Correct Error Handling to avoid panics and add more logging to template

When a type error is found we return an empty object of the expected
type(Example: return "" for string return type). Also makes adds logging
to all errors caused by type and corrects all related logging for consistency.

controllers/nginx/pkg/template/template.go

@@ -171,9 +171,14 @@ func formatIP(input string) string {
 }
 
 // buildResolvers returns the resolvers reading the /etc/resolv.conf file
-func buildResolvers(a interface{}) string {
+func buildResolvers(input interface{}) string {
 	// NGINX need IPV6 addresses to be surrounded by brackets
-	nss := a.([]net.IP)
+	nss, ok := input.([]net.IP)
+	if !ok {
+		glog.Errorf("expected a '[]net.IP' type but %T was returned", input)
+		return ""
+	}
+
 	if len(nss) == 0 {
 		return ""
 	}
@@ -196,6 +201,7 @@ func buildResolvers(a interface{}) string {
 func buildLocation(input interface{}) string {
 	location, ok := input.(*ingress.Location)
 	if !ok {
+		glog.Errorf("expected an '*ingress.Location' type but %T was returned", input)
 		return slash
 	}
 
@@ -220,6 +226,7 @@ func buildLocation(input interface{}) string {
 func buildAuthLocation(input interface{}) string {
 	location, ok := input.(*ingress.Location)
 	if !ok {
+		glog.Errorf("expected an '*ingress.Location' type but %T was returned", input)
 		return ""
 	}
 
@@ -237,6 +244,7 @@ func buildAuthResponseHeaders(input interface{}) []string {
 	location, ok := input.(*ingress.Location)
 	res := []string{}
 	if !ok {
+		glog.Errorf("expected an '*ingress.Location' type but %T was returned", input)
 		return res
 	}
 
@@ -256,7 +264,8 @@ func buildAuthResponseHeaders(input interface{}) []string {
 func buildLogFormatUpstream(input interface{}) string {
 	cfg, ok := input.(config.Configuration)
 	if !ok {
-		glog.Errorf("error an ingress.buildLogFormatUpstream type but %T was returned", input)
+		glog.Errorf("expected a 'config.Configuration' type but %T was returned", input)
+		return ""
 	}
 
 	return cfg.BuildLogFormatUpstream()
@@ -267,9 +276,15 @@ func buildLogFormatUpstream(input interface{}) string {
 // If the annotation ingress.kubernetes.io/add-base-url:"true" is specified it will
 // add a base tag in the head of the response from the service
 func buildProxyPass(host string, b interface{}, loc interface{}) string {
-	backends := b.([]*ingress.Backend)
+	backends, ok := b.([]*ingress.Backend)
+	if !ok {
+		glog.Errorf("expected an '[]*ingress.Backend' type but %T was returned", b)
+		return ""
+	}
+
 	location, ok := loc.(*ingress.Location)
 	if !ok {
+		glog.Errorf("expected a '*ingress.Location' type but %T was returned", loc)
 		return ""
 	}
 
@@ -345,6 +360,7 @@ func filterRateLimits(input interface{}) []ratelimit.RateLimit {
 
 	servers, ok := input.([]*ingress.Server)
 	if !ok {
+		glog.Errorf("expected a '[]ratelimit.RateLimit' type but %T was returned", input)
 		return ratelimits
 	}
 	for _, server := range servers {
@@ -368,6 +384,7 @@ func buildRateLimitZones(input interface{}) []string {
 
 	servers, ok := input.([]*ingress.Server)
 	if !ok {
+		glog.Errorf("expected a '[]*ingress.Server' type but %T was returned", input)
 		return zones.List()
 	}
 
@@ -417,6 +434,7 @@ func buildRateLimit(input interface{}) []string {
 
 	loc, ok := input.(*ingress.Location)
 	if !ok {
+		glog.Errorf("expected an '*ingress.Location' type but %T was returned", input)
 		return limits
 	}
 
