Introduce Rapid library for property based tests. Initial cut of doma…

…in generators for use with Rapid testing library.

go.mod

@@ -36,6 +36,7 @@ require (
 	golang.org/x/sys v0.1.0
 	golang.org/x/text v0.4.0
 	gopkg.in/sohlich/elogrus.v3 v3.0.0-20180410122755-1fa29e2f2009
+	pgregory.net/rapid v0.4.8
 )
 
 require (

go.sum

@@ -204,3 +204,5 @@ gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C
 gopkg.in/yaml.v3 v3.0.0/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+pgregory.net/rapid v0.4.8 h1:d+5SGZWUbJPbl3ss6tmPFqnNeQR6VDOFly+eTjwPiEw=
+pgregory.net/rapid v0.4.8/go.mod h1:Z5PbWqjvWR1I3UGjvboUuan4fe4ZYEYNLNQLExzCoUs=

test/rapidgen/rapidgenerators.go

@@ -0,0 +1,55 @@
+package rapidgen
+
+// See https://github.com/flyingmutant/rapid/pull/18
+
+import (
+	"fmt"
+	"pgregory.net/rapid"
+)
+
+const (
+	domainMaxLength        = 255
+	domainMaxElementLength = 63
+)
+
+// Domain generates an RFC 1035 compliant domain name.
+func Domain() *rapid.Generator {
+	return DomainOf(255, 63)
+}
+
+// DomainOf generates an RFC 1035 compliant domain name,
+// with a maximum overall length of maxLength
+// and a maximum number of elements of maxElements.
+func DomainOf(maxLength, maxElementLength int) *rapid.Generator {
+	assertf(4 <= maxLength, "maximum length (%v) should not be less than 4, to generate a two character domain and a one character subdomain", maxLength)
+	assertf(maxLength <= 255, "maximum length (%v) should not be greater than 255 to comply with RFC 1035", maxLength)
+	assertf(1 <= maxElementLength, "maximum element length (%v) should not be less than 1 to comply with RFC 1035", maxElementLength)
+	assertf(maxElementLength <= 63, "maximum element length (%v) should not be greater than 63 to comply with RFC 1035", maxElementLength)
+
+	return rapid.Custom(func(t *rapid.T) string {
+		domain := fmt.Sprint(tldGenerator.
+			Filter(func(s string) bool { return len(s)+2 <= domainMaxLength }).
+			Draw(t, "domain"))
+
+		expr := fmt.Sprintf(`[a-zA-Z]([a-zA-Z0-9\-]{0,%d}[a-zA-Z0-9])?`, domainMaxElementLength-2)
+
+		el := rapid.Int8Range(1, 126).Example().(int)
+		for i := 0; i < el; i++ {
+			subDomain := fmt.Sprint(rapid.StringMatching(expr).Draw(t, "subdomain"))
+			if len(domain)+len(subDomain) >= domainMaxLength {
+				break
+			}
+			domain = subDomain + "." + domain
+		}
+
+		return domain
+	})
+}
+
+var tldGenerator = rapid.SampledFrom(tlds)
+
+func assertf(ok bool, format string, args ...interface{}) {
+	if !ok {
+		panic(fmt.Sprintf(format, args...))
+	}
+}