pkg/tracer: added glob matcher for span sampling

ddtrace/tracer/util.go

@@ -8,6 +8,7 @@ package tracer
 import (
 	"encoding/base64"
 	"fmt"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -129,3 +130,15 @@ var b64 = base64.StdEncoding.WithPadding(base64.NoPadding)
 func b64Encode(s string) string {
 	return b64.EncodeToString([]byte(s))
 }
+
+// globMatch compiles pattern string into glob format, i.e. regular expressions with only '?'
+// and '*' treated as regex metacharacters.
+func globMatch(pattern string) (*regexp.Regexp, error) {
+	// escaping regex characters
+	pattern = regexp.QuoteMeta(pattern)
+	// replacing '?' and '*' with regex characters
+	pattern = strings.Replace(pattern, "\\?", ".", -1)
+	pattern = strings.Replace(pattern, "\\*", ".*", -1)
+	//pattern must match an entire string
+	return regexp.Compile(fmt.Sprintf("^%s$", pattern))
+}

ddtrace/tracer/util_test.go

@@ -115,3 +115,54 @@ func TestParsePropagatableTraceTags(t *testing.T) {
 		})
 	}
 }
+
+func TestGlobMatch(t *testing.T) {
+	for i, tt := range []struct {
+		pattern     string
+		input       string
+		shouldMatch bool
+	}{
+		// pattern with *
+		{"test*", "test", true},
+		{"test*", "test-case", true},
+		{"test*", "a-test", false},
+		{"*test", "a-test", true},
+		{"a*case", "acase", true},
+		{"a*case", "a-test-case", true},
+		{"a*test*case", "a-test-case", true},
+		{"a*test*case", "atestcase", true},
+		{"a*test*case", "abadcase", false},
+		// pattern with ?
+		{"test?", "test", false},
+		{"test?", "test-case", false},
+		{"test?", "a-test", false},
+		{"?test", "a-test", false},
+		{"a?case", "acase", false},
+		{"a?case", "a-case", true},
+		{"a?test?case", "a-test-case", true},
+		{"a?test?case", "a-test--case", false},
+		// pattern with ? and *
+		{"?test*", "atest", true},
+		{"?test*", "atestcase", true},
+		{"?test*", "testcase", false},
+		{"?test*", "testcase", false},
+		{"test*case", "testcase", true},
+		{"a?test*", "a-test-case", true},
+		{"a?test*", "atestcase", false},
+		{"a*test?", "a-test-", true},
+		{"a*test?", "atestcase", false},
+		{"a*test?case", "a--test-case", true},
+		{"a*test?case", "a--test--case", false},
+		{"a?test*case", "a-testing--case", true},
+		{"the?test*case", "the-test-cases", false},
+	} {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			rg, _ := globMatch(tt.pattern)
+			if tt.shouldMatch {
+				assert.Regexp(t, rg, tt.input)
+			} else {
+				assert.NotRegexp(t, rg, tt.input)
+			}
+		})
+	}
+}