Winlogbeat: add caching of metadata handles

CHANGELOG.asciidoc

@@ -68,13 +68,8 @@ https://github.com/elastic/beats/compare/v1.1.0...master[Check the HEAD diff]
 - Add close_older configuration option to complete ignore_older https://github.com/elastic/filebeat/issues/181[181]
 - Add experimental option to enable filebeat publisher pipeline to operate asynchonrously {pull}782[782]
 
-*Packetbeat*
-
-*Topbeat*
-
-*Filebeat*
-
 *Winlogbeat*
+- Add caching of event metadata handles and the system render context for the wineventlog API {pull}888[888]
 
 ==== Deprecated
 

winlogbeat/eventlog/wineventlog.go

@@ -6,13 +6,14 @@ import (
 	"fmt"
 
 	"github.com/elastic/beats/libbeat/logp"
+	"github.com/elastic/beats/winlogbeat/sys/eventlogging"
 	sys "github.com/elastic/beats/winlogbeat/sys/wineventlog"
 	"golang.org/x/sys/windows"
 )
 
 const (
 	// defaultMaxNumRead is the maximum number of event Read will return.
-	defaultMaxNumRead = 50
+	defaultMaxNumRead = 100
 
 	// renderBufferSize is the size in bytes of the buffer used to render events.
 	renderBufferSize = 1 << 14
@@ -33,7 +34,9 @@ type winEventLog struct {
 	subscription sys.EvtHandle // Handle to the subscription.
 	maxRead      int           // Maximum number returned in one Read.
 
-	renderBuf []byte // Buffer used for rendering event.
+	renderBuf []byte             // Buffer used for rendering event.
+	systemCtx sys.EvtHandle      // System render context.
+	cache     *messageFilesCache // Cached mapping of source name to event message file handles.
 
 	logPrefix string // String to prefix on log messages.
 }
@@ -91,7 +94,7 @@ func (l *winEventLog) Read() ([]Record, error) {
 
 	var records []Record
 	for _, h := range handles {
-		e, err := sys.RenderEvent(h, 0, 0, l.renderBuf, nil)
+		e, err := sys.RenderEvent(h, l.systemCtx, 0, l.renderBuf, l.cache.get)
 		if err != nil {
 			logp.Err("%s Dropping event with rendering error. %v", l.logPrefix, err)
 			continue
@@ -138,11 +141,34 @@ func (l *winEventLog) Close() error {
 // newWinEventLog creates and returns a new EventLog for reading event logs
 // using the Windows Event Log.
 func newWinEventLog(c Config) (EventLog, error) {
+	eventMetadataHandle := func(providerName, sourceName string) eventlogging.MessageFiles {
+		mf := eventlogging.MessageFiles{SourceName: sourceName}
+		h, err := sys.OpenPublisherMetadata(0, providerName, 0)
+		if err != nil {
+			mf.Err = err
+			return mf
+		}
+
+		mf.Handles = []eventlogging.FileHandle{eventlogging.FileHandle{Handle: uintptr(h)}}
+		return mf
+	}
+
+	freeHandle := func(handle uintptr) error {
+		return sys.Close(sys.EvtHandle(handle))
+	}
+
+	ctx, err := sys.CreateRenderContext(nil, sys.EvtRenderContextSystem)
+	if err != nil {
+		return nil, err
+	}
+
 	return &winEventLog{
 		channelName:  c.Name,
 		remoteServer: c.RemoteAddress,
 		maxRead:      defaultMaxNumRead,
 		renderBuf:    make([]byte, renderBufferSize),
+		systemCtx:    ctx,
+		cache:        newMessageFilesCache(c.Name, eventMetadataHandle, freeHandle),
 		logPrefix:    fmt.Sprintf("WinEventLog[%s]", c.Name),
 	}, nil
 }

winlogbeat/sys/wineventlog/wineventlog_windows.go

@@ -144,7 +144,7 @@ func RenderEvent(
 	systemContext EvtHandle,
 	lang uint32,
 	renderBuf []byte,
-	pubHandleProvider func(string) uintptr,
+	pubHandleProvider func(string) eventlogging.MessageFiles,
 ) (Event, error) {
 	var err error
 
@@ -187,7 +187,12 @@ func RenderEvent(
 
 	var publisherHandle uintptr
 	if pubHandleProvider != nil {
-		publisherHandle = pubHandleProvider(e.ProviderName)
+		messageFiles := pubHandleProvider(e.ProviderName)
+		if messageFiles.Err == nil {
+			// There is only ever a single handle when using the Windows Event
+			// Log API.
+			publisherHandle = messageFiles.Handles[0].Handle
+		}
 	}
 
 	// Populate strings that must be looked up.
@@ -311,6 +316,17 @@ func CreateBookmark(channel string, recordID uint64) (EvtHandle, error) {
 	return h, nil
 }
 
+// Create a render context. Close must be called on returned EvtHandle when
+// finished with the handle.
+func CreateRenderContext(valuePaths []string, flag EvtRenderContextFlag) (EvtHandle, error) {
+	context, err := _EvtCreateRenderContext(0, nil, EvtRenderContextSystem)
+	if err != nil {
+		return 0, err
+	}
+
+	return context, nil
+}
+
 // OpenPublisherMetadata opens a handle to the publisher's metadata. Close must
 // be called on returned EvtHandle when finished with the handle.
 func OpenPublisherMetadata(