OSGi.fx Remote Agent

The OSGi.fx Remote Agent is a lightweight, high-performance management agent designed to run inside a target OSGi framework. It acts as the bridge between the remote runtime and the OSGi.fx Desktop Console, enabling deep introspection, real-time diagnostics, and lifecycle management of OSGi systems.

📋 Requirements

The agent is designed for broad compatibility across legacy and modern environments:

• Java: Version 1.8 or higher (tested up to Java 25).
• OSGi: Core R6 or higher (Equinox, Felix, Concierge, etc.).

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🚀 Key Advantages

Feature	Description
High Performance	Utilizes binary serialization (BinaryCodec) and LZ4 compression to minimize network traffic and heap occupancy.
Reactive Snapshotting	Implements a debounced, deadline-aware snapshotting mechanism that only updates data when the framework state changes.
Transport Agnostic	Supports communication over standard Sockets (TCP/TLS) or MQTT 5 (OSGi Messaging or Custom).
Graceful Degradation	Operates on minimal runtimes by dynamically detecting available services (ConfigAdmin, SCR, etc.) without requiring them.
Security First	Built-in support for password authentication and TLS-secured communication.

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🏗️ Module Architecture

The agent is split into three OSGi bundles for clean separation of concerns:

com.osgifx.console.agent.api

The architectural contract defining:

• Agent / AgentSnapshot: Primary management interfaces for control and inspection
• dto: Comprehensive DTO suite optimized for minimal serialization footprints
• rpc: Binary codec (BinaryCodec), LZ4 compression (Lz4Codec), transport abstractions, and SnapshotDecoder
• spi: Extension points (AgentExtension, LargePayloadHandler) for custom logic

com.osgifx.console.agent

The core implementation containing:

• admin: Domain-specific managers (Bundles, Components, Configurations, Services, Conditions, etc.)
• redirector: I/O hijacking engine for multi-mode terminal proxies (Console, Gogo, Socket, Telnet)
• provider: Agent server, binary log buffer, classloader leak detector, startup time calculator
• starter: Zero-dependency Activator and Gogo command bridge
• helper: Utility classes for OSGi compendium service detection and agent operations

com.osgifx.console.agent.di

Standalone micro-DI container:

• JSR-330 compliant: Full support for @Inject, @Singleton, and Provider<T>
• Lambda-accelerated: Injection optimized via LambdaMetafactory for high-speed instantiation
• Zero dependencies: Operates without OSGi SCR, making it portable across minimal runtimes
• Dynamic binding: Runtime binding of interfaces to implementations and custom providers

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🏗️ Architecture

The agent is built on a modular, DI-based architecture to ensure extensibility and clean lifecycle management.

🧩 Lightweight Internal DI

To remain portable and operate even when OSGi Declarative Services (SCR) is missing, the agent uses a bespoke, lightweight Dependency Injection container.

• Standalone: Zero dependencies on heavy DI frameworks (Guice, Spring, OSGi DS).
• Fast: Uses LambdaMetafactory for high-speed constructor and field injection.
• Lazy Providers: Supports jakarta.inject.Provider for services that may be wired later in the framework lifecycle.
• Lifecycle Integrated: Closely tied to the Bundle Activator for deterministic startup/shutdown of all internal “Admin” services.

🛡️ Class Space Resilience

The agent is designed to be injected into existing frameworks where classloader conflicts are common:

• Proxying Strategy: The GogoRedirector and other redirection components use java.lang.reflect.Proxy to interact with Gogo APIs. This prevents ClassCastException if the agent and Gogo are in different class spaces, a common issue in complex OSGi deployments.

The agent defines its contract across two primary interfaces in the com.osgifx.console.agent.api bundle:

1. AgentSnapshot (The “Inspection” Layer)

Focuses exclusively on high-performance state retrieval.

• Design: All methods return byte[] (pre-serialized, LZ4-compressed binary blobs).
• Goal: Minimize heap occupancy and serialization overhead. This is the “Monitoring” interface used by OSGi.fx to visualize the runtime.

2. Agent (The “Control” Layer)

Focuses on lifecycle management and runtime manipulation.

• Design: Extends AgentSnapshot. Includes methods with side effects: install(), start(), stop(), updateConfiguration(), sendEvent(), etc.
• Goal: Act as the authority for remote management.

💡 Why the separation?

This “Control vs. Inspection” split allows the agent to serve hundreds of monitoring requests (Snapshots) with near-zero CPU cost by using atoms and binary caches, while keeping the management logic (Agent) clean and focused on framework side effects.

• The Monitoring Flow: OSGi.fx calls AgentSnapshot.bundles(). The agent returns a pre-cached binary blob. No locks, no DTO creation, no serialization.
• The Control Flow: OSGi.fx calls Agent.stop(id). The agent executes the side effect, which triggers a framework event, which in turn invalidates the AgentSnapshot cache for a future request.

🛡️ Sub-System Self-Protection

To prevent accidental “suicide” of the management bridge or catastrophic framework failure, the agent implements strict self-protection:

• Immutable Critical Bundles: The AgentServer explicitly blocks stop() and uninstall() operations targeting the System Bundle (ID 0) or the Agent Bundle itself.
• Execution Allowlisting: All remote Gogo and CLI commands are verified against a property-based allowlist before invocation.
• Path Traversal Guard: Methods like getBundleDataFile and local creation commands strictly validate paths to prevent escaping the bundle’s private data storage or the designated output directories.

