From b99a435f52de826327ea3e4cc8cc8aaf348d5b53 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Fri, 18 Sep 2015 02:35:30 +0100
Subject: Use resolvers to load libraries automagically on demand

---
 libadhocutil/Jamfile.jam                      |  2 ++
 libadhocutil/plugins.cpp                      | 24 +++++++++++++
 libadhocutil/plugins.h                        |  9 +++++
 libadhocutil/unittests/testPluginsRuntime.cpp | 50 ++++++++++++++++++++++++---
 4 files changed, 80 insertions(+), 5 deletions(-)

diff --git a/libadhocutil/Jamfile.jam b/libadhocutil/Jamfile.jam
index 45bbeec..861509a 100644
--- a/libadhocutil/Jamfile.jam
+++ b/libadhocutil/Jamfile.jam
@@ -6,6 +6,7 @@ lib Ice : ;
 lib IceUtil ;
 lib pthread ;
 lib curl ;
+lib dl ;
 
 alias iceall : : : : <library>Ice <library>IceUtil <library>pthread ;
 
@@ -15,6 +16,7 @@ lib adhocutil :
 	<include>.
 	<library>iceall
 	<library>curl
+	<library>dl
 	<cflags>-fvisibility=hidden
 	<variant>release:<cflags>-flto
 	: :
diff --git a/libadhocutil/plugins.cpp b/libadhocutil/plugins.cpp
index 6caf34f..a1eef70 100644
--- a/libadhocutil/plugins.cpp
+++ b/libadhocutil/plugins.cpp
@@ -1,5 +1,6 @@
 #include "plugins.h"
 #include <string.h>
+#include <dlfcn.h>
 #include <boost/multi_index_container.hpp>
 #include <boost/multi_index/ordered_index.hpp>
 #include "buffer.h"
@@ -73,6 +74,11 @@ namespace AdHoc {
 	{
 	}
 
+	LoadLibraryException::LoadLibraryException(const std::string & f, const char * msg) :
+		std::runtime_error(stringbf("Failed to load library [%s]; %s", f, msg))
+	{
+	}
+
 	PluginManager::PluginManager() :
 		plugins(new PluginStore()),
 		resolvers(new TypePluginResolvers())
@@ -111,12 +117,30 @@ namespace AdHoc {
 	PluginManager::get(const std::string & n, const std::type_info & t) const
 	{
 		auto r = plugins->get<2>().equal_range(boost::make_tuple(n, std::cref(t)));
+		if (r.first == r.second) {
+			auto tr = resolvers->find(t.hash_code());
+			if (tr != resolvers->end()) {
+				if (auto lib = tr->second(t, n)) {
+					loadLibrary(*lib);
+				}
+			}
+			r = plugins->get<2>().equal_range(boost::make_tuple(n, std::cref(t)));
+		}
 		if (r.first != r.second) {
 			return (*r.first);
 		}
 		throw NoSuchPluginException(n, t);
 	}
 
+	void
+	PluginManager::loadLibrary(const std::string & f)
+	{
+		void * handle = dlopen(f.c_str(), RTLD_NOW);
+		if (!handle) {
+			throw LoadLibraryException(f, dlerror());
+		}
+	}
+
 	std::set<PluginPtr>
 	PluginManager::getAll() const
 	{
diff --git a/libadhocutil/plugins.h b/libadhocutil/plugins.h
index 8b8efac..03d59fb 100644
--- a/libadhocutil/plugins.h
+++ b/libadhocutil/plugins.h
@@ -63,6 +63,13 @@ namespace AdHoc {
 			DuplicateResolverException(const std::type_info &);
 	};
 
+	/// Thrown when an attempt to load a library fails.
+	class LoadLibraryException : public std::runtime_error {
+		public:
+			/// Constuctor taking syscall error details.
+			LoadLibraryException(const std::string & f, const char * msg);
+	};
+
 	template <typename T>
 	/// Typed plugin and handle to implementation.
 	class DLL_PUBLIC PluginOf : public Plugin {
@@ -171,6 +178,8 @@ namespace AdHoc {
 			static PluginManager * getDefault();
 
 		private:
+			static void loadLibrary(const std::string &);
+
 			typedef boost::multi_index_container<PluginPