned Row. That Row will
// error with ErrNoRows if no rows are returned.
func (c *Conn) QueryRow(ctx context.Context, sql string, args ...any) Row {
	rows, _ := c.Query(ctx, sql, args...)
	return (*connRow)(rows.(*baseRows))
}

// SendBatch sends all queued queries to the server at once. All queries are run in an implicit transaction unless
// 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) (br BatchResults) {
	if c.batchTracer != nil {
		ctx = c.batchTracer.TraceBatchStart(ctx, c, TraceBatchStartData{Batch: b})
		defer func() {
			err := br.(interface{ earlyError() error }).earlyError()
			if err != nil {
				c.batchTracer.TraceBatchEnd(ctx, c, TraceBatchEndData{Err: err})
			}
		}()
	}

	if err := c.deallocateInvalidatedCachedStatements(ctx); err != nil {
		return &batchResults{ctx: ctx, conn: c, err: err}
	}

	mode := c.config.DefaultQueryExecMode

	for _, bi := range b.queuedQueries {
		var queryRewriter QueryRewriter
		sql := bi.query
		arguments := bi.arguments

	optionLoop:
		for len(arguments) > 0 {
			switch arg := arguments[0].(type) {
			case QueryRewriter:
				queryRewriter = arg
				arguments = arguments[1:]
			default:
				break optionLoop
			}
		}

		if queryRewriter != nil {
			sql, arguments = queryRewriter.RewriteQuery(ctx, c, sql, arguments)
		}

		bi.query = sql
		bi.arguments = arguments
	}

	if mode == QueryExecModeSimpleProtocol {
		return c.sendBatchQueryExecModeSimpleProtocol(ctx, b)
	}

	// All other modes use extended protocol and thus can use prepared statements.
	for _, bi := range b.queuedQueries {
		if sd, ok := c.preparedStatements[bi.query]; ok {
			bi.sd = sd
		}
	}

	switch mode {
	case QueryExecModeExec:
		return c.sendBatchQueryExecModeExec(ctx, b)
	case QueryExecModeCacheStatement:
		return c.sendBatchQueryExecModeCacheStatement(ctx, b)
	case QueryExecModeCacheDescribe:
		return c.sendBatchQueryExecModeCacheDescribe(ctx, b)
	case QueryExecModeDescribeExec:
		return c.sendBatchQueryExecModeDescribeExec(ctx, b)
	default:
		panic("unknown QueryExecMode")
	}
}

func (c *Conn) sendBatchQueryExecModeSimpleProtocol(ctx context.Context, b *Batch) *batchResults {
	var sb strings.Builder
	for i, bi := range b.queuedQueries {
		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,
		qqIdx: 0,
	}
}

func (c *Conn) sendBatchQueryExecModeExec(ctx context.Context, b *Batch) *batchResults {
	batch := &pgconn.Batch{}

	for _, bi := range b.queuedQueries {
		sd := bi.sd
		if sd != nil {
			err := c.eqb.Build(c.typeMap, sd, bi.arguments)
			if err != nil {
				return &batchResults{ctx: ctx, conn: c, err: err}
			}

			batch.ExecPrepared(sd.Name, c.eqb.ParamValues, c.eqb.ParamFormats, c.eqb.ResultFormats)
		} else {
			err := c.eqb.Build(c.typeMap, nil, bi.arguments)
			if err != nil {
				return &batchResults{ctx: ctx, conn: c, err: err}
			}
			batch.ExecParams(bi.query, c.eqb.ParamValues, nil, c.eqb.ParamFormats, c.eqb.ResultFormats)
		}
	}

	c.eqb.reset() // Allow c.eqb internal memory to be GC'ed as soon as possible.

	mrr := c.pgConn.ExecBatch(ctx, batch)

	return &batchResults{
		ctx:   ctx,
		conn:  c,
		mrr:   mrr,
		b:     b,
		qqIdx: 0,
	}
}

func (c *Conn) sendBatchQueryExecModeCacheStatement(ctx context.Context, b *Batch) (pbr *pipelineBatchResults) {
	if c.statementCache == nil {
		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledStatementCache}
	}

	distinctNewQueries := []*pgconn.StatementDescription{}
	distinctNewQueriesIdxMap := make(map[string]int)

	for _, bi := range b.queuedQueries {
		if bi.sd == nil {
			sd := c.statementCache.Get(bi.query)
			if sd != nil {
				bi.sd = sd
			} else {
				if idx, present := distinctNewQueriesIdxMap[bi.query]; present {
					bi.sd = distinctNewQueries[idx]
				} else {
					sd = &pgconn.StatementDescription{
						Name: stmtcache.NextStatementName(),
						SQL:  bi.query,
					}
					distinctNewQueriesIdxMap[sd.SQL] = len(distinctNewQueries)
					distinctNewQueries = append(distinctNewQueries, sd)
					bi.sd = sd
				}
			}
		}
	}

