Fix convert processor conversion of string to integer

The conversion failed when for strings with leading zeroes and a decimal
digit 8 or 9, as the underlying runtime function would try to parse that
as an octal number.

This is fixed by only allowing decimal and hex, which in turns makes the
processor more aligned to its Elasticsearch counterpart.

Fixes #15513

CHANGELOG.next.asciidoc

@@ -151,6 +151,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix bug with potential concurrent reads and writes from event.Meta map by Kafka output. {issue}14542[14542] {pull}14568[14568]
 - Fix spooling to disk blocking infinitely if the lock file can not be acquired. {pull}15338[15338]
 - Fix `metricbeat test output` with an ipv6 ES host in the output.hosts. {pull}15368[15368]
+- Fix `convert` processor conversion of string to integer with leading zeros. {issue}15513[15513]
 
 *Auditbeat*
 

libbeat/processors/convert/convert.go

@@ -205,7 +205,7 @@ func toString(value interface{}) (string, error) {
 func toLong(value interface{}) (int64, error) {
 	switch v := value.(type) {
 	case string:
-		return strconv.ParseInt(v, 0, 64)
+		return strToInt(v, 64)
 	case int:
 		return int64(v), nil
 	case int8:
@@ -238,7 +238,7 @@ func toLong(value interface{}) (int64, error) {
 func toInteger(value interface{}) (int32, error) {
 	switch v := value.(type) {
 	case string:
-		i, err := strconv.ParseInt(v, 0, 32)
+		i, err := strToInt(v, 32)
 		return int32(i), err
 	case int:
 		return int32(v), nil
@@ -403,3 +403,13 @@ func cloneValue(value interface{}) interface{} {
 		return value
 	}
 }
+
+// Helper to interpret a string as either base-10 or base-16.
+func strToInt(v string, bitSize int) (int64, error) {
+	base := 10
+	if strings.IndexAny(v, "xX") != -1 {
+		// strconv.ParseInt only accepts the '0x' prefix when base is 0.
+		base = 0
+	}
+	return strconv.ParseInt(v, base, bitSize)
+}

libbeat/processors/convert/convert_test.go

@@ -276,8 +276,16 @@ var testCases = []testCase{
 
 	{Long, nil, nil, true},
 	{Long, "x", nil, true},
+	{Long, "0x", nil, true},
+	{Long, "0b1", nil, true},
+	{Long, "1x2", nil, true},
 	{Long, true, nil, true},
 	{Long, "1", int64(1), false},
+	{Long, "-1", int64(-1), false},
+	{Long, "017", int64(17), false},
+	{Long, "08", int64(8), false},
+	{Long, "0X0A", int64(10), false},
+	{Long, "-0x12", int64(-18), false},
 	{Long, int(1), int64(1), false},
 	{Long, int8(1), int64(1), false},
 	{Long, int16(1), int64(1), false},
@@ -294,6 +302,17 @@ var testCases = []testCase{
 	{Integer, nil, nil, true},
 	{Integer, "x", nil, true},
 	{Integer, true, nil, true},
+	{Integer, "x", nil, true},
+	{Integer, "0x", nil, true},
+	{Integer, "0b1", nil, true},
+	{Integer, "1x2", nil, true},
+	{Integer, true, nil, true},
+	{Integer, "1", int32(1), false},
+	{Integer, "-1", int32(-1), false},
+	{Integer, "017", int32(7), false},
+	{Integer, "08", int32(8), false},
+	{Integer, "0X0A", int32(10), false},
+	{Integer, "-0x12", int32(-18), false},
 	{Integer, "1", int32(1), false},
 	{Integer, int(1), int32(1), false},
 	{Integer, int8(1), int32(1), false},