templates: add new relativeURL function

Signed-off-by: Yannis Zarkadas <yanniszark@arrikto.com>

server/templates.go

@@ -6,7 +6,9 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"os"
+	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -94,7 +96,7 @@ func loadWebConfig(c webConfig) (static, theme http.Handler, templates *template
 		c.dir = "./web"
 	}
 	if c.logoURL == "" {
-		c.logoURL = join(c.issuerURL, "theme/logo.png")
+		c.logoURL = "theme/logo.png"
 	}
 
 	if err := dirExists(c.dir); err != nil {
@@ -136,10 +138,15 @@ func loadTemplates(c webConfig, templatesDir string) (*templates, error) {
 		return nil, fmt.Errorf("no files in template dir %q", templatesDir)
 	}
 
+	issuerURL, err := url.Parse(c.issuerURL)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing issuerURL: %v", err)
+	}
+
 	funcs := map[string]interface{}{
 		"issuer": func() string { return c.issuer },
 		"logo":   func() string { return c.logoURL },
-		"url":    func(s string) string { return join(c.issuerURL, s) },
+		"url":    func(reqPath, assetPath string) string { return relativeURL(issuerURL.Path, reqPath, assetPath) },
 		"lower":  strings.ToLower,
 		"extra":  func(k string) string { return c.extra[k] },
 	}
@@ -166,6 +173,69 @@ func loadTemplates(c webConfig, templatesDir string) (*templates, error) {
 	}, nil
 }
 
+// relativeURL returns the URL of the asset relative to the URL of the request path.
+// The serverPath is consulted to trim any prefix due in case it is not listening
+// to the root path.
+//
+// Algorithm:
+// 1. Remove common prefix of serverPath and reqPath
+// 2. Remove common prefix of assetPath and reqPath
+// 3. For each part of reqPath remaining(minus one), go up one level (..)
+// 4. For each part of assetPath remaining, append it to result
+//
+//eg
+//server listens at localhost/dex so serverPath is dex
+//reqPath is /dex/auth
+//assetPath is static/main.css
+//relativeURL("/dex", "/dex/auth", "static/main.css") = "../static/main.css"
+func relativeURL(serverPath, reqPath, assetPath string) string {
+
+	splitPath := func(p string) []string {
+		res := []string{}
+		parts := strings.Split(path.Clean(p), "/")
+		for _, part := range parts {
+			if part != "" {
+				res = append(res, part)
+			}
+		}
+		return res
+	}
+
+	stripCommonParts := func(s1, s2 []string) ([]string, []string) {
+		min := len(s1)
+		if len(s2) < min {
+			min = len(s2)
+		}
+
+		splitIndex := min
+		for i := 0; i < min; i++ {
+			if s1[i] != s2[i] {
+				splitIndex = i
+				break
+			}
+		}
+		return s1[splitIndex:], s2[splitIndex:]
+	}
+
+	server, req, asset := splitPath(serverPath), splitPath(reqPath), splitPath(assetPath)
+
+	// Remove common prefix of request path with server path
+	server, req = stripCommonParts(server, req)
+
+	// Remove common prefix of request path with asset path
+	asset, req = stripCommonParts(asset, req)
+
+	// For each part of the request remaining (minus one) -> go up one level (..)
+	// For each part of the asset remaining               -> append it
+	var relativeURL string
+	for i := 0; i < len(req)-1; i++ {
+		relativeURL = path.Join("..", relativeURL)
+	}
+	relativeURL = path.Join(relativeURL, path.Join(asset...))
+
+	return relativeURL
+}
+
 var scopeDescriptions = map[string]string{
 	"offline_access": "Have offline access",
 	"profile":        "View basic profile information",
@@ -184,26 +254,28 @@ func (n byName) Len() int           { return len(n) }
 func (n byName) Less(i, j int) bool { return n[i].Name < n[j].Name }
 func (n byName) Swap(i, j int)      { n[i], n[j] = n[j], n[i] }
 