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⚡ Deep Dive: Binary Caching & Performance

The agent’s state-retrieval mechanism is built for extreme efficiency in high-churn OSGi environments. Unlike traditional agents that serialize objects on-demand, this agent uses a Reactive Binary Snapshot strategy.

1. Why Reactive Snapshots?

• CPU Rationale: Serialization (especially of large DTO trees) is one of the most expensive operations. By snapshotting once per stable state, we move the cost from the request path to the background path.
• Memory Rationale: Holding a full tree of DTO objects in memory is expensive for the GC. Instead, the agent holds a single compressed byte[]. This significantly reduces heap occupancy.
• Network Rationale: Data is encoded using a compact binary format and further compressed with LZ4. This minimizes bandwidth without the high CPU overhead of GZIP.

2. Hybrid Binary Serialization (BinaryCodec)

The agent uses a custom-built, schema-less binary codec that outperforms standard Java serialization and JSON by orders of magnitude:

• JIT-Inlined Raw Memory Access (With Graceful Fallback): Uses sun.misc.Unsafe wrapped seamlessly via LambdaMetafactory. This dynamically spins up @FunctionalInterface implementations at runtime invoking precise MethodHandles, guaranteeing the HotSpot JIT compiler completely inlines the memory access.
  • Future-Proof (Java 25+): Direct references to sun.misc.Unsafe break strict Gradle builds and module boundaries (Jigsaw) in modern JVMs. The agent strictly loads Unsafe dynamically via Class.forName(). If restricted or removed in future JVMs (like Java 25+), the agent implements a zero-exception Standard Fallback strategy. It gracefully degrades to standard MethodHandle unreflected getters/setters (lookup.unreflectGetter()). Crucially, these fallback handles are also passed through LambdaMetafactory to guarantee the exact same JIT inlining speed, executing natively without ever touching sun.misc.
• Internal Micro-DI Engine (com.osgifx.console.agent.di): The agent does not rely on heavy frameworks like Spring or Guice, nor does it use native OSGi SCR for its internal plumbing. It utilizes a bespoke, zero-dependency Dependency Injection engine that supports:
  • JSR-330 Compliance: Full support for @Inject, @Singleton, and Provider<T>.
  • Dynamic Binding: Runtime binding of interfaces to implementations and custom providers.
  • Lambda-Accelerated Injection: Constructor and field injection are optimized to bypass standard reflection overhead where possible.
  • Ultra-Portable: Operates in environments where full OSGi component runtimes are unavailable or restricted.
• Schema-less Payload: Field names are never sent. Data is serialized in a deterministic order (sorted by field name), drastically reducing payload size.
• Zero-Boxing: Primitive fields (int, long, double, etc.) are packed directly into the binary stream without object allocation.
• Non-Blocking I/O: Utilizes internal FastByteArray streams that eliminate synchronization overhead and defensive array copies.

3. Adaptive & Reactive Snapshotting Strategy (AbstractSnapshotAdmin)

To prevent the agent from thrashing the CPU during high-frequency OSGi events (e.g., a burst of 1000 service registrations), all “Admins” (Bundles, Services, Components) utilize a sophisticated debouncing mechanism:

• Debounce Window: 200ms of “silence” required before a snapshot is generated.
• Hard Deadline: 5000ms maximum wait. If events keep flooding in, the snapshot is forced at the deadline to ensure the Console isn’t starved of data.
• Change-Count Synchronization: Snapshots are only recalculated if the internal pendingChangeCount exceeds the lastChangeCount, ensuring zero CPU cycles are wasted on redundant serializations.
• Lazy Serialization: Snapshots are encoded/compressed on a background thread and cached as immutable byte arrays, minimizing the duration of locks on core OSGi structures.

Most data points (Bundles, Services, Configs) are served via a thread-safe caching mechanism:

1. Change Detection: The agent monitors framework change counts (e.g. SERVICE_CHANGECOUNT).
2. Debouncing (200ms): During “event storms” (e.g., a burst of 50 service registrations), the agent waits for a 200ms silence period before triggering a re-snapshot.
3. The Deadline (5s): If the system is in constant flux and never reaches the “silence” threshold, a snapshot is forced every 5 seconds to ensure the remote UI stays reasonably fresh.
4. Atomic Binary Cache: The resulting byte[] is stored in an AtomicReference.
   • Direct-to-Wire: If a supervisor requests the same data multiple times, the agent sends the same byte array directly to the socket/MQTT link. Zero serialization is performed for subsequent requests until the next framework change.

