implement default values for header directive

closes caddyserver#3804

modules/caddyhttp/headers/caddyfile.go

@@ -30,8 +30,9 @@ func init() {
 // parseCaddyfile sets up the handler for response headers from
 // Caddyfile tokens. Syntax:
 //
-//     header [<matcher>] [[+|-]<field> [<value|regexp>] [<replacement>]] {
+//     header [<matcher>] [[+|-|?]<field> [<value|regexp>] [<replacement>]] {
 //         [+]<field> [<value|regexp> [<replacement>]]
+//         ?<field> <default_value>
 //         -<field>
 //         [defer]
 //     }
@@ -102,7 +103,7 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 // parseReqHdrCaddyfile sets up the handler for request headers
 // from Caddyfile tokens. Syntax:
 //
-//     request_header [<matcher>] [[+|-]<field> [<value|regexp>] [<replacement>]]
+//     request_header [<matcher>] [[+|-|?]<field> [<value|regexp>] [<replacement>]]
 //
 func parseReqHdrCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
 	hdr := new(Handler)
@@ -142,12 +143,12 @@ func parseReqHdrCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler,
 
 // CaddyfileHeaderOp applies a new header operation according to
 // field, value, and replacement. The field can be prefixed with
-// "+" or "-" to specify adding or removing; otherwise, the value
-// will be set (overriding any previous value). If replacement is
-// non-empty, value will be treated as a regular expression which
-// will be used to search and then replacement will be used to
-// complete the substring replacement; in that case, any + or -
-// prefix to field will be ignored.
+// "+", "-" or "?" to specify adding, removing or setting a default
+// value; otherwise, the value will be set (overriding any previous
+// value). If replacement is non-empty, value will be treated as a
+// regular expression which will be used to search and then replacement
+// will be used to complete the substring replacement; in that case,
+// any "+", "-" or "?" prefix to field will be ignored.
 func CaddyfileHeaderOp(ops *HeaderOps, field, value, replacement string) {
 	if strings.HasPrefix(field, "+") {
 		if ops.Add == nil {
@@ -156,6 +157,11 @@ func CaddyfileHeaderOp(ops *HeaderOps, field, value, replacement string) {
 		ops.Add.Set(field[1:], value)
 	} else if strings.HasPrefix(field, "-") {
 		ops.Delete = append(ops.Delete, field[1:])
+	} else if strings.HasPrefix(field, "?") {
+		if ops.SetDefault == nil {
+			ops.SetDefault = make(http.Header)
+		}
+		ops.SetDefault.Set(field[1:], value)
 	} else {
 		if replacement == "" {
 			if ops.Set == nil {
@@ -166,7 +172,7 @@ func CaddyfileHeaderOp(ops *HeaderOps, field, value, replacement string) {
 			if ops.Replace == nil {
 				ops.Replace = make(map[string][]Replacement)
 			}
-			field = strings.TrimLeft(field, "+-")
+			field = strings.TrimLeft(field, "+-?")
 			ops.Replace[field] = append(
 				ops.Replace[field],
 				Replacement{

modules/caddyhttp/headers/headers.go

@@ -118,6 +118,9 @@ type HeaderOps struct {
 	// Sets HTTP headers; replaces existing header fields.
 	Set http.Header `json:"set,omitempty"`
 
+	// Sets a default value for HTTP headers.
+	SetDefault http.Header `json:"set_default,omitempty"`
+
 	// Names of HTTP header fields to delete.
 	Delete []string `json:"delete,omitempty"`
 
@@ -206,6 +209,18 @@ func (ops HeaderOps) ApplyTo(hdr http.Header, repl *caddy.Replacer) {
 		hdr.Set(fieldName, strings.Join(newVals, ","))
 	}
 
