0
# Socket Capabilities
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Runtime capability detection and platform support validation for socket features and protocol availability across different operating systems and environments.
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## Core Imports
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```java
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import org.newsclub.net.unix.AFSocketCapability;
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import org.newsclub.net.unix.AFUNIXSocketCapability;
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import org.newsclub.net.unix.AFSocketCapabilityRequirement;
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```
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## Capabilities
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### AFSocketCapability
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Base enumeration for testing socket type and protocol support on the current platform.
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```java { .api }
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/**
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 * Enumeration of socket capabilities that can be tested
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 */
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public enum AFSocketCapability {
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    /** Peer credential support */
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    CAPABILITY_PEER_CREDENTIALS,
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    /** Ancillary message support */
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    CAPABILITY_ANCILLARY_MESSAGES,
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    /** File descriptor passing support */
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    CAPABILITY_FILE_DESCRIPTORS,
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    /** Linux abstract namespace support */
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    CAPABILITY_ABSTRACT_NAMESPACE,
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    /** Unix Domain Socket support */
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    CAPABILITY_UNIX_DOMAIN,
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    /** Unix datagram socket support */
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    CAPABILITY_UNIX_DATAGRAMS,
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    /** Native socket pair support */
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    CAPABILITY_NATIVE_SOCKETPAIR,
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    /** TIPC socket support (Linux) */
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    CAPABILITY_TIPC,
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    /** VSOCK socket support (VM communication) */
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    CAPABILITY_VSOCK,
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    /** AF_SYSTEM socket support (macOS) */
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    CAPABILITY_SYSTEM;
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    /**
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     * Tests if this capability is supported on the current platform
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     * @return true if capability is supported
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     */
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    public boolean isSupported();
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    /**
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     * Gets a human-readable description of this capability
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     * @return capability description
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     */
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    public String getDescription();
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}
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```
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**Usage Examples:**
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```java
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import org.newsclub.net.unix.*;
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// Test basic socket support
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public class CapabilityTester {
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    public static void main(String[] args) {
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        System.out.println("Socket Capability Report:");
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        for (AFSocketCapability capability : AFSocketCapability.values()) {
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            boolean supported = capability.isSupported();
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            System.out.printf("  %-20s: %s - %s%n", 
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                capability.name(), 
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                supported ? "✓ SUPPORTED" : "✗ NOT SUPPORTED",
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                capability.getDescription());
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        }
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        // Make decisions based on capabilities
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        if (AFSocketCapability.CAPABILITY_UNIX_DOMAIN.isSupported()) {
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            System.out.println("\nUnix Domain Sockets are available - proceeding with UDS implementation");
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            initializeUnixSocketService();
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        } else {
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            System.out.println("\nUnix Domain Sockets not available - falling back to TCP");
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            initializeTcpService();
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        }
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        // Test advanced features
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        if (AFSocketCapability.CAPABILITY_PEER_CREDENTIALS.isSupported()) {
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            System.out.println("Peer credentials available - enabling authentication");
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        }
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        if (AFSocketCapability.CAPABILITY_FILE_DESCRIPTORS.isSupported()) {
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            System.out.println("File descriptor passing available - enabling advanced IPC");
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        }
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        if (AFSocketCapability.CAPABILITY_ABSTRACT_NAMESPACE.isSupported()) {
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            System.out.println("Abstract namespace available - Linux features enabled");
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        }
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        if (AFSocketCapability.CAPABILITY_TIPC.isSupported()) {
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            System.out.println("TIPC support available for cluster communication");
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        }
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        if (AFSocketCapability.CAPABILITY_VSOCK.isSupported()) {
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            System.out.println("VSOCK support available for VM communication");
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        }
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    }
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    private static void initializeUnixSocketService() {
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        // Unix socket service initialization
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    }
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    private static void initializeTcpService() {
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        // TCP fallback service initialization
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    }
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}
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```
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### AFUNIXSocketCapability
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Unix Domain Socket-specific capabilities for platform-specific features and advanced functionality.