📸 Snapshot Tracking Strategy

Admin	Tracking Strategy	Trigger Event
Bundles	BundleTracker + FrameworkListener	Bundle lifecycle, Startlevel changes
Services	ServiceTracker	Service registration/modification/removal
Components	ServiceComponentRuntime Tracker	SCR Component state changes (changecount)
Conditions	ServiceTracker	Condition service registration/modification/removal
Configurations	ConfigurationListener	ConfigAdmin PID/Factory updates
HTTP/JAX-RS/CDI	changecount Monitoring	Remote DTO state changes via R7/R8 specs
User Admin	UserAdminListener	Roles, Groups, and Credential changes
Loggers	BundleListener	Bundle attachment (logger context availability)
Health Checks	ServiceTracker	HealthCheck service registration changes
Threads/Props	Live (On-demand)	Real-time JVM state (Too volatile to cache)

🛠️ Concrete Example: XBundleAdmin

Here is how a real Snapshot provider implements change detection and adaptive scheduling:

@Singleton
public final class XBundleAdmin extends AbstractSnapshotAdmin<XBundleDTO> {
    // 1. Initialise trackers for the state we care about
    public void init() {
        bundleTracker = new BundleTracker<>(context, INSTALLED | ACTIVE | ...) {
            @Override
            public Object addingBundle(Bundle b, BundleEvent e) {
                // 2. Increment change count and schedule background re-snapshot
                scheduleUpdate(pendingChangeCount.incrementAndGet());
                return new Object();
            }
            // ... similar for removed/modified
        };
        bundleTracker.open();
    }

    // 3. The "map" method is called in the background when the 200ms debounce expires
    @Override
    protected List<XBundleDTO> map() throws Exception {
        Bundle[] bundles = context.getBundles();
        return Arrays.stream(bundles).map(this::toDTO).collect(Collectors.toList());
    }
}

This pattern ensures that the intensive map() (DTO creation + OSGi API calls) happens away from the remote request path.

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📊 Full Snapshot Catalog

All the following data points are available as binary snapshots via the AgentSnapshot interface:

Snapshot Method	DTO Type	Description
bundles()	XBundleDTO	Comprehensive bundle metadata and wiring
components()	XComponentDTO	Declarative Services (SCR) state
conditions()	XConditionDTO	OSGi R8 Condition services and component dependencies
services()	XServiceDTO	OSGi service registry snapshot
configurations()	XConfigurationDTO	ConfigAdmin properties and Metatype info
properties()	XPropertyDTO	System and Framework properties
threads()	XThreadDTO	JVM thread states and stack traces
roles()	XRoleDTO	UserAdmin roles and members
healthChecks()	XHealthCheckDTO	Registered Felix Health Checks
httpComponents()	XHttpComponentDTO	Servlets, Filters, Resources (R7/R8)
jaxRsComponents()	XJaxRsComponentDTO	JAX-RS Whiteboard components
cdiContainers()	XCdiContainerDTO	CDI Container and Component status
bundleLoggerContexts()	XBundleLoggerContextDTO	R7 Logger Admin contexts
leaks()	XBundleDTO	Potential classloader leaks
runtime()	RuntimeDTO	Framework and System information
heapUsage()	XHeapUsageDTO	Real-time memory/heap statistics
runtimeCapabilities()	XRuntimeCapabilityDTO	Detected framework capabilities

🔍 Live vs. Cached Snapshots

The agent intelligently distinguishes between data that benefits from reactive caching and data that should always be retrieved live:

Admin	Strategy	Rationale
Bundles	Cached	Expensive to build (wiring, packages, services). Infrequent changes.
Services	Cached	Moderate cost. Service registry changes trigger re-snapshot.
Components	Cached	Moderate cost. SCR component state tracked via changecount.
Conditions	Cached	Moderate cost. Condition services tracked via ServiceTracker.
Configurations	Cached	Moderate cost. ConfigAdmin + Metatype processing.
User Roles	Cached	Cheap but infrequent changes. Caching prevents redundant processing.
Health Checks	Cached	Service tracker monitors HealthCheck registrations.
HTTP Components	Cached	R7/R8 Whiteboard runtime tracked via changecount.
JAX-RS Components	Cached	JAX-RS runtime tracked via changecount.
CDI Containers	Cached	CDI runtime tracked via changecount.
Logger Contexts	Cached	Bundle-based logger contexts change with bundle lifecycle.
Classloader Leaks	Cached	Phantom reference tracking updates on GC events.
Threads	Live	Constantly changing. Caching would provide stale data.
Properties	Live	Cheap to retrieve. Rarely change.
Heap Usage	Live	Real-time memory statistics. Must always be current.
Runtime Info	Live	Framework DTO is cheap to retrieve.

📦 Compression Format

All snapshot methods return data compressed using Lz4Codec.compressWithLength(), which produces a self-describing payload:

Binary Format:

[1-byte flag][4-byte big-endian length][compressed/raw data]

• Flag (1 byte): 0x00 = uncompressed, 0x01 = LZ4 compressed
• Length (4 bytes): Original uncompressed size in big-endian format (supports up to 2GB payloads)
• Data: LZ4-compressed bytes or raw bytes if compression didn’t reduce size

Compression Threshold: Payloads smaller than 512 bytes are not compressed to avoid overhead.

