cmd/tlsconfig: build tags to turn off TLSv1.3 in go1.11

Author: alrs

cmd/tlsconfig/tls_version_go11.go

@@ -0,0 +1,31 @@
+// +build !go1.12
+
+// This file can be removed once go1.11 is no longer supported
+
+package main
+
+import (
+	"crypto/tls"
+	"sort"
+)
+
+func mapTLSVersions(tlsVersions []string) []int {
+	var versions []int
+	for _, tlsVersion := range tlsVersions {
+		switch tlsVersion {
+		case "TLSv1.2":
+			versions = append(versions, tls.VersionTLS12)
+		case "TLSv1.1":
+			versions = append(versions, tls.VersionTLS11)
+		case "TLSv1":
+			versions = append(versions, tls.VersionTLS10)
+		case "SSLv3":
+			// unsupported from go1.14
+			versions = append(versions, tls.VersionSSL30)
+		default:
+			continue
+		}
+	}
+	sort.Ints(versions)
+	return versions
+}

cmd/tlsconfig/tls_version_deprecated.go renamed to cmd/tlsconfig/tls_version_go12_go13.go

@@ -1,4 +1,4 @@
-// +build !go1.14
+// +build go1.12,!go1.14
 
 // This file can be removed once go1.13 is no longer supported
 

cmd/tlsconfig/tls_version_future.go renamed to cmd/tlsconfig/tls_version_go14.go

@@ -1,4 +1,4 @@
-// +build go1.14
+// +build go1.14 !go1.11
 
 // main
 package main