fix: disable standalone SSE stream in streamable HTTP transport to prevent HTTP MCP server startup failures by Copilot · Pull Request #4428 · github/gh-aw-mcpg

Copilot · 2026-04-23T22:39:11Z

HTTP MCP servers (e.g. Unwrap) show status: error at gateway startup and advertise no tools to Copilot CLI, despite the endpoint being reachable.

Root cause

The SDK's StreamableClientTransport automatically issues a GET request for a persistent SSE stream synchronously inside client.Connect(), immediately after the initialize POST succeeds:

POST initialize → server responds ✓
sessionUpdated() → connectStandaloneSSE() → GET request
Server returns 5xx (or any non-4xx/non-405) → c.fail() marks connection as broken
client.Connect() tries to send initialized notification → c.Write() sees failure → returns error
All three transports fail → recordError() → /health reports status: error

Additionally, MaxRetries: 0 in the SDK defaults to 5 retries, not 0, contrary to the existing comment.

Changes

internal/mcp/http_transport.go / connection.go: Set DisableStandaloneSSE: true and MaxRetries: -1 on StreamableClientTransport in both tryStreamableHTTPTransport and reconnectSDKTransport. The gateway is a request-response proxy and has no use for server-initiated SSE notifications from backends.

return &sdk.StreamableClientTransport{
    Endpoint:             url,
    HTTPClient:           httpClient,
    MaxRetries:           -1, // Disable retries (-1 = 0 retries; SDK treats 0 as "use default: 5")
    DisableStandaloneSSE: true,
}

internal/mcp/http_connection_test.go: Adds regression test TestNewHTTPConnection_StreamableTransport_BadSSEEndpoint — server returns valid initialize result for POST but 500 for GET; connection must succeed via streamable transport with zero GET requests issued.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

example.com
- Triggering command: /tmp/go-build900524329/b513/launcher.test /tmp/go-build900524329/b513/launcher.test -test.testlogfile=/tmp/go-build900524329/b513/testlog.txt -test.paniconexit0 -test.timeout=10m0s /tmp/go-build900524329/b410/vet.cfg g_.a o_.o x_amd64/vet 01.o roundrobin 03.o x_amd64/vet -W wkO_kTNLT .cfg x_amd64/vet . --gdwarf2 --64 x_amd64/vet (dns block)
invalid-host-that-does-not-exist-12345.com
- Triggering command: /tmp/go-build900524329/b495/config.test /tmp/go-build900524329/b495/config.test -test.testlogfile=/tmp/go-build900524329/b495/testlog.txt -test.paniconexit0 -test.timeout=10m0s /tmp/go-build900524329/b399/vet.cfg g_.a 9742532/b151/ x_amd64/vet --gdwarf-5 grpcsync p=/opt/hostedtoolcache/go/1.25.9/tmp/go-build511290287/b107/vet.cfg x_amd64/vet -W ABSZSCNGR .cfg x_amd64/vet . --gdwarf2 --64 x_amd64/vet (dns block)
nonexistent.local
- Triggering command: /tmp/go-build900524329/b513/launcher.test /tmp/go-build900524329/b513/launcher.test -test.testlogfile=/tmp/go-build900524329/b513/testlog.txt -test.paniconexit0 -test.timeout=10m0s /tmp/go-build900524329/b410/vet.cfg g_.a o_.o x_amd64/vet 01.o roundrobin 03.o x_amd64/vet -W wkO_kTNLT .cfg x_amd64/vet . --gdwarf2 --64 x_amd64/vet (dns block)
slow.example.com
- Triggering command: /tmp/go-build900524329/b513/launcher.test /tmp/go-build900524329/b513/launcher.test -test.testlogfile=/tmp/go-build900524329/b513/testlog.txt -test.paniconexit0 -test.timeout=10m0s /tmp/go-build900524329/b410/vet.cfg g_.a o_.o x_amd64/vet 01.o roundrobin 03.o x_amd64/vet -W wkO_kTNLT .cfg x_amd64/vet . --gdwarf2 --64 x_amd64/vet (dns block)
this-host-does-not-exist-12345.com
- Triggering command: /tmp/go-build3852249779/b001/mcp.test /tmp/go-build3852249779/b001/mcp.test -test.testlogfile=/tmp/go-build3852249779/b001/testlog.txt -test.paniconexit0 -test.run=TestNewHTTPConnection|TestHTTPConnection -test.v=true -test.timeout=1m0s 0/internal/tracetransform/instrumentation.go x_amd64/compile OUTPUT 9742532/b015/ 168.63.129.16 x_amd64/compile -w p/go-build security 64=/_/GOROOT OUTPUT 64/src/runtime/c-unsafeptr=false 168.63.129.16 git (dns block)
- Triggering command: /tmp/go-build900524329/b522/mcp.test /tmp/go-build900524329/b522/mcp.test -test.testlogfile=/tmp/go-build900524329/b522/testlog.txt -test.paniconexit0 -test.timeout=10m0s 9742�� olang.org/protob-errorsas .cfg x_amd64/vet --gdwarf-5 --64 -o x_amd64/vet -o 9742532/b408/_pk-s -trimpath x_amd64/vet -p g/grpc/binarylog/usr/bin/runc -lang=go1.25 x_amd64/vet (dns block)
- Triggering command: /tmp/go-build3289280713/b001/mcp.test /tmp/go-build3289280713/b001/mcp.test -test.testlogfile=/tmp/go-build3289280713/b001/testlog.txt -test.paniconexit0 -test.run=TestNewHTTPConnection -test.v=true -test.timeout=1m0s y bin/bash ntime.v2.task/mogit .cfg x_amd64/vet /usr/bin/runc.original --ve�� 30977974af8f49f3088e082efdf88695 runtime-runc/moby /usr/local/bin/iptables io.containerd.ru/bin/sh .cfg x_amd64/vet b83/log.json (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