🚀 Performance Benchmarks

The reactive binary snapshot architecture delivers massive performance improvements over traditional on-demand serialization:

Metric	Before (On-Demand)	After (Reactive Snapshots)	Improvement
CPU per request	~50ms	~0.1ms	500x faster
Heap pressure	High (transient DTOs)	Minimal (single byte[])	10-20x reduction
Latency (cached)	50-100ms	<1ms	50-100x faster
Throughput	~20 req/s	~1000 req/s	50x higher
Network efficiency	LZ4 compressed	LZ4 compressed	Same

Real-World Impact:

• A supervisor polling 10 snapshots/second consumes <1% CPU on the agent (vs. 50%+ with on-demand serialization)
• During OSGi event storms (100+ events/sec), debouncing prevents CPU thrashing while ensuring UI updates within 5 seconds
• Constrained devices (Raspberry Pi, industrial gateways) can serve monitoring requests with near-zero performance impact

🔧 Using SnapshotDecoder (Supervisor Side)

The SnapshotDecoder utility simplifies decoding compressed snapshots on the supervisor side:

// Initialize once
BinaryCodec codec = new BinaryCodec(bundleContext);
SnapshotDecoder decoder = new SnapshotDecoder(codec);

// Decode list snapshots
byte[] bundlesSnapshot = agent.bundles();
List<XBundleDTO> bundles = decoder.decodeList(bundlesSnapshot, XBundleDTO.class);

// Decode set snapshots
byte[] leaksSnapshot = agent.leaks();
Set<XBundleDTO> leaks = decoder.decodeSet(leaksSnapshot, XBundleDTO.class);

// Decode single object snapshots
byte[] runtimeSnapshot = agent.runtime();
RuntimeDTO runtime = decoder.decode(runtimeSnapshot, RuntimeDTO.class);

// Decode single bundle snapshot (efficient for detail views)
byte[] bundleSnapshot = agent.bundle(42L);
XBundleDTO bundle = decoder.decode(bundleSnapshot, XBundleDTO.class);

Key Features:

• Type-safe decoding: Generic methods for List<T>, Set<T>, and single objects
• Automatic decompression: Handles Lz4Codec.decompressWithLength() format transparently
• Null-safe: Returns empty collections for null/empty snapshots
• Exception handling: Wraps decompression failures in RuntimeException with clear error messages
• Single-object snapshots: Use agent.bundle(id) for efficient retrieval of individual bundle details without fetching the entire list

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🕹️ Full Control API Catalog

While AgentSnapshot is strictly for reading state, the Agent interface provides a comprehensive set of operations with side-effects for manipulating the remote runtime.

Category	Methods	Description
Bundle Management	installWithData, installWithMultipleData, installFromURL, start, stop, uninstall	Lifecycle management. installWithMultipleData batch-installs bundles and performs a single refresh to avoid internal framework thrashing.
Bundle Introspection	getBundleRevisons, getBundleDataFile	Inspecting wiring revisions and reading persistent data files from the bundle’s private getDataFile() area.
Resource Browsing	findBundleEntries, listBundleResources, getBundleEntryBytes, getBundleResourceBytes	Deep inspection of bundle contents. Physical JAR search: findBundleEntries searches strictly inside the physical JAR (bypassing the classloader). Classpath search: listBundleResources searches the entire class space (including imports and fragments). The *Bytes variants retrieve raw content from either the physical JAR (getBundleEntryBytes) or the classloader (getBundleResourceBytes).
Component Management	enableComponentByName, enableComponentById, disableComponentByName, disableComponentById	Fine-grained control over Declarative Services (SCR) components.
Configuration Admin	createOrUpdateConfigurations, deleteConfiguration, createFactoryConfiguration	Create, update, and delete standard and factory configurations natively.
User Admin	createRole, updateRole, removeRole	Modifying roles, groups, and credentials within the OSGi User Admin service.
Logger Admin	updateBundleLoggerContext	Dynamically changing OSGi R7 log levels per bundle without restarts.
Event Admin	sendEvent (Sync), postEvent (Async)	Publishing custom OSGi events directly into the remote framework’s event bus.
Health Checks	executeHealthChecks	On-demand execution of specific Felix Health Checks via tags or names.
DMT Admin	readDmtNode, updateDmtNode	Reads and updates nodes in the Device Management Tree.
Process & Shell	execGogoCommand, execCliCommand	Remote execution of Gogo commands or underlying OS shell (CLI) commands (tightly protected by allowlists).
JMX / Memory	heapdump, getMemoryInfo, gc	Triggering garbage collection, inspecting OS vs JVM memory, or requesting full JVM heap dumps over the wire.
Diagnostics	threadDump, estimateThreadDumpSize, createThreadDumpLocally	Generate jstack-style thread dumps (GZIP-compressed), estimate size, or save locally for later retrieval.
Agent Lifecycle	disconnect, ping, refresh	Checking connectivity, safely detaching the agent, or triggering a framework wiring refresh.

🔌 SPIs & Extension Points

The agent is designed to be highly extensible via standard OSGi service-based SPIs. This allows users to add custom management logic or alternative large-payload handling strategies.

1. AgentExtension SPI

Dynamic extensions allow you to execute custom code in the remote runtime and return JSON-compliant results (DTOs).

• Interface: com.osgifx.console.agent.spi.extension.AgentExtension<C, R>
• Registration: Register as an OSGi service with the property agent.extension.name. This can be done via the @Component property or more concisely using the @AgentExtensionName annotation.
• Discovery: Automatically discovered by the agent’s DI container via ServiceTracker.

Example Extension (Option 1: Using @AgentExtensionName):

@Component
@AgentExtensionName("cpu.monitor")
public class CpuMonitorExtension implements AgentExtension<CpuContext, CpuResult> {
    @Override
    public CpuResult execute(CpuContext context) {
        // Custom logic here
        return new CpuResult(os.getLoad());
    }
}

Example Extension (Option 2: Using @Component Property):

@Component(property = "agent.extension.name=cpu.monitor")
public class CpuMonitorExtension implements AgentExtension<CpuContext, CpuResult> {
    // ... same as above
}

2. LargePayloadHandler SPI

For massive files (e.g., a 2GB Heap Dump) that exceed RPC transport limits or network timeouts, the agent provides an out-of-band transfer SPI.

