From d1378dc5d1cc6a0f4750621b5276e124f0e924ca Mon Sep 17 00:00:00 2001
From: Herman Slatman <hermanslatman@hotmail.com>
Date: Wed, 22 Feb 2023 15:58:53 +0100
Subject: [PATCH] Return the actual number of bytes written to through command
 buffer

The `Write` function returned the number of bytes written to the
internal command response buffer. Depending on the type of command
executed against the TPM, this would usually result in a different
number of bytes being written than the original input.

The fix is useful if one wants to wrap the `io.ReadWriterCloser`
functions with implementations that perform strict checks. An example
is using an `io.MultiWriter` to capture the bytes sent to the TPM
for debugging purposes, which will fail if the number of bytes
written does not equal the original length of the input bytes.
---
 simulator/simulator.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/simulator/simulator.go b/simulator/simulator.go
index eed7e2ab2..1a8fef1f9 100644
--- a/simulator/simulator.go
+++ b/simulator/simulator.go
@@ -109,7 +109,14 @@ func (s *Simulator) Write(commandBuffer []byte) (int, error) {
 	if err != nil {
 		return 0, err
 	}
-	return s.buf.Write(resp)
+	n, err := s.buf.Write(resp)
+	if err != nil {
+		return 0, err
+	}
+	if n != (len(resp)) {
+		return 0, fmt.Errorf("expected %d bytes to be written to command response buffer, but actual number is %d", n, len(resp))
+	}
+	return len(commandBuffer), nil
 }
 
 // Read gets the response of a command previously issued by calling Write().