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Align x-mcp-header implementation with SEP-2243 spec clarifications (#1619)

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Co-authored-by: Tarek Mahmoud Sayed <tarekms@ntdev.microsoft.com>
This commit is contained in:
Tarek Mahmoud Sayed 2026-06-05 15:45:08 -07:00 • committed by GitHub
commit ed19286a08
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2 changed files with 1035 additions and 116 deletions
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16
src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs
View file

@ -630,8 +630,8 @@ internal sealed partial class AIFunctionMcpServerTool : McpServerTool
if (!IsPrimitiveHeaderType(paramType))
{
throw new InvalidOperationException(
$"Parameter '{param.Name}' on method '{method.Name}' has [McpHeader] but is not a primitive type. " +
"Only string, numeric, and boolean types may be annotated with [McpHeader].");
$"Parameter '{param.Name}' on method '{method.Name}' has [McpHeader] but is not a supported type. " +
"Only string, integer, and boolean types may be annotated with [McpHeader].");
}
// Validate case-insensitive uniqueness
@ -673,6 +673,12 @@ internal sealed partial class AIFunctionMcpServerTool : McpServerTool
private static bool IsPrimitiveHeaderType(Type type)
{
// Per SEP-2243, x-mcp-header may only be applied to integer, string, or boolean parameters,
// and integer values must stay within the JavaScript safe integer range (-2^53+1 to 2^53-1).
// ulong is excluded because its upper range (above long.MaxValue) cannot be represented as a
// signed integer and the bulk of its domain falls outside the safe range. Remaining integer
// types are allowed here; long values are additionally range-checked per value when emitted
// (client) and validated (server).
return type == typeof(string) ||
type == typeof(bool) ||
type == typeof(byte) ||
@ -681,10 +687,6 @@ internal sealed partial class AIFunctionMcpServerTool : McpServerTool
type == typeof(ushort) ||
type == typeof(int) ||
type == typeof(uint) ||
type == typeof(long) ||
type == typeof(ulong) ||
type == typeof(float) ||
type == typeof(double) ||
type == typeof(decimal);
type == typeof(long);
}
}

27
src/ModelContextProtocol.Core/Server/McpHeaderAttribute.cs
View file

@ -1,3 +1,5 @@
using ModelContextProtocol.Client;
namespace ModelContextProtocol.Server;
/// <summary>
@ -10,8 +12,8 @@ namespace ModelContextProtocol.Server;
/// HTTP header named <c>Mcp-Param-{Name}</c>.
/// </para>
/// <para>
/// Only parameters with primitive types (string, number, boolean) may use this attribute.
/// The header name must contain only ASCII characters (0x21-0x7E, excluding space and colon)
/// Only parameters with primitive types (integer, string, boolean) may use this attribute.
/// The header name must match HTTP field-name token syntax (tchar per RFC 9110 Section 5.6.2)
/// and must be case-insensitively unique within the tool's input schema.
/// </para>
/// <para>
@ -38,7 +40,7 @@ public sealed class McpHeaderAttribute : Attribute
/// </summary>
/// <param name="name">
/// The name portion of the header. The full header name will be <c>Mcp-Param-{name}</c>.
/// Must contain only ASCII characters (0x21-0x7E, excluding space and colon).
/// Must match HTTP field-name token syntax (tchar per RFC 9110 Section 5.6.2).
/// </param>
/// <exception cref="ArgumentException">
/// The name is null, empty, or contains invalid characters.
@ -59,23 +61,20 @@ public sealed class McpHeaderAttribute : Attribute
public string Name { get; }
/// <summary>
/// Validates that a header name contains only valid characters.
/// Validates that a header name contains only valid HTTP token characters (tchar) per RFC 9110 Section 5.6.2.
/// </summary>
/// <param name="name">The header name to validate.</param>
/// <exception cref="ArgumentException">The name contains invalid characters.</exception>
internal static void ValidateHeaderName(string name)
{
foreach (char c in name)
int idx = McpHeaderExtractor.FindFirstNonTchar(name);
if (idx >= 0)
{
// Valid token characters per RFC 9110: visible ASCII (0x21-0x7E) excluding delimiters.
// Space (0x20) and colon (':') are explicitly prohibited.
if (c < 0x21 || c > 0x7E || c == ':')
{
throw new ArgumentException(
$"Header name contains invalid character '{c}' (0x{(int)c:X2}). " +
"Only ASCII characters (0x21-0x7E) excluding colon are allowed.",
nameof(name));
}
char c = name[idx];
throw new ArgumentException(
$"Header name contains invalid character '{c}' (0x{(int)c:X2}). " +
"Only HTTP token characters (tchar per RFC 9110 Section 5.6.2) are allowed.",
nameof(name));
}
}
}