tcp: endpoint.Write has to send all data that has been read from payload

io.Reader.ReadFull returns the number of bytes copied and an error if fewer
bytes were read.

PiperOrigin-RevId: 360247614

pkg/tcpip/transport/tcp/endpoint.go

@@ -1552,10 +1552,11 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, tcp
 				return nil, nil
 			}
 			v := make([]byte, avail)
-			if _, err := io.ReadFull(p, v); err != nil {
+			n, err := p.Read(v)
+			if err != nil && err != io.EOF {
 				return nil, &tcpip.ErrBadBuffer{}
 			}
-			return v, nil
+			return v[:n], nil
 		}()
 		if len(v) == 0 || err != nil {
 			return nil, 0, err

test/syscalls/linux/BUILD

@@ -2384,6 +2384,7 @@ cc_library(
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/time",
         gtest,
+        "//test/util:temp_path",
         "//test/util:test_util",
         "//test/util:thread_util",
     ],

test/syscalls/linux/socket_ip_tcp_generic.cc

@@ -29,6 +29,7 @@
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
 #include "test/syscalls/linux/socket_test_util.h"
+#include "test/util/temp_path.h"
 #include "test/util/test_util.h"
 #include "test/util/thread_util.h"
 
@@ -1059,6 +1060,28 @@ TEST_P(TCPSocketPairTest, SpliceToPipe) {
               SyscallSucceedsWithValue(buf.size()));
   EXPECT_EQ(memcmp(rbuf.data(), buf.data(), buf.size()), 0);
 }
+
+#include <sys/sendfile.h>
+
+TEST_P(TCPSocketPairTest, SendfileFromRegularFileSucceeds) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor in_fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDWR));
+  // Fill with some random data.
+  std::vector<char> buf(kPageSize / 2);
+  RandomizeBuffer(buf.data(), buf.size());
+  ASSERT_THAT(pwrite(in_fd.get(), buf.data(), buf.size(), 0),
+              SyscallSucceedsWithValue(buf.size()));
+
+  EXPECT_THAT(
+      sendfile(sockets->first_fd(), in_fd.get(), nullptr, buf.size() + 1),
+      SyscallSucceedsWithValue(buf.size()));
+  std::vector<char> rbuf(buf.size() + 1);
+  ASSERT_THAT(read(sockets->second_fd(), rbuf.data(), rbuf.size()),
+              SyscallSucceedsWithValue(buf.size()));
+  EXPECT_EQ(memcmp(rbuf.data(), buf.data(), buf.size()), 0);
+}
 #endif  // __linux__
 
 TEST_P(TCPSocketPairTest, SetTCPWindowClampBelowMinRcvBufConnectedSocket) {