Precompile log buffer regular expressions

Compile fixed patterns during monitor and log counter initialization, pass compiled expressions to the log buffer, and reject invalid log counter patterns before watching logs.

pkg/systemlogmonitor/log_buffer.go

@@ -28,7 +28,7 @@ type LogBuffer interface {
 	// Push pushes log into the log buffer.
 	Push(*types.Log)
 	// Match with regular expression in the log buffer.
-	Match(string) []*types.Log
+	Match(*regexp.Regexp) []*types.Log
 	// String returns a concatenated string of the buffered logs.
 	String() string
 }
@@ -39,8 +39,6 @@ type logBuffer struct {
 	msg     []string
 	max     int
 	current int
-	// regexps caches compiled regular expressions.
-	regexps map[string]*regexp.Regexp
 }
 
 // NewLogBuffer creates log buffer with max line number limit. Because we only match logs
@@ -49,26 +47,28 @@ type logBuffer struct {
 // lines of patterns we support.
 func NewLogBuffer(maxLines int) *logBuffer {
 	return &logBuffer{
-		buffer:  make([]*types.Log, maxLines),
-		msg:     make([]string, maxLines),
-		max:     maxLines,
-		regexps: make(map[string]*regexp.Regexp),
+		buffer: make([]*types.Log, maxLines),
+		msg:    make([]string, maxLines),
+		max:    maxLines,
 	}
 }
 
+// CompilePattern compiles a log buffer pattern that must match to the end of
+// the buffered logs.
+func CompilePattern(expr string) (*regexp.Regexp, error) {
+	if _, err := regexp.Compile(expr); err != nil {
+		return nil, err
+	}
+	return regexp.Compile(expr + `\z`)
+}
+
 func (b *logBuffer) Push(log *types.Log) {
 	b.buffer[b.current%b.max] = log
 	b.msg[b.current%b.max] = log.Message
 	b.current++
 }
 
-func (b *logBuffer) Match(expr string) []*types.Log {
-	// The expression should be checked outside, and it must match to the end.
-	reg, ok := b.regexps[expr]
-	if !ok {
-		reg = regexp.MustCompile(expr + `\z`)
-		b.regexps[expr] = reg
-	}
+func (b *logBuffer) Match(reg *regexp.Regexp) []*types.Log {
 	log := b.String()
 	loc := reg.FindStringIndex(log)
 	if loc == nil {