Unified exception messages and read buffer management

Author: sakno

src/DotNext.IO/Buffers/IBufferedReader.cs

@@ -1,5 +1,8 @@
 namespace DotNext.Buffers;
 
+/// <summary>
+/// Represents buffered reader.
+/// </summary>
 public interface IBufferedReader : IBufferedChannel
 {
     /// <summary>

src/DotNext.IO/ExceptionMessages.cs

@@ -22,7 +22,9 @@ internal static string DirectoryNotFound(string path)
 
     internal static string WriterInReadMode => (string)Resources.Get();
 
-    internal static string NoConsumerProvided => (string)Resources.Get();
-
     internal static string FileHandleClosed => (string)Resources.Get();
+
+    internal static string ReadBufferNotEmpty => (string)Resources.Get();
+
+    internal static string WriteBufferNotEmpty => (string)Resources.Get();
 }

src/DotNext.IO/ExceptionMessages.restext

@@ -3,5 +3,6 @@ StreamNotWritable=Stream is not writable
 StreamNotReadable=Stream is not readable
 DirectoryNotFound=Directory {0} doesn't exist
 WriterInReadMode=The writer is in read-only mode. Dispose active memory manager obtained from writer
-NoConsumerProvided=No actual consumer is provided
-FileHandleClosed=The file handle is closed
+FileHandleClosed=The file handle is closed
+ReadBufferNotEmpty=The internal buffer has unconsumed data to read
+WriteBufferNotEmpty=The internal buffer has data to flush

src/DotNext.IO/IO/FileReader.cs

@@ -75,7 +75,7 @@ public long FilePosition
             ArgumentOutOfRangeException.ThrowIfNegative(value);
 
             if (HasBufferedData)
-                throw new InvalidOperationException();
+                throw new InvalidOperationException(ExceptionMessages.ReadBufferNotEmpty);
 
             fileOffset = value;
         }
@@ -199,25 +199,32 @@ public ValueTask<bool> ReadAsync(CancellationToken token = default)
 
     private ValueTask<int> ReadCoreAsync(CancellationToken token)
     {
-        Memory<byte> buffer;
+        return PrepareReadBuffer(out var readBuffer)
+            ? RandomAccess.ReadAsync(handle, readBuffer.Slice(bufferEnd), fileOffset + bufferEnd, token)
+            : ValueTask.FromException<int>(new InternalBufferOverflowException());
+    }
+
+    private bool PrepareReadBuffer(out Memory<byte> readBuffer)
+    {
         switch (bufferStart)
         {
             case 0 when bufferEnd == maxBufferSize:
-                return ValueTask.FromException<int>(new InternalBufferOverflowException());
+                readBuffer = default;
+                return false;
             case > 0:
-                buffer = this.buffer.Memory;
+                readBuffer = buffer.Memory;
 
                 // compact buffer
-                buffer[bufferStart..bufferEnd].CopyTo(buffer);
+                readBuffer[bufferStart..bufferEnd].CopyTo(readBuffer);
                 bufferEnd -= bufferStart;
                 bufferStart = 0;
                 break;
             default:
-                buffer = EnsureBufferAllocated().Memory;
+                readBuffer = EnsureBufferAllocated().Memory;
                 break;
         }
 
-        return RandomAccess.ReadAsync(handle, buffer.Slice(bufferEnd), fileOffset + bufferEnd, token);
+        return true;
     }
 
     /// <summary>
@@ -238,24 +245,10 @@ public bool Read()
 
     private bool ReadCore()
     {
-        Span<byte> buffer;
-        switch (bufferStart)
-        {
-            case 0 when bufferEnd == maxBufferSize:
-                throw new InternalBufferOverflowException();
-            case > 0:
-                // compact buffer
-                buffer = this.buffer.Span;
-                buffer[bufferStart..bufferEnd].CopyTo(buffer);
-                bufferEnd -= bufferStart;
-                bufferStart = 0;
-                break;
-            default:
-                buffer = EnsureBufferAllocated().Span;
-                break;
-        }
+        if (!PrepareReadBuffer(out var readBuffer))
+            throw new InternalBufferOverflowException();
 
-        var count = RandomAccess.Read(handle, buffer.Slice(bufferEnd), fileOffset + bufferEnd);
+        var count = RandomAccess.Read(handle, readBuffer.Span.Slice(bufferEnd), fileOffset + bufferEnd);
         bufferEnd += count;
 
         ResetIfNeeded();

src/DotNext.IO/IO/FileWriter.cs

@@ -169,7 +169,7 @@ public long FilePosition
             ArgumentOutOfRangeException.ThrowIfNegative(value);
 
             if (HasBufferedData)
-                throw new InvalidOperationException();
+                throw new InvalidOperationException(ExceptionMessages.WriteBufferNotEmpty);
 
             fileOffset = value;
         }