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Merged
merged 3 commits into from
Nov 27, 2025
+60 −22
Merged

mcp: add more useful stats #42282

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7b4f5ae
add stats
botengyao Nov 26, 2025
9502996
minors
botengyao Nov 26, 2025
fd54982
fix format
botengyao Nov 26, 2025
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7 changes: 4 additions & 3 deletions source/extensions/filters/http/mcp/config.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,11 @@ namespace HttpFilters {
namespace Mcp {

Http::FilterFactoryCb McpFilterConfigFactory::createFilterFactoryFromProtoTyped(
const envoy::extensions::filters::http::mcp::v3::Mcp& proto_config, const std::string&,
Server::Configuration::FactoryContext&) {
const envoy::extensions::filters::http::mcp::v3::Mcp& proto_config,
const std::string& stats_prefix, Server::Configuration::FactoryContext& context) {

auto config = std::make_shared<McpFilterConfig>(proto_config);
auto config = std::make_shared<McpFilterConfig>(proto_config, stats_prefix,
context.serverFactoryContext().scope());

return [config](Http::FilterChainFactoryCallbacks& callbacks) -> void {
callbacks.addStreamFilter(std::make_shared<McpFilter>(config));
Expand Down
20 changes: 20 additions & 0 deletions source/extensions/filters/http/mcp/mcp_filter.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,22 @@ namespace Extensions {
namespace HttpFilters {
namespace Mcp {

namespace {
McpFilterStats generateStats(const std::string& prefix, Stats::Scope& scope) {
const std::string final_prefix = absl::StrCat(prefix, "mcp.");
return McpFilterStats{MCP_FILTER_STATS(POOL_COUNTER_PREFIX(scope, final_prefix))};
}
} // namespace

McpFilterConfig::McpFilterConfig(const envoy::extensions::filters::http::mcp::v3::Mcp& proto_config,
const std::string& stats_prefix, Stats::Scope& scope)
: traffic_mode_(proto_config.traffic_mode()),
clear_route_cache_(proto_config.clear_route_cache()),
max_request_body_size_(proto_config.has_max_request_body_size()
? proto_config.max_request_body_size().value()
: 8192), // Default: 8KB
stats_(generateStats(stats_prefix, scope)) {}

bool McpFilter::isValidMcpSseRequest(const Http::RequestHeaderMap& headers) const {
// Check if this is a GET request for SSE stream
if (headers.getMethodValue() != Http::Headers::get().MethodValues.Get) {
Expand Down Expand Up @@ -111,6 +127,7 @@ Http::FilterHeadersStatus McpFilter::decodeHeaders(Http::RequestHeaderMap& heade

if (!is_mcp_request_ && shouldRejectRequest()) {
ENVOY_LOG(debug, "rejecting non-MCP traffic");
config_->stats().requests_rejected_.inc();
decoder_callbacks_->sendLocalReply(Http::Code::BadRequest, "Only MCP traffic is allowed",
nullptr, absl::nullopt, "mcp_filter_reject_no_mcp");
return Http::FilterHeadersStatus::StopIteration;
Expand All @@ -134,6 +151,7 @@ Http::FilterDataStatus McpFilter::decodeData(Buffer::Instance& data, bool end_st

if (total_size > max_size) {
ENVOY_LOG(debug, "request body size {} exceeds maximum {}", total_size, max_size);
config_->stats().body_too_large_.inc();
decoder_callbacks_->sendLocalReply(
Http::Code::PayloadTooLarge,
absl::StrCat("Request body size exceeds maximum allowed size of ", max_size, " bytes"),
Expand All @@ -155,6 +173,7 @@ Http::FilterDataStatus McpFilter::decodeData(Buffer::Instance& data, bool end_st
if (!status.ok()) {
is_mcp_request_ = false;
ENVOY_LOG(debug, "failed to parse the JSON");
config_->stats().invalid_json_.inc();
decoder_callbacks_->sendLocalReply(Envoy::Http::Code::BadRequest,
"Request body is not a valid JSON.", nullptr,
absl::nullopt, "");
Expand All @@ -173,6 +192,7 @@ Http::FilterDataStatus McpFilter::decodeData(Buffer::Instance& data, bool end_st
is_mcp_request_ = false;
ENVOY_LOG(debug, "non-JSON-RPC 2.0 request is detected");
if (shouldRejectRequest()) {
config_->stats().requests_rejected_.inc();
decoder_callbacks_->sendLocalReply(Http::Code::BadRequest,
"request must be a valid JSON-RPC 2.0 message for MCP",
nullptr, absl::nullopt, "mcp_filter_not_jsonrpc");
Expand Down
28 changes: 22 additions & 6 deletions source/extensions/filters/http/mcp/mcp_filter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@
#include "envoy/extensions/filters/http/mcp/v3/mcp.pb.h"
#include "envoy/http/filter.h"
#include "envoy/server/filter_config.h"
#include "envoy/stats/scope.h"
#include "envoy/stats/stats_macros.h"

#include "source/common/common/logger.h"
#include "source/common/protobuf/protobuf.h"
Expand All @@ -26,17 +28,28 @@ namespace McpConstants {
constexpr absl::string_view JsonRpcVersion = "2.0";
} // namespace McpConstants

/**
* All MCP filter stats. @see stats_macros.h
*/
#define MCP_FILTER_STATS(COUNTER) \
COUNTER(requests_rejected) \
COUNTER(invalid_json) \
COUNTER(body_too_large)

/**
* Struct definition for MCP filter stats. @see stats_macros.h
*/
struct McpFilterStats {
MCP_FILTER_STATS(GENERATE_COUNTER_STRUCT)
};