+	// set default
+	for fieldName, vals := range ops.SetDefault {
+		fieldName = repl.ReplaceAll(fieldName, "")
+		if hdr.Get(fieldName) != "" {
+			continue
+		}
+
+		for _, v := range vals {
+			hdr.Add(fieldName, repl.ReplaceAll(v, ""))
+		}
+	}
+
 	// delete
 	for _, fieldName := range ops.Delete {
 		hdr.Del(repl.ReplaceAll(fieldName, ""))

modules/caddyhttp/headers/headers_test.go

@@ -14,8 +14,125 @@
 
 package headers
 
-import "testing"
+import (
+	"context"
+	"net/http"
+	"reflect"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2"
+)
 
 func TestReqHeaders(t *testing.T) {
 	// TODO: write tests
 }
+
+func TestHeaderOps(t *testing.T) {
+	for i, tc := range []struct {
+		headerOps HeaderOps
+		input     http.Header
+		expected  http.Header
+	}{
+		{
+			headerOps: HeaderOps{
+				Add: http.Header{
+					"Expose-Secrets": []string{"always"},
+				},
+			},
+			input: http.Header{
+				"Expose-Secrets": []string{"i'm serious"},
+			},
+			expected: http.Header{
+				"Expose-Secrets": []string{"i'm serious", "always"},
+			},
+		},
+		{
+			headerOps: HeaderOps{
+				Set: http.Header{
+					"Who-Wins": []string{"batman"},
+				},
+			},
+			input: http.Header{
+				"Who-Wins": []string{"joker"},
+			},
+			expected: http.Header{
+				"Who-Wins": []string{"batman"},
+			},
+		},
+		{
+			headerOps: HeaderOps{
+				SetDefault: http.Header{
+					"Cache-Control": []string{"default"},
+				},
+			},
+			input: http.Header{
+				"Not-Cache-Control": []string{"cache-cache"},
+			},
+			expected: http.Header{
+				"Cache-Control":     []string{"default"},
+				"Not-Cache-Control": []string{"cache-cache"},
+			},
+		},
+		{
+			headerOps: HeaderOps{
+				SetDefault: http.Header{
+					"Cache-Control": []string{"no-store"},
+				},
+			},
+			input: http.Header{
+				"Cache-Control": []string{"max-age=3600"},
+			},
+			expected: http.Header{
+				"Cache-Control": []string{"max-age=3600"},
+			},
+		},
+		{
+			headerOps: HeaderOps{
+				Delete: []string{"Kick-Me"},
+			},
+			input: http.Header{
+				"Kick-Me": []string{"if you can"},
+				"Keep-Me": []string{"i swear i'm innocent"},
+			},
+			expected: http.Header{
+				"Keep-Me": []string{"i swear i'm innocent"},
+			},
+		},
+		{
+			headerOps: HeaderOps{
+				Replace: map[string][]Replacement{
+					"Best-Server": []Replacement{
+						Replacement{
+							Search:  "NGINX",
+							Replace: "the Caddy web server",
+						},
+						Replacement{
+							SearchRegexp: `Apache(\d+)`,
+							Replace:      "Caddy",
+						},
+					},
+				},
+			},
+			input: http.Header{
+				"Best-Server": []string{"it's NGINX, undoubtedly", "I love Apache2"},
+			},
+			expected: http.Header{
+				"Best-Server": []string{"it's the Caddy web server, undoubtedly", "I love Caddy"},
+			},
+		},
+	} {
+		req := &http.Request{Header: tc.input}
+		repl := caddy.NewReplacer()
+		ctx := context.WithValue(req.Context(), caddy.ReplacerCtxKey, repl)
+		req = req.WithContext(ctx)
+
+		tc.headerOps.Provision(caddy.Context{})
+		tc.headerOps.ApplyToRequest(req)
+		actual := req.Header
+
+		if !reflect.DeepEqual(actual, tc.expected) {
+			t.Errorf("Test %d: Expected %v, got %v", i, tc.expected, actual)
+			continue
+		}
+	}
+}