driver: context support (#997)

* wip

* poc: context support

* move context management into driver
Close instead of SetTimeout hack
implement more interfaces, with assertions

* lint

* avoid excessive spinning when context canceled & waiting on contexts channel to close

* compressedHeader tweak

* mysql doesn't have named parameters

---------

Co-authored-by: lance6716 <lance6716@gmail.com>

Author: serprex

client/conn.go

@@ -382,6 +382,21 @@ func (c *Conn) Begin() error {
 	return errors.Trace(err)
 }
 
+func (c *Conn) BeginTx(readOnly bool, txIsolation string) error {
+	if txIsolation != "" {
+		if _, err := c.exec("SET TRANSACTION ISOLATION LEVEL " + txIsolation); err != nil {
+			return errors.Trace(err)
+		}
+	}
+	var err error
+	if readOnly {
+		_, err = c.exec("START TRANSACTION READ ONLY")
+	} else {
+		_, err = c.exec("START TRANSACTION")
+	}
+	return errors.Trace(err)
+}
+
 func (c *Conn) Commit() error {
 	_, err := c.exec("COMMIT")
 	return errors.Trace(err)

driver/driver.go

@@ -3,6 +3,7 @@
 package driver
 
 import (
+	"context"
 	"crypto/tls"
 	"database/sql"
 	sqldriver "database/sql/driver"
@@ -21,6 +22,23 @@ import (
 	"github.com/pingcap/errors"
 )
 
+var (
+	_ sqldriver.Driver             = &driver{}
+	_ sqldriver.DriverContext      = &driver{}
+	_ sqldriver.Connector          = &connInfo{}
+	_ sqldriver.NamedValueChecker  = &conn{}
+	_ sqldriver.Validator          = &conn{}
+	_ sqldriver.Conn               = &conn{}
+	_ sqldriver.Pinger             = &conn{}
+	_ sqldriver.ConnBeginTx        = &conn{}
+	_ sqldriver.ConnPrepareContext = &conn{}
+	_ sqldriver.ExecerContext      = &conn{}
+	_ sqldriver.QueryerContext     = &conn{}
+	_ sqldriver.Stmt               = &stmt{}
+	_ sqldriver.StmtExecContext    = &stmt{}
+	_ sqldriver.StmtQueryContext   = &stmt{}
+)
+
 var customTLSMutex sync.Mutex
 
 // Map of dsn address (makes more sense than full dsn?) to tls Config
@@ -101,16 +119,18 @@ func parseDSN(dsn string) (connInfo, error) {
 // Open takes a supplied DSN string and opens a connection
 // See ParseDSN for more information on the form of the DSN
 func (d driver) Open(dsn string) (sqldriver.Conn, error) {
-	var (
-		c *client.Conn
-		// by default database/sql driver retries will be enabled
-		retries = true
-	)
-
 	ci, err := parseDSN(dsn)
 	if err != nil {
 		return nil, err
 	}
+	return ci.Connect(context.Background())
+}
+
+func (ci connInfo) Connect(ctx context.Context) (sqldriver.Conn, error) {
+	var c *client.Conn
+	var err error
+	// by default database/sql driver retries will be enabled
+	retries := true
 
 	if ci.standardDSN {
 		var timeout time.Duration
@@ -159,45 +179,86 @@ func (d driver) Open(dsn string) (sqldriver.Conn, error) {
 			}
 		}
 
-		if timeout > 0 {
-			c, err = client.ConnectWithTimeout(ci.addr, ci.user, ci.password, ci.db, timeout, configuredOptions...)
-		} else {
-			c, err = client.Connect(ci.addr, ci.user, ci.password, ci.db, configuredOptions...)
+		if timeout <= 0 {
+			timeout = 10 * time.Second
 		}
+		c, err = client.ConnectWithContext(ctx, ci.addr, ci.user, ci.password, ci.db, timeout, configuredOptions...)
 	} else {
 		// No more processing here. Let's only support url parameters with the newer style DSN
-		c, err = client.Connect(ci.addr, ci.user, ci.password, ci.db)
+		c, err = client.ConnectWithContext(ctx, ci.addr, ci.user, ci.password, ci.db, 10*time.Second)
 	}
 	if err != nil {
 		return nil, err
 	}
 
