Add Link header with xRegistry root URL to all API responses

registry/httpStuff.go

@@ -3436,6 +3436,7 @@ func HTTPProxy(w http.ResponseWriter, r *http.Request) {
 	w.Header().Add("Access-Control-Allow-Origin", "*")
 	w.Header().Add("Access-Control-Allow-Methods",
 		"GET, PATCH, POST, PUT, DELETE")
+	w.Header().Add("Link", fmt.Sprintf("<http://%s>;rel=xregistry-root", r.Host))
 
 	html := GenerateUI(info, data)
 	w.Write(html)
@@ -3456,6 +3457,30 @@ func HTTPWriteError(info *RequestInfo, errAny any) {
 	if info.GetHeader("Content-Type") == "" {
 		info.SetHeader("Content-Type", "application/json; charset=utf-8")
 	}
+	// Add or replace Link header with xregistry-root rel
+	// Check if there's already a Link header with rel=xregistry-root
+	linkValue := fmt.Sprintf("<%s>;rel=xregistry-root", info.BaseURL)
+	existingLinks := info.GetHeaderValues("Link")
+	hasXRegistryLink := false
+	for i, v := range existingLinks {
+		// Check if this Link header has rel=xregistry-root
+		if strings.Contains(v, "rel=xregistry-root") || strings.Contains(v, "rel=\"xregistry-root\"") {
+			// Replace it with the current value
+			existingLinks[i] = linkValue
+			hasXRegistryLink = true
+			break
+		}
+	}
+	if hasXRegistryLink {
+		// Clear all Link headers and re-add them with the updated value
+		info.OriginalResponse.Header().Del("Link")
+		for _, v := range existingLinks {
+			info.AddHeader("Link", v)
+		}
+	} else {
+		// No existing xregistry-root link, just add it
+		info.AddHeader("Link", linkValue)
+	}
 
 	for k, v := range xErr.Headers {
 		info.AddHeader(k, v)

registry/info.go

@@ -266,6 +266,7 @@ func ParseRequest(tx *Tx, w http.ResponseWriter, r *http.Request) (*RequestInfo,
 	w.Header().Add("Access-Control-Allow-Origin", "*")
 	w.Header().Add("Access-Control-Allow-Methods",
 		"GET, PATCH, POST, PUT, DELETE")
+	w.Header().Add("Link", fmt.Sprintf("<%s>;rel=xregistry-root", info.BaseURL))
 
 	if log.GetVerbose() > 2 {
 		defer func() { log.Printf("Info:\n%s\n", ToJSON(info)) }()

tests/http3_test.go

@@ -2779,6 +2779,59 @@ func TestHTTPVersWithResLevel(t *testing.T) {
 `)
 }
 
+func TestHTTPLinkHeader(t *testing.T) {
+	reg := NewRegistry("TestHTTPLinkHeader")
+	defer PassDeleteReg(t, reg)
+
+	// Test Link header on registry root GET
+	XCheckHTTP(t, reg, &HTTPTest{
+		Name:       "Link header on registry root",
+		URL:        "/",
+		Method:     "GET",
+		ReqHeaders: []string{},
+		ReqBody:    "",
+
+		Code:       200,
+		ResHeaders: []string{"Link:<http://localhost:8181>;rel=xregistry-root"},
+		ResBody:    "*",
+	})
+
+	// Test Link header on error response
+	XCheckHTTP(t, reg, &HTTPTest{
+		Name:       "Link header on error",
+		URL:        "/notfound",
+		Method:     "GET",
+		ReqHeaders: []string{},
+		ReqBody:    "",
+
+		Code:       404,
+		ResHeaders: []string{"Link:<http://localhost:8181>;rel=xregistry-root"},
+		ResBody:    "*",
+	})
+
+	// Test Link header with non-default registry (reg- prefix)
+	XCheckHTTP(t, reg, &HTTPTest{
+		Name:       "Link header with reg- prefix",
+		URL:        "/reg-TestHTTPLinkHeader",
+		Method:     "GET",
+		ReqHeaders: []string{},
+		ReqBody:    "",
+
+		Code:       200,
+		ResHeaders: []string{"Link:<http://localhost:8181/reg-TestHTTPLinkHeader>;rel=xregistry-root"},
+		ResBody:    "*",
+	})
+
+	// Test to ensure Link header doesn't appear twice in error cases
+	res := XDoHTTP(t, reg, "GET", "/notfound", "")
+	linkHeaders := res.Header.Values("Link")
+	XCheck(t, len(linkHeaders) == 1,
+		"Link header should appear exactly once, got %d occurrences: %v",
+		len(linkHeaders), linkHeaders)
+	XEqual(t, "Link header value",
+		linkHeaders[0], "<http://localhost:8181>;rel=xregistry-root")
+}
+
 func TestHTTPIgnore(t *testing.T) {
 	reg := NewRegistry("TestHTTPIgnore")
 	defer PassDeleteReg(t, reg)

tests/misc_test.go

@@ -149,6 +149,16 @@ func TestMiscCORS(t *testing.T) {
 		XEqual(t, "cors header",
 			res.Header.Get("Access-Control-Allow-Methods"),
 			"GET, PATCH, POST, PUT, DELETE")
+
+		linkHeader := res.Header.Get("Link")
+		XCheck(t, linkHeader != "", "Link header should be present for %s %s", test.method, test.url)
+
+		expectedURL := "http://localhost:8181"
+		if test.url == "/reg-TestMiscCORS" {
+			expectedURL = "http://localhost:8181/reg-TestMiscCORS"
+		}
+		XEqual(t, "link header",
+			linkHeader, fmt.Sprintf("<%s>;rel=xregistry-root", expectedURL))
 	}
 }
 

todo

@@ -136,7 +136,6 @@ TODOs:
 - make model changes via API show up in modelsource
 - ban model changes that turn on hasDoc if Resources have RESOURCE* attribute
   extension names
-- support Link: <URL-TO-XREGISTRY-ROOT>;rel=xregistry-root http header
 - make sure ?defaultversionid only processed on write ops (bad_flag)
 - look for more bad_request error that we can specialize
 - add tests for setting modelsource with $include stuff - and upload data at the same time