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Fix potential blocking read by detecting end of decryption block #24

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Fix potential blocking read by detecting end of decryption block #24

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13 changes: 11 additions & 2 deletions Zstandard.Net/ZstandardStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -224,6 +224,7 @@ public override int Read(byte[] buffer, int offset, int count)
try
{
var length = 0;
var endOfBlockFound = false;

if (this.isInitialized == false)
{
Expand Down Expand Up @@ -262,14 +263,22 @@ public override int Read(byte[] buffer, int offset, int count)
this.outputBuffer.Position = UIntPtr.Zero;

// decompress inputBuffer to outputBuffer
Interop.ThrowIfError(Interop.ZSTD_decompressStream(this.zstream, this.outputBuffer, this.inputBuffer));
var nextSrcNeeded = Interop.ZSTD_decompressStream(this.zstream, this.outputBuffer, this.inputBuffer);
Interop.ThrowIfError(nextSrcNeeded);

//It is possible that nextSrcNeeded == 0 when at the end of a block but outputBufferPosition is not yet 0, and there are not any more bytes to be read on the incoming stream.
//If that happens the next time ZSTD_decompressStream() is called then nextSrcNeeded will be the next header size (i.e. 9) instead of 0, then when when outputBufferPosition does hit 0
//it will not "break" which will result in an additional stream read, which can hang.
//To avoid that we need to set a flag when nextSrcNeeded == 0, so when outputBufferPosition also reaches 0, it will hit the "break".
if (nextSrcNeeded.ToUInt64() == 0UL) endOfBlockFound = true;

// calculate progress in outputBuffer
var outputBufferPosition = (int)this.outputBuffer.Position.ToUInt32();

if (outputBufferPosition == 0)
{
// the internal buffer is depleted, we're either done
if (this.dataDepleted) break;
if (this.dataDepleted || endOfBlockFound) break;

// or we need more bytes
this.dataSkipRead = false;
Expand Down