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fix(asar): emit integrity blocks on real block boundaries #171

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fix(asar): emit integrity blocks on real block boundaries #171

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26 changes: 21 additions & 5 deletions AsarSharp/Integrity/IntegrityHelper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,8 +46,10 @@ public static FileIntegrity CreatePlaceholder(long fileSize)

public static FileIntegrity GetFileIntegrity(string path, byte[] reusableBuffer = null)
{
bool ownBuffer = reusableBuffer == null;
if (ownBuffer) reusableBuffer = new byte[BLOCK_SIZE];
// A block must be exactly BLOCK_SIZE for Electron to validate it, so a buffer
// that cannot hold a whole block is replaced rather than used as-is.
if (reusableBuffer == null || reusableBuffer.Length < BLOCK_SIZE)
reusableBuffer = new byte[BLOCK_SIZE];

using (var fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read,
65536, FileOptions.SequentialScan))
Expand All @@ -58,14 +60,28 @@ public static FileIntegrity GetFileIntegrity(string path, byte[] reusableBuffer
? (int)((fileStream.Length + BLOCK_SIZE - 1) / BLOCK_SIZE)
: 0;
var blockHashes = new List<string>(estimatedBlockCount);
int blockFill = 0;
int bytesRead;

while ((bytesRead = fileStream.Read(reusableBuffer, 0, reusableBuffer.Length)) > 0)
// Stream.Read may return fewer bytes than requested at any point, so reads
// accumulate into the block buffer and a hash is only emitted once a full
// block is present. Hashing each read directly would turn a short read into
// an undersized block and desynchronise every boundary after it.
while ((bytesRead = fileStream.Read(reusableBuffer, blockFill, BLOCK_SIZE - blockFill)) > 0)
{
blockHashes.Add(ToLowerHex(blockHash.ComputeHash(reusableBuffer, 0, bytesRead)));
fileHash.AppendData(reusableBuffer, 0, bytesRead);
fileHash.AppendData(reusableBuffer, blockFill, bytesRead);
blockFill += bytesRead;

if (blockFill == BLOCK_SIZE)
{
blockHashes.Add(ToLowerHex(blockHash.ComputeHash(reusableBuffer, 0, BLOCK_SIZE)));
blockFill = 0;
}
}

if (blockFill > 0)
blockHashes.Add(ToLowerHex(blockHash.ComputeHash(reusableBuffer, 0, blockFill)));

return new FileIntegrity
{
Algorithm = ALGORITHM,
Expand Down