+	contexts := make(chan context.Context)
+	go func() {
+		ctx := context.Background()
+		for {
+			var ok bool
+			select {
+			case <-ctx.Done():
+				ctx = context.Background()
+				_ = c.Conn.Close()
+			case ctx, ok = <-contexts:
+				if !ok {
+					return
+				}
+			}
+		}
+	}()
+
 	// if retries are 'on' then return sqldriver.ErrBadConn which will trigger up to 3
 	// retries by the database/sql package. If retries are 'off' then we'll return
 	// the native go-mysql-org/go-mysql 'mysql.ErrBadConn' erorr which will prevent a retry.
 	// In this case the sqldriver.Validator interface is implemented and will return
 	// false for IsValid() signaling the connection is bad and should be discarded.
-	return &conn{Conn: c, state: &state{valid: true, useStdLibErrors: retries}}, nil
+	return &conn{
+		Conn:  c,
+		state: &state{contexts: contexts, valid: true, useStdLibErrors: retries},
+	}, nil
 }
 
-type CheckNamedValueFunc func(*sqldriver.NamedValue) error
+func (d driver) OpenConnector(name string) (sqldriver.Connector, error) {
+	return parseDSN(name)
+}
 
-var (
-	_ sqldriver.NamedValueChecker = &conn{}
-	_ sqldriver.Validator         = &conn{}
-)
+func (ci connInfo) Driver() sqldriver.Driver {
+	return driver{}
+}
+
+type CheckNamedValueFunc func(*sqldriver.NamedValue) error
 
 type state struct {
-	valid bool
+	contexts chan context.Context
+	valid    bool
 	// when true, the driver connection will return ErrBadConn from the golang Standard Library
 	useStdLibErrors bool
 }
 
+func (s *state) watchCtx(ctx context.Context) func() {
+	s.contexts <- ctx
+	return func() {
+		s.contexts <- context.Background()
+	}
+}
+
+func (s *state) Close() {
+	if s.contexts != nil {
+		close(s.contexts)
+		s.contexts = nil
+	}
+}
+
 type conn struct {
 	*client.Conn
 	state *state
 }
 
+func (c *conn) watchCtx(ctx context.Context) func() {
+	return c.state.watchCtx(ctx)
+}
+
 func (c *conn) CheckNamedValue(nv *sqldriver.NamedValue) error {
 	for _, nvChecker := range namedValueCheckers {
 		err := nvChecker(nv)
@@ -220,6 +281,17 @@ func (c *conn) IsValid() bool {
 	return c.state.valid
 }
 
+func (c *conn) Ping(ctx context.Context) error {
+	defer c.watchCtx(ctx)()
+	if err := c.Conn.Ping(); err != nil {
+		if err == context.DeadlineExceeded || err == context.Canceled {
+			return err
+		}
+		return sqldriver.ErrBadConn
+	}
+	return nil
+}
+
 func (c *conn) Prepare(query string) (sqldriver.Stmt, error) {
 	st, err := c.Conn.Prepare(query)
 	if err != nil {
@@ -229,7 +301,13 @@ func (c *conn) Prepare(query string) (sqldriver.Stmt, error) {
 	return &stmt{Stmt: st, connectionState: c.state}, nil
 }
 
+func (c *conn) PrepareContext(ctx context.Context, query string) (sqldriver.Stmt, error) {
+	defer c.watchCtx(ctx)()
+	return c.Prepare(query)
+}
+
 func (c *conn) Close() error {
+	c.state.Close()
 	return c.Conn.Close()
 }
 
@@ -242,6 +320,29 @@ func (c *conn) Begin() (sqldriver.Tx, error) {
 	return &tx{c.Conn}, nil
 }
 
+var isolationLevelTransactionIsolation = map[sql.IsolationLevel]string{
+	sql.LevelDefault:         "",
+	sql.LevelRepeatableRead:  "REPEATABLE READ",
+	sql.LevelReadCommitted:   "READ COMMITTED",
+	sql.LevelReadUncommitted: "READ UNCOMMITTED",
+	sql.LevelSerializable:    "SERIALIZABLE",
+}
+
+func (c *conn) BeginTx(ctx context.Context, opts sqldriver.TxOptions) (sqldriver.Tx, error) {
+	defer c.watchCtx(ctx)()
+
+	isolation := sql.IsolationLevel(opts.Isolation)
+	txIsolation, ok := isolationLevelTransactionIsolation[isolation]
+	if !ok {
+		return nil, fmt.Errorf("invalid mysql transaction isolation level %s", isolation)
+	}
+	err := c.Conn.BeginTx(opts.ReadOnly, txIsolation)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+	return &tx{c.Conn}, nil
+}
+
 func buildArgs(args []sqldriver.Value) []interface{} {
 	a := make([]interface{}, len(args))
 
