POCO (Portable Components)

The Poco::MongoDB implementation follows the MongoDB Server Discovery and Monitoring (SDAM) Specification.

Implemented Features

• Server Type Detection: Identifies Primary, Secondary, Arbiter, Standalone, Mongos, etc.
• Topology Discovery: Discovers members via hello command responses.
• Background Monitoring: Periodic heartbeat checks (default 10s, minimum 500ms).
• Topology Type Detection: Supports Single, ReplicaSetWithPrimary, ReplicaSetNoPrimary, Sharded, and Unknown.
• Read Preference Support: All 5 modes including tag-based selection.
• Automatic Failover: Detects and recovers from server failures.
• Cross-Contamination Prevention: Prevents adding hosts from mismatched replica sets.

Known Limitations & Risks

• Security: Missing "me" field validation (risk of topology poisoning).
• Data Integrity: Missing setVersion and electionId tracking (potential split-brain during network partitions).
• Topology Management: Server removal logic is incomplete; decommissioned servers may remain in the topology indefinitely.
• Staleness: Uses updateTime instead of lastWriteDate for staleness calculations.
• Latency: The "nearest" read preference selects members randomly rather than using RTT-based selection.

To add a new benchmark, create a .cpp file in the src/ directory. Use the benchmark::State object to control the loop and benchmark::DoNotOptimize to prevent compiler optimizations from skewing results.

Example Benchmark Implementation:

#include <benchmark/benchmark.h>
#include "Poco/MyComponent.h"

using Poco::MyComponent;

static void BM_MyOperation(benchmark::State& state)
{
    MyComponent component;

    for (auto _ : state)
    {
        auto result = component.doSomething();
        benchmark::DoNotOptimize(result);
    }

    state.SetBytesProcessed(state.iterations() * sizeof(result));
}
BENCHMARK(BM_MyOperation);

Registering the new benchmark:

1. Update CMakeLists.txt:

set(SRCS
    src/BenchmarkApp.cpp
    src/PatternFormatterBench.cpp
    src/MyComponentBench.cpp  # Add your file here
)

2. Update Makefile:

objects = BenchmarkApp PatternFormatterBench MyComponentBench

The ReplicaSet automatically posts TopologyChangeNotification objects to Poco::NotificationCenter::defaultCenter() whenever the topology changes (e.g., primary election, server count changes, or type changes). You can use NObserver to listen for these changes without manual polling.

#include "Poco/MongoDB/ReplicaSet.h"
#include "Poco/MongoDB/TopologyChangeNotification.h"
#include "Poco/NotificationCenter.h"
#include "Poco/NObserver.h"

class MyMongoObserver {
public:
    MyMongoObserver() {
        NotificationCenter::defaultCenter().addNObserver(*this, &MyMongoObserver::handleTopologyChange);
    }
    ~MyMongoObserver() {
        NotificationCenter::defaultCenter().removeNObserver(*this);
    }
    void handleTopologyChange(const AutoPtr<TopologyChangeNotification>& pNf) {
        const auto& data = pNf->data();
        std::string topologyType = data["topologyType"];
        // React to "Replica Set (with Primary)" or "Replica Set (no Primary)"
    }
};

NetSSL_Win is a Schannel-based implementation of the POCO NetSSL library. While code based on NetSSL_OpenSSL can generally be ported with minor changes, be aware of the following API differences:

Context Differences

• Constructor: The Context constructor uses different arguments. Instead of a certificate file name, you must specify a certificate subject name.
• Certificate Loading: Certificates can be loaded from the Windows certificate store or from PKCS #12 files (.pfx, .p12) if OPT_LOAD_CERT_FROM_FILE is specified. If using files, a private key passphrase handler must be set up.
• Unavailable Methods: The following methods are not available in NetSSL_Win:
  • addChainCertificate()
  • disableStatelessSessionResumption()
  • enableSessionCache()
  • flushSessionCache()
  • getSessionCacheSize()
  • getSessionTimeout()
  • setSessionCacheSize()
  • setSessionTimeout()
  • sslContext()
  • useCertificate()
  • usePrivateKey()

SSLManager Differences

• Configuration properties differ from NetSSL_OpenSSL. Refer to the SSLManager header file for the correct properties.
• The isFIPSEnabled() method is not available.

X509Certificate Differences

• Saving a certificate is not supported.