[metricbeat/zookeeper] Fix panics in server parser and add edge case tests

- Add bounds checking for version and date regex matches to prevent
  index-out-of-range panics on specific input
- Fix off-by-one error in mode split check (< 1 → < 2)
- Remove unused regex variables (ipCapturer, thatNumberCapturer,
  portCapturer, dataCapturer)
- Add TestParseSrvrEdgeCases with table-driven tests for edge cases

Author: shmsr

metricbeat/module/zookeeper/server/data.go

@@ -34,10 +34,6 @@ import (
 )
 
 var latencyCapturer = regexp.MustCompile(`(\d+)/(\d+)/(\d+)`)
-var ipCapturer = regexp.MustCompile(`\d+\.\d+\.\d+\.\d+`)
-var thatNumberCapturer = regexp.MustCompile(`\[(\d+)\]`)
-var portCapturer = regexp.MustCompile(`:(\d+)\[`)
-var dataCapturer = regexp.MustCompile(`(\w+)=(\d+)`)
 var fieldsCapturer = regexp.MustCompile(`^([a-zA-Z\s]+):\s(\d+)`)
 var versionCapturer = regexp.MustCompile(`:\s(.*),`)
 var dateCapturer = regexp.MustCompile(`built on (.*)`)
@@ -54,8 +50,17 @@ func parseSrvr(i io.Reader, logger *logp.Logger) (mapstr.M, string, error) {
 
 	output := mapstr.M{}
 
-	version := versionCapturer.FindStringSubmatch(scanner.Text())[1]
-	dateString := dateCapturer.FindStringSubmatch(scanner.Text())[1]
+	versionMatches := versionCapturer.FindStringSubmatch(scanner.Text())
+	if len(versionMatches) < 2 {
+		return nil, "", errors.New("no match found for version")
+	}
+	version := versionMatches[1]
+
+	dateStringMatches := dateCapturer.FindStringSubmatch(scanner.Text())
+	if len(dateStringMatches) < 2 {
+		return nil, "", errors.New("no match found for build date")
+	}
+	dateString := dateStringMatches[1]
 
 	date, err := time.Parse("01/02/2006 03:04 GMT", dateString)
 	if err != nil {
@@ -108,7 +113,7 @@ func parseSrvr(i io.Reader, logger *logp.Logger) (mapstr.M, string, error) {
 
 		if strings.Contains(line, "Mode") {
 			modeSplit := strings.Split(line, " ")
-			if len(modeSplit) < 1 {
+			if len(modeSplit) < 2 {
 				logger.Debugf("no tokens after splitting line '%s'", line)
 				continue
 			}

metricbeat/module/zookeeper/server/server_test.go

@@ -70,3 +70,63 @@ func TestParser(t *testing.T) {
 	assert.Equal(t, uint32(7), mapStr["epoch"])
 	assert.Equal(t, uint32(0x601132), mapStr["count"])
 }
+
+func TestParseSrvrEdgeCases(t *testing.T) {
+	tests := []struct {
+		name        string
+		input       string
+		expectError bool
+		checkMode   bool
+		hasMode     bool
+	}{
+		{
+			name:        "invalid version line",
+			input:       "some invalid first line\n",
+			expectError: true,
+		},
+		{
+			name: "mode line without value",
+			input: `Zookeeper version: 3.5.5, built on 05/03/2019 12:07 GMT
+Mode:
+`,
+			expectError: false,
+			checkMode:   true,
+			hasMode:     false,
+		},
+		{
+			name:        "malformed input",
+			input:       "00000000",
+			expectError: true,
+		},
+		{
+			name:        "missing date",
+			input:       ": ,00000",
+			expectError: true,
+		},
+		{
+			name:        "malformed mode line",
+			input:       ": ,built on \nMode",
+			expectError: false,
+			checkMode:   true,
+			hasMode:     false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			logger := logptest.NewTestingLogger(t, "zookeeper.server")
+			mapStr, _, err := parseSrvr(bytes.NewReader([]byte(tt.input)), logger)
+
+			if tt.expectError {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+
+			if tt.checkMode {
+				_, hasMode := mapStr["mode"]
+				assert.Equal(t, tt.hasMode, hasMode)
+			}
+		})
+	}
+}