filters/builtin: drop specified header value

Extend `dropRequestHeader` and `dropResponseHeader` to support
optional second value argument and drop only this value when specified.

Signed-off-by: Alexander Yastrebov <[email protected]>

Author: AlexanderYastrebov

docs/reference/filters.md

@@ -163,18 +163,25 @@ but appends the provided value to the already existing ones.
 
 ### dropRequestHeader
 
-Removes a header from the request
+Removes a header or a value from the request.
 
 Parameters:
 
 * header name (string)
+* header value (string) - optional
 
 Example:
 
 ```
 foo: * -> dropRequestHeader("User-Agent") -> "https://backend.example.org";
 ```
 
+Drop specific value and keep others:
+
+```
+foo: * -> dropRequestHeader("Connection", "Upgrade") -> "https://backend.example.org";
+```
+
 ### modResponseHeader
 
 Same as [modRequestHeader](#modrequestheader), only for responses

filters/builtin/header_test.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/zalando/skipper/eskip"
 	"github.com/zalando/skipper/filters"
 	"github.com/zalando/skipper/filters/filtertest"
@@ -85,12 +86,7 @@ func testHeaders(t *testing.T, got, expected http.Header) {
 			delete(got, n)
 		}
 	}
-
-	if !compareHeaders(got, expected) {
-		printHeader(t, expected, "invalid header", "expected")
-		printHeader(t, got, "invalid header", "got")
-		t.Error("invalid header")
-	}
+	assert.Equal(t, expected, got)
 }
 
