Show descriptive error when Fanout is not enabled #116

Open
Open
Show descriptive error when Fanout is not enabled#116

Description

@serra-fastly
serra-fastly
opened on Aug 18, 2026

Summary

When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.

Expected behavior

When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:

"Fanout or WebSockets are not enabled on this service; please contact support for help"

Current behavior

The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.

Reference implementations

Go SDK: fastly/compute-sdk-go#275
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Show descriptive error when Fanout is not enabled #116
      Open
      Open
      Show descriptive error when Fanout is not enabled#116
      Description
      @serra-fastly
      serra-fastly
      opened on Aug 18, 2026
      Summary
      When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
      Expected behavior
      When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
      "Fanout or WebSockets are not enabled on this service; please contact support for help"
      Current behavior
      The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
      Reference implementations
      Go SDK: fastly/compute-sdk-go#275
      
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
      Activity
      Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
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          None yet
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Show descriptive error when Fanout is not enabled #116
          Open
          Open
          Show descriptive error when Fanout is not enabled#116
          Description
          @serra-fastly
          serra-fastly
          opened on Aug 18, 2026
          Summary
          When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
          Expected behavior
          When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
          "Fanout or WebSockets are not enabled on this service; please contact support for help"
          Current behavior
          The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
          Reference implementations
          Go SDK: fastly/compute-sdk-go#275
          
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
          Activity
          Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
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          Metadata
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              No milestone
              Relationships
              None yet
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              No branches or pull requests
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Show descriptive error when Fanout is not enabled #116
              Open
              Open
              Show descriptive error when Fanout is not enabled#116
              Description
              @serra-fastly
              serra-fastly
              opened on Aug 18, 2026
              Summary
              When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
              Expected behavior
              When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
              "Fanout or WebSockets are not enabled on this service; please contact support for help"
              Current behavior
              The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
              Reference implementations
              Go SDK: fastly/compute-sdk-go#275
              
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
              Activity
              Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
              Metadata
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              Assignees
              No one assigned
                Labels
                No labels
                No labels
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                No type
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                  No milestone
                  Relationships
                  None yet
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                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Show descriptive error when Fanout is not enabled #116
                  Open
                  Open
                  Show descriptive error when Fanout is not enabled#116
                  Description
                  @serra-fastly
                  serra-fastly
                  opened on Aug 18, 2026
                  Summary
                  When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
                  Expected behavior
                  When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
                  "Fanout or WebSockets are not enabled on this service; please contact support for help"
                  Current behavior
                  The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
                  Reference implementations
                  Go SDK: fastly/compute-sdk-go#275
                  
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
                  Activity
                  Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    No labels
                    No labels
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Show descriptive error when Fanout is not enabled #116
                      Open
                      Open
                      Show descriptive error when Fanout is not enabled#116
                      Description
                      @serra-fastly
                      serra-fastly
                      opened on Aug 18, 2026
                      Summary
                      When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
                      Expected behavior
                      When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
                      "Fanout or WebSockets are not enabled on this service; please contact support for help"
                      Current behavior
                      The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
                      Reference implementations
                      Go SDK: fastly/compute-sdk-go#275
                      
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
                      Activity
                      Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        No labels
                        No labels
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Show descriptive error when Fanout is not enabled #116
                          Open
                          Open
                          Show descriptive error when Fanout is not enabled#116
                          Description
                          @serra-fastly
                          serra-fastly
                          opened on Aug 18, 2026
                          Summary
                          When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
                          Expected behavior
                          When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
                          "Fanout or WebSockets are not enabled on this service; please contact support for help"
                          Current behavior
                          The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
                          Reference implementations
                          Go SDK: fastly/compute-sdk-go#275
                          
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
                          Activity
                          Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            No labels
                            No labels
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                            No type
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                              Skip to content
                              Show descriptive error when Fanout is not enabled #116
                              Open
                              Open
                              Show descriptive error when Fanout is not enabled#116
                              Description
                              @serra-fastly
                              serra-fastly
                              opened on Aug 18, 2026
                              Summary
                              When handoff_fanout / createFanoutHandoff is called on a service that does not have Fanout enabled, the platform now returns a specific status code indicating the feature is not available. The SDK should catch this and surface a clear, actionable error message to the developer rather than a generic/opaque failure.
                              Expected behavior
                              When a developer calls the fanout handoff on a service without Fanout enabled, they should receive an error with a message like:
                              "Fanout or WebSockets are not enabled on this service; please contact support for help"
                              Current behavior
                              The SDK returns a generic error (or empty error) with no indication of what went wrong or how to fix it.
                              Reference implementations
                              Go SDK: fastly/compute-sdk-go#275
                              
Checks for the Unsupported status from the redirect_to_grip_proxy / redirect_to_websocket_proxy hostcalls and return a specific error variant with the descriptive message.
                              Activity
                              Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                              Metadata
                              Metadata
                              Assignees
                              No one assigned
                                Labels
                                No labels
                                No labels
                                Type
                                No type
                                Projects
                                No projects
                                  Milestone
                                  No milestone
                                  Relationships
                                  None yet
                                  Development
                                  No branches or pull requests
                                  Issue actions