Add support for UUID generation

1 files changed, 145 insertions, 0 deletions

diff --git a/libbutl/uuid-linux.cxx b/libbutl/uuid-linux.cxx
new file mode 100644
index 0000000..7396910
--- /dev/null
+++ b/libbutl/uuid-linux.cxx
@@ -0,0 +1,145 @@
+// file      : libbutl/uuid-linux.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD2_BOOTSTRAP
+
+#include <libbutl/uuid.hxx>
+
+#include <errno.h>
+#include <dlfcn.h>
+
+#include <mutex>
+#include <cassert>
+#include <utility>      // move()
+#include <system_error>
+
+using namespace std;
+
+namespace butl
+{
+  // While we can safely assume libuuid.so.1 is present on every Linux machine
+  // (it is part of the essential util-linux package since version 2.15.1),
+  // the development files (uuid.h, .so/.a symlinks) are a different story.
+  // So for maximum portability we will use dlopen()/dlsym() to "link" to this
+  // library without any development files.
+  //
+  // It appears that not all execution paths in uuid_generate() are thread-
+  // safe (see Ubuntu bug #1005878). So for now the calls are serialized but
+  // maybe this could be optimized (e.g., if we can be sure a thread-safe path
+  // will be taken). Note also that we may still end up in trouble if someone
+  // else in the process calls libuuid directly.
+  //
+  // Note also that the Linux kernel has support for generatin random UUIDs
+  // which is exposed to userspace via /proc/sys/kernel/random/uuid. This
+  // could be another implementation option (though it's not clear since which
+  // version it is available, seem at least from the 2.6 days).
+  //
+  using lock = unique_lock<mutex>;
+
+  static mutex uuid_mutex;
+
+  // <uuid.h>
+  //
+  using uuid_t = unsigned char[16];
+
+  static void (*uuid_generate)           (uuid_t);
+  static int  (*uuid_generate_time_safe) (uuid_t);
+
+  static void* libuuid;
+
+  // Use a union to cleanly cast dlsym() result (void*) to a function pointer.
+  //
+  template <typename F>
+  static inline F
+  function_cast (void* p)
+  {
+    union { void* p; F f; } r;
+    r.p = p;
+    return r.f;
+  };
+
+  static inline void
+  dlfail (string what)
+  {
+    what += ": ";
+    what += dlerror ();
+    throw system_error (ENOSYS, system_category (), move (what));
+  };
+
+  void uuid_system_generator::
+  initialize ()
+  {
+    assert (libuuid == nullptr);
+
+    libuuid = dlopen ("libuuid.so.1", RTLD_LAZY | RTLD_GLOBAL);
+
+    if (libuuid == nullptr)
+      dlfail ("unable to load libuuid.so.1");
+
+    uuid_generate =
+      function_cast<decltype(uuid_generate)> (
+        dlsym (libuuid, "uuid_generate"));
+
+    if (uuid_generate == nullptr)
+      dlfail ("unable to lookup uuid_generate() in libuuid.so.1");
+
+    uuid_generate_time_safe =
+      function_cast<decltype(uuid_generate_time_safe)> (
+        dlsym (libuuid, "uuid_generate_time_safe"));
+
+    // Delay the failure until/if we need this function (it was only added in
+    // 2011 so may not be available on older systems).
+    //
+    //if (uuid_generate_time_safe == nullptr)
+    //  dlfail ("unable to lookup uuid_generate_time_safe() in libuuid.so.1");
+  }
+
+  void uuid_system_generator::
+  terminate ()
+  {
+    assert (libuuid != nullptr);
+
+    if (dlclose (libuuid) != 0)
+      dlfail ("unable to unload libuuid.so.1");
+
+    libuuid = nullptr;
+  }
+
+  void
+  uuid_throw_weak (); // uuid.cxx
+
+  uuid uuid_system_generator::
+  generate (bool strong)
+  {
+    lock l (uuid_mutex);
+
+    if (libuuid == nullptr)
+      initialize ();
+
+    uuid_t d;
+    uuid_generate (d);
+
+    uuid r (d);
+    assert (r.variant () == uuid_variant::dce); // Sanity check.
+
+    // According to the uuid_generate() documentation (and confirmed by the
+    // implementation) it generates a random uuid if high-quality randomness
+    // is available and a MAC/time-based one otherwise (in other words, it
+    // should never generate a pseudo-random UUID).
+    //
+    if (strong && r.version () != uuid_version::random)
+    {
+      if (uuid_generate_time_safe == nullptr ||
+          uuid_generate_time_safe (d) == -1)
+        uuid_throw_weak ();
+
+      r.assign (d);
+      assert (r.variant () == uuid_variant::dce);
+    }
+
+    return r;
+  }
+}
+
+#endif // BUILD2_BOOTSTRAP