-func (t *templates) login(w http.ResponseWriter, connectors []connectorInfo) error {
+func (t *templates) login(r *http.Request, w http.ResponseWriter, connectors []connectorInfo, reqPath string) error {
 	sort.Sort(byName(connectors))
 	data := struct {
 		Connectors []connectorInfo
-	}{connectors}
+		ReqPath    string
+	}{connectors, r.URL.Path}
 	return renderTemplate(w, t.loginTmpl, data)
 }
 
-func (t *templates) password(w http.ResponseWriter, postURL, lastUsername, usernamePrompt string, lastWasInvalid, showBacklink bool) error {
+func (t *templates) password(r *http.Request, w http.ResponseWriter, postURL, lastUsername, usernamePrompt string, lastWasInvalid, showBacklink bool, reqPath string) error {
 	data := struct {
 		PostURL        string
 		BackLink       bool
 		Username       string
 		UsernamePrompt string
 		Invalid        bool
-	}{postURL, showBacklink, lastUsername, usernamePrompt, lastWasInvalid}
+		ReqPath        string
+	}{postURL, showBacklink, lastUsername, usernamePrompt, lastWasInvalid, r.URL.Path}
 	return renderTemplate(w, t.passwordTmpl, data)
 }
 
-func (t *templates) approval(w http.ResponseWriter, authReqID, username, clientName string, scopes []string) error {
+func (t *templates) approval(r *http.Request, w http.ResponseWriter, authReqID, username, clientName string, scopes []string, reqPath string) error {
 	accesses := []string{}
 	for _, scope := range scopes {
 		access, ok := scopeDescriptions[scope]
@@ -217,23 +289,26 @@ func (t *templates) approval(w http.ResponseWriter, authReqID, username, clientN
 		Client    string
 		AuthReqID string
 		Scopes    []string
-	}{username, clientName, authReqID, accesses}
+		ReqPath   string
+	}{username, clientName, authReqID, accesses, r.URL.Path}
 	return renderTemplate(w, t.approvalTmpl, data)
 }
 
-func (t *templates) oob(w http.ResponseWriter, code string) error {
+func (t *templates) oob(r *http.Request, w http.ResponseWriter, code string, reqPath string) error {
 	data := struct {
-		Code string
-	}{code}
+		Code    string
+		ReqPath string
+	}{code, r.URL.Path}
 	return renderTemplate(w, t.oobTmpl, data)
 }
 
-func (t *templates) err(w http.ResponseWriter, errCode int, errMsg string) error {
+func (t *templates) err(r *http.Request, w http.ResponseWriter, errCode int, errMsg string) error {
 	w.WriteHeader(errCode)
 	data := struct {
 		ErrType string
 		ErrMsg  string
-	}{http.StatusText(errCode), errMsg}
+		ReqPath string
+	}{http.StatusText(errCode), errMsg, r.URL.Path}
 	if err := t.errorTmpl.Execute(w, data); err != nil {
 		return fmt.Errorf("Error rendering template %s: %s", t.errorTmpl.Name(), err)
 	}

server/templates_test.go

 package server
+
+import "testing"
+
+func TestRelativeURL(t *testing.T) {
+	tests := []struct {
+		name       string
+		serverPath string
+		reqPath    string
+		assetPath  string
+		expected   string
+	}{
+		{
+			name:       "server-root-req-one-level-asset-two-level",
+			serverPath: "/",
+			reqPath:    "/auth",
+			assetPath:  "/theme/main.css",
+			expected:   "theme/main.css",
+		},
+		{
+			name:       "server-one-level-req-one-level-asset-two-level",
+			serverPath: "/dex",
+			reqPath:    "/dex/auth",
+			assetPath:  "/theme/main.css",
+			expected:   "theme/main.css",
+		},
+		{
+			name:       "server-root-req-two-level-asset-three-level",
+			serverPath: "/dex",
+			reqPath:    "/dex/auth/connector",
+			assetPath:  "assets/css/main.css",
+			expected:   "../assets/css/main.css",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			actual := relativeURL(test.serverPath, test.reqPath, test.assetPath)
+			if actual != test.expected {
+				t.Fatalf("Got '%s'. Expected '%s'", actual, test.expected)
+			}
+		})
+	}
+}