Add support for a handler func that receives notice messages from Pg

Fixes #580

conn.go

@@ -149,6 +149,9 @@ type conn struct {
 
 	// If true this connection is in the middle of a COPY
 	inCopy bool
+
+	// If not nil, notices will be synchronously sent here
+	noticeHandler func(*Error)
 }
 
 // Handle driver-side settings in parsed connection string.
@@ -971,7 +974,9 @@ func (cn *conn) recv() (t byte, r *readBuf) {
 		case 'E':
 			panic(parseError(r))
 		case 'N':
-			// ignore
+			if n := cn.noticeHandler; n != nil {
+				n(parseError(r))
+			}
 		default:
 			return
 		}
@@ -988,8 +993,12 @@ func (cn *conn) recv1Buf(r *readBuf) byte {
 		}
 
 		switch t {
-		case 'A', 'N':
+		case 'A':
 			// ignore
+		case 'N':
+			if n := cn.noticeHandler; n != nil {
+				n(parseError(r))
+			}
 		case 'S':
 			cn.processParameterStatus(r)
 		default:

copy.go

@@ -152,7 +152,9 @@ func (ci *copyin) resploop() {
 		case 'C':
 			// complete
 		case 'N':
-			// NoticeResponse
+			if n := ci.cn.noticeHandler; n != nil {
+				n(parseError(&r))
+			}
 		case 'Z':
 			ci.cn.processReadyForQuery(&r)
 			ci.done <- true

notice.go

@@ -0,0 +1,71 @@
+// +build go1.10
+
+package pq
+
+import (
+	"context"
+	"database/sql/driver"
+)
+
+// NoticeHandler returns the notice handler on the given connection, if any. A
+// runtime panic occurs if c is not a pq connection. This is rarely used
+// directly, use ConnectorNoticeHandler and ConnectorWithNoticeHandler instead.
+func NoticeHandler(c driver.Conn) func(*Error) {
+	return c.(*conn).noticeHandler
+}
+
+// SetNoticeHandler sets the given notice handler on the given connection. A
+// runtime panic occurs if c is not a pq connection. A nil handler may be used
+// to unset it. This is rarely used directly, use ConnectorNoticeHandler and
+// ConnectorWithNoticeHandler instead.
+//
+// Note: Notice handlers are executed synchronously by pq meaning commands
+// won't continue to be processed until the handler returns.
+func SetNoticeHandler(c driver.Conn, handler func(*Error)) {
+	c.(*conn).noticeHandler = handler
+}
+
+// NoticeHandlerConnector wraps a regular connector and sets a notice handler
+// on it.
+type NoticeHandlerConnector struct {
+	driver.Connector
+	noticeHandler func(*Error)
+}
+
+// Connect calls the underlying connector's connect method and then sets the
+// notice handler.
+func (n *NoticeHandlerConnector) Connect(ctx context.Context) (driver.Conn, error) {
+	c, err := n.Connector.Connect(ctx)
+	if err == nil {
+		SetNoticeHandler(c, n.noticeHandler)
+	}
+	return c, err
+}
+
+// ConnectorNoticeHandler returns the currently set notice handler, if any. If
+// the given connector is not a result of ConnectorWithNoticeHandler, nil is
+// returned.
+func ConnectorNoticeHandler(c driver.Connector) func(*Error) {
+	if c, ok := c.(*NoticeHandlerConnector); ok {
+		return c.noticeHandler
+	}
+	return nil
+}
+
+// ConnectorWithNoticeHandler creates or sets the given handler for the given
+// connector. If the given connector is a result of calling this function
+// previously, it is simply set on the given connector and returned. Otherwise,
+// this returns a new connector wrapping the given one and setting the notice
+// handler. A nil notice handler may be used to unset it.
+//
+// The returned connector is intended to be used with database/sql.OpenDB.
+//
+// Note: Notice handlers are executed synchronously by pq meaning commands
+// won't continue to be processed until the handler returns.
+func ConnectorWithNoticeHandler(c driver.Connector, handler func(*Error)) *NoticeHandlerConnector {
+	if c, ok := c.(*NoticeHandlerConnector); ok {
+		c.noticeHandler = handler
+		return c
+	}
+	return &NoticeHandlerConnector{Connector: c, noticeHandler: handler}
+}

notice_example_test.go

@@ -0,0 +1,33 @@
+// +build go1.10
+
+package pq_test
+
+import (
+	"database/sql"
+	"fmt"
+	"log"
+
+	"github.com/lib/pq"
+)
+
+func ExampleConnectorWithNoticeHandler() {
+	name := ""
+	// Base connector to wrap
+	base, err := pq.NewConnector(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// Wrap the connector to simply print out the message
+	connector := pq.ConnectorWithNoticeHandler(base, func(notice *pq.Error) {
+		fmt.Println("Notice sent: " + notice.Message)
+	})
+	db := sql.OpenDB(connector)
+	defer db.Close()
+	// Raise a notice
+	sql := "DO language plpgsql $$ BEGIN RAISE NOTICE 'test notice'; END $$"
+	if _, err := db.Exec(sql); err != nil {
+		log.Fatal(err)
+	}
+	// Output:
+	// Notice sent: test notice
+}

notice_test.go

@@ -0,0 +1,49 @@
+// +build go1.10
+
+package pq
+
+import (
+	"database/sql"
+	"database/sql/driver"
+	"testing"
+)
+
+func TestConnectorWithNoticeHandler_Simple(t *testing.T) {
+	b, err := NewConnector("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var notice *Error
+	// Make connector w/ handler to set the local var
+	c := ConnectorWithNoticeHandler(b, func(n *Error) { notice = n })
+	raiseNotice(c, t, "Test notice #1")
+	if notice == nil || notice.Message != "Test notice #1" {
+		t.Fatalf("Expected notice w/ message, got %v", notice)
+	}
+	// Unset the handler on the same connector
+	prevC := c
+	if c = ConnectorWithNoticeHandler(c, nil); c != prevC {
+		t.Fatalf("Expected to not create new connector but did")
+	}
+	raiseNotice(c, t, "Test notice #2")
+	if notice == nil || notice.Message != "Test notice #1" {
+		t.Fatalf("Expected notice to not change, got %v", notice)
+	}
+	// Set it back on the same connector
+	if c = ConnectorWithNoticeHandler(c, func(n *Error) { notice = n }); c != prevC {
+		t.Fatal("Expected to not create new connector but did")
+	}
+	raiseNotice(c, t, "Test notice #3")
+	if notice == nil || notice.Message != "Test notice #3" {
+		t.Fatalf("Expected notice w/ message, got %v", notice)
+	}
+}
+
+func raiseNotice(c driver.Connector, t *testing.T, escapedNotice string) {
+	db := sql.OpenDB(c)
+	defer db.Close()
+	sql := "DO language plpgsql $$ BEGIN RAISE NOTICE '" + escapedNotice + "'; END $$"
+	if _, err := db.Exec(sql); err != nil {
+		t.Fatal(err)
+	}
+}

notify.go

@@ -174,8 +174,12 @@ func (l *ListenerConn) listenerConnLoop() (err error) {
 			}
 			l.replyChan <- message{t, nil}
 
-		case 'N', 'S':
+		case 'S':
 			// ignore
+		case 'N':
+			if n := l.cn.noticeHandler; n != nil {
+				n(parseError(r))
+			}
 		default:
 			return fmt.Errorf("unexpected message %q from server in listenerConnLoop", t)
 		}