Refactor RESPTranslator to mutate the passed ByteBuffer directly.

Motivation:

During proposal review, it was pointed out that the code with a position index was redundant and error prone over relying on `ByteBuffer`'s `readerIndex`.

Modifications:

Refactored `RESPTranslator` to rely on `ByteBuffer.readerIndex` for position of current parsing cursor,
and eliminated `ParsingResult` enum to instead return `RESPValue?`.

The implementation for writing out `RESPValue` has been expanded to `RESPValueConvertible` and moved to an extension of `ByteBuffer`.

Result:

Parsing `RESPValue` into and out of `ByteBuffer` should be less error-prone and more straight forward.

This contributes to issues #47 and #55

Author: Mordil

Sources/RedisNIO/ChannelHandlers/RedisByteDecoder.swift

@@ -21,18 +21,19 @@ import NIO
 public final class RedisByteDecoder: ByteToMessageDecoder {
     /// `ByteToMessageDecoder.InboundOut`
     public typealias InboundOut = RESPValue
+    
+    private let parser: RESPTranslator
+    
+    public init() {
+        self.parser = RESPTranslator()
+    }
 
     /// See `ByteToMessageDecoder.decode(context:buffer:)`
     public func decode(context: ChannelHandlerContext, buffer: inout ByteBuffer) throws -> DecodingState {
-        var position = 0
-
-        switch try RESPTranslator.parseBytes(&buffer, fromIndex: &position) {
-        case .incomplete: return .needMoreData
-        case let .parsed(value):
-            context.fireChannelRead(wrapInboundOut(value))
-            buffer.moveReaderIndex(forwardBy: position)
-            return .continue
-        }
+        guard let value = try self.parser.parseBytes(from: &buffer) else { return .needMoreData }
+        
+        context.fireChannelRead(wrapInboundOut(value))
+        return .continue
     }
 
     /// See `ByteToMessageDecoder.decodeLast(context:buffer:seenEOF)`

Sources/RedisNIO/ChannelHandlers/RedisMessageEncoder.swift

@@ -33,7 +33,7 @@ public final class RedisMessageEncoder: MessageToByteEncoder {
     ///
     /// See [https://redis.io/topics/protocol](https://redis.io/topics/protocol) and `RESPEncoder.encode(data:out:)`
     public func encode(data: RESPValue, out: inout ByteBuffer) throws {
-        RESPTranslator.writeValue(data, into: &out)
+        out.writeRESPValue(data)
 
         logger.debug("Encoded \(data) to \(getPrintableString(for: &out))")
     }