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Require nested metadata for stateless HTTP #247

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leehack wants to merge 1 commit into from
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Require nested metadata for stateless HTTP #247

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22 changes: 19 additions & 3 deletions lib/src/server/streamable_https.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -439,6 +439,18 @@ class StreamableHTTPServerTransport
return null;
}

String? _nestedMetadataProtocolVersion(Map<String, dynamic> messageJson) {
final params = messageJson['params'];
if (params is Map) {
final meta = params['_meta'];
if (meta is Map) {
final version = meta[McpMetaKey.protocolVersion];
return version is String ? version : null;
}
}
return null;
}

bool _usesStatelessHttpValidation(
HttpRequest req,
List<JsonRpcMessage> messages,
Expand Down Expand Up @@ -756,6 +768,7 @@ class StreamableHTTPServerTransport
Future<bool> _validateStatelessHttpHeaders(
HttpRequest req,
List<JsonRpcMessage> messages,
List<Map<String, dynamic>> messageJsons,
) async {
if (!_usesStatelessHttpValidation(req, messages)) {
return true;
Expand All @@ -773,6 +786,7 @@ class StreamableHTTPServerTransport
}

final message = messages.single;
final messageJson = messageJsons.single;
final protocolHeader = req.headers.value('mcp-protocol-version')?.trim();
if (protocolHeader == null || protocolHeader.isEmpty) {
await _writeHeaderMismatchResponse(
Expand All @@ -791,12 +805,12 @@ class StreamableHTTPServerTransport
return false;
}

final metadataVersion = _metadataProtocolVersion(message);
final metadataVersion = _nestedMetadataProtocolVersion(messageJson);
if (metadataVersion == null) {
await _writeHeaderMismatchResponse(
req.response,
message,
'MCP-Protocol-Version header has no matching request _meta protocol version',
'MCP-Protocol-Version header has no matching request _meta protocol version in params._meta',
);
return false;
}
Expand Down Expand Up @@ -1336,6 +1350,7 @@ class StreamableHTTPServerTransport
}

final List<JsonRpcMessage> messages = [];
final List<Map<String, dynamic>> messageJsons = [];
if (rawMessages.isEmpty) {
await _writeJsonRpcErrorResponse(
req.response,
Expand All @@ -1362,6 +1377,7 @@ class StreamableHTTPServerTransport
final messageJson = rawItem is Map<String, dynamic>
? rawItem
: rawItem.cast<String, dynamic>();
messageJsons.add(messageJson);
messages.add(JsonRpcMessage.fromJson(messageJson));
} catch (e) {
await _writeJsonRpcErrorResponse(
Expand All @@ -1376,7 +1392,7 @@ class StreamableHTTPServerTransport
}
}

if (!await _validateStatelessHttpHeaders(req, messages)) {
if (!await _validateStatelessHttpHeaders(req, messages, messageJsons)) {
return;
}

Expand Down
12 changes: 12 additions & 0 deletions test/server/streamable_https_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -2730,6 +2730,18 @@ void main() {
contains('no matching request _meta protocol version'),
);

final topLevelMetaOnly = const JsonRpcListToolsRequest(id: 20).toJson()
..['_meta'] = _statelessMeta();
body = await postJson(
topLevelMetaOnly,
headers: {
'MCP-Protocol-Version': draftProtocolVersion2026_07_28,
'Mcp-Method': Method.toolsList,
},
);
expect(body['id'], 20);
expect(body['error']['message'], contains('params._meta'));

body = await postJson(
JsonRpcListToolsRequest(id: 5, meta: _statelessMeta()).toJson(),
headers: {
Expand Down