Health check for SSL/TLS services (#177)

* protocol: starttls: add timeout support

Signed-off-by: Charles Decoux <charles@phowork.fr>

* protocol: add ssl support

Signed-off-by: Charles Decoux <charles@phowork.fr>

client/client_test.go

@@ -91,6 +91,56 @@ func TestCanPerformStartTLS(t *testing.T) {
 	}
 }
 
+func TestCanPerformTLS(t *testing.T) {
+       type args struct {
+               address  string
+               insecure bool
+       }
+       tests := []struct {
+               name          string
+               args          args
+               wantConnected bool
+               wantErr       bool
+       }{
+               {
+                       name: "invalid address",
+                       args: args{
+                               address: "test",
+                       },
+                       wantConnected: false,
+                       wantErr:       true,
+               },
+               {
+                       name: "error dial",
+                       args: args{
+                               address: "test:1234",
+                       },
+                       wantConnected: false,
+                       wantErr:       true,
+               },
+               {
+                       name: "valid tls",
+                       args: args{
+                               address: "smtp.gmail.com:465",
+                       },
+                       wantConnected: true,
+                       wantErr:       false,
+               },
+       }
+       for _, tt := range tests {
+               t.Run(tt.name, func(t *testing.T) {
+                       connected, _, err := CanPerformTLS(tt.args.address, &Config{Insecure: tt.args.insecure, Timeout: 5 * time.Second})
+                       if (err != nil) != tt.wantErr {
+                               t.Errorf("CanPerformTLS() err=%v, wantErr=%v", err, tt.wantErr)
+                               return
+                       }
+                       if connected != tt.wantConnected {
+                               t.Errorf("CanPerformTLS() connected=%v, wantConnected=%v", connected, tt.wantConnected)
+                       }
+               })
+       }
+}
+
 func TestCanCreateTCPConnection(t *testing.T) {
 	if CanCreateTCPConnection("127.0.0.1", &Config{Timeout: 5 * time.Second}) {
 		t.Error("should've failed, because there's no port in the address")