feat: introduce konghq.com/headers-separator annotation and make parsing more robust

CHANGELOG.md

@@ -126,6 +126,10 @@ Adding a new version? You'll need three changes:
 - Improve validation - reject `Ingresses`, `Services` or `KongConsumers` that have multiple instances
   of the same type plugin attached.
   [#5972](https://github.com/Kong/kubernetes-ingress-controller/pull/5972)
+- Added support for `konghq.com/headers-separator` that allows to set custom separator (instead of default `,`)
+  for headers specified with `konghq.com/headers.*` annotations. Moreover parsing a content of `konghq.com/headers.*`
+  is more robust - leading and trailing whitespace characters are discarded.
+  [#5977](https://github.com/Kong/kubernetes-ingress-controller/pull/5977)
 
 ### Fixed
 

internal/annotations/annotations.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/samber/lo"
 	netv1 "k8s.io/api/networking/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
@@ -61,6 +62,7 @@ const (
 	ReadTimeoutKey       = "/read-timeout"
 	RetriesKey           = "/retries"
 	HeadersKey           = "/headers"
+	HeadersSeparatorKey  = "/headers-separator"
 	PathHandlingKey      = "/path-handling"
 	UserTagKey           = "/tags"
 	RewriteURIKey        = "/rewrite"
@@ -311,14 +313,20 @@ func ExtractRetries(anns map[string]string) (string, bool) {
 // ExtractHeaders extracts the parsed headers annotations values. It returns a map of header names to slices of values.
 func ExtractHeaders(anns map[string]string) (map[string][]string, bool) {
 	headers := make(map[string][]string)
-	prefix := AnnotationPrefix + HeadersKey + "."
+	const prefix = AnnotationPrefix + HeadersKey + "."
+	separator, ok := anns[AnnotationPrefix+HeadersSeparatorKey]
+	if !ok {
+		separator = ","
+	}
 	for key, val := range anns {
 		if strings.HasPrefix(key, prefix) {
 			header := strings.TrimPrefix(key, prefix)
 			if len(header) == 0 || len(val) == 0 {
 				continue
 			}
-			headers[header] = strings.Split(val, ",")
+			headers[header] = lo.Map(strings.Split(val, separator), func(hv string, _ int) string {
+				return strings.TrimSpace(hv)
+			})
 		}
 	}
 	if len(headers) == 0 {

internal/annotations/annotations_test.go

@@ -845,6 +845,15 @@ func TestExtractHeaders(t *testing.T) {
 			name: "empty",
 			want: map[string][]string{},
 		},
+		{
+			name: "empty with custom separator",
+			args: args{
+				anns: map[string]string{
+					"konghq.com/headers-separator": ";",
+				},
+			},
+			want: map[string][]string{},
+		},
 		{
 			name: "non-empty",
 			args: args{
@@ -863,6 +872,15 @@ func TestExtractHeaders(t *testing.T) {
 			},
 			want: map[string][]string{},
 		},
+		{
+			name: "separator with no header results in empty header value",
+			args: args{
+				anns: map[string]string{
+					"konghq.com/headers.foo": "foo,",
+				},
+			},
+			want: map[string][]string{"foo": {"foo", ""}},
+		},
 		{
 			name: "no header name",
 			args: args{
@@ -872,6 +890,47 @@ func TestExtractHeaders(t *testing.T) {
 			},
 			want: map[string][]string{},
 		},
+		{
+			name: "multiple header, multiple values, trailing spaces",
+			args: args{
+				anns: map[string]string{
+					"konghq.com/headers.x-example":    "foo, bar, baz  ",
+					"konghq.com/headers.x-additional": "foo",
+				},
+			},
+			want: map[string][]string{
+				"x-example":    {"foo", "bar", "baz"},
+				"x-additional": {"foo"},
+			},
+		},
+		{
+			name: "multiple header, multiple values, custom separator",
+			args: args{
+				anns: map[string]string{
+					"konghq.com/headers-separator":    ";",
+					"konghq.com/headers.x-example":    "foo, bar;baz",
+					"konghq.com/headers.x-additional": "foo",
+				},
+			},
+			want: map[string][]string{
+				"x-example":    {"foo, bar", "baz"},
+				"x-additional": {"foo"},
+			},
+		},
+		{
+			name: "multiple header, multiple values, custom separator, leading & trailing spaces",
+			args: args{
+				anns: map[string]string{
+					"konghq.com/headers-separator":    ";",
+					"konghq.com/headers.x-example":    " foo, bar;cat,dog ;   baz ",
+					"konghq.com/headers.x-additional": "foo;",
+				},
+			},
+			want: map[string][]string{
+				"x-example":    {"foo, bar", "cat,dog", "baz"},
+				"x-additional": {"foo", ""},
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {