[NaCl SDK] nacl_io: Add support for basic socketpairs.

native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc

Index: native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc b/native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc
index b554ade35226994cee50d28578dfc2fba3e156db..a141923de0dec3ada5f6a2b3a7d9d10a07a9e908 100644
--- a/native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc
+++ b/native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc
@@ -39,6 +39,7 @@
 #include "nacl_io/pipe/pipe_node.h"
 #include "nacl_io/socket/tcp_node.h"
 #include "nacl_io/socket/udp_node.h"
+#include "nacl_io/socket/unix_node.h"
 #include "nacl_io/stream/stream_fs.h"
 #include "nacl_io/typed_fs_factory.h"
 #include "sdk_util/auto_lock.h"
@@ -1813,21 +1814,73 @@ int KernelProxy::socketpair(int domain, int type, int protocol, int* sv) {
     return -1;
   }
 
-  // Catch-22: We don't support AF_UNIX, but any other AF doesn't support
-  // socket pairs. Thus, this function always fails.
-  if (AF_UNIX != domain) {
-    errno = EPROTONOSUPPORT;
+  if (AF_INET == domain || AF_INET6 == domain) {
+    errno = EOPNOTSUPP;
     return -1;
   }
 
-  if (AF_INET != domain && AF_INET6 != domain) {
+  if (AF_UNIX != domain) {
     errno = EAFNOSUPPORT;
     return -1;
   }
 
-  // We cannot reach this point.
-  errno = ENOSYS;
-  return -1;
+  if (SOCK_STREAM != type) {
+    errno = EPROTOTYPE;
+    return -1;
+  }
+
+  int open_flags = O_RDWR;
+
+#if defined(SOCK_CLOEXEC)
+  if (type & SOCK_CLOEXEC) {
+#if defined(O_CLOEXEC)
+    // The NaCl newlib version of fcntl.h doesn't currently define
+    // O_CLOEXEC.
+    // TODO(sbc): remove this guard once it gets added.
+    open_flags |= O_CLOEXEC;
+#endif
+    type &= ~SOCK_CLOEXEC;
+  }
+#endif
+
+#if defined(SOCK_NONBLOCK)
+  if (type & SOCK_NONBLOCK) {
+    open_flags |= O_NONBLOCK;
+    type &= ~SOCK_NONBLOCK;
+  }
+#endif
+
+  UnixNode* socket = new UnixNode(stream_fs_.get());
+  Error rtn = socket->Init(O_RDWR);
+  if (rtn != 0) {
+    errno = rtn;
+    return -1;
+  }
+  ScopedNode node0(socket);
+  socket = new UnixNode(stream_fs_.get(), *socket);
+  rtn = socket->Init(O_RDWR);
+  if (rtn != 0) {
+    errno = rtn;
+    return -1;
+  }
+  ScopedNode node1(socket);
+  ScopedKernelHandle handle0(new KernelHandle(stream_fs_, node0));
+  rtn = handle0->Init(open_flags);
+  if (rtn != 0) {
+    errno = rtn;
+    return -1;
+  }
+  ScopedKernelHandle handle1(new KernelHandle(stream_fs_, node1));
+  rtn = handle1->Init(open_flags);
+  if (rtn != 0) {
+    errno = rtn;
+    return -1;
+  }
+
+  sv[0] = AllocateFD(handle0);
+  sv[1] = AllocateFD(handle1);
+
+  return 0;
 }
 
 int KernelProxy::AcquireSocketHandle(int fd, ScopedKernelHandle* handle) {