From af56b5b233a200d83b427d967bac7453f4043f6f Mon Sep 17 00:00:00 2001
From: Hugo Santos <hugosantos@nowhere.fake>
Date: Tue, 10 Apr 2007 19:04:13 +0000
Subject: [PATCH] fixed add_tcp_header() as it wasn't considering the
 possibility that prepending data would not result in a contiguous buffer.
 This would result in wrong checksums for apparent no reason.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20643 a95241bf-73f2-0310-859d-f6bbb57e9c96
---
 headers/private/net/NetBufferUtilities.h      | 45 +++++++++++++------
 .../kernel/network/protocols/tcp/tcp.cpp      |  9 +++-
 2 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/headers/private/net/NetBufferUtilities.h b/headers/private/net/NetBufferUtilities.h
index 3045cff7e9..290d496c95 100644
--- a/headers/private/net/NetBufferUtilities.h
+++ b/headers/private/net/NetBufferUtilities.h
@@ -81,21 +81,24 @@ template<typename Type, typename Module = NetBufferModuleGetter > class NetBuffe
 		Type		fDataBuffer;
 };
 
-//! A class to add a header to a buffer
-template<typename Type, typename Module = NetBufferModuleGetter > class NetBufferPrepend {
+//! A class to access a header safely across data node boundaries
+template<typename Type, typename Module = NetBufferModuleGetter>
+class NetBufferSafeHeader {
 	public:
-		NetBufferPrepend(net_buffer *buffer, size_t size = 0)
+		NetBufferSafeHeader(net_buffer *buffer)
 			:
-			fBuffer(buffer),
-			fData(NULL)
+			fBuffer(buffer)
 		{
-			if (size == 0)
-				size = sizeof(Type);
-
-			fStatus = Module::Get()->prepend_size(buffer, size, (void **)&fData);
+			fStatus = Module::Get()->direct_access(fBuffer, 0,
+				sizeof(Type), (void **)&fData);
+			if (fStatus != B_OK) {
+				fData = NULL;
+				fStatus = Module::Get()->read(fBuffer, 0, &fDataBuffer,
+					sizeof(Type));
+			}
 		}
 
-		~NetBufferPrepend()
+		~NetBufferSafeHeader()
 		{
 			if (fBuffer != NULL)
 				Detach();
@@ -116,8 +119,6 @@ template<typename Type, typename Module = NetBufferModuleGetter > class NetBuffe
 			return fDataBuffer;
 		}
 
-		// TODO: I'm not sure it's a good idea to have Detach() routines
-		//	in NetBufferHeader and here with such a different outcome...
 		void
 		Detach()
 		{
@@ -126,11 +127,29 @@ template<typename Type, typename Module = NetBufferModuleGetter > class NetBuffe
 			fBuffer = NULL;
 		}
 
-	private:
+	protected:
+		NetBufferSafeHeader() {}
+
 		net_buffer	*fBuffer;
 		status_t	fStatus;
 		Type		*fData;
 		Type		fDataBuffer;
 };
 
+//! A class to add a header to a buffer
+template<typename Type, typename Module = NetBufferModuleGetter>
+class NetBufferPrepend : public NetBufferSafeHeader<Type, Module> {
+	public:
+		NetBufferPrepend(net_buffer *buffer, size_t size = 0)
+		{
+			fBuffer = buffer;
+			fData = NULL;
+
+			if (size == 0)
+				size = sizeof(Type);
+
+			fStatus = Module::Get()->prepend_size(buffer, size, (void **)&fData);
+		}
+};
+
 #endif	// NET_BUFFER_UTILITIES_H
diff --git a/src/add-ons/kernel/network/protocols/tcp/tcp.cpp b/src/add-ons/kernel/network/protocols/tcp/tcp.cpp
index b22e2e45bc..e9fb65f8b0 100644
--- a/src/add-ons/kernel/network/protocols/tcp/tcp.cpp
+++ b/src/add-ons/kernel/network/protocols/tcp/tcp.cpp
@@ -148,6 +148,10 @@ add_tcp_header(tcp_segment_header &segment, net_buffer *buffer)
 	header.urgent_offset = 0;
 		// TODO: urgent pointer not yet supported
 
+	// we must detach before calculating the checksum as we may
+	// not have a contiguous buffer.
+	bufferHeader.Detach();
+
 	if (optionsLength > 0)
 		gBufferModule->write(buffer, sizeof(tcp_header), optionsBuffer, optionsLength);
 
@@ -162,7 +166,10 @@ add_tcp_header(tcp_segment_header &segment, net_buffer *buffer)
 		<< (uint16)htons(IPPROTO_TCP)
 		<< (uint16)htons(buffer->size)
 		<< Checksum::BufferHelper(buffer, gBufferModule);
-	header.checksum = checksum;
+
+	// we are pretty sure the header is there.
+	NetBufferSafeHeader<tcp_header> headerRef(buffer);
+	headerRef.Data().checksum = checksum;
 
 	return B_OK;
 }