Channel Management

/**
 * Primary channel provider for creating gRPC ManagedChannels
 * Supports connection pooling, DirectPath, and comprehensive configuration
 */
public final class InstantiatingGrpcChannelProvider implements TransportChannelProvider {
    /** Create a new builder for channel provider configuration */
    public static Builder newBuilder();
    
    /** Get the transport name identifier */
    public String getTransportName();
    
    /** Create and return the configured transport channel */
    public TransportChannel getTransportChannel() throws IOException;
    
    /** Get the configured endpoint */
    public String getEndpoint();
    
    /** Get keep-alive time duration setting */
    public Duration getKeepAliveTimeDuration();
    
    /** Get keep-alive timeout duration setting */
    public Duration getKeepAliveTimeoutDuration();
    
    /** Get keep-alive without calls setting */
    public Boolean getKeepAliveWithoutCalls();
    
    /** Get maximum inbound metadata size setting */
    public Integer getMaxInboundMetadataSize();
    
    /** Get channel pool configuration settings */
    public ChannelPoolSettings getChannelPoolSettings();
    
    /** Create a new builder from this provider */
    public Builder toBuilder();
}

/**
 * Builder for InstantiatingGrpcChannelProvider with comprehensive configuration
 */
public static final class InstantiatingGrpcChannelProvider.Builder {
    /** Set the service endpoint URL */
    public Builder setEndpoint(String endpoint);
    
    /** Set credentials for authentication */
    public Builder setCredentials(Credentials credentials);
    
    /** Set the header provider for request headers */
    public Builder setHeaderProvider(HeaderProvider headerProvider);
    
    /** Set channel configurator for advanced ManagedChannelBuilder customization */
    public Builder setChannelConfigurator(ApiFunction<ManagedChannelBuilder, ManagedChannelBuilder> channelConfigurator);
    
    /** Set keep-alive time for connections */
    public Builder setKeepAliveTime(Duration keepAliveTime);
    
    /** Set keep-alive timeout for connections */
    public Builder setKeepAliveTimeout(Duration keepAliveTimeout);
    
    /** Set whether to send keep-alive pings without active calls */
    public Builder setKeepAliveWithoutCalls(Boolean keepAliveWithoutCalls);
    
    /** Set maximum inbound message size */
    public Builder setMaxInboundMessageSize(Integer maxInboundMessageSize);
    
    /** Set maximum inbound metadata size */
    public Builder setMaxInboundMetadataSize(Integer maxInboundMetadataSize);
    
    /** Set channel pool settings for connection pooling */
    public Builder setChannelPoolSettings(ChannelPoolSettings channelPoolSettings);
    
    /** Set DirectPath service configuration */
    public Builder setDirectPathServiceConfig(Map<String, ?> serviceConfig);
    
    /** Set quota project ID for billing */
    public Builder setQuotaProjectId(String quotaProjectId);
    
    /** Set custom client interceptor provider */
    public Builder setInterceptorProvider(GrpcInterceptorProvider interceptorProvider);
    
    /** Build the configured channel provider */
    public InstantiatingGrpcChannelProvider build();
}

/**
 * Settings for channel pool behavior and scaling
 * Supports dynamic scaling based on RPC load
 */
public abstract class ChannelPoolSettings {
    /** Create a statically sized channel pool */
    public static ChannelPoolSettings staticallySized(int size);
    
    /** Create a new builder for channel pool settings */
    public static Builder builder();
    
    /** Get minimum RPCs per channel threshold */
    public int getMinRpcsPerChannel();
    
    /** Get maximum RPCs per channel threshold */
    public int getMaxRpcsPerChannel();
    
    /** Get minimum number of channels in pool */
    public int getMinChannelCount();
    
    /** Get maximum number of channels in pool */
    public int getMaxChannelCount();
    
    /** Get initial number of channels to create */
    public int getInitialChannelCount();
    
    /** Check if preemptive refresh is enabled */
    public boolean isPreemptiveRefreshEnabled();
    