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```java { .api }
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/**
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 * Unix Domain Socket specific capabilities
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 */
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public enum AFUNIXSocketCapability {
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    /** Peer credentials support (PID, UID, GID) */
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    CAPABILITY_PEER_CREDENTIALS,
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    /** File descriptor passing support */
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    CAPABILITY_FILE_DESCRIPTORS,
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    /** Abstract namespace support (Linux) */
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    CAPABILITY_ABSTRACT_NAMESPACE,
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    /** Ancillary message support */
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    CAPABILITY_ANCILLARY_MESSAGES,
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    /** Socket pair creation support */
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    CAPABILITY_SOCKET_PAIRS,
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    /** Large buffer support for high-throughput operations */
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    CAPABILITY_LARGE_BUFFERS,
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    /** Non-blocking I/O support */
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    CAPABILITY_NON_BLOCKING_IO,
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    /** Address reuse support */
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    CAPABILITY_ADDRESS_REUSE;
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    /**
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     * Tests if this Unix socket capability is supported
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     * @return true if capability is supported
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     */
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    public boolean isSupported();
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    /**
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     * Gets the minimum version requirement for this capability
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     * @return version string or null if no specific requirement
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     */
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    public String getMinimumVersion();
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    /**
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     * Gets platform-specific notes for this capability
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     * @return platform notes or empty string
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     */
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    public String getPlatformNotes();
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}
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```
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**Usage Examples:**
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```java
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// Platform-specific feature detection
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public class UnixSocketFeatures {
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    public static void demonstrateCapabilities() {
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        System.out.println("Unix Domain Socket Feature Report:");
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        // Check peer credentials support
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        if (AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS.isSupported()) {
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            System.out.println("✓ Peer credentials available - can authenticate connections");
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            demonstratePeerCredentials();
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        } else {
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            System.out.println("✗ Peer credentials not available - using alternative auth");
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        }
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        // Check abstract namespace (Linux-specific)
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        if (AFUNIXSocketCapability.CAPABILITY_ABSTRACT_NAMESPACE.isSupported()) {
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            System.out.println("✓ Abstract namespace available - using abstract sockets");
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            demonstrateAbstractSockets();
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        } else {
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            System.out.println("✗ Abstract namespace not available - using filesystem sockets");
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        }
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        // Check file descriptor passing
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        if (AFUNIXSocketCapability.CAPABILITY_FILE_DESCRIPTORS.isSupported()) {
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            System.out.println("✓ File descriptor passing available");
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            demonstrateFileDescriptorPassing();
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        }
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        // Check large buffer support for high-performance scenarios
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        if (AFUNIXSocketCapability.CAPABILITY_LARGE_BUFFERS.isSupported()) {
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            System.out.println("✓ Large buffer support - optimizing for high throughput");
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            configureHighThroughput();
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        }
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    }
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    private static void demonstratePeerCredentials() {
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        try {
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            // Implementation would use peer credentials
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            System.out.println("  Peer credential authentication enabled");
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        } catch (Exception e) {
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            System.err.println("  Failed to configure peer credentials: " + e.getMessage());
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        }
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    }
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    private static void demonstrateAbstractSockets() {
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        try {
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            AFUNIXSocketAddress abstractAddr = AFUNIXSocketAddress.inAbstractNamespace("test-service");
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            System.out.println("  Using abstract socket: " + abstractAddr.getPathname());
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        } catch (Exception e) {
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            System.err.println("  Failed to create abstract socket: " + e.getMessage());
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        }
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    }
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    private static void demonstrateFileDescriptorPassing() {
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        System.out.println("  File descriptor passing configured");
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        // Implementation would set up FD passing
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    }
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    private static void configureHighThroughput() {
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        System.out.println("  Configuring large buffers for high throughput");
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        // Implementation would configure buffer sizes
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    }
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}
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```
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### AFSocketCapabilityRequirement
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Capability requirement specification for validating platform support before socket operations.