• Interface: com.osgifx.console.agent.spi.payload.LargePayloadHandler
• Mechanism: When a large payload is generated, the agent searches for a registered LargePayloadHandler. If found, it delegates the “handling” (e.g., uploading to an S3 bucket, SFTP server, or Corporate Artifactory).
• Result: The agent returns the URL or reference provided by the handler to the Supervisor, which can then download it separately.

Example Use Case: On a factory-floor IoT device with limited RAM, a Heap Dump cannot be streamed over the socket. A registered S3PayloadHandler can upload the file to AWS and return a pre-signed URL to the engineer’s OSGi.fx console.

3. I/O Redirection & Telnet Bridge

The agent can dynamically redirect the terminal I/O of the remote framework.

• CONSOLE Mode: Global hijacking of System.in, System.out, and System.err. All log messages and standard output are streamed back to the Supervisor in real-time.
• COMMAND_SESSION Mode: Creates a fresh, virtual Gogo CommandSession. This allows executing commands in a private context without interfering with other administrators.
• Telnet Mode: Acts as a transparent bridge. If the agent detects a Telnet-based shell (e.g. Felix Shell TUI) running on a specific port, it can connect to it and pipe the I/O through the RPC channel.

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🪵 Logging & Eventing Architecture

The agent features a high-performance logging and eventing system designed for industrial-grade data rates and memory-constrained runtimes.

💾 Persistent Binary Logging

Beyond real-time streaming, the agent can capture logs even when no Supervisor is connected:

• osgifx_logs.bin: If osgi.fx.agent.auto.start.log.capture=true is set, the agent immediately begins recording logs to a local file in the bundle’s data area.
• Persistence: This allows OSGi.fx to retrieve “post-mortem” logs after a framework crash or restart.
• History Recovery: Upon connection, the Supervisor can query the BinaryLogBuffer for historical data stored in this file.

Binary Log Buffer (BinaryLogBuffer)

Traditional log collection (e.g. List<LogEntry>) creates massive heap pressure. The agent uses a packed binary circular buffer:

• Zero-Allocation Writes: Primitive types (longs, ints) are packed directly into a pre-allocated byte array using bitwise shifts. This completely eliminates object allocation during logging, preventing GC-induced jitter in real-time systems.
• Persistent Flight Recorder: If osgi.fx.agent.auto.start.log.capture=true is set, the buffer persists to osgifx_logs.bin. Upon agent restart, it automatically restores the buffer from disk, allowing for true post-mortem analysis even if the framework crashed and rebooted.
• Two-Pass Sequential Retrieval: When querying logs by a time range, the agent performs a two-pass scan on the index ring:
  1. Pass 1 (Backward Scan): Identifies the start/end logical indices and calculates the exact byte size required for the result.
  2. Pass 2 (Forward Copy): Allocates the result array once and performs a high-speed System.arraycopy (handling wrap-around). This minimizes garbage collection overhead and ensures deterministic performance.

In-Depth Packing Format: The buffer doesn’t store Strings directly to avoid heap fragmentation. Instead:

1. String Pooling: Common tags/loggers are indexed.
2. Binary Packing:
   • Long (Timestamp) -> 8 bytes
   • Byte (Level) -> 1 byte
   • Int (Message Ref) -> 4 bytes
3. Atomic Updates: The write pointer is managed via VarHandle or Unsafe to allow concurrent logging without global locks.

Example: Snapshot Retrieval

// Retrieve logs from the last 5 minutes
long fiveMinsAgo = System.currentTimeMillis() - 300_000;

5. Advanced Path Resolution & Variable Substitution

The agent provides a powerful variable substitution engine for all filesystem-related RPC calls (Heap Dumps, Snapshots, Data-File retrieval). Paths can contain placeholders that are resolved against System Properties, Framework Properties, or Environment Variables.

Supported Placeholders:

• {prop.key}: Resolves to bundleContext.getProperty("prop.key") or System.getProperty("prop.key").
• {env:VAR_NAME}: Resolves to System.getenv("VAR_NAME").
• {timestamp}: Resolves to the current time in yyyy-MM-dd-HH-mm-ss format.

Example Path: /tmp/osgifx/{framework.name}/heap-{timestamp}.hprof.gz

6. Internal “Micro-DI” Engine (com.osgifx.console.agent.di)

To maintain a small footprint (< 200KB) and zero external dependencies, the agent uses a custom, high-performance Dependency Injection engine.

• Jakarta Inject Support: Native support for @Inject, @Singleton, and Provider<T>.
• Zero-Annotation Wiring: Interfaces can be bound to implementations manually via DI.bindInterface().
• Fast Startup: No classpath scanning or heavy reflection. All bindings are resolved lazily upon first request.
• Provider Pattern: Supports lazy-loaded services that are only instantiated when an RPC call actually requires them. byte[] logSnapshot = logBuffer.snapshot(fiveMinsAgo, Long.MAX_VALUE); // Result is a packed binary blob, ready for LZ4 compression and transmission

Remote Eventing

When enabled (osgi.fx.enable.eventing=true), the agent subscribes to all OSGi EventAdmin topics and streams them in real-time to the Supervisor. Events are debounced and batched to prevent flooding over slow MQTT or Socket links.