/**
* Configuration for the MCP filter.
*/
class McpFilterConfig {
public:
explicit McpFilterConfig(const envoy::extensions::filters::http::mcp::v3::Mcp& proto_config)
: traffic_mode_(proto_config.traffic_mode()),
clear_route_cache_(proto_config.clear_route_cache()),
max_request_body_size_(proto_config.has_max_request_body_size()
? proto_config.max_request_body_size().value()
: 8192) {} // Default: 8KB
McpFilterConfig(const envoy::extensions::filters::http::mcp::v3::Mcp& proto_config,
const std::string& stats_prefix, Stats::Scope& scope);

envoy::extensions::filters::http::mcp::v3::Mcp::TrafficMode trafficMode() const {
return traffic_mode_;
Expand All @@ -50,10 +63,13 @@ class McpFilterConfig {

uint32_t maxRequestBodySize() const { return max_request_body_size_; }

McpFilterStats& stats() { return stats_; }

private:
const envoy::extensions::filters::http::mcp::v3::Mcp::TrafficMode traffic_mode_;
const bool clear_route_cache_;
const uint32_t max_request_body_size_;
McpFilterStats stats_;
};

/**
Expand Down
27 changes: 14 additions & 13 deletions test/extensions/filters/http/mcp/mcp_filter_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ class McpFilterTest : public testing::Test {
// Default config with PASS_THROUGH mode
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.set_traffic_mode(envoy::extensions::filters::http::mcp::v3::Mcp::PASS_THROUGH);
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);
filter_->setEncoderFilterCallbacks(encoder_callbacks_);
Expand All @@ -32,7 +32,7 @@ class McpFilterTest : public testing::Test {
void setupRejectMode() {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.set_traffic_mode(envoy::extensions::filters::http::mcp::v3::Mcp::REJECT_NO_MCP);
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);
filter_->setEncoderFilterCallbacks(encoder_callbacks_);
Expand All @@ -42,13 +42,14 @@ class McpFilterTest : public testing::Test {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.set_traffic_mode(envoy::extensions::filters::http::mcp::v3::Mcp::PASS_THROUGH);
proto_config.set_clear_route_cache(clear_route_cache);
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);
filter_->setEncoderFilterCallbacks(encoder_callbacks_);
}

protected:
NiceMock<Server::Configuration::MockFactoryContext> factory_context_;
NiceMock<Http::MockStreamDecoderFilterCallbacks> decoder_callbacks_;
NiceMock<Http::MockStreamEncoderFilterCallbacks> encoder_callbacks_;
McpFilterConfigSharedPtr config_;
Expand Down Expand Up @@ -286,31 +287,31 @@ TEST_F(McpFilterTest, PostWithWrongContentType) {
TEST_F(McpFilterTest, DefaultMaxBodySizeIsEightKB) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
// Don't set max_request_body_size, should default to 8KB
auto config = std::make_shared<McpFilterConfig>(proto_config);
auto config = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
EXPECT_EQ(8192u, config->maxRequestBodySize());
}

// Test custom max body size configuration
TEST_F(McpFilterTest, CustomMaxBodySizeConfiguration) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(16384);
auto config = std::make_shared<McpFilterConfig>(proto_config);
auto config = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
EXPECT_EQ(16384u, config->maxRequestBodySize());
}

// Test disabled max body size (0 = no limit)
TEST_F(McpFilterTest, DisabledMaxBodySizeConfiguration) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(0);
auto config = std::make_shared<McpFilterConfig>(proto_config);
auto config = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
EXPECT_EQ(0u, config->maxRequestBodySize());
}

// Test request body under the limit succeeds
TEST_F(McpFilterTest, RequestBodyUnderLimitSucceeds) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(1024); // 1KB limit
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand Down Expand Up @@ -339,7 +340,7 @@ TEST_F(McpFilterTest, RequestBodyUnderLimitSucceeds) {
TEST_F(McpFilterTest, RequestBodyExceedingLimitRejected) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(100); // Very small limit
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand Down Expand Up @@ -373,7 +374,7 @@ TEST_F(McpFilterTest, RequestBodyExceedingLimitRejected) {
TEST_F(McpFilterTest, RequestBodyWithDisabledLimitAllowsLargeBodies) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(0); // Disable limit
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand Down Expand Up @@ -406,7 +407,7 @@ TEST_F(McpFilterTest, RequestBodyWithDisabledLimitAllowsLargeBodies) {
TEST_F(McpFilterTest, RequestBodyExactlyAtLimitSucceeds) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(100); // 100 byte limit
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand Down Expand Up @@ -446,7 +447,7 @@ TEST_F(McpFilterTest, RequestBodyExactlyAtLimitSucceeds) {
TEST_F(McpFilterTest, BufferLimitSetForValidMcpPostRequest) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(8192);
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand All @@ -463,7 +464,7 @@ TEST_F(McpFilterTest, BufferLimitSetForValidMcpPostRequest) {
TEST_F(McpFilterTest, BufferLimitNotSetWhenDisabled) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.mutable_max_request_body_size()->set_value(0); // Disabled
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand All @@ -481,7 +482,7 @@ TEST_F(McpFilterTest, BodySizeLimitInPassThroughMode) {
envoy::extensions::filters::http::mcp::v3::Mcp proto_config;
proto_config.set_traffic_mode(envoy::extensions::filters::http::mcp::v3::Mcp::PASS_THROUGH);
proto_config.mutable_max_request_body_size()->set_value(50); // Small limit
config_ = std::make_shared<McpFilterConfig>(proto_config);
config_ = std::make_shared<McpFilterConfig>(proto_config, "test.", factory_context_.scope());
filter_ = std::make_unique<McpFilter>(config_);
filter_->setDecoderFilterCallbacks(decoder_callbacks_);

Expand Down