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```java { .api }
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/**
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 * Defines capability requirements for socket operations
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 */
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public class AFSocketCapabilityRequirement {
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    /**
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     * Creates a requirement for a single capability
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     * @param capability The required capability
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     * @return AFSocketCapabilityRequirement instance
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     */
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    public static AFSocketCapabilityRequirement require(AFSocketCapability capability);
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    /**
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     * Creates a requirement for a Unix-specific capability
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     * @param capability The required Unix capability
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     * @return AFSocketCapabilityRequirement instance
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     */
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    public static AFSocketCapabilityRequirement require(AFUNIXSocketCapability capability);
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    /**
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     * Creates a requirement for multiple capabilities (all must be supported)
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     * @param capabilities Required capabilities
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     * @return AFSocketCapabilityRequirement instance
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     */
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    public static AFSocketCapabilityRequirement requireAll(AFSocketCapability... capabilities);
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    /**
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     * Creates a requirement where at least one capability must be supported
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     * @param capabilities Alternative capabilities
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     * @return AFSocketCapabilityRequirement instance
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     */
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    public static AFSocketCapabilityRequirement requireAny(AFSocketCapability... capabilities);
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    /**
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     * Tests if the requirements are satisfied on current platform
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     * @return true if all requirements are met
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     */
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    public boolean isSatisfied();
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    /**
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     * Gets detailed information about unsatisfied requirements
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     * @return list of unsatisfied requirements
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     */
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    public List<String> getUnsatisfiedRequirements();
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    /**
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     * Throws exception if requirements are not satisfied
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     * @throws OperationNotSupportedSocketException if requirements not met
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     */
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    public void validateOrThrow() throws OperationNotSupportedSocketException;
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}
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```
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**Usage Examples:**
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```java
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// Requirement validation for robust applications
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public class RequirementBasedSocketService {
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    public void initializeService() throws OperationNotSupportedSocketException {
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        // Define service requirements
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        AFSocketCapabilityRequirement requirements = AFSocketCapabilityRequirement.requireAll(
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            AFSocketCapability.CAPABILITY_UNIX_DOMAIN,
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            AFSocketCapability.CAPABILITY_SERVER_SOCKETS,
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            AFSocketCapability.CAPABILITY_NIO_CHANNELS
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        );
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        // Validate requirements before proceeding
320
        if (!requirements.isSatisfied()) {
321
            List<String> unsatisfied = requirements.getUnsatisfiedRequirements();
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            System.err.println("Service requirements not met:");
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            for (String requirement : unsatisfied) {
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                System.err.println("  - " + requirement);
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            }
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            throw new OperationNotSupportedSocketException("Platform does not meet service requirements");
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        }
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        System.out.println("All requirements satisfied - initializing service");
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        startSocketService();
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    }
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    public void initializeAuthenticationService() {
