Fix go-sdk integration: content types, error messages, pagination, tool annotations by Copilot · Pull Request #2647 · github/gh-aw-mcpg

Copilot · 2026-03-27T14:53:43Z

Four issues identified in the Go Fan audit of modelcontextprotocol/go-sdk usage — one bug causing silent data loss, three enhancements.

Bug: Non-text content silently dropped (`internal/mcp/tool_result.go`)

ConvertToCallToolResult only parsed type+text fields, so image, audio, and resource content items were replaced with empty TextContent. Now properly converts to sdk.ImageContent, sdk.AudioContent, and sdk.EmbeddedResource:

// Before: image/audio/resource hit the default case → &sdk.TextContent{Text: ""}
// After:
case "image":
    content = append(content, &sdk.ImageContent{Data: item.Data, MIMEType: item.MIMEType})
case "audio":
    content = append(content, &sdk.AudioContent{Data: item.Data, MIMEType: item.MIMEType})
case "resource":
    content = append(content, &sdk.EmbeddedResource{Resource: &sdk.ResourceContents{...}})

Data []byte auto-decodes from the base64-encoded JSON field via Go's standard JSON unmarshaler.

Error results now include message (`internal/server/unified.go`)

newErrorCallToolResult returned IsError: true with no content, leaving MCP clients with no explanation. Now includes the error as TextContent.

Paginated list methods (`internal/mcp/connection.go`)

listTools, listResources, and listPrompts each made a single call, silently dropping tools/resources/prompts beyond the first page. All three now loop on NextCursor until exhausted. First-page result used as initial slice capacity to reduce allocations.

Forward tool annotations (`internal/server/tool_registry.go`)

Backend tool Annotations (readOnlyHint, destructiveHint, openWorldHint, etc.) were not captured during tools/list parsing. Now forwarded through to the registered sdk.Tool and stored in ToolInfo.