@@ -456,7 +474,7 @@ func buildRateLimit(input interface{}) []string {
 func isLocationAllowed(input interface{}) bool {
 	loc, ok := input.(*ingress.Location)
 	if !ok {
-		glog.Errorf("expected an ingress.Location type but %T was returned", input)
+		glog.Errorf("expected an '*ingress.Location' type but %T was returned", input)
 		return false
 	}
 
@@ -473,7 +491,11 @@ var (
 // size of the string to be used as a variable in nginx to avoid
 // issue with the size of the variable bucket size directive
 func buildDenyVariable(a interface{}) string {
-	l := a.(string)
+	l, ok := a.(string)
+	if !ok {
+		glog.Errorf("expected a 'string' type but %T was returned", a)
+		return ""
+	}
 
 	if _, ok := denyPathSlugMap[l]; !ok {
 		denyPathSlugMap[l] = buildRandomUUID()
@@ -484,9 +506,16 @@ func buildDenyVariable(a interface{}) string {
 
 // TODO: Needs Unit Tests
 func buildUpstreamName(host string, b interface{}, loc interface{}) string {
-	backends := b.([]*ingress.Backend)
+
+	backends, ok := b.([]*ingress.Backend)
+	if !ok {
+		glog.Errorf("expected an '[]*ingress.Backend' type but %T was returned", b)
+		return ""
+	}
+
 	location, ok := loc.(*ingress.Location)
 	if !ok {
+		glog.Errorf("expected a '*ingress.Location' type but %T was returned", loc)
 		return ""
 	}
 
@@ -522,7 +551,8 @@ func isSticky(host string, loc *ingress.Location, stickyLocations map[string][]s
 func buildNextUpstream(input interface{}) string {
 	nextUpstream, ok := input.(string)
 	if !ok {
-		glog.Errorf("expected an string type but %T was returned", input)
+		glog.Errorf("expected a 'string' type but %T was returned", input)
+		return ""
 	}
 
 	parts := strings.Split(nextUpstream, " ")
@@ -540,7 +570,8 @@ func buildNextUpstream(input interface{}) string {
 func buildAuthSignURL(input interface{}) string {
 	s, ok := input.(string)
 	if !ok {
-		glog.Errorf("expected an string type but %T was returned", input)
+		glog.Errorf("expected an 'string' type but %T was returned", input)
+		return ""
 	}
 
 	u, _ := url.Parse(s)
@@ -561,7 +592,7 @@ func buildRandomUUID() string {
 func isValidClientBodyBufferSize(input interface{}) bool {
 	s, ok := input.(string)
 	if !ok {
-		glog.Errorf("expected an string type but %T was returned", input)
+		glog.Errorf("expected an 'string' type but %T was returned", input)
 		return false
 	}
 
@@ -602,13 +633,13 @@ type ingressInformation struct {
 func getIngressInformation(i, p interface{}) *ingressInformation {
 	ing, ok := i.(*extensions.Ingress)
 	if !ok {
-		glog.V(3).Infof("expected an Ingress type but %T was returned", i)
+		glog.Errorf("expected an '*extensions.Ingress' type but %T was returned", i)
 		return &ingressInformation{}
 	}
 
 	path, ok := p.(string)
 	if !ok {
-		glog.V(3).Infof("expected a string type but %T was returned", p)
+		glog.Errorf("expected a 'string' type but %T was returned", p)
 		return &ingressInformation{}
 	}
 
@@ -645,7 +676,8 @@ func getIngressInformation(i, p interface{}) *ingressInformation {
 func buildForwardedFor(input interface{}) string {
 	s, ok := input.(string)
 	if !ok {
-		glog.Errorf("expected an string type but %T was returned", input)
+		glog.Errorf("expected a 'string' type but %T was returned", input)
+		return ""
 	}
 
 	ffh := strings.Replace(s, "-", "_", -1)