HCL relative_url() function

CHANGELOG.md

@@ -6,7 +6,8 @@ Unreleased changes are available as `avenga/couper:edge` container.
 
 * **Added**
   * Register `default` function as `coalesce` alias ([#356](https://github.com/avenga/couper/pull/356))
-
+  * New HCL function [`relative_url()`](./docs/REFERENCE.md#functions) ([#361](https://github.com/avenga/couper/pull/361))
+
 * **Fixed**
   * Handling of [`accept_forwarded_url`](./docs/REFERENCE.md#settings-block) "host" if `H-Forwarded-Host` request header field contains a port ([#360](https://github.com/avenga/couper/pull/360))
   * Setting `Vary` response header fields for [CORS](./doc/REFERENCE.md#cors-block) ([#362](https://github.com/avenga/couper/pull/362))

docs/REFERENCE.md

@@ -670,6 +670,7 @@ To access the HTTP status code of the `default` response use `backend_responses.
 | `merge`                        | object or tuple | Deep-merges two or more of either objects or tuples. `null` arguments are ignored. A `null` attribute value in an object removes the previous attribute value. An attribute value with a different type than the current value is set as the new value. `merge()` with no parameters returns `null`. | `arg...` (object or tuple)          | `merge(request.headers, { x-additional = "myval" })` |
 | `beta_oauth_authorization_url` | string          | Creates an OAuth2 authorization URL from a referenced [OAuth2 AC Block](#oauth2-ac-block-beta) or [OIDC Block](#oidc-block-beta).                                                                                                                                                                                                      | `label` (string)                    | `beta_oauth_authorization_url("myOAuth2")`           |
 | `beta_oauth_verifier`          | string          | Creates a cryptographically random key as specified in RFC 7636, applicable for all verifier methods; e.g. to be set as a cookie and read into `verifier_value`. Multiple calls of this function in the same client request context return the same value.                                           |                                     | `beta_oauth_verifier()`                         |
+| `relative_url`                 | string          | Returns a relative URL by retaining `path`, `query` and `fragment` components.  The input URL `s` must begin with `/<path>`, `//<authority>`, `http://` or `https://`, otherwise an error is thrown. | s (string) | `relative_url("https://httpbin.org/anything?query#fragment") // returns "/anything?query#fragment"` |
 | `saml_sso_url`                 | string          | Creates a SAML SingleSignOn URL (including the `SAMLRequest` parameter) from a referenced [SAML Block](#saml-block).                                                                                                                                                                                 | `label` (string)                    | `saml_sso_url("mySAML")`                             |
 | `to_lower`                     | string          | Converts a given string to lowercase.                                                                                                                                                                                                                                                                | `s` (string)                        | `to_lower(request.cookies.name)`                     |
 | `to_upper`                     | string          | Converts a given string to uppercase.                                                                                                                                                                                                                                                                | `s` (string)                        | `to_upper("CamelCase")`                              |

eval/context.go

@@ -498,6 +498,7 @@ func newFunctionsMap() map[string]function.Function {
 		"json_decode":   stdlib.JSONDecodeFunc,
 		"json_encode":   stdlib.JSONEncodeFunc,
 		"merge":         lib.MergeFunc,
+		"relative_url":  lib.RelativeUrlFunc,
 		"to_lower":      stdlib.LowerFunc,
 		"to_upper":      stdlib.UpperFunc,
 		"unixtime":      lib.UnixtimeFunc,

eval/lib/url.go

@@ -1,15 +1,20 @@
 package lib
 
 import (
+	"fmt"
 	"net/url"
+	"regexp"
 	"strings"
 
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/function"
 )
 
 var (
-	UrlEncodeFunc = newUrlEncodeFunction()
+	// https://datatracker.ietf.org/doc/html/rfc3986#page-50
+	regexParseURL   = regexp.MustCompile(`^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?`)
+	UrlEncodeFunc   = newUrlEncodeFunction()
+	RelativeUrlFunc = newRelativeUrlFunction()
 )
 
