Add support for UUID generation

1 files changed, 81 insertions, 0 deletions

diff --git a/libbutl/uuid-macos.cxx b/libbutl/uuid-macos.cxx
new file mode 100644
index 0000000..1003501
--- /dev/null
+++ b/libbutl/uuid-macos.cxx
@@ -0,0 +1,81 @@
+// file      : libbutl/uuid-macos.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD2_BOOTSTRAP
+
+#include <libbutl/uuid.hxx>
+
+#include <CoreFoundation/CFUUID.h>
+
+#include <cassert>
+#include <cstring>   // memcpy()
+
+using namespace std;
+
+namespace butl
+{
+  void
+  uuid_throw_weak (); // uuid.cxx
+
+  uuid uuid_system_generator::
+  generate (bool strong)
+  {
+    // The common way to generate a UUID on Mac OS is with the CFUUIDCreate()
+    // function from the CoreFoundation framework. Interestingly, if we look
+    // at the implementation (yes, the CF source code is available), we will
+    // see that it uses the <uuid/uuid.h> API which looks like a customized
+    // implementation from e2fsprogs that itself is a precursor to libuuid
+    // from util-linux.
+    //
+    // More specifically (and at least as of CF version 1153.18), it calls
+    // uuid_generate_random() unless the CFUUIDVersionNumber environment
+    // variable is set to 1, in which case it calls uuid_generate_time(). It
+    // also appears to serialize these calls so the implementation should be
+    // thread-safe (see the Linux implementation for background; this is also
+    // the reason why we don't want to use the low-level API directly even if
+    // we provide our own synchronization: if other code in the process calls
+    // CFUUIDCreate() then we will end up with a race).
+    //
+    // In theory the use of uuid_generate_random() is bad news since it will
+    // produce weak pseudo-random UUIDs if no high-quality randomness is
+    // available (unlike uuid_generate() which will only produce strong random
+    // UUIDs falling back to the MAC/time-based ones; see uuid_generate(3) for
+    // details).
+    //
+    // In practice (and at least as of Mac OS libc version 1244.30), however,
+    // uuid_generate_random() uses arc4random(3) which reportedly produces
+    // high-quality randomness (and uuid_generate() simply always calls it).
+    //
+    CFUUIDRef h (CFUUIDCreate (NULL));
+    CFUUIDBytes d (CFUUIDGetUUIDBytes (h));
+    CFRelease (h);
+
+    uint8_t a[16];
+    memcpy (a, &d, 16); // CFUUIDBytes is POD.
+
+    uuid r (a);
+    assert (r.variant () == uuid_variant::dce); // Sanity check.
+
+    // If this is a MAC/time-based UUID, then it's possible the time was not
+    // obtained in a collision-safe manner (looking at the implementation this
+    // seems to be the case; see the Linux implementation for background).
+    //
+    if (strong && r.version () != uuid_version::random)
+      uuid_throw_weak ();
+
+    return r;
+  }
+
+  void uuid_system_generator::
+  initialize ()
+  {
+  }
+
+  void uuid_system_generator::
+  terminate ()
+  {
+  }
+}
+
+#endif // BUILD2_BOOTSTRAP