 func TestHeader(t *testing.T) {
@@ -132,10 +128,11 @@ func TestHeader(t *testing.T) {
 			requestHeader:  http.Header{"X-Test-Name": []string{"value0", "value1"}},
 			expectedHeader: http.Header{"X-Test-Request-Name": []string{"value"}},
 		}, {
-			msg:   "set outgoing host on set",
-			args:  []interface{}{"Host", "www.example.org"},
-			valid: true,
-			host:  "www.example.org",
+			msg:            "set outgoing host on set",
+			args:           []interface{}{"Host", "www.example.org"},
+			valid:          true,
+			host:           "www.example.org",
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "set request header from path params",
 			args:           []interface{}{"X-Test-Name", "Mit ${was} zu ${wo}"},
@@ -161,10 +158,11 @@ func TestHeader(t *testing.T) {
 			requestHeader:  http.Header{"X-Test-Name": []string{"value0", "value1"}},
 			expectedHeader: http.Header{"X-Test-Request-Name": []string{"value0", "value1", "value"}},
 		}, {
-			msg:   "append outgoing host on set",
-			args:  []interface{}{"Host", "www.example.org"},
-			valid: true,
-			host:  "www.example.org",
+			msg:            "append outgoing host on set",
+			args:           []interface{}{"Host", "www.example.org"},
+			valid:          true,
+			host:           "www.example.org",
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "append request header from path params",
 			args:           []interface{}{"X-Test-Name", "a ${foo}ter"},
@@ -186,19 +184,40 @@ func TestHeader(t *testing.T) {
 			expectedHeader: http.Header{"X-Test-Request-Name": []string{"Value"}},
 		}},
 		"dropRequestHeader": {{
-			msg:   "drop request header when none",
-			args:  []interface{}{"X-Test-Name"},
-			valid: true,
+			msg:            "drop request header when none",
+			args:           []interface{}{"X-Test-Name"},
+			valid:          true,
+			expectedHeader: http.Header{},
 		}, {
-			msg:           "drop request header when exists",
-			args:          []interface{}{"X-Test-Name"},
-			valid:         true,
-			requestHeader: http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			msg:            "drop request header when exists",
+			args:           []interface{}{"X-Test-Name"},
+			valid:          true,
+			requestHeader:  http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			expectedHeader: http.Header{},
 		}, {
-			msg:           "name parameter is case-insensitive",
-			args:          []interface{}{"x-test-name"},
-			valid:         true,
-			requestHeader: http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			msg:            "name parameter is case-insensitive",
+			args:           []interface{}{"x-test-name"},
+			valid:          true,
+			requestHeader:  http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			expectedHeader: http.Header{},
+		}, {
+			msg:            "drop matching value",
+			args:           []interface{}{"X-Test-Name", "bar"},
+			valid:          true,
+			requestHeader:  http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Request-Name": []string{"foo", "baz"}},
+		}, {
+			msg:            "ignore non-matching",
+			args:           []interface{}{"X-Test-Name", "qux"},
+			valid:          true,
+			requestHeader:  http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Request-Name": []string{"foo", "bar", "baz"}},
+		}, {
+			msg:            "drop matching value name parameter is case-insensitive",
+			args:           []interface{}{"x-test-name", "bar"},
+			valid:          true,
+			requestHeader:  http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Request-Name": []string{"foo", "baz"}},
 		}},
 		"setResponseHeader": {{
 			msg:            "set response header when none",
@@ -220,9 +239,10 @@ func TestHeader(t *testing.T) {
 			valid:          true,
 			expectedHeader: http.Header{"X-Test-Name": []string{"a small barter"}},
 		}, {
-			msg:   "set response header from path params when missing",
-			args:  []interface{}{"X-Test-Name", "a ${foo}ter"},
-			valid: true,
+			msg:            "set response header from path params when missing",
+			args:           []interface{}{"X-Test-Name", "a ${foo}ter"},
+			valid:          true,
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "name parameter is case-insensitive",
 			args:           []interface{}{"x-test-name", "Value"},
@@ -261,19 +281,40 @@ func TestHeader(t *testing.T) {
 			expectedHeader: http.Header{"X-Test-Name": []string{"Value"}},
 		}},
 		"dropResponseHeader": {{
-			msg:   "drop response header when none",
-			args:  []interface{}{"X-Test-Name"},
-			valid: true,
+			msg:            "drop response header when none",
+			args:           []interface{}{"X-Test-Name"},
+			valid:          true,
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "drop response header when exists",
 			args:           []interface{}{"X-Test-Name"},
 			valid:          true,
 			responseHeader: http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "name parameter is case-insensitive",
 			args:           []interface{}{"x-test-name"},
 			valid:          true,
 			responseHeader: http.Header{"X-Test-Name": []string{"value0", "value1"}},
+			expectedHeader: http.Header{},
+		}, {
+			msg:            "drop matching value",
+			args:           []interface{}{"X-Test-Name", "bar"},
+			valid:          true,
+			responseHeader: http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Name": []string{"foo", "baz"}},
+		}, {
+			msg:            "ignore non-matching",
+			args:           []interface{}{"X-Test-Name", "qux"},
+			valid:          true,
+			responseHeader: http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+		}, {
+			msg:            "drop matching value name parameter is case-insensitive",
+			args:           []interface{}{"x-test-name", "bar"},
+			valid:          true,
+			responseHeader: http.Header{"X-Test-Name": []string{"foo", "bar", "baz"}},
+			expectedHeader: http.Header{"X-Test-Name": []string{"foo", "baz"}},
 		}},
 		"setContextRequestHeader": {{
 			msg:            "set request header from context",
@@ -282,11 +323,12 @@ func TestHeader(t *testing.T) {
 			valid:          true,
 			expectedHeader: http.Header{"X-Test-Request-Foo": []string{"bar"}},
 		}, {
-			msg:     "set request host header from context",
-			args:    []interface{}{"Host", "foo"},
-			context: map[string]interface{}{"foo": "www.example.org"},
-			valid:   true,
-			host:    "www.example.org",
+			msg:            "set request host header from context",
+			args:           []interface{}{"Host", "foo"},
+			context:        map[string]interface{}{"foo": "www.example.org"},
+			valid:          true,
+			host:           "www.example.org",
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "name parameter is case-insensitive",
 			args:           []interface{}{"x-test-foo", "foo"},
@@ -302,11 +344,12 @@ func TestHeader(t *testing.T) {
 			requestHeader:  http.Header{"X-Test-Foo": []string{"bar"}},
 			expectedHeader: http.Header{"X-Test-Request-Foo": []string{"bar", "baz"}},
 		}, {
-			msg:     "append request host header from context",
-			args:    []interface{}{"Host", "foo"},
-			context: map[string]interface{}{"foo": "www.example.org"},
-			valid:   true,
-			host:    "www.example.org",
+			msg:            "append request host header from context",
+			args:           []interface{}{"Host", "foo"},
+			context:        map[string]interface{}{"foo": "www.example.org"},
+			valid:          true,
+			host:           "www.example.org",
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "name parameter is case-insensitive",
 			args:           []interface{}{"x-test-foo", "foo"},
@@ -356,9 +399,10 @@ func TestHeader(t *testing.T) {
 			msg:  "invalid target header name",
 			args: []interface{}{"X-Test-Foo", 42},
 		}, {
-			msg:   "no header to copy",
-			args:  []interface{}{"X-Test-Foo", "X-Test-Bar"},
-			valid: true,
+			msg:            "no header to copy",
+			args:           []interface{}{"X-Test-Foo", "X-Test-Bar"},
+			valid:          true,
+			expectedHeader: http.Header{},
 		}, {
 			msg:           "copy header",
 			args:          []interface{}{"X-Test-Foo", "X-Test-Bar"},
@@ -414,9 +458,10 @@ func TestHeader(t *testing.T) {
 			msg:  "invalid target header name",
 			args: []interface{}{"X-Test-Foo", 42},
 		}, {
-			msg:   "no header to copy",
-			args:  []interface{}{"X-Test-Foo", "X-Test-Bar"},
-			valid: true,
+			msg:            "no header to copy",
+			args:           []interface{}{"X-Test-Foo", "X-Test-Bar"},
+			valid:          true,
+			expectedHeader: http.Header{},
 		}, {
 			msg:            "copy header",
 			args:           []interface{}{"X-Test-Foo", "X-Test-Bar"},

