httpserver: Placeholder for response header fields (#2029)

* Allow Response Headers in logs

* Remove log line

* remove unneeded log import

* Check if rr is nil.  Added test to check

* merge if statements

* remove temp file

caddyhttp/httpserver/replacer.go

@@ -224,6 +224,16 @@ func (r *replacer) getSubstitution(key string) string {
 			}
 		}
 	}
+	// search response headers then
+	if r.responseRecorder != nil && key[1] == '<' {
+		want := key[2 : len(key)-1]
+		for key, values := range r.responseRecorder.Header() {
+			// Header placeholders (case-insensitive)
+			if strings.EqualFold(key, want) {
+				return strings.Join(values, ",")
+			}
+		}
+	}
 	// next check for cookies
 	if key[1] == '~' {
 		name := key[2 : len(key)-1]

caddyhttp/httpserver/replacer_test.go

@@ -67,6 +67,9 @@ func TestReplace(t *testing.T) {
 	request.Header.Set("CustomAdd", "caddy")
 	request.Header.Set("Cookie", "foo=bar; taste=delicious")
 
+	// add some respons headers
+	recordRequest.Header().Set("Custom", "CustomResponseHeader")
+
 	hostname, err := os.Hostname()
 	if err != nil {
 		t.Fatalf("Failed to determine hostname: %v", err)
@@ -92,10 +95,13 @@ func TestReplace(t *testing.T) {
 		{"{when_unix}", "1136214252"},
 		{"The Custom header is {>Custom}.", "The Custom header is foobarbaz."},
 		{"The CustomAdd header is {>CustomAdd}.", "The CustomAdd header is caddy."},
+		{"The Custom response header is {<Custom}.", "The Custom response header is CustomResponseHeader."},
+		{"Bad {>Custom placeholder", "Bad {>Custom placeholder"},
 		{"The request is {request}.", "The request is POST /?foo=bar HTTP/1.1\\r\\nHost: localhost\\r\\n" +
 			"Cookie: foo=bar; taste=delicious\\r\\nCustom: foobarbaz\\r\\nCustomadd: caddy\\r\\n" +
 			"Shorterval: 1\\r\\n\\r\\n."},
 		{"The cUsToM header is {>cUsToM}...", "The cUsToM header is foobarbaz..."},
+		{"The cUsToM response header is {<CuSTom}.", "The cUsToM response header is CustomResponseHeader."},
 		{"The Non-Existent header is {>Non-Existent}.", "The Non-Existent header is -."},
 		{"Bad {host placeholder...", "Bad {host placeholder..."},
 		{"Bad {>Custom placeholder", "Bad {>Custom placeholder"},
@@ -138,6 +144,43 @@ func TestReplace(t *testing.T) {
 	}
 }
 
+func TestResponseRecorderNil(t *testing.T) {
+
+	reader := strings.NewReader(`{"username": "dennis"}`)
+
+	request, err := http.NewRequest("POST", "http://localhost/?foo=bar", reader)
+	if err != nil {
+		t.Fatalf("Failed to make request: %v", err)
+	}
+
+	request.Header.Set("Custom", "foobarbaz")
+	repl := NewReplacer(request, nil, "-")
+	// add some headers after creating replacer
+	request.Header.Set("CustomAdd", "caddy")
+	request.Header.Set("Cookie", "foo=bar; taste=delicious")
+
+	old := now
+	now = func() time.Time {
+		return time.Date(2006, 1, 2, 15, 4, 5, 02, time.FixedZone("hardcoded", -7))
+	}
+	defer func() {
+		now = old
+	}()
+	testCases := []struct {
+		template string
+		expect   string
+	}{
+		{"The Custom response header is {<Custom}.", "The Custom response header is -."},
+	}
+
+	for _, c := range testCases {
+		if expected, actual := c.expect, repl.Replace(c.template); expected != actual {
+			t.Errorf("for template '%s', expected '%s', got '%s'", c.template, expected, actual)
+		}
+	}
+
+}
+
 func TestSet(t *testing.T) {
 	w := httptest.NewRecorder()
 	recordRequest := NewResponseRecorder(w)