Update vendor github.com/lib/pq (#2752)

vendor/github.com/lib/pq/conn_go18.go

@@ -0,0 +1,128 @@
+// +build go1.8
+
+package pq
+
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"fmt"
+	"io"
+	"io/ioutil"
+)
+
+// Implement the "QueryerContext" interface
+func (cn *conn) QueryContext(ctx context.Context, query string, args []driver.NamedValue) (driver.Rows, error) {
+	list := make([]driver.Value, len(args))
+	for i, nv := range args {
+		list[i] = nv.Value
+	}
+	finish := cn.watchCancel(ctx)
+	r, err := cn.query(query, list)
+	if err != nil {
+		if finish != nil {
+			finish()
+		}
+		return nil, err
+	}
+	r.finish = finish
+	return r, nil
+}
+
+// Implement the "ExecerContext" interface
+func (cn *conn) ExecContext(ctx context.Context, query string, args []driver.NamedValue) (driver.Result, error) {
+	list := make([]driver.Value, len(args))
+	for i, nv := range args {
+		list[i] = nv.Value
+	}
+
+	if finish := cn.watchCancel(ctx); finish != nil {
+		defer finish()
+	}
+
+	return cn.Exec(query, list)
+}
+
+// Implement the "ConnBeginTx" interface
+func (cn *conn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, error) {
+	var mode string
+
+	switch sql.IsolationLevel(opts.Isolation) {
+	case sql.LevelDefault:
+		// Don't touch mode: use the server's default
+	case sql.LevelReadUncommitted:
+		mode = " ISOLATION LEVEL READ UNCOMMITTED"
+	case sql.LevelReadCommitted:
+		mode = " ISOLATION LEVEL READ COMMITTED"
+	case sql.LevelRepeatableRead:
+		mode = " ISOLATION LEVEL REPEATABLE READ"
+	case sql.LevelSerializable:
+		mode = " ISOLATION LEVEL SERIALIZABLE"
+	default:
+		return nil, fmt.Errorf("pq: isolation level not supported: %d", opts.Isolation)
+	}
+
+	if opts.ReadOnly {
+		mode += " READ ONLY"
+	} else {
+		mode += " READ WRITE"
+	}
+
+	tx, err := cn.begin(mode)
+	if err != nil {
+		return nil, err
+	}
+	cn.txnFinish = cn.watchCancel(ctx)
+	return tx, nil
+}
+
+func (cn *conn) watchCancel(ctx context.Context) func() {
+	if done := ctx.Done(); done != nil {
+		finished := make(chan struct{})
+		go func() {
+			select {
+			case <-done:
+				_ = cn.cancel()
+				finished <- struct{}{}
+			case <-finished:
+			}
+		}()
+		return func() {
+			select {
+			case <-finished:
+			case finished <- struct{}{}:
+			}
+		}
+	}
+	return nil
+}
+
+func (cn *conn) cancel() error {
+	c, err := dial(cn.dialer, cn.opts)
+	if err != nil {
+		return err
+	}
+	defer c.Close()
+
+	{
+		can := conn{
+			c: c,
+		}
+		can.ssl(cn.opts)
+
+		w := can.writeBuf(0)
+		w.int32(80877102) // cancel request code
+		w.int32(cn.processID)
+		w.int32(cn.secretKey)
+
+		if err := can.sendStartupPacket(w); err != nil {
+			return err
+		}
+	}
+
+	// Read until EOF to ensure that the server received the cancel.
+	{
+		_, err := io.Copy(ioutil.Discard, c)
+		return err
+	}
+}