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Fix pagination handling in McpServer (#177)

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- We were adding tools/prompts from the collections on every request. If multiple requests came in with different cursors, we'd re-add the same tools each time.
- We were defeating the purpose of pagination by doing all of the aggregation in the server. If a custom handler returns a paginated result, we should instead propagate that back to the client, who can choose to get more results when needed.
This commit is contained in:
Stephen Toub 2025-04-01 09:54:19 -04:00 • committed by GitHub
commit b12d728700
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3 changed files with 193 additions and 66 deletions
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1
src/ModelContextProtocol/Server/AIFunctionMcpServerTool.cs
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@ -1,7 +1,6 @@
using Microsoft.Extensions.AI;
using Microsoft.Extensions.DependencyInjection;
using ModelContextProtocol.Protocol.Types;
using ModelContextProtocol.Shared;
using ModelContextProtocol.Utils;
using ModelContextProtocol.Utils.Json;
using System.Diagnostics.CodeAnalysis;

61
src/ModelContextProtocol/Server/McpServer.cs
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@ -1,5 +1,4 @@
using Microsoft.Extensions.Logging;
using ModelContextProtocol.Logging;
using ModelContextProtocol.Protocol.Messages;
using ModelContextProtocol.Protocol.Transport;
using ModelContextProtocol.Protocol.Types;
@ -214,41 +213,26 @@ internal sealed class McpServer : McpJsonRpcEndpoint, IMcpServer
throw new McpServerException("ListPrompts and GetPrompt handlers should be specified together.");
}
// Handle tools provided via DI.
// Handle prompts provided via DI.
if (prompts is { IsEmpty: false })
{
// Synthesize the handlers, making sure a PromptsCapability is specified.
var originalListPromptsHandler = listPromptsHandler;
var originalGetPromptHandler = getPromptHandler;
// Synthesize the handlers, making sure a ToolsCapability is specified.
listPromptsHandler = async (request, cancellationToken) =>
{
ListPromptsResult result = new();
foreach (McpServerPrompt prompt in prompts)
{
result.Prompts.Add(prompt.ProtocolPrompt);
}
ListPromptsResult result = originalListPromptsHandler is not null ?
await originalListPromptsHandler(request, cancellationToken).ConfigureAwait(false) :
new();
if (originalListPromptsHandler is not null)
if (request.Params?.Cursor is null)
{
string? nextCursor = null;
do
{
ListPromptsResult extraResults = await originalListPromptsHandler(request, cancellationToken).ConfigureAwait(false);
result.Prompts.AddRange(extraResults.Prompts);
nextCursor = extraResults.NextCursor;
if (nextCursor is not null)
{
request = request with { Params = new() { Cursor = nextCursor } };
}
}
while (nextCursor is not null);
result.Prompts.AddRange(prompts.Select(t => t.ProtocolPrompt));
}
return result;
};
var originalGetPromptHandler = getPromptHandler;
getPromptHandler = (request, cancellationToken) =>
{
if (request.Params is null ||
@ -316,38 +300,23 @@ internal sealed class McpServer : McpJsonRpcEndpoint, IMcpServer
// Handle tools provided via DI.
if (tools is { IsEmpty: false })
{
var originalListToolsHandler = listToolsHandler;
var originalCallToolHandler = callToolHandler;
// Synthesize the handlers, making sure a ToolsCapability is specified.
var originalListToolsHandler = listToolsHandler;
listToolsHandler = async (request, cancellationToken) =>
{
ListToolsResult result = new();
foreach (McpServerTool tool in tools)
{
result.Tools.Add(tool.ProtocolTool);
}
ListToolsResult result = originalListToolsHandler is not null ?
await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false) :
new();
if (originalListToolsHandler is not null)
if (request.Params?.Cursor is null)
{
string? nextCursor = null;
do
{
ListToolsResult extraResults = await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false);
result.Tools.AddRange(extraResults.Tools);
nextCursor = extraResults.NextCursor;
if (nextCursor is not null)
{
request = request with { Params = new() { Cursor = nextCursor } };
}
}
while (nextCursor is not null);
result.Tools.AddRange(tools.Select(t => t.ProtocolTool));
}
return result;
};
var originalCallToolHandler = callToolHandler;
callToolHandler = (request, cancellationToken) =>
{
if (request.Params is null ||

1
src/ModelContextProtocol/TokenProgress.cs
View file

@ -1,6 +1,5 @@
using ModelContextProtocol.Protocol.Messages;
using ModelContextProtocol.Server;
using ModelContextProtocol.Shared;
namespace ModelContextProtocol;