    /** Create a builder from these settings */
    public Builder toBuilder();
}

/**
 * Builder for ChannelPoolSettings with scaling configuration
 */
public abstract static class ChannelPoolSettings.Builder {
    /** Set minimum RPCs per channel before scaling up */
    public Builder setMinRpcsPerChannel(int minRpcsPerChannel);
    
    /** Set maximum RPCs per channel before scaling up */
    public Builder setMaxRpcsPerChannel(int maxRpcsPerChannel);
    
    /** Set minimum number of channels to maintain */
    public Builder setMinChannelCount(int minChannelCount);
    
    /** Set maximum number of channels allowed */
    public Builder setMaxChannelCount(int maxChannelCount);
    
    /** Set initial number of channels to create */
    public Builder setInitialChannelCount(int initialChannelCount);
    
    /** Enable or disable preemptive refresh of channels */
    public Builder setPreemptiveRefreshEnabled(boolean preemptiveRefreshEnabled);
    
    /** Build the channel pool settings */
    public ChannelPoolSettings build();
}

/**
 * Factory interface for custom channel creation
 */
public interface ChannelFactory {
    /** Create a ManagedChannel with the given configuration */
    ManagedChannel createChannel(String endpoint, Map<String, ?> channelArgs);
}

/**
 * Interface for preparing ManagedChannels for requests
 * Used for connection warming and pre-loading
 */
public interface ChannelPrimer {
    /** Prepare the given channel for use */
    void primeChannel(ManagedChannel managedChannel);
}

import com.google.api.gax.grpc.InstantiatingGrpcChannelProvider;
import com.google.auth.oauth2.GoogleCredentials;

// Create basic channel provider
InstantiatingGrpcChannelProvider provider = 
    InstantiatingGrpcChannelProvider.newBuilder()
        .setEndpoint("translate.googleapis.com:443")
        .setCredentials(GoogleCredentials.getApplicationDefault())
        .build();

// Get the transport channel
TransportChannel channel = provider.getTransportChannel();

import com.google.api.gax.grpc.ChannelPoolSettings;
import com.google.api.gax.grpc.InstantiatingGrpcChannelProvider;

// Configure sophisticated channel pooling
ChannelPoolSettings poolSettings = ChannelPoolSettings.builder()
    .setMinChannelCount(2)
    .setMaxChannelCount(10)
    .setMinRpcsPerChannel(5)
    .setMaxRpcsPerChannel(100)
    .setPreemptiveRefreshEnabled(true)
    .build();

InstantiatingGrpcChannelProvider provider = 
    InstantiatingGrpcChannelProvider.newBuilder()
        .setEndpoint("your-service.googleapis.com:443")
        .setChannelPoolSettings(poolSettings)
        .setKeepAliveTime(Duration.ofMinutes(2))
        .setKeepAliveTimeout(Duration.ofSeconds(30))
        .build();

import io.grpc.ManagedChannelBuilder;
import io.grpc.netty.shaded.io.grpc.netty.NettyChannelBuilder;

// Advanced channel configuration with custom configurator
InstantiatingGrpcChannelProvider provider = 
    InstantiatingGrpcChannelProvider.newBuilder()
        .setEndpoint("your-service.googleapis.com:443")
        .setChannelConfigurator(channelBuilder -> {
            return ((NettyChannelBuilder) channelBuilder)
                .maxInboundMessageSize(4 * 1024 * 1024) // 4MB
                .usePlaintext(); // For testing only
        })
        .build();

import java.util.Map;
import java.util.HashMap;

// Configure DirectPath for optimized Google Cloud connections
Map<String, Object> directPathConfig = new HashMap<>();
directPathConfig.put("loadBalancingConfig", 
    List.of(Map.of("grpclb", Map.of("serviceName", "your-service"))));

InstantiatingGrpcChannelProvider provider = 
    InstantiatingGrpcChannelProvider.newBuilder()
        .setEndpoint("your-service.googleapis.com:443")
        .setDirectPathServiceConfig(directPathConfig)
        .build();