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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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1 changed files with 193 additions and 66 deletions
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84
tests/ModelContextProtocol.Tests/Configuration/McpServerBuilderExtensionsPromptsTests.cs
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@ -6,12 +6,13 @@ using ModelContextProtocol.Protocol.Messages;
using ModelContextProtocol.Protocol.Transport;
using ModelContextProtocol.Protocol.Types;
using ModelContextProtocol.Server;
using ModelContextProtocol.Tests.Transport;
using ModelContextProtocol.Tests.Utils;
using System.ComponentModel;
using System.IO.Pipelines;
using System.Threading.Channels;
#pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
namespace ModelContextProtocol.Tests.Configuration;
public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposable
@ -28,7 +29,70 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
{
ServiceCollection sc = new();
sc.AddSingleton(LoggerFactory);
_builder = sc.AddMcpServer().WithStdioServerTransport().WithPrompts<SimplePrompts>();
_builder = sc
.AddMcpServer()
.WithStdioServerTransport()
.WithListPromptsHandler(async (request, cancellationToken) =>
{
var cursor = request.Params?.Cursor;
switch (cursor)
{
case null:
return new()
{
NextCursor = "abc",
Prompts = [new()
{
Name = "FirstCustomPrompt",
Description = "First prompt returned by custom handler",
}],
};
case "abc":
return new()
{
NextCursor = "def",
Prompts = [new()
{
Name = "SecondCustomPrompt",
Description = "Second prompt returned by custom handler",
}],
};
case "def":
return new()
{
NextCursor = null,
Prompts = [new()
{
Name = "FinalCustomPrompt",
Description = "Final prompt returned by custom handler",
}],
};
default:
throw new Exception("Unexpected cursor");
}
})
.WithGetPromptHandler(async (request, cancellationToken) =>
{
switch (request.Params?.Name)
{
case "FirstCustomPrompt":
case "SecondCustomPrompt":
case "FinalCustomPrompt":
return new GetPromptResult()
{
Messages = [new() { Role = Role.User, Content = new() { Text = $"hello from {request.Params.Name}", Type = "text" } }],
};
default:
throw new Exception($"Unknown prompt '{request.Params?.Name}'");
}
})
.WithPrompts<SimplePrompts>();
// Call WithStdioServerTransport to get the IMcpServer registration, then overwrite default transport with a pipe transport.
sc.AddSingleton<ITransport>(new StreamServerTransport(_clientToServerPipe.Reader.AsStream(), _serverToClientPipe.Writer.AsStream(), loggerFactory: LoggerFactory));
sc.AddSingleton(new ObjectWithId());
@ -85,7 +149,7 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
IMcpClient client = await CreateMcpClientForServer();
var prompts = await client.ListPromptsAsync(TestContext.Current.CancellationToken);
Assert.Equal(3, prompts.Count);
Assert.Equal(6, prompts.Count);
var prompt = prompts.First(t => t.Name == nameof(SimplePrompts.ReturnsChatMessages));
Assert.Equal("Returns chat messages", prompt.Description);
@ -98,6 +162,14 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
Assert.Equal(2, chatMessages.Count);
Assert.Equal("The prompt is: hello", chatMessages[0].Text);
Assert.Equal("Summarize.", chatMessages[1].Text);
prompt = prompts.First(t => t.Name == "SecondCustomPrompt");
Assert.Equal("Second prompt returned by custom handler", prompt.Description);
result = await prompt.GetAsync(cancellationToken: TestContext.Current.CancellationToken);
chatMessages = result.ToChatMessages();
Assert.NotNull(chatMessages);
Assert.Single(chatMessages);
Assert.Equal("hello from SecondCustomPrompt", chatMessages[0].Text);
}
[Fact]
@ -106,7 +178,7 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
IMcpClient client = await CreateMcpClientForServer();
var prompts = await client.ListPromptsAsync(TestContext.Current.CancellationToken);
Assert.Equal(3, prompts.Count);
Assert.Equal(6, prompts.Count);
Channel<JsonRpcNotification> listChanged = Channel.CreateUnbounded<JsonRpcNotification>();
client.AddNotificationHandler("notifications/prompts/list_changed", notification =>
@ -127,7 +199,7 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
await notificationRead;
prompts = await client.ListPromptsAsync(TestContext.Current.CancellationToken);
Assert.Equal(4, prompts.Count);
Assert.Equal(7, prompts.Count);
Assert.Contains(prompts, t => t.Name == "NewPrompt");
notificationRead = listChanged.Reader.ReadAsync(TestContext.Current.CancellationToken);
@ -136,7 +208,7 @@ public class McpServerBuilderExtensionsPromptsTests : LoggedTest, IAsyncDisposab
await notificationRead;
prompts = await client.ListPromptsAsync(TestContext.Current.CancellationToken);
Assert.Equal(3, prompts.Count);
Assert.Equal(6, prompts.Count);
Assert.DoesNotContain(prompts, t => t.Name == "NewPrompt");
}