filters/builtin/headerfilter.go

@@ -2,6 +2,8 @@ package builtin
 
 import (
 	"fmt"
+	"net/textproto"
+	"slices"
 	"strings"
 
 	"github.com/zalando/skipper/eskip"
@@ -47,7 +49,7 @@ type headerFilter struct {
 func headerFilterConfig(typ headerType, config []interface{}) (string, string, *eskip.Template, error) {
 	switch typ {
 	case dropRequestHeader, dropResponseHeader:
-		if len(config) != 1 {
+		if len(config) < 1 || len(config) > 2 {
 			return "", "", nil, filters.ErrInvalidFilterParameters
 		}
 	default:
@@ -281,7 +283,12 @@ func (f *headerFilter) Request(ctx filters.FilterContext) {
 			ctx.SetOutgoingHost(f.value)
 		}
 	case dropRequestHeader:
-		header.Del(f.key)
+		if f.value == "" {
+			header.Del(f.key)
+		} else {
+			k := textproto.CanonicalMIMEHeaderKey(f.key)
+			header[k] = slices.DeleteFunc(header[k], func(v string) bool { return v == f.value })
+		}
 	case setContextRequestHeader:
 		valueFromContext(ctx, f.key, f.value, true, header.Set)
 	case appendContextRequestHeader:
@@ -313,7 +320,12 @@ func (f *headerFilter) Response(ctx filters.FilterContext) {
 	case depResponseHeader:
 		header.Add(f.key, f.value)
 	case dropResponseHeader:
-		header.Del(f.key)
+		if f.value == "" {
+			header.Del(f.key)
+		} else {
+			k := textproto.CanonicalMIMEHeaderKey(f.key)
+			header[k] = slices.DeleteFunc(header[k], func(v string) bool { return v == f.value })
+		}
 	case setContextResponseHeader:
 		valueFromContext(ctx, f.key, f.value, false, header.Set)
 	case appendContextResponseHeader: