improved upon '*' matching

ddtrace/tracer/rules_sampler.go

@@ -185,6 +185,9 @@ func (sr *SamplingRule) match(s *span) bool {
 	defer s.Unlock()
 	if sr.Tags != nil {
 		for k, regex := range sr.Tags {
+			if regex == nil {
+				continue
+			}
 			if s.Meta != nil {
 				v, ok := s.Meta[k]
 				if ok && regex.MatchString(v) {
@@ -683,7 +686,7 @@ func newSingleSpanRateLimiter(mps float64) *rateLimiter {
 // globMatch compiles pattern string into glob format, i.e. regular expressions with only '?'
 // and '*' treated as regex metacharacters.
 func globMatch(pattern string) *regexp.Regexp {
-	if pattern == "" {
+	if pattern == "" || pattern == "*" {
 		return nil
 	}
 	// escaping regex characters

ddtrace/tracer/sampler_test.go

@@ -721,6 +721,11 @@ func TestRulesSampler(t *testing.T) {
 				spanSrv:  "test-service",
 				spanName: "abcde",
 			},
+			{
+				rules:    []SamplingRule{SpanTagsResourceRule(map[string]string{"hostname": "hn*", "tag": "*"}, "", "abc*", "test*", 1.0)},
+				spanSrv:  "test-service",
+				spanName: "abcde",
+			},
 			{
 				rules:    []SamplingRule{SpanNameServiceRule("", "web*", 1.0)},
 				spanSrv:  "wEbServer",
@@ -904,13 +909,20 @@ func TestRulesSampler(t *testing.T) {
 				spanSrv:  "wEbServer",
 				spanName: "web.reqUEst",
 			},
+			{
+				rules:    []SamplingRule{SpanTagsResourceRule(map[string]string{"hostname": "hn*", "tag": "2*"}, "", "abc*", "test*", 1.0)},
+				spanSrv:  "test-service",
+				spanName: "abcde",
+			},
 		} {
 			t.Run("", func(t *testing.T) {
 				assert := assert.New(t)
 				c := newConfig(WithSamplingRules(tt.rules))
 				rs := newRulesSampler(nil, c.spanRules, globalSampleRate())
 
-				span := makeFinishedSpan(tt.spanName, tt.spanSrv, "res-10", map[string]interface{}{"hostname": "hn-30"})
+				span := makeFinishedSpan(tt.spanName, tt.spanSrv, "res-10", map[string]interface{}{"hostname": "hn-30",
+					"tag": 20.1,
+				})
 				result := rs.SampleSpan(span)
 				assert.False(result)
 				assert.NotContains(span.Metrics, keySpanSamplingMechanism)