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-build1361167601/b330/launcher.test /tmp/go-build1361167601/b330/launcher.test -test.testlogfile=/tmp/go-build1361167601/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true -c=4 -nolocalimports -importcfg /tmp/go-build1361167601/b311/importcfg -pack /home/REDACTED/work/gh-aw-mcpg/gh-aw-mcpg/internal/middleware/jqschema.go _linux_amd64.o 64/s�� 64/src/runtime/c-p lzHvcSTIL ache/go/1.25.8/x-lang=go1.25 (dns block)
- Triggering command: /tmp/go-build1147003510/b330/launcher.test /tmp/go-build1147003510/b330/launcher.test -test.testlogfile=/tmp/go-build1147003510/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -I ache/go/1.25.8/x64/src/net -I docker-buildx --gdwarf-5 --64 -o docker-buildx (dns block)
- Triggering command: /tmp/go-build1286029736/b330/launcher.test /tmp/go-build1286029736/b330/launcher.test -test.testlogfile=/tmp/go-build1286029736/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -V=f�� (dns block)
invalid-host-that-does-not-exist-12345.com
- Triggering command: /tmp/go-build1361167601/b315/config.test /tmp/go-build1361167601/b315/config.test -test.testlogfile=/tmp/go-build1361167601/b315/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true go ternal/fips140/r--64 64/pkg/tool/linu-o (dns block)
- Triggering command: /tmp/go-build3971546875/b315/config.test /tmp/go-build3971546875/b315/config.test -test.testlogfile=/tmp/go-build3971546875/b315/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true ports/wasi_snapshot_preview1/args.go ports/wasi_snapshot_preview1/clock.go x_amd64/compile -p encoding -lang=go1.25 x_amd64/compile go_.�� ache/go/1.25.8/x64/src/runtime/c-errorsas ache/go/1.25.8/x64/src/crypto/de-ifaceassert x_amd64/vet -I ions =0 x_amd64/vet (dns block)
- Triggering command: /tmp/go-build1147003510/b315/config.test /tmp/go-build1147003510/b315/config.test -test.testlogfile=/tmp/go-build1147003510/b315/testlog.txt -test.paniconexit0 -test.timeout=10m0s 1167�� /opt/hostedtoolcache/go/1.25.8/x64/src/runtime/c-p 1167601/b165/ .cfg --gdwarf-5 --64 -o as estl�� ache/go/1.25.8/x64/src/net --debug-prefix-map .cfg -I /opt/hostedtoolc--norc -I ache/go/1.25.8/x64/pkg/tool/linu-buildtags (dns block)
nonexistent.local
- Triggering command: /tmp/go-build1361167601/b330/launcher.test /tmp/go-build1361167601/b330/launcher.test -test.testlogfile=/tmp/go-build1361167601/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true -c=4 -nolocalimports -importcfg /tmp/go-build1361167601/b311/importcfg -pack /home/REDACTED/work/gh-aw-mcpg/gh-aw-mcpg/internal/middleware/jqschema.go _linux_amd64.o 64/s�� 64/src/runtime/c-p lzHvcSTIL ache/go/1.25.8/x-lang=go1.25 (dns block)
- Triggering command: /tmp/go-build1147003510/b330/launcher.test /tmp/go-build1147003510/b330/launcher.test -test.testlogfile=/tmp/go-build1147003510/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -I ache/go/1.25.8/x64/src/net -I docker-buildx --gdwarf-5 --64 -o docker-buildx (dns block)
- Triggering command: /tmp/go-build1286029736/b330/launcher.test /tmp/go-build1286029736/b330/launcher.test -test.testlogfile=/tmp/go-build1286029736/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -V=f�� (dns block)
slow.example.com
- Triggering command: /tmp/go-build1361167601/b330/launcher.test /tmp/go-build1361167601/b330/launcher.test -test.testlogfile=/tmp/go-build1361167601/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true -c=4 -nolocalimports -importcfg /tmp/go-build1361167601/b311/importcfg -pack /home/REDACTED/work/gh-aw-mcpg/gh-aw-mcpg/internal/middleware/jqschema.go _linux_amd64.o 64/s�� 64/src/runtime/c-p lzHvcSTIL ache/go/1.25.8/x-lang=go1.25 (dns block)
- Triggering command: /tmp/go-build1147003510/b330/launcher.test /tmp/go-build1147003510/b330/launcher.test -test.testlogfile=/tmp/go-build1147003510/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -I ache/go/1.25.8/x64/src/net -I docker-buildx --gdwarf-5 --64 -o docker-buildx (dns block)
- Triggering command: /tmp/go-build1286029736/b330/launcher.test /tmp/go-build1286029736/b330/launcher.test -test.testlogfile=/tmp/go-build1286029736/b330/testlog.txt -test.paniconexit0 -test.timeout=10m0s -V=f�� (dns block)
this-host-does-not-exist-12345.com
- Triggering command: /tmp/go-build1361167601/b339/mcp.test /tmp/go-build1361167601/b339/mcp.test -test.testlogfile=/tmp/go-build1361167601/b339/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true 64/src/runtime/cgo 64/src/vendor/golang.org/x/text/--64 64/pkg/tool/linux_amd64/vet (dns block)
- Triggering command: /tmp/go-build1147003510/b339/mcp.test /tmp/go-build1147003510/b339/mcp.test -test.testlogfile=/tmp/go-build1147003510/b339/testlog.txt -test.paniconexit0 -test.timeout=10m0s (dns block)
- Triggering command: /tmp/go-build1286029736/b339/mcp.test /tmp/go-build1286029736/b339/mcp.test -test.testlogfile=/tmp/go-build1286029736/b339/testlog.txt -test.paniconexit0 -test.timeout=10m0s -uns�� -unreachable=false /tmp/go-build1361167601/b221/vet.cfg ache/go/1.25.8/x64/pkg/tool/linux_amd64/vet go ternal/fips140/a10 64/pkg/tool/linu--64 ache/go/1.25.8/x64/pkg/tool/linux_amd64/vet -qE (create|run) 64/pkg/tool/linu-I ker/cli-plugins/docker-compose go lang.org/x/text/cat-file x_amd64/vet ker/cli-plugins/blob (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)

💬 Send tasks to Copilot coding agent from Slack and Teams to turn conversations into code. Copilot posts an update in your thread when it's finished.

… pagination, and tool annotations Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/12ad1499-dedf-449f-906b-7ec1b9be9ada Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

…llocation Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/12ad1499-dedf-449f-906b-7ec1b9be9ada Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot

Pull request overview

This PR fixes several MCP gateway integration gaps with modelcontextprotocol/go-sdk, focusing on preserving non-text tool content, improving client-visible tool errors, correctly handling paginated list endpoints, and forwarding tool annotations from backend servers.

Changes:

Fix ConvertToCallToolResult to correctly map backend image, audio, and resource content items into SDK content types (instead of silently producing empty text).
Include error messages as TextContent in error CallToolResults so MCP clients receive actionable failure details.
Implement cursor-based pagination loops for tools/resources/prompts listing, aggregating all pages.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/server/unified.go	Adds ToolInfo annotations field and includes error message text content in error CallToolResult helper.
internal/server/tool_registry.go	Parses backend tool annotations and forwards them into stored ToolInfo and registered sdk.Tool objects.
internal/server/call_tool_result_test.go	Extends tests to assert error message content is present in error CallToolResult.
internal/mcp/tool_result.go	Adds conversion support for image/audio/resource content items in backend tool results.
internal/mcp/tool_result_test.go	Adds coverage for image/audio/resource conversion and adjusts unknown-type behavior test.
internal/mcp/connection.go	Fixes silent truncation by fetching all pages for listTools/listResources/listPrompts via NextCursor.