334
        // Authentication service with peer credentials or alternative
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        AFSocketCapabilityRequirement authRequirement = AFSocketCapabilityRequirement.requireAny(
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            AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS,
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            AFUNIXSocketCapability.CAPABILITY_FILE_DESCRIPTORS
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        );
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340
        if (authRequirement.isSatisfied()) {
341
            if (AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS.isSupported()) {
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                initializePeerCredentialAuth();
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            } else {
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                initializeFileDescriptorAuth();
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            }
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        } else {
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            initializeTokenBasedAuth();
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        }
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    }
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    public void validateCapabilitiesWithFeedback() {
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        // Comprehensive capability validation with user feedback
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        System.out.println("Validating platform capabilities...");
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355
        try {
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            AFSocketCapabilityRequirement.require(AFSocketCapability.CAPABILITY_UNIX_DOMAIN)
357
                .validateOrThrow();
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            System.out.println("✓ Unix Domain Sockets supported");
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        } catch (OperationNotSupportedSocketException e) {
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            System.err.println("✗ Unix Domain Sockets not supported: " + e.getMessage());
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            return;
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        }
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        // Check optional features
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        AFSocketCapabilityRequirement optionalFeatures = AFSocketCapabilityRequirement.requireAny(
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            AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS,
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            AFUNIXSocketCapability.CAPABILITY_ABSTRACT_NAMESPACE,
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            AFUNIXSocketCapability.CAPABILITY_FILE_DESCRIPTORS
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        );
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        if (optionalFeatures.isSatisfied()) {
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            System.out.println("✓ Advanced Unix socket features available");
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        } else {
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            System.out.println("! No advanced features available - using basic functionality");
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        }
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    }
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    private void startSocketService() {
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        System.out.println("Socket service started");
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    }
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    private void initializePeerCredentialAuth() {
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        System.out.println("Initializing peer credential authentication");
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    }
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386
    private void initializeFileDescriptorAuth() {
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        System.out.println("Initializing file descriptor authentication");
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    }
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    private void initializeTokenBasedAuth() {
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        System.out.println("Initializing token-based authentication");
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    }
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}
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```
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## Capability Detection Patterns
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### Runtime Platform Detection
399

400
```java
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// Comprehensive platform capability detection
402
public class PlatformCapabilities {
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404
    public static class CapabilityReport {
405
        private final Map<AFSocketCapability, Boolean> socketCapabilities;
406
        private final Map<AFUNIXSocketCapability, Boolean> unixCapabilities;
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        private final String platformInfo;
408
        
409
        public CapabilityReport() {
410
            this.socketCapabilities = detectSocketCapabilities();
411
            this.unixCapabilities = detectUnixCapabilities();
412
            this.platformInfo = detectPlatformInfo();
413
        }
414
        
415
        public boolean hasCapability(AFSocketCapability capability) {
416
            return socketCapabilities.getOrDefault(capability, false);
417
        }
418
        
419
        public boolean hasCapability(AFUNIXSocketCapability capability) {
420
            return unixCapabilities.getOrDefault(capability, false);
421
        }
422
        
423
        public String getPlatformInfo() {
424
            return platformInfo;
425
        }
426
        
427
        public void printReport() {
428
            System.out.println("Platform Capability Report");
429
            System.out.println("==========================");
430
            System.out.println("Platform: " + platformInfo);
431