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📡 MQTT 5 & OSGi Messaging Integration

While Socket communication is great for direct diagnostics, OSGi.fx is heavily optimized for IoT and Edge gateway monitoring through MQTT.

The agent uses the OSGi Messaging library (in.bytehue.messaging.mqtt5.provider) as its default provider for MQTT 5 RPC.

Why osgi-messaging?

1. OSGi Native: It seamlessly integrates MQTT 5 capabilities with OSGi framework services using the OSGi Messaging specification.
2. High Throughput: Capable of streaming large binary snapshots and LZ4-compressed RPC payloads with a very low footprint, which is crucial for embedded OSGi runtimes.
3. Pluggable Architecture: Configurable via osgi.fx.agent.mqtt.provider=osgi-messaging. If your infrastructure requires a different MQTT ecosystem, you can set the provider to custom and register your own Mqtt5Publisher and Mqtt5Subscriber OSGi services.

This integration empowers OSGi.fx to securely manage and introspect edge devices acting as MQTT clients, without needing to establish complex TCP reverse-tunnels into firewalled networks.

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🔄 I/O Redirection

The agent provides a flexible Redirection SPI (com.osgifx.console.agent.redirector.Redirector) to capture and stream system I/O.

• Gogo Redirector (COMMAND_SESSION / -1): Connects a remote Gogo CommandSession to the Supervisor’s terminal. Uses proxied access to Gogo APIs to avoid classloader constraints.
• Console Redirector (CONSOLE / -2): Captures System.out and System.err and streams them as remote events.
• Socket Redirector (PORT): Pipes I/O directly over the active agent socket or a dedicated secondary port.
• Null Redirector (NONE / 0): Silently discards I/O or detaches active redirectors.

This sub-system leverages the redirect(int port) and stdin(String) remote APIs to hook into and push characters to the chosen backend stream.

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🛡️ Command Security & Allowlisting

To prevent accidental or malicious execution of sensitive commands, the agent implements a dual-layer allowlist system:

1. Gogo Allowlist (osgi.fx.agent.gogo.allowlist):
   • Comma-separated list of scopes or functions (e.g., osgi:*, equinox:start).
   • Defaults to * (All permitted).
2. CLI Allowlist (osgi.fx.agent.cli.allowlist):
   • Restricts what shell commands can be executed via execCliCommand.
   • Defaults to *.

How it works: Before any execution, the agent checks the command against these patterns. If a match is not found, the operation is blocked with a security exception, protecting the underlying host OS.

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The agent registers several commands under the osgifx scope for dynamic control via the Gogo shell.

Command	Usage	Description
osgifx:startSocket	startSocket [host=.. port=.. secure=..]	Starts the Socket RPC server.
osgifx:stopSocket	stopSocket	Stops the Socket RPC server and clears properties.
osgifx:startMqtt	startMqtt [provider=.. pubTopic=.. subTopic=..]	Starts the MQTT RPC endpoint.
osgifx:stopMqtt	stopMqtt	Stops the MQTT RPC endpoint.
osgifx:status	status	Displays running status and current configuration.

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📦 Optional Dependencies & Dynamic Wiring (Graceful Degradation)

To ensure the agent remains ultra-lightweight and heavily portable, it does not rely on strict Import-Package manifest headers for heavily utilized OSGi compendium specifications (like ConfigAdmin, SCR, EventAdmin).

If the agent strictly imported org.osgi.service.cm, it would fail to resolve on minimal OSGi gateways or embedded IoT devices that do not have a ConfigAdmin implementation deployed.

Instead, the agent uses the PackageWirings subsystem. It dynamically interrogates the framework’s BundleWiring state to check if optional specification packages are physically wired to the agent bundle.

How PackageWirings benefits the runtime:

1. Zero-Friction Deployment: Drop the agent into any OSGi framework (Equinox, Felix, Concierge) regardless of what other bundles are installed.
2. Graceful Degradation: If isScrWired() returns false, the agent cleanly skips initializing the XComponentAdmin service. RPC calls for DS Components gracefully return empty collections instead of throwing NoClassDefFoundError.
3. High Performance Cache: To avoid the massive overhead of walking the OSGi wiring graph for every network request, wiring results are cached concurrently. The cache is totally stable because once a package is wired to a bundle revision, it cannot change without a framework-level bundle update/refresh.

Technical Design: The agent adapts its own Bundle to BundleWiring and inspects getRequiredWires(osgi.wiring.package). This allows it to detect if an optional dependency (e.g., org.osgi.service.cm) has been resolved by the framework. This approach is superior to Class.forName() as it respects the OSGi visibility rules and avoids unnecessary class loading if the package is not actually available.

Supported Optional Capabilities:

The following specifications are dynamically detected via PackageWirings. If installed on the system, the agent automatically exposes their management capabilities to OSGi.fx:

• Declarative Services (SCR) (org.osgi.service.component.runtime)
• Configuration Admin (org.osgi.service.cm)
• Metatype Service (org.osgi.service.metatype)
• User Admin (org.osgi.service.useradmin)
• Event Admin (org.osgi.service.event)
• Log Service & R7 Logger (org.osgi.service.log / org.osgi.service.log.admin)
• HTTP & JAX-RS Whiteboard (org.osgi.service.http.runtime / org.osgi.service.jaxrs.runtime)
• CDI Integration (org.osgi.service.cdi.runtime)
• Felix Health Checks (org.apache.felix.hc.api)
• Gogo Shell (org.apache.felix.gogo.runtime)
• DMT Admin (org.osgi.service.dmt)

(Note: OSGi.fx queries Agent.getRuntimeCapabilities() to dynamically toggle UI elements based on the exact wirings active on the remote agent).

