') + ')', 'gi'); if (regex.test(text)) { found = true; var frag = document.createDocumentFragment(); var parts = text.split(regex); parts.forEach(function(part, i) { if (i % 2 === 0) { frag.appendChild(document.createTextNode(part)); } else { var span = document.createElement('span'); span.className = 'userscript-highlight'; span.textContent = part; frag.appendChild(span); } }); node.parentNode.replaceChild(frag, node); } }); } else if (node.nodeType === 1 && node.childNodes) { // element var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT']; if (!skipTags.includes(node.tagName)) { Array.from(node.childNodes).forEach(highlight); } } } highlight(document.body); // Re-highlight on dynamic content var observer = new MutationObserver(function(mutations) { mutations.forEach(function(m) { m.addedNodes.forEach(function(node) { if (node.nodeType === 1 || node.nodeType === 3) highlight(node); }); }); }); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ', 'i'); if (__m === '*' || __re.test(location.href)) { // Strip utm_, fbclid, gclid, etc. from all links on page (function() { var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content', 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid', 'ref', 'ref_src', 'source', 'medium', 'campaign']; function cleanUrl(url) { try { var u = new URL(url, window.location.origin); var changed = false; trackingParams.forEach(function(p) { if (u.searchParams.has(p)) { u.searchParams.delete(p); changed = true; } }); return changed ? u.toString() : url; } catch (e) { return url; } } function cleanLinks() { document.querySelectorAll('a[href]').forEach(function(a) { var clean = cleanUrl(a.href); if (clean !== a.href) a.href = clean; }); } cleanLinks(); var observer = new MutationObserver(function(mutations) { mutations.forEach(function(m) { m.addedNodes.forEach(function(node) { if (node.nodeType === 1) { if (node.tagName === 'A') cleanLinks(); node.querySelectorAll('a[href]').forEach(function(a) { var clean = cleanUrl(a.href); if (clean !== a.href) a.href = clean; }); } }); }); }); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); } })(); (function(){ try { var __m = "youtube.com"; var __re = new RegExp('^' + "youtube\\.com" + ', 'i'); if (__m === '*' || __re.test(location.href)) { // Auto-enable theater mode on YouTube (function() { function tryTheater() { var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]'); if (btn && !btn.classList.contains('activated')) { btn.click(); } } // Try immediately tryTheater(); // Try after navigation (SPA) var lastUrl = location.href; setInterval(function() { if (location.href !== lastUrl) { lastUrl = location.href; setTimeout(tryTheater, 500); } }, 1000); // Also try on player load var observer = new MutationObserver(tryTheater); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ', 'i'); if (__m === '*' || __re.test(location.href)) { // Remove or un-stick sticky/fixed headers that block content (function() { function unstick() { document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) { if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') { el.style.position = 'static'; el.style.top = 'auto'; el.style.zIndex = 'auto'; } }); } unstick(); var observer = new MutationObserver(unstick); observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] }); })(); } } catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); } })(); })(); fix: call onerror callback for all transport error responses by dpdanpittman · Pull Request #1636 · modelcontextprotocol/typescript-sdk · GitHub
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fix: call onerror callback for all transport error responses - #1636

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dpdanpittman:fix/transport-onerror-callbacks
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fix: call onerror callback for all transport error responses#1636
dpdanpittman wants to merge 1 commit into
modelcontextprotocol:mainfrom
dpdanpittman:fix/transport-onerror-callbacks

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@dpdanpittman

@dpdanpittmandpdanpittman commented Mar 5, 2026

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Several error paths in WebStandardStreamableHTTPServerTransport returned error responses via createJsonErrorResponse() without calling the onerror callback, making these errors unobservable for debugging and logging purposes.

Fixes#1395

Motivation and Context

As described in #1395, nested try/catch blocks in handlePostRequest and other methods return error responses without calling this.onerror?.(). The outer catch block at the end of handlePostRequest does call it, but inner early-return paths bypass it entirely. This makes it impossible to log or observe errors like invalid JSON, bad headers, session validation failures, etc.

The validateRequestHeaders method already correctly calls this.onerror?.() before returning error responses — this PR makes the rest of the codebase consistent with that pattern.

Affected locations:

  • handlePostRequest: Accept header (406), Content-Type (415), invalid JSON (400), invalid JSON-RPC message (400), duplicate initialization (400), batch initialization (400)
  • handleGetRequest: Accept header (406), duplicate SSE stream (409)
  • validateSession: server not initialized (400), missing session ID (400), invalid session ID (404)
  • validateProtocolVersion: unsupported version (400)
  • handleUnsupportedRequest: method not allowed (405)
  • replayEvents: event store not configured (400), invalid event ID (400), stream conflict (409)

How Has This Been Tested?

Added 13 new tests in packages/server/test/server/streamableHttp.test.ts under a new HTTPServerTransport - onerror callback describe block. Each test sets an onerror spy on the transport and verifies it is called with the expected error message for each error condition. All 50 server tests pass. Full test suite passes (383/384 — single failure is a pre-existing Cloudflare Workers timeout unrelated to this change). Lint passes.

Breaking Changes

None. The onerror callback is optional (this.onerror?.()) and this only adds calls where none existed before. Existing code that doesn't set onerror is unaffected.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

@dpdanpittman
fix: call onerror callback for all transport error responses
ef0769e
Several error paths in WebStandardStreamableHTTPServerTransport returned
error responses via createJsonErrorResponse() without calling the
onerror callback, making these errors unobservable for debugging and
logging purposes.
Fixesmodelcontextprotocol#1395
@dpdanpittman
dpdanpittman requested a review from a team as a code ownerMarch 5, 2026 23:04
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commit: 5a6ca4d

@felixweinberger

felixweinberger commented Mar 25, 2026

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Thanks for the contribution! Closing in favor of #1433.

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Successfully merging this pull request may close these issues.

Some transport errors are silently swallowed due to missing onerror callback usage

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@dpdanpittman@felixweinberger