Fix Collabora: Fetch versioned editor URL from discovery endpoint

- Added getCollaboraEditorURL() to fetch correct /browser/{version}/cool.html path
- Cache discovery response for 5 minutes to avoid repeated requests
- Fixed 'Invalid URI' error caused by version mismatch

go_cloud/internal/http/wopi_handlers.go

@@ -2,6 +2,7 @@ package http
 
 import (
 	"encoding/json"
+	"encoding/xml"
 	"fmt"
 	"io"
 	"net/http"
@@ -21,6 +22,89 @@ import (
 	"go.b0esche.cloud/backend/pkg/jwt"
 )
 
+// Collabora discovery cache
+var (
+	collaboraEditorURL      string
+	collaboraDiscoveryCache time.Time
+	collaboraDiscoveryMu    sync.RWMutex
+)
+
+// getCollaboraEditorURL fetches the editor URL from Collabora's discovery endpoint
+func getCollaboraEditorURL(collaboraBaseURL string) string {
+	collaboraDiscoveryMu.RLock()
+	// Cache for 5 minutes
+	if collaboraEditorURL != "" && time.Since(collaboraDiscoveryCache) < 5*time.Minute {
+		url := collaboraEditorURL
+		collaboraDiscoveryMu.RUnlock()
+		return url
+	}
+	collaboraDiscoveryMu.RUnlock()
+
+	// Fetch discovery
+	collaboraDiscoveryMu.Lock()
+	defer collaboraDiscoveryMu.Unlock()
+
+	// Double-check after acquiring write lock
+	if collaboraEditorURL != "" && time.Since(collaboraDiscoveryCache) < 5*time.Minute {
+		return collaboraEditorURL
+	}
+
+	discoveryURL := collaboraBaseURL + "/hosting/discovery"
+	resp, err := http.Get(discoveryURL)
+	if err != nil {
+		fmt.Printf("[COLLABORA] Failed to fetch discovery: %v\n", err)
+		// Fallback to guessed URL
+		return collaboraBaseURL + "/browser/dist/cool.html"
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		fmt.Printf("[COLLABORA] Failed to read discovery: %v\n", err)
+		return collaboraBaseURL + "/browser/dist/cool.html"
+	}
+
+	// Parse XML to extract urlsrc
+	type Action struct {
+		Name   string `xml:"name,attr"`
+		Ext    string `xml:"ext,attr"`
+		URLSrc string `xml:"urlsrc,attr"`
+	}
+	type App struct {
+		Name    string   `xml:"name,attr"`
+		Actions []Action `xml:"action"`
+	}
+	type NetZone struct {
+		Apps []App `xml:"app"`
+	}
+	type WopiDiscovery struct {
+		NetZone NetZone `xml:"net-zone"`
+	}
+
+	var discovery WopiDiscovery
+	if err := xml.Unmarshal(body, &discovery); err != nil {
+		fmt.Printf("[COLLABORA] Failed to parse discovery XML: %v\n", err)
+		return collaboraBaseURL + "/browser/dist/cool.html"
+	}
+
+	// Find the first edit action URL (they all have the same base)
+	for _, app := range discovery.NetZone.Apps {
+		for _, action := range app.Actions {
+			if action.URLSrc != "" {
+				// Extract base URL (remove query string marker)
+				url := strings.TrimSuffix(action.URLSrc, "?")
+				collaboraEditorURL = url
+				collaboraDiscoveryCache = time.Now()
+				fmt.Printf("[COLLABORA] Discovered editor URL: %s\n", url)
+				return url
+			}
+		}
+	}
+
+	fmt.Printf("[COLLABORA] No editor URL found in discovery\n")
+	return collaboraBaseURL + "/browser/dist/cool.html"
+}
+
 // WOPILockManager manages file locks to prevent concurrent editing conflicts
 type WOPILockManager struct {
 	locks map[string]*models.WOPILockInfo
@@ -665,6 +749,9 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
 	// Build WOPISrc URL (without access_token - that goes in a separate form field)
 	wopiSrc := fmt.Sprintf("https://go.b0esche.cloud/wopi/files/%s", fileID)
 
+	// Get the correct Collabora editor URL from discovery (includes version hash)
+	editorURL := getCollaboraEditorURL(collaboraURL)
+
 	// Return HTML page with auto-submitting form
 	// The form POSTs to Collabora from within an iframe to work around CSP frame-ancestors restrictions
 	// The iframe is hosted on the same domain as the embedded page, allowing the POST to complete
@@ -684,7 +771,7 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
   <div class="loading">
     <p>Loading Collabora Online...</p>
   </div>
-  <form method="POST" action="%s/browser/dist/cool.html" target="_self" id="collaboraForm" style="display: none;">
+  <form method="POST" action="%s" target="_self" id="collaboraForm" style="display: none;">
     <input type="hidden" name="WOPISrc" value="%s">
     <input type="hidden" name="access_token" value="%s">
   </form>
@@ -692,19 +779,19 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
     // Auto-submit the form to Collabora
     var form = document.getElementById('collaboraForm');
     if (form) {
-      console.log('[COLLABORA] Submitting form to /browser/dist/cool.html');
+      console.log('[COLLABORA] Submitting form to %s');
       form.submit();
     } else {
       console.error('[COLLABORA] Form not found');
     }
   </script>
 </body>
-</html>`, collaboraURL, wopiSrc, accessToken)
+</html>`, editorURL, wopiSrc, accessToken, editorURL)
 
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	// Don't set X-Frame-Options - this endpoint is meant to be loaded in an iframe
 	w.WriteHeader(http.StatusOK)
 	w.Write([]byte(htmlContent))
 
-	fmt.Printf("[COLLABORA-PROXY] Served HTML form: file=%s user=%s wopi_src=%s\n", fileID, userID.String(), wopiSrc)
+	fmt.Printf("[COLLABORA-PROXY] Served HTML form: file=%s user=%s wopi_src=%s editor_url=%s\n", fileID, userID.String(), wopiSrc, editorURL)
 }