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fix mcp inspector v0.22.0 connection using streamable http transport #49

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fix mcp inspector v0.22.0 connection using streamable http transport #49

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40 changes: 32 additions & 8 deletions src/mcp_server.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -67,8 +67,8 @@ bool server::start(bool blocking) {
http_server_->Options(".*", [](const httplib::Request& req, httplib::Response& res) {
res.set_header("Access-Control-Allow-Origin", "*");
res.set_header("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id, MCP-Protocol-Version");
res.status = 204; // No Content
});

Expand Down Expand Up @@ -829,8 +829,9 @@ void server::handle_mcp_post(const httplib::Request& req, httplib::Response& res
// CORS headers
res.set_header("Access-Control-Allow-Origin", "*");
res.set_header("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("MCP-Protocol-Version", MCP_VERSION);

// Parse JSON body
json body;
Expand Down Expand Up @@ -998,8 +999,9 @@ void server::handle_mcp_post(const httplib::Request& req, httplib::Response& res
void server::handle_mcp_get(const httplib::Request& req, httplib::Response& res) {
// CORS headers
res.set_header("Access-Control-Allow-Origin", "*");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("MCP-Protocol-Version", MCP_VERSION);


std::string session_id = req.get_header_value("Mcp-Session-Id");
Expand Down Expand Up @@ -1033,18 +1035,37 @@ void server::handle_mcp_get(const httplib::Request& req, httplib::Response& res)
res.set_header("Cache-Control", "no-cache");
res.set_header("Connection", "keep-alive");

auto sent_initial = std::make_shared<std::atomic<bool>>(false);

// Use chunked content provider — same pattern as legacy SSE
res.set_chunked_content_provider(
"text/event-stream",
[this, session_id, dispatcher](size_t, httplib::DataSink& sink) {
[this, session_id, dispatcher, sent_initial](size_t, httplib::DataSink& sink) {
try {
if (dispatcher->is_closed() || !running_) {
return false;
}

if (!sent_initial->exchange(true, std::memory_order_acq_rel)) {
static constexpr const char* kInitialComment = ": connected\r\n\r\n";
if (!sink.write(kInitialComment, sizeof(": connected\r\n\r\n") - 1)) {
return false;
}
}

dispatcher->update_activity();
bool result = dispatcher->wait_event(&sink);
if (!result) {
return false;
if (dispatcher->is_closed() || !running_) {
return false;
}

static constexpr const char* kHeartbeatComment = ": heartbeat\r\n\r\n";
if (!sink.write(kHeartbeatComment, sizeof(": heartbeat\r\n\r\n") - 1)) {
return false;
}
dispatcher->update_activity();
return true;
}
dispatcher->update_activity();
return true;
Expand All @@ -1056,6 +1077,9 @@ void server::handle_mcp_get(const httplib::Request& req, httplib::Response& res)

void server::handle_mcp_delete(const httplib::Request& req, httplib::Response& res) {
res.set_header("Access-Control-Allow-Origin", "*");
res.set_header("Access-Control-Allow-Headers", "Content-Type, Accept, Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("Access-Control-Expose-Headers", "Mcp-Session-Id, MCP-Protocol-Version");
res.set_header("MCP-Protocol-Version", MCP_VERSION);

std::string session_id = req.get_header_value("Mcp-Session-Id");
if (session_id.empty()) {
Expand Down