 func newUrlEncodeFunction() function.Function {
@@ -38,3 +43,35 @@ func AbsoluteURL(urlRef string, origin *url.URL) (string, error) {
 	}
 	return urlRef, nil
 }
+
+func newRelativeUrlFunction() function.Function {
+	return function.New(&function.Spec{
+		Params: []function.Parameter{{
+			Name: "s",
+			Type: cty.String,
+		}},
+		Type: function.StaticReturnType(cty.String),
+		Impl: func(args []cty.Value, _ cty.Type) (ret cty.Value, err error) {
+			absURL := strings.TrimSpace(args[0].AsString())
+
+			if !strings.HasPrefix(absURL, "/") && !strings.HasPrefix(absURL, "http://") && !strings.HasPrefix(absURL, "https://") {
+				return cty.StringVal(""), fmt.Errorf("invalid url given: %q", absURL)
+			}
+
+			// Do not use the result of url.Parse() to preserve the # character in an emtpy fragment.
+			if _, err := url.Parse(absURL); err != nil {
+				return cty.StringVal(""), err
+			}
+
+			// The regexParseURL garanties the len of 10 in the result.
+			urlParts := regexParseURL.FindStringSubmatch(absURL)
+
+			// The path must begin w/ a slash.
+			if !strings.HasPrefix(urlParts[5], "/") {
+				urlParts[5] = "/" + urlParts[5]
+			}
+
+			return cty.StringVal(urlParts[5] + urlParts[6] + urlParts[8]), nil
+		},
+	})
+}

eval/lib/url_test.go

@@ -1,6 +1,7 @@
 package lib_test
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/zclconf/go-cty/cty"
@@ -33,3 +34,71 @@ func TestUrlEncode(t *testing.T) {
 		t.Errorf("Wrong return value; expected %s, got: %s", expected, encoded)
 	}
 }
+
+func TestRelativeUrl(t *testing.T) {
+	helper := test.New(t)
+
+	cf, err := configload.LoadBytes([]byte(`server "test" {}`), "couper.hcl")
+	helper.Must(err)
+
+	hclContext := cf.Context.Value(request.ContextType).(*eval.Context).HCLContext()
+	relativeUrlFunc := hclContext.Functions["relative_url"]
+
+	type testCase struct {
+		url    string
+		expURL string
+		expErr string
+	}
+
+	for _, tc := range []testCase{
+		// Invalid
+		{"", "", `invalid url given: ""`},
+		{"rel", "", `invalid url given: "rel"`},
+		{"?q", "", `invalid url given: "?q"`},
+		{"?", "", `invalid url given: "?"`},
+		{"#f", "", `invalid url given: "#f"`},
+		{"#", "", `invalid url given: "#"`},
+		{"~", "", `invalid url given: "~"`},
+		{"abc@def.org", "", `invalid url given: "abc@def.org"`},
+		{"ftp://127.0.0.1", "", `invalid url given: "ftp://127.0.0.1"`},
+
+		// Valid
+		{"/abs", "/abs", ``},
+		{"//path", "/", ``},
+		{"///path", "/path", ``},
+		{"/abs:8080", "/abs:8080", ``},
+		{"https://abc.def:8443:9443", "/", ``},
+		{"http://", "/", ``},
+		{"http://abc", "/", ``},
+		{"http://abc.def", "/", ``},
+		{"http://abc.def?", "/?", ``},
+		{"http://abc.def#", "/#", ``},
+		{"http://abc.def/#", "/#", ``},
+		{"http://abc.def?#", "/?#", ``},
+		{"http://abc.def/?#", "/?#", ``},
+		{"https://abc.def/path", "/path", ``},
+		{"https://abc.def/path?a+b", "/path?a+b", ``},
+		{"https://abc.def/path?a%20b", "/path?a%20b", ``},
+		{"https://abc.def:8443/path?q", "/path?q", ``},
+		{"https://abc.def:8443/path?q#f", "/path?q#f", ``},
+		{"https://user:pass@abc.def:8443/path?q#f", "/path?q#f", ``},
+		{"//user:pass@abc.def:8443/path?q#f", "/path?q#f", ``},
+		{"//abc.def:8443/path?q#f", "/path?q#f", ``},
+	} {
+		t.Run(tc.url, func(subT *testing.T) {
+			got, err := relativeUrlFunc.Call([]cty.Value{cty.StringVal(tc.url)})
+
+			if tc.expURL != "" && got.AsString() != tc.expURL {
+				t.Errorf("'%#v': expected %q, got %q", tc.url, tc.expURL, got.AsString())
+			}
+			if got != cty.NilVal && tc.expURL == "" {
+				t.Errorf("'%#v': expected 'cty.NilVal', got %q", tc.url, got.AsString())
+			}
+			if tc.expErr != "" || err != nil {
+				if eerr := fmt.Sprintf("%s", err); tc.expErr != eerr {
+					t.Errorf("'%#v': expected %q, got %q", tc.url, tc.expErr, eerr)
+				}
+			}
+		})
+	}
+}