	return c.sendBatchExtendedWithDescription(ctx, b, distinctNewQueries, c.statementCache)
}

func (c *Conn) sendBatchQueryExecModeCacheDescribe(ctx context.Context, b *Batch) (pbr *pipelineBatchResults) {
	if c.descriptionCache == nil {
		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledDescriptionCache}
	}

	distinctNewQueries := []*pgconn.StatementDescription{}
	distinctNewQueriesIdxMap := make(map[string]int)

	for _, bi := range b.queuedQueries {
		if bi.sd == nil {
			sd := c.descriptionCache.Get(bi.query)
			if sd != nil {
				bi.sd = sd
			} else {
				if idx, present := distinctNewQueriesIdxMap[bi.query]; present {
					bi.sd = distinctNewQueries[idx]
				} else {
					sd = &pgconn.StatementDescription{
						SQL: bi.query,
					}
					distinctNewQueriesIdxMap[sd.SQL] = len(distinctNewQueries)
					distinctNewQueries = append(distinctNewQueries, sd)
					bi.sd = sd
				}
			}
		}
	}

	return c.sendBatchExtendedWithDescription(ctx, b, distinctNewQueries, c.descriptionCache)
}

func (c *Conn) sendBatchQueryExecModeDescribeExec(ctx context.Context, b *Batch) (pbr *pipelineBatchResults) {
	distinctNewQueries := []*pgconn.StatementDescription{}
	distinctNewQueriesIdxMap := make(map[string]int)

	for _, bi := range b.queuedQueries {
		if bi.sd == nil {
			if idx, present := distinctNewQueriesIdxMap[bi.query]; present {
				bi.sd = distinctNewQueries[idx]
			} else {
				sd := &pgconn.StatementDescription{
					SQL: bi.query,
				}
				distinctNewQueriesIdxMap[sd.SQL] = len(distinctNewQueries)
				distinctNewQueries = append(distinctNewQueries, sd)
				bi.sd = sd
			}
		}
	}

	return c.sendBatchExtendedWithDescription(ctx, b, distinctNewQueries, nil)
}

func (c *Conn) sendBatchExtendedWithDescription(ctx context.Context, b *Batch, distinctNewQueries []*pgconn.StatementDescription, sdCache stmtcache.Cache) (pbr *pipelineBatchResults) {
	pipeline := c.pgConn.StartPipeline(context.Background())
	defer func() {
		if pbr.err != nil {
			pipeline.Close()
		}
	}()

	// Prepare any needed queries
	if len(distinctNewQueries) > 0 {
		for _, sd := range distinctNewQueries {
			pipeline.SendPrepare(sd.Name, sd.SQL, nil)
		}

		err := pipeline.Sync()
		if err != nil {
			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
		}

		for _, sd := range distinctNewQueries {
			results, err := pipeline.GetResults()
			if err != nil {
				return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
			}

			resultSD, ok := results.(*pgconn.StatementDescription)
			if !ok {
				return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected statement description, got %T", results)}
			}

			// Fill in the previously empty / pending statement descriptions.
			sd.ParamOIDs = resultSD.ParamOIDs
			sd.Fields = resultSD.Fields
		}

		results, err := pipeline.GetResults()
		if err != nil {
			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
		}

		_, ok := results.(*pgconn.PipelineSync)
		if !ok {
			return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected sync, got %T", results)}
		}
	}

	// Put all statements into the cache. It's fine if it overflows because HandleInvalidated will clean them up later.
	if sdCache != nil {
		for _, sd := range distinctNewQueries {
			sdCache.Put(sd)
		}
	}

	// Queue the queries.
	for _, bi := range b.queuedQueries {
		err := c.eqb.Build(c.typeMap, bi.sd, bi.arguments)
		if err != nil {
			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
		}

		if bi.sd.Name == "" {
			pipeline.SendQueryParams(bi.sd.SQL, c.eqb.ParamValues, bi.sd.ParamOIDs, c.eqb.ParamFormats, c.eqb.ResultFormats)
		} else {
			pipeline.SendQueryPrepared(bi.sd.Name, c.eqb.ParamValues, c.eqb.ParamFormats, c.eqb.ResultFormats)
		}
	}

	err := pipeline.Sync()
	if err != nil {
		return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
	}