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⚙️ Configuration & Diagnostics

The agent behavior is controlled via OSGi Framework Properties (or System Properties). Overriding via System Properties is supported to allow dynamic recalibration via Gogo shell.

🌐 Connectivity & Transport

Property	Default	Description
osgi.fx.agent.socket.port	1234	TCP port for the management server. Format: [interface:]port.
osgi.fx.agent.socket.password	(none)	Shared secret for Socket authentication.
osgi.fx.agent.socket.secure	false	Enable TLS/SSL for the socket server.
osgi.fx.agent.socket.secure.sslcontext.filter	(none)	OSGi filter for a custom SSLContext.
osgi.fx.agent.mqtt.provider	osgi-messaging	MQTT implementation (osgi-messaging or custom). When using custom, the agent expects Mqtt5Publisher and Mqtt5Subscriber OSGi services.
osgi.fx.agent.mqtt.pubtopic	(none)	MQTT topic for outbound messages (Required for MQTT).
osgi.fx.agent.mqtt.subtopic	(none)	MQTT topic for inbound messages (Required for MQTT).

🔐 Authentication Configuration

Socket Password Authentication: To require password authentication for socket connections:

1. Set the osgi.fx.agent.socket.password system property on the agent (e.g., -Dosgi.fx.agent.socket.password=your-secure-password).
2. In the OSGi.fx Client connection settings, check “Requires Authentication” and enter the matching password. You can check “Save Password” to store credentials securely (encrypted with AES-256).

Socket Secure Configuration (SSL/TLS):

1. Set osgi.fx.agent.socket.secure=true.
2. Set osgi.fx.agent.socket.secure.sslcontext.filter to a filter string (e.g., (name=my_sslcontext)) to look up the SSLContext service.
3. Ensure a TrustStore is configured in the OSGi.fx Client to match the server’s KeyStore.

MQTT Username/Password Authentication: For MQTT brokers requiring authentication:

1. In the OSGi.fx Client connection settings, check “Requires Authentication” and enter your MQTT broker username and password.

MQTT OAuth/Token Authentication: If your MQTT broker requires OAuth tokens:

1. Configure the Token Configuration in the OSGi.fx Client.
2. Leave the Password field empty in the connection settings.

Token Configuration Format (JSON):

{
    "authServerURL": "https://auth.example.com/token",
    "clientId": "my-client-id",
    "clientSecret": "my-secret",
    "audience": "my-audience",
    "scope": "mqtt-scope"
}

🛡️ Resource Protection (Injection Attacks)

| Property | Default | Description | | :— | :— | :— | | osgi.fx.agent.rpc.max.decompressed.size | 250MB | Max GZIP decompression size (Zip Bomb Protection). | | osgi.fx.agent.rpc.max.collection.size | 1,000,000 | Max elements in decoded collections. | | osgi.fx.agent.rpc.max.map.size | 500,000 | Max entries in decoded maps. | | osgi.fx.agent.rpc.max.byte.array.size| 100MB | Max length of decoded byte arrays. | | osgi.fx.agent.gogo.allowlist | * | Allowed Gogo commands (e.g., osgi:*, equinox:start). | | osgi.fx.agent.cli.allowlist | * | Allowed OS shell commands. |

📝 Behavioral Configuration

| Property | Default | Description | | :— | :— | :— | | osgi.fx.enable.logging | false | Enable real-time log streaming. | | osgi.fx.enable.eventing | false | Enable real-time OSGi event streaming. | | osgi.fx.agent.auto.start.log.capture | false | Start circular log buffer on bundle activation. | | osgi.fx.agent.cli.enabled | true | Globally enable/disable underlying shell execution. | | osgi.fx.agent.gogo.enabled | true | Globally enable/disable Gogo shell execution. |

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🛡️ Security & Resilience

The agent implements several layers of protection to ensure secure and stable operation:

• Decompression Guard: Rejects LZ4 streams that expand beyond osgi.fx.agent.rpc.max.decompressed.size to prevent CPU exhaustion.
• Collection Bounds: Decoding is interrupted if a malicious payload requests the allocation of massive Maps or Lists (Collection Bombs).
• Sub-System Self-Protection: Explicitly blocks stop() and uninstall() operations targeting the System Bundle (ID 0) or the Agent Bundle itself to prevent management bridge “suicide”.
• Path Traversal Guard: Strictly validates file paths for data-file retrieval and local creation commands.
• Authentication: Socket transport can be locked behind a shared secret/password.
• TLS/SSL: All Socket communication can be encrypted via a framework-provided SSLContext.

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🔍 Advanced Diagnostics

🕵️ Classloader Leaks (Phantom Reference Graph)

The leaks() snapshot identifies bundles whose classes are improperly pinned in memory after the bundle has been uninstalled, updated, or refreshed.

