SseMcpTransport

Namespace: Vercel.AI.Mcp

public sealed class SseMcpTransport : IMcpTransport, IDisposable

MCP over the legacy HTTP+SSE transport. StartAsync(CancellationToken) opens a GET event stream, waits for the endpoint event, then CancellationToken) posts JSON-RPC messages to that endpoint. Responses arrive on the stream.

Inheritance: object

Implements: IMcpTransport, IDisposable

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Constructors

SseMcpTransport(HttpClient, Uri, IReadOnlyDictionary<string, string>?)

public SseMcpTransport(HttpClient httpClient, Uri url, IReadOnlyDictionary<string, string>? headers = null)

Creates a transport for the SSE endpoint at <code class=“paramref”>url</code>.

Parameters

Name	Type	Description
httpClient	HttpClient
url	Uri
headers	IReadOnlyDictionary<string, string>

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Fields

LatestLegacyProtocolVersion

public const string LatestLegacyProtocolVersion = "2024-11-05"

Protocol version sent in mcp-protocol-version until ProtocolVersion is set.

Value: string

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Properties

OnClose

public Action? OnClose { get; set; }

Called when the stream closes after CloseAsync().

Value: Action

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OnError

public Action<Exception>? OnError { get; set; }

Called with each transport error, such as a failed connection or an unparsable message.

Value: Action<Exception>

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OnMessage

public Action<JsonElement>? OnMessage { get; set; }

Called with each JSON-RPC message the server sends.

Value: Action<JsonElement>

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ProtocolVersion

public string? ProtocolVersion { get; set; }

Negotiated protocol version. Defaults to LatestLegacyProtocolVersion when unset.

Value: string

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Methods

CallAsync(string, JsonElement, CancellationToken)

public Task<JsonElement> CallAsync(string method, JsonElement parameters, CancellationToken cancellationToken)

Calls <code class=“paramref”>method</code> and returns the JSON-RPC result.

Parameters

Name	Type	Description
method	string
parameters	JsonElement
cancellationToken	CancellationToken

Returns: Task<JsonElement>

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CloseAsync()

public Task CloseAsync()

Closes the event stream and fails pending calls.

Returns: Task

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DeserializeMessage(string)

public static JsonElement DeserializeMessage(string line)

Parses one JSON-RPC message. Prototype-pollution keys are rejected.

Parameters

Name	Type	Description
line	string

Returns: JsonElement

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Dispose()

public void Dispose()

Closes the transport.

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SendAsync(JsonElement, CancellationToken)

public Task SendAsync(JsonElement message, CancellationToken cancellationToken = default)

Posts one JSON-RPC message to the endpoint the server announced.

Parameters

Name	Type	Description
message	JsonElement
cancellationToken	CancellationToken

Returns: Task

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StartAsync(CancellationToken)

public Task StartAsync(CancellationToken cancellationToken = default)

Opens the event stream and completes once the server has sent its endpoint event.

Parameters

Name	Type	Description
cancellationToken	CancellationToken

Returns: Task

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