Fixes zlib function + write function

Author: mustii

Sources/GRPC/Compression/Zlib.swift

@@ -57,9 +57,7 @@ enum Zlib {
       //   by deflateBound() if flush options other than Z_FINISH or Z_NO_FLUSH are used.
       let upperBound = CGRPCZlib_deflateBound(&self.stream.zstream, UInt(input.readableBytes))
 
-      // Note: readWithUnsafeMutableReadableBytes leads to an assertion whenever used
-      // while the writer is bigger than the reader
-      return try input.withUnsafeMutableReadableBytes { inputPointer in
+      return try input.readWithUnsafeMutableReadableBytes { inputPointer -> (Int, Int) in
 
         self.stream.nextInputBuffer = CGRPCZlib_castVoidToBytefPointer(inputPointer.baseAddress!)
         self.stream.availableInputBytes = inputPointer.count
@@ -69,12 +67,15 @@ enum Zlib {
           self.stream.availableInputBytes = 0
         }
 
-        return try output.writeWithUnsafeMutableBytes(minimumWritableBytes: Int(upperBound)) { outputPointer in
+        let writtenBytes = try output.writeWithUnsafeMutableBytes(minimumWritableBytes: Int(upperBound)) { outputPointer in
           try self.stream.deflate(
              outputBuffer: CGRPCZlib_castVoidToBytefPointer(outputPointer.baseAddress!),
              outputBufferSize: outputPointer.count
           )
         }
+        
+        let bytesRead = inputPointer.count - self.stream.availableInputBytes
+        return (bytesRead, writtenBytes)
       }
     }
 

Sources/GRPC/LengthPrefixedMessageWriter.swift

@@ -50,8 +50,7 @@ internal struct LengthPrefixedMessageWriter {
   /// - Precondition: `compression.supported` is `true`.
   /// - Note: See `LengthPrefixedMessageReader` for more details on the format.
   func write(_ payload: GRPCPayload, into buffer: inout ByteBuffer, disableCompression: Bool = false) throws {
-    buffer.reserveCapacity(MemoryLayout.size(ofValue: payload) + LengthPrefixedMessageWriter.metadataLength)
-    
+    buffer.reserveCapacity(buffer.writerIndex + LengthPrefixedMessageWriter.metadataLength)
     if !disableCompression, let compressor = self.compressor {
       // Set the compression byte.
       buffer.writeInteger(UInt8(1))