Instead of relying on standard heap analysis which is incredibly slow, the agent utilizes a highly targeted Phantom Reference Graph:

1. Interception: A custom BundleTracker intercepts all bundle start events and extracts the internal BundleWiring classloader instance.
2. Phantom Queuing: It wraps the target classloader in a java.lang.ref.PhantomReference securely tied to a background ReferenceQueue.
3. Usage Counting: It maintains a thread-safe strict counter of active classloader instances per bundleId.
4. Daemon Polling: A zero-cost daemon thread (classloader-leak-detector) constantly polls the reference queue. When the JVM’s Garbage Collector successfully finalizes an old, unreferenced classloader, the counter is safely decremented.
5. Anomaly Detection: If the UI calls leaks() and the agent detects that an ACTIVE bundle possesses > 1 tracked classloaders (or an inactive bundle possesses any), it mathematically proves that a rogue thread, ThreadLocal, or external variable is illegally retaining the old bundle revision in memory, causing a severe memory leak.

⏱️ Startup Duration Tracking (BundleStartTimeCalculator)

The agent implements a SynchronousBundleListener that intercepts STARTING and STARTED events across the entire framework to provide precise boot analytics.

• Microsecond Precision: It calculates the exact clock-time delta for every bundle’s activation cycle.
• Bottleneck Identification: This allows the Console to visualize a “Waterfall” view of framework startup, highlighting slow-starting or blocking bundles.
• Persistence: Startup timings are available even for bundles that started before the agent was fully initialized, thanks to deep integration with the framework’s historical bundle states.

📉 Network-Aware Estimation & Local Storage

For environments with strict network limits (e.g., narrow-band IoT), the agent supports a “Save-then-Pull” workflow.

1. Estimation: The supervisor first calls estimation algorithms to decide if the payload is safe for the current network:
   • estimateHeapdumpSize(): Uses current memory usage and a conservative 25% GZIP compression estimate.
   • estimateSnapshotSize(): Reactively calculates size based on the count of active bundles, components, and services.
   • estimateThreadDumpSize(): Estimates size based on active thread counts and expected stack frame depth.
2. Local Creation: If the estimate is too large for real-time RPC, the UI can request local creation:
   • createHeapdumpLocally(path)
   • createSnapshotLocally(path)
   • createThreadDumpLocally(path) The resulting file can then be retrieved later or via a LargePayloadHandler.

📡 MQTT RPC & OSGi Messaging

The agent supports a fully decoupled MQTT 5 transport, which is essential for managing devices behind restrictive firewalls or NATs.

• OSGi Messaging Integration: By default, it leverages the osgi-messaging library (specifically in.bytehue.messaging.mqtt5.provider). This provides a standardized, industrial-strength way to handle asynchronous RPC over MQTT.
• Payload Compression: Just like the socket transport, MQTT payloads are LZ4 compressed and binary-encoded to stay within typical MQTT broker message limits (e.g., 256KB).
• Topic-Based Routing: Communication is Multiplexed over a pair of pubtopic and subtopic, allowing a single broker to manage thousands of agents.

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• com.osgifx.console.agent: The core implementation bundle.
  • admin: Domain-specific managers for OSGi services (Components, Config, Events, Metatype, etc.).
  • di: A high-performance, Jakarta-compliant Micro-DI engine.
  • redirector: The I/O hijacking engine supporting multi-mode terminal proxies.
  • rpc: The heart of the agent. Contains the BinaryCodec, LZ4 compression logic, and transport-agnostic framing.
  • starter: Contains the zero-dependency Activator and Gogo command bridge.
• com.osgifx.console.agent.api: The architectural contract.
  • Agent / AgentSnapshot: The primary management interfaces.
  • dto: A comprehensive suite of “Anemic” DTOs designed for minimal serialization footprints.
  • spi: Extension points for custom diagnostic logic and large payload offloading.

🕹️ Runtime Calibration (Gogo Shell)

The agent can be dynamically reconfigured at runtime without restarting the bundle. It registers several commands under the osgifx scope:

Command	Usage	Description
osgifx:startSocket	osgifx:startSocket [port=X host=Y]	Starts the socket server with optional overrides.
osgifx:stopSocket	osgifx:stopSocket	Gracefully shuts down the socket server.
osgifx:startMqtt	osgifx:startMqtt [provider=A pubTopic=B subTopic=C]	Starts the MQTT bridge.
osgifx:stopMqtt	osgifx:stopMqtt	shuts down the MQTT bridge.
osgifx:status	osgifx:status	Displays running endpoints and active configs.

Pro Tip: You can change the RPC behavior on-the-fly:

g! osgifx:startSocket [port=2222 host=0.0.0.0 secure=true]

🏗️ JVM Compatibility & Resilience

The agent is designed to be “Future-Proof” and compatible with Java 8 through Java 25+.

• Unsafe Fallback: To achieve maximum performance on HotSpot JVMs, it utilizes sun.misc.Unsafe for zero-copy memory operations.
• Graceful Degradation: If sun.misc.Unsafe is inaccessible (e.g., on newer Runtimes or non-HotSpot JVMs), it automatically falls back to LambdaMetafactory or standard Reflection without any functional loss.
• Zero-Dependency Core: It does not depend on any third-party libraries (except the optional MQTT provider), making it immune to “Dependency Hell”.

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© 2021-2026 Amit Kumar Mondal. Licensed under the Apache License, Version 2.0.