@@ -252,6 +353,16 @@ func buildArgs(args []sqldriver.Value) []interface{} {
 	return a
 }
 
+func buildNamedArgs(args []sqldriver.NamedValue) []interface{} {
+	a := make([]interface{}, len(args))
+
+	for i, arg := range args {
+		a[i] = arg.Value
+	}
+
+	return a
+}
+
 func (st *state) replyError(err error) error {
 	isBadConnection := mysql.ErrorEqual(err, mysql.ErrBadConn)
 
@@ -275,6 +386,16 @@ func (c *conn) Exec(query string, args []sqldriver.Value) (sqldriver.Result, err
 	return &result{r}, nil
 }
 
+func (c *conn) ExecContext(ctx context.Context, query string, args []sqldriver.NamedValue) (sqldriver.Result, error) {
+	defer c.watchCtx(ctx)()
+	a := buildNamedArgs(args)
+	r, err := c.Conn.Execute(query, a...)
+	if err != nil {
+		return nil, c.state.replyError(err)
+	}
+	return &result{r}, nil
+}
+
 func (c *conn) Query(query string, args []sqldriver.Value) (sqldriver.Rows, error) {
 	a := buildArgs(args)
 	r, err := c.Conn.Execute(query, a...)
@@ -284,11 +405,25 @@ func (c *conn) Query(query string, args []sqldriver.Value) (sqldriver.Rows, erro
 	return newRows(r.Resultset)
 }
 
+func (c *conn) QueryContext(ctx context.Context, query string, args []sqldriver.NamedValue) (sqldriver.Rows, error) {
+	defer c.watchCtx(ctx)()
+	a := buildNamedArgs(args)
+	r, err := c.Conn.Execute(query, a...)
+	if err != nil {
+		return nil, c.state.replyError(err)
+	}
+	return newRows(r.Resultset)
+}
+
 type stmt struct {
 	*client.Stmt
 	connectionState *state
 }
 
+func (s *stmt) watchCtx(ctx context.Context) func() {
+	return s.connectionState.watchCtx(ctx)
+}
+
 func (s *stmt) Close() error {
 	return s.Stmt.Close()
 }
@@ -306,6 +441,17 @@ func (s *stmt) Exec(args []sqldriver.Value) (sqldriver.Result, error) {
 	return &result{r}, nil
 }
 
+func (s *stmt) ExecContext(ctx context.Context, args []sqldriver.NamedValue) (sqldriver.Result, error) {
+	defer s.watchCtx(ctx)()
+
+	a := buildNamedArgs(args)
+	r, err := s.Stmt.Execute(a...)
+	if err != nil {
+		return nil, s.connectionState.replyError(err)
+	}
+	return &result{r}, nil
+}
+
 func (s *stmt) Query(args []sqldriver.Value) (sqldriver.Rows, error) {
 	a := buildArgs(args)
 	r, err := s.Stmt.Execute(a...)
@@ -315,6 +461,17 @@ func (s *stmt) Query(args []sqldriver.Value) (sqldriver.Rows, error) {
 	return newRows(r.Resultset)
 }
 
+func (s *stmt) QueryContext(ctx context.Context, args []sqldriver.NamedValue) (sqldriver.Rows, error) {
+	defer s.watchCtx(ctx)()
+
+	a := buildNamedArgs(args)
+	r, err := s.Stmt.Execute(a...)
+	if err != nil {
+		return nil, s.connectionState.replyError(err)
+	}
+	return newRows(r.Resultset)
+}
+
 type tx struct {
 	*client.Conn
 }

packet/conn.go

@@ -360,7 +360,7 @@ func (c *Conn) writeCompressed(data []byte) (n int, err error) {
 	var (
 		compressedLength, uncompressedLength int
 		payload                              *bytes.Buffer
-		compressedHeader                     = make([]byte, 7)
+		compressedHeader                     [7]byte
 	)
 
 	if len(data) > MinCompressionLength {
@@ -406,7 +406,7 @@ func (c *Conn) writeCompressed(data []byte) (n int, err error) {
 	compressedHeader[4] = byte(uncompressedLength)
 	compressedHeader[5] = byte(uncompressedLength >> 8)
 	compressedHeader[6] = byte(uncompressedLength >> 16)
-	if _, err = compressedPacket.Write(compressedHeader); err != nil {
+	if _, err = compressedPacket.Write(compressedHeader[:]); err != nil {
 		return 0, err
 	}
 	c.CompressedSequence++