	return &pipelineBatchResults{
		ctx:      ctx,
		conn:     c,
		pipeline: pipeline,
		b:        b,
	}
}

func (c *Conn) sanitizeForSimpleQuery(sql string, args ...any) (string, error) {
	if c.pgConn.ParameterStatus("standard_conforming_strings") != "on" {
		return "", errors.New("simple protocol queries must be run with standard_conforming_strings=on")
	}

	if c.pgConn.ParameterStatus("client_encoding") != "UTF8" {
		return "", errors.New("simple protocol queries must be run with client_encoding=UTF8")
	}

	var err error
	valueArgs := make([]any, len(args))
	for i, a := range args {
		valueArgs[i], err = convertSimpleArgument(c.typeMap, a)
		if err != nil {
			return "", err
		}
	}

	return sanitize.SanitizeSQL(sql, valueArgs...)
}

// LoadType inspects the database for typeName and produces a pgtype.Type suitable for registration.
func (c *Conn) LoadType(ctx context.Context, typeName string) (*pgtype.Type, error) {
	var oid uint32

	err := c.QueryRow(ctx, "select $1::text::regtype::oid;", typeName).Scan(&oid)
	if err != nil {
		return nil, err
	}

	var typtype string

	err = c.QueryRow(ctx, "select typtype::text from pg_type where oid=$1", oid).Scan(&typtype)
	if err != nil {
		return nil, err
	}

	switch typtype {
	case "b": // array
		elementOID, err := c.getArrayElementOID(ctx, oid)
		if err != nil {
			return nil, err
		}

		dt, ok := c.TypeMap().TypeForOID(elementOID)
		if !ok {
			return nil, errors.New("array element OID not registered")
		}

		return &pgtype.Type{Name: typeName, OID: oid, Codec: &pgtype.ArrayCodec{ElementType: dt}}, nil
	case "c": // composite
		fields, err := c.getCompositeFields(ctx, oid)
		if err != nil {
			return nil, err
		}

		return &pgtype.Type{Name: typeName, OID: oid, Codec: &pgtype.CompositeCodec{Fields: fields}}, nil
	case "e": // enum
		return &pgtype.Type{Name: typeName, OID: oid, Codec: &pgtype.EnumCodec{}}, nil
	default:
		return &pgtype.Type{}, errors.New("unknown typtype")
	}
}

func (c *Conn) getArrayElementOID(ctx context.Context, oid uint32) (uint32, error) {
	var typelem uint32

	err := c.QueryRow(ctx, "select typelem from pg_type where oid=$1", oid).Scan(&typelem)
	if err != nil {
		return 0, err
	}

	return typelem, nil
}

func (c *Conn) getCompositeFields(ctx context.Context, oid uint32) ([]pgtype.CompositeCodecField, error) {
	var typrelid uint32

	err := c.QueryRow(ctx, "select typrelid from pg_type where oid=$1", oid).Scan(&typrelid)
	if err != nil {
		return nil, err
	}

	var fields []pgtype.CompositeCodecField
	var fieldName string
	var fieldOID uint32
	rows, _ := c.Query(ctx, `select attname, atttypid
from pg_attribute
where attrelid=$1
order by attnum`,
		typrelid,
	)
	_, err = ForEachRow(rows, []any{&fieldName, &fieldOID}, func() error {
		dt, ok := c.TypeMap().TypeForOID(fieldOID)
		if !ok {
			return fmt.Errorf("unknown composite type field OID: %v", fieldOID)
		}
		fields = append(fields, pgtype.CompositeCodecField{Name: fieldName, Type: dt})
		return nil
	})
	if err != nil {
		return nil, err
	}

	return fields, nil
}

func (c *Conn) deallocateInvalidatedCachedStatements(ctx context.Context) error {
	if c.pgConn.TxStatus() != 'I' {
		return nil
	}

	if c.descriptionCache != nil {
		c.descriptionCache.HandleInvalidated()
	}

	var invalidatedStatements []*pgconn.StatementDescription
	if c.statementCache != nil {
		invalidatedStatements = c.statementCache.HandleInvalidated()
	}

	if len(invalidatedStatements) == 0 {
		return nil
	}

	pipeline := c.pgConn.StartPipeline(ctx)
	defer pipeline.Close()

	for _, sd := range invalidatedStatements {
		pipeline.SendDeallocate(sd.Name)
	}

	err := pipeline.Sync()
	if err != nil {
		return fmt.Errorf("failed to deallocate cached statement(s): %w", err)
	}

	err = pipeline.Close()
	if err != nil {
		return fmt.Errorf("failed to deallocate cached statement(s): %w", err)
	}

	return nil
}