Add a few more comments.

Author: MrMage

Sources/SwiftGRPCNIO/GRPCChannelHandler.swift

@@ -4,17 +4,22 @@ import SwiftGRPC
 import NIO
 import NIOHTTP1
 
+// Processes individual gRPC messages and stream-close events on a HTTP2 channel.
 public protocol GRPCCallHandler {
   func messageReceived(_ message: inout NIO.ByteBuffer)
   func endOfStreamReceived()
 }
 
+// Provides `GRPCCallHandler` objects for the methods on a particular service name.
 public protocol CallHandlerProvider {
   var serviceName: String { get }
 
   func handleMethod(_ methodName: String, headers: HTTPHeaders, serverHandler: GRPCChannelHandler, ctx: ChannelHandlerContext) -> GRPCCallHandler?
 }
 
+// Listens on a newly-opened HTTP2 channel and waits for the request headers to become available.
+// Once those are available, asks the `CallHandlerProvider` corresponding to the request's service name for an
+// `GRPCCallHandler` object. That object is then forwarded the individual gRPC messages.
 public final class GRPCChannelHandler: ChannelInboundHandler {
   public typealias InboundIn = RawGRPCServerRequestPart
   public typealias OutboundOut = RawGRPCServerResponsePart

Sources/SwiftGRPCNIO/GRPCServer.swift

@@ -3,6 +3,7 @@ import NIO
 import NIOHTTP1
 import NIOHTTP2
 
+// Wrapper object to manage the lifecycle of a gRPC server.
 public final class GRPCServer {
   public static func start(
     hostname: String,
@@ -17,6 +18,7 @@ public final class GRPCServer {
 
       // Set the handlers that are applied to the accepted Channels
       .childChannelInitializer { channel in
+        //! FIXME: Add an option for gRPC-via-HTTP1 (pPRC).
         return channel.pipeline.add(handler: HTTP2Parser(mode: .server)).then {
           let multiplexer = HTTP2StreamMultiplexer { (channel, streamID) -> EventLoopFuture<Void> in
             return channel.pipeline.add(handler: HTTP2ToHTTP1ServerCodec(streamID: streamID))

Sources/SwiftGRPCNIO/GRPCServerCodec.swift

@@ -17,6 +17,7 @@ public enum GRPCServerResponsePart<MessageType: Message> {
 
 /// A simple channel handler that translates raw gRPC packets into decoded protobuf messages,
 /// and vice versa.
+/// **Currently unused, as we do not yet know the request's method name (and thus message types) when this object is instantiated.**
 public final class GRPCServerCodec<RequestMessage: Message, ResponseMessage: Message>: ChannelInboundHandler, ChannelOutboundHandler {
   public typealias InboundIn = RawGRPCServerRequestPart
   public typealias InboundOut = GRPCServerRequestPart<RequestMessage>

Sources/SwiftGRPCNIO/StatusSendingHandler.swift

@@ -4,6 +4,8 @@ import SwiftGRPC
 import NIO
 import NIOHTTP1
 
+// Provides a means for decoding incoming gRPC messages into protobuf objects, and exposes a promise that should be
+// fulfilled when it is time to return a status to the client.
 public class StatusSendingHandler<RequestMessage: Message>: GRPCCallHandler {
   let statusPromise: EventLoopPromise<ServerStatus>
 

Sources/SwiftGRPCNIO/UnaryResponseHandler.swift

@@ -4,6 +4,8 @@ import SwiftGRPC
 import NIO
 import NIOHTTP1
 
+// Exposes a promise that should be fulfilled when it is time to return a unary response (for unary and client-streaming
+// calls) to the client. Also see `StatusSendingHandler`.
 public class UnaryResponseHandler<RequestMessage: Message, ResponseMessage: Message>: StatusSendingHandler<RequestMessage> {
   let responsePromise: EventLoopPromise<ResponseMessage>