            System.out.println();
432
            
433
            System.out.println("Socket Capabilities:");
434
            for (Map.Entry<AFSocketCapability, Boolean> entry : socketCapabilities.entrySet()) {
435
                System.out.printf("  %-25s: %s%n", 
436
                    entry.getKey().name(), 
437
                    entry.getValue() ? "✓" : "✗");
438
            }
439
            
440
            System.out.println();
441
            System.out.println("Unix Socket Capabilities:");
442
            for (Map.Entry<AFUNIXSocketCapability, Boolean> entry : unixCapabilities.entrySet()) {
443
                System.out.printf("  %-30s: %s%n", 
444
                    entry.getKey().name(), 
445
                    entry.getValue() ? "✓" : "✗");
446
                
447
                if (entry.getValue()) {
448
                    String notes = entry.getKey().getPlatformNotes();
449
                    if (!notes.isEmpty()) {
450
                        System.out.println("    " + notes);
451
                    }
452
                }
453
            }
454
        }
455
        
456
        private Map<AFSocketCapability, Boolean> detectSocketCapabilities() {
457
            Map<AFSocketCapability, Boolean> capabilities = new HashMap<>();
458
            for (AFSocketCapability capability : AFSocketCapability.values()) {
459
                capabilities.put(capability, capability.isSupported());
460
            }
461
            return capabilities;
462
        }
463
        
464
        private Map<AFUNIXSocketCapability, Boolean> detectUnixCapabilities() {
465
            Map<AFUNIXSocketCapability, Boolean> capabilities = new HashMap<>();
466
            for (AFUNIXSocketCapability capability : AFUNIXSocketCapability.values()) {
467
                capabilities.put(capability, capability.isSupported());
468
            }
469
            return capabilities;
470
        }
471
        
472
        private String detectPlatformInfo() {
473
            return System.getProperty("os.name") + " " + 
474
                   System.getProperty("os.version") + " " + 
475
                   System.getProperty("os.arch");
476
        }
477
    }
478
    
479
    public static void main(String[] args) {
480
        CapabilityReport report = new CapabilityReport();
481
        report.printReport();
482
        
483
        // Example usage based on capabilities
484
        if (report.hasCapability(AFSocketCapability.CAPABILITY_UNIX_DOMAIN)) {
485
            System.out.println("\nUnix Domain Sockets available - configuring UDS service");
486
            
487
            if (report.hasCapability(AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS)) {
488
                System.out.println("Enabling peer credential authentication");
489
            }
490
            
491
            if (report.hasCapability(AFUNIXSocketCapability.CAPABILITY_ABSTRACT_NAMESPACE)) {
492
                System.out.println("Using abstract namespace for temporary sockets");
493
            }
494
        }
495
    }
496
}
497
```
498

499
### Application Configuration Based on Capabilities
500

501
```java
502
// Application configuration that adapts to platform capabilities
503
public class AdaptiveSocketConfiguration {
504
    private final CapabilityReport capabilities;
505
    
506
    public AdaptiveSocketConfiguration() {
507
        this.capabilities = new PlatformCapabilities.CapabilityReport();
508
    }
509
    
510
    public SocketConfiguration getOptimalConfiguration() {
511
        SocketConfiguration config = new SocketConfiguration();
512
        
513
        // Base configuration
514
        if (capabilities.hasCapability(AFSocketCapability.CAPABILITY_UNIX_DOMAIN)) {
515
            config.setSocketType(SocketType.UNIX_DOMAIN);
516
        } else {
517
            config.setSocketType(SocketType.TCP_FALLBACK);
518
        }
519
        
520
        // Authentication configuration
521
        if (capabilities.hasCapability(AFUNIXSocketCapability.CAPABILITY_PEER_CREDENTIALS)) {
522
            config.setAuthenticationMethod(AuthMethod.PEER_CREDENTIALS);
523
        } else if (capabilities.hasCapability(AFUNIXSocketCapability.CAPABILITY_FILE_DESCRIPTORS)) {
524
            config.setAuthenticationMethod(AuthMethod.FILE_DESCRIPTOR);
525
        } else {
526
            config.setAuthenticationMethod(AuthMethod.TOKEN_BASED);
527
        }
528
        
529
        // Address configuration
530
        if (capabilities.hasCapability(AFUNIXSocketCapability.CAPABILITY_ABSTRACT_NAMESPACE)) {
531
            config.setAddressType(AddressType.ABSTRACT);
532
        } else {
533
            config.setAddressType(AddressType.FILESYSTEM);
534
        }
535
        
536
        // Performance configuration
537
        if (capabilities.hasCapability(AFUNIXSocketCapability.CAPABILITY_LARGE_BUFFERS)) {
538
            config.setBufferSize(65536); // 64KB buffers
539
        } else {
540
            config.setBufferSize(8192);  // 8KB buffers
541
        }
542
        
543
        return config;
544
    }
545
    
546
    public static class SocketConfiguration {
547
        private SocketType socketType;
548
        private AuthMethod authenticationMethod;
549
        private AddressType addressType;
550
        private int bufferSize;
551
        
552
        // Getters and setters
553
        public SocketType getSocketType() { return socketType; }
554
        public void setSocketType(SocketType socketType) { this.socketType = socketType; }
555
        
556
        public AuthMethod getAuthenticationMethod() { return authenticationMethod; }
557
        public void setAuthenticationMethod(AuthMethod authenticationMethod) { this.authenticationMethod = authenticationMethod; }
558
        
559
        public AddressType getAddressType() { return addressType; }
560
        public void setAddressType(AddressType addressType) { this.addressType = addressType; }
561
        
562
        public int getBufferSize() { return bufferSize; }
563
        public void setBufferSize(int bufferSize) { this.bufferSize = bufferSize; }
564
        
565
        @Override
566
        public String toString() {
567
            return String.format("SocketConfiguration{socketType=%s, auth=%s, address=%s, buffer=%d}",
568
                socketType, authenticationMethod, addressType, bufferSize);
569
        }
570
    }
571
    
572
    public enum SocketType { UNIX_DOMAIN, TCP_FALLBACK }
573
    public enum AuthMethod { PEER_CREDENTIALS, FILE_DESCRIPTOR, TOKEN_BASED }
574
    public enum AddressType { ABSTRACT, FILESYSTEM }
575
}
576
```