…revent startup failures Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/b3a7a4cf-4e3a-41da-90f0-b7c5624d2a27 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

…name variable Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/b3a7a4cf-4e3a-41da-90f0-b7c5624d2a27 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot

Pull request overview

Disables the SDK’s standalone SSE GET stream (and implicit retries) for streamable HTTP transports to prevent MCP HTTP backends from causing gateway startup/connect failures, and adds a regression test for the failure mode.

Changes:

Configure sdk.StreamableClientTransport with DisableStandaloneSSE: true and MaxRetries: -1 on initial connect.
Apply the same streamable transport configuration during SDK transport reconnects.
Add a regression test ensuring no SSE GET is issued when the server would error on GET.

Show a summary per file

File	Description
internal/mcp/http_transport.go	Disables standalone SSE and SDK retries for streamable HTTP transport creation.
internal/mcp/connection.go	Ensures reconnect path uses the same streamable transport settings (no SSE GET, no retries).
internal/mcp/http_connection_test.go	Adds regression test asserting streamable connect succeeds without issuing any GET requests.

Copilot's findings

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Files reviewed: 3/3 changed files
Comments generated: 1

+	getMethodCount := 0
+
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == http.MethodGet {
+			// Simulate a server that returns 500 for the SSE GET stream.
+			// Before the fix this would call c.fail() and break the connection;
+			// after the fix the GET is never issued.
+			getMethodCount++
+			w.WriteHeader(http.StatusInternalServerError)


lpcox · 2026-04-23T23:10:51Z

@copilot address this review feedback #4428 (review)

Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/cc87c7cf-5340-4ef1-bedc-58d9feaffc20 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot · 2026-04-23T23:12:46Z

@copilot address this review feedback #4428 (review)

Fixed in fc18b1e — replaced the plain int with atomic.Int32 (increment via .Add(1), read via .Load()). The test now passes cleanly under -race.

Initial plan

3a6a67f

Copilot AI assigned Copilot and lpcox Apr 23, 2026

Copilot started work on behalf of lpcox April 23, 2026 22:39 View session

Copilot AI linked an issue Apr 23, 2026 that may be closed by this pull request

HTTP MCP server enters error state on startup; tools never advertised to Copilot CLI (Unwrap MCP repro) #4418

Closed

Copilot AI and others added 2 commits April 23, 2026 22:55

fix: disable standalone SSE stream for streamable HTTP transport to p…

2156729

…revent startup failures Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/b3a7a4cf-4e3a-41da-90f0-b7c5624d2a27 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

fix: address code review comments - improve MaxRetries comment and re…

7838d27

…name variable Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/b3a7a4cf-4e3a-41da-90f0-b7c5624d2a27 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix HTTP MCP server error state on startup~~ fix: disable standalone SSE stream in streamable HTTP transport to prevent HTTP MCP server startup failures Apr 23, 2026

Copilot finished work on behalf of lpcox April 23, 2026 22:57

Copilot AI requested a review from lpcox April 23, 2026 22:57

lpcox marked this pull request as ready for review April 23, 2026 23:06

Copilot AI review requested due to automatic review settings April 23, 2026 23:06

Copilot started reviewing on behalf of lpcox April 23, 2026 23:06 View session

Copilot AI reviewed Apr 23, 2026

View reviewed changes

Copilot started work on behalf of lpcox April 23, 2026 23:11 View session

fix: use atomic.Int32 for getMethodCount to prevent data race in test

fc18b1e

Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/cc87c7cf-5340-4ef1-bedc-58d9feaffc20 Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot finished work on behalf of lpcox April 23, 2026 23:13

lpcox merged commit 6332c79 into main Apr 23, 2026
10 of 11 checks passed

lpcox deleted the copilot/fix-http-mcp-server-error branch April 23, 2026 23:16

This was referenced Apr 23, 2026

Smoke Test: Copilot - 24863669359 #4441

Closed

Smoke Test: Copilot - 24865897501 #4442

Closed

[ca] CLI Version Updates: Claude Code, Copilot CLI, Codex, GitHub MCP Server, MCP Gateway github/gh-aw#28199

Closed

Copilot AI mentioned this pull request Apr 24, 2026

chore: bump CLI tool versions (Claude Code, Copilot, Codex, MCP Server, MCP Gateway) + fix comment memory rendering + fix Claude install github/gh-aw#28200

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fix: disable standalone SSE stream in streamable HTTP transport to prevent HTTP MCP server startup failures#4428

fix: disable standalone SSE stream in streamable HTTP transport to prevent HTTP MCP server startup failures#4428
lpcox merged 4 commits intomainfrom
copilot/fix-http-mcp-server-error

Copilot AI commented Apr 23, 2026 •

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Copilot AI commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Root cause

Changes

I tried to connect to the following addresses, but was blocked by firewall rules:

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Pull request overview

Copilot's findings

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lpcox commented Apr 23, 2026

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Copilot AI commented Apr 23, 2026 •

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