Implementation for SEP-2243 Http Standardization (#1553)

Co-authored-by: Tarek Mahmoud Sayed <tarekms@microsoft.com>
Co-authored-by: Tarek Mahmoud Sayed <tarekms@ntdev.microsoft.com>
Co-authored-by: Tarek Mahmoud Sayed <10833894+tarekgh@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/Common/McpHttpHeaders.cs

@@ -0,0 +1,78 @@
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Constants for MCP-specific HTTP header names used in the Streamable HTTP transport.
+/// </summary>
+/// <remarks>
+/// Per RFC 9110, HTTP header names are case-insensitive. Clients and servers must
+/// use case-insensitive comparisons when processing these headers.
+/// </remarks>
+internal static class McpHttpHeaders
+{
+    /// <summary>
+    /// The minimum protocol version that requires standard MCP request headers.
+    /// </summary>
+    /// <remarks>
+    /// Servers enforce missing <c>Mcp-Method</c> and <c>Mcp-Name</c> headers as errors only when
+    /// the client's <c>MCP-Protocol-Version</c> header indicates this version or later.
+    /// Clients using older versions are not required to send these headers.
+    /// </remarks>
+    public static readonly string MinVersionForStandardHeaders = "DRAFT-2026-v1";
+
+    /// <summary>The session identifier header.</summary>
+    public const string SessionId = "Mcp-Session-Id";
+
+    /// <summary>The negotiated protocol version header.</summary>
+    public const string ProtocolVersion = "MCP-Protocol-Version";
+
+    /// <summary>The last event ID for SSE stream resumption.</summary>
+    public const string LastEventId = "Last-Event-ID";
+
+    /// <summary>
+    /// The JSON-RPC method being invoked (e.g., "tools/call", "resources/read").
+    /// </summary>
+    /// <remarks>
+    /// Required on all Streamable HTTP POST requests. The value must match the <c>method</c>
+    /// field in the JSON-RPC request body.
+    /// </remarks>
+    public const string Method = "Mcp-Method";
+
+    /// <summary>
+    /// The name or URI of the target resource for the request.
+    /// </summary>
+    /// <remarks>
+    /// Required for <c>tools/call</c>, <c>resources/read</c>, and <c>prompts/get</c> requests.
+    /// For <c>tools/call</c> and <c>prompts/get</c>, the value is taken from <c>params.name</c>.
+    /// For <c>resources/read</c>, the value is taken from <c>params.uri</c>.
+    /// </remarks>
+    public const string Name = "Mcp-Name";
+
+    /// <summary>
+    /// Prefix for custom parameter headers (<c>Mcp-Param-{Name}</c>).
+    /// </summary>
+    /// <remarks>
+    /// When a tool's <c>inputSchema</c> includes properties annotated with <c>x-mcp-header</c>,
+    /// clients mirror those parameter values into HTTP headers using this prefix.
+    /// </remarks>
+    public const string ParamPrefix = "Mcp-Param-";
+
+    /// <summary>
+    /// Key used in <see cref="JsonRpcMessageContext.Items"/> to store the tool
+    /// definition for the current request, enabling the transport to add custom parameter headers.
+    /// </summary>
+    internal const string ToolContextKey = "Mcp.Tool";
+
+    /// <summary>
+    /// Protocol versions that require standard MCP request headers (Mcp-Method, Mcp-Name).
+    /// </summary>
+    private static readonly HashSet<string> s_versionsWithStandardHeaders = new(StringComparer.Ordinal)
+    {
+        MinVersionForStandardHeaders,
+    };
+
+    /// <summary>
+    /// Returns <see langword="true"/> if the given protocol version requires standard MCP request headers.
+    /// </summary>
+    public static bool SupportsStandardHeaders(string? protocolVersion)
+        => !string.IsNullOrEmpty(protocolVersion) && s_versionsWithStandardHeaders.Contains(protocolVersion!);
+}