rest/request: skip empty strings in values of Access-Control-Request-…

…Headers

WebKit browsers may send a preflight CORS request setting
Access-Control-Request-Headers to an empty value, what is in turn interpreted as
an empty string on Golang's http server side. An example scenario that triggers
this behavior in Chrome is doing a xhr POST request and setting progress
callback. Request headers reported by browser's developer tools are then the
following:

:authority:docker.mender.io:8080
:method:OPTIONS
:path:/api/integrations/0.1/deployments/images
:scheme:https
accept:*/*
accept-encoding:gzip, deflate, sdch, br
accept-language:en-US,en;q=0.8,pl;q=0.6
access-control-request-headers:      <--- empty value here
access-control-request-method:POST
dnt:1
origin:http://localhost:9999
referer:http://localhost:9999/test.html
user-agent:Mozilla/5.0 (X11; Linux x86_64) ...

It is unclear whether in such case, the client wants to send no headers in the
actual request or just a bug in client's code.

Since the original request is cured and repacked into CorsInfo it makes sense to
skip Access-Control-Request-Headers values that are empty.

Signed-off-by: Maciej Borzecki <maciej.borzecki@rndity.com>

rest/request.go

@@ -120,6 +120,9 @@ func (r *Request) GetCorsInfo() *CorsInfo {
 	reqHeaders := []string{}
 	rawReqHeaders := r.Header[http.CanonicalHeaderKey("Access-Control-Request-Headers")]
 	for _, rawReqHeader := range rawReqHeaders {
+		if len(rawReqHeader) == 0 {
+			continue
+		}
 		// net/http does not handle comma delimited headers for us
 		for _, reqHeader := range strings.Split(rawReqHeader, ",") {
 			reqHeaders = append(reqHeaders, http.CanonicalHeaderKey(strings.TrimSpace(reqHeader)))

rest/request_test.go

@@ -148,3 +148,41 @@ func TestCorsInfoPreflightCors(t *testing.T) {
 		t.Error("OriginUrl must be set")
 	}
 }
+
+func TestCorsInfoEmptyAccessControlRequestHeaders(t *testing.T) {
+	req := defaultRequest("OPTIONS", "http://localhost", nil, t)
+	req.Request.Header.Set("Origin", "http://another.host")
+
+	// make it a preflight request
+	req.Request.Header.Set("Access-Control-Request-Method", "PUT")
+
+	// WebKit based browsers may send `Access-Control-Request-Headers:` with
+	// no value, in which case, the header will be present in requests
+	// Header map, but its value is an empty string.
+	req.Request.Header.Set("Access-Control-Request-Headers", "")
+	corsInfo := req.GetCorsInfo()
+	if corsInfo == nil {
+		t.Error("Expected non nil CorsInfo")
+	}
+	if corsInfo.IsCors == false {
+		t.Error("This is a CORS request")
+	}
+	if len(corsInfo.AccessControlRequestHeaders) > 0 {
+		t.Error("Access-Control-Request-Headers should have been removed")
+	}
+
+	req.Request.Header.Set("Access-Control-Request-Headers", "")
+	corsInfo = req.GetCorsInfo()
+	if corsInfo == nil {
+		t.Error("Expected non nil CorsInfo")
+	}
+	if corsInfo.IsCors == false {
+		t.Error("This is a CORS request")
+	}
+	if corsInfo.IsPreflight == false {
+		t.Error("This is a Preflight request")
+	}
+	if len(corsInfo.AccessControlRequestHeaders) > 0 {
+		t.Error("Empty Access-Control-Request-Headers header should have been removed")
+	}
+}