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Copilot · 2026-03-27T15:21:23Z

 func newErrorCallToolResult(err error) (*sdk.CallToolResult, interface{}, error) {
-	return &sdk.CallToolResult{IsError: true}, nil, err
+	return &sdk.CallToolResult{
+		IsError: true,
+		Content: []sdk.Content{
+			&sdk.TextContent{Text: err.Error()},
+		},
+	}, nil, err


newErrorCallToolResult dereferences err via err.Error() without guarding against a nil error. If this helper is ever called with nil (even accidentally), it will panic. Consider enforcing non-nil (e.g., return a generic error/result when err==nil) or changing the signature/contract to guarantee err is non-nil.

Copilot · 2026-03-27T15:21:23Z

 	Name        string
 	Description string
 	InputSchema map[string]interface{}
+	Annotations *sdk.ToolAnnotations
 	BackendID   string // Which backend this tool belongs to


ToolInfo now stores Annotations, but routed mode builds per-backend servers from ToolInfo (see createFilteredServer in internal/server/routed.go) and currently does not set sdk.Tool.Annotations when registering those tools. As a result, clients using routed mode still won't receive tool annotations in tools/list. Please plumb ToolInfo.Annotations through when creating the filtered server's sdk.Tool.

Copilot · 2026-03-27T15:21:23Z

+	cursor := first.NextCursor
+	for cursor != "" {
+		result, err := c.getSDKSession().ListTools(c.ctx, &sdk.ListToolsParams{Cursor: cursor})
+		if err != nil {
+			return nil, err
 		}
-		return result, err
-	})
+		allTools = append(allTools, result.Tools...)
+		logConn.Printf("listTools: received page of %d tools (total so far: %d) from serverID=%s", len(result.Tools), len(allTools), c.serverID)
+		cursor = result.NextCursor
+	}


Pagination logic for tools/resources/prompts now loops on NextCursor, but there are no tests asserting that multi-page results are fully aggregated. Given connection.go already has extensive transport/method-dispatch tests, please add coverage that stubs a session returning multiple pages and verifies listTools/listResources/listPrompts return the full combined set.

Initial plan

20539d7

Copilot AI assigned Copilot and lpcox Mar 27, 2026

Copilot started work on behalf of lpcox March 27, 2026 14:53 View session

Copilot AI linked an issue Mar 27, 2026 that may be closed by this pull request

[go-fan] Go Module Review: modelcontextprotocol/go-sdk #2633

Closed

6 tasks

Copilot AI and others added 2 commits March 27, 2026 15:03

Fix go-sdk integration: image/audio/resource content, error messages,…

7c03aa9

… pagination, and tool annotations Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/12ad1499-dedf-449f-906b-7ec1b9be9ada Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Address code review: fix Data field comment, improve pagination pre-a…

38e9d2b

…llocation Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/12ad1499-dedf-449f-906b-7ec1b9be9ada Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Review Go SDK module for Model Context Protocol~~ Fix go-sdk integration: content types, error messages, pagination, tool annotations Mar 27, 2026

Copilot finished work on behalf of lpcox March 27, 2026 15:08

Copilot AI requested a review from lpcox March 27, 2026 15:08

lpcox marked this pull request as ready for review March 27, 2026 15:16

Copilot AI review requested due to automatic review settings March 27, 2026 15:16

lpcox merged commit 972510c into main Mar 27, 2026
21 of 22 checks passed

lpcox deleted the copilot/go-fan-review-go-sdk-module branch March 27, 2026 15:16

Copilot started reviewing on behalf of lpcox March 27, 2026 15:17 View session

Copilot AI reviewed Mar 27, 2026

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Fix go-sdk integration: content types, error messages, pagination, tool annotations#2647

Fix go-sdk integration: content types, error messages, pagination, tool annotations#2647
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Copilot AI commented Mar 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Bug: Non-text content silently dropped (internal/mcp/tool_result.go)

Error results now include message (internal/server/unified.go)

Paginated list methods (internal/mcp/connection.go)

Forward tool annotations (internal/server/tool_registry.go)

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

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Copilot AI commented Mar 27, 2026 •

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Bug: Non-text content silently dropped (`internal/mcp/tool_result.go`)

Error results now include message (`internal/server/unified.go`)

Paginated list methods (`internal/mcp/connection.go`)

Forward tool annotations (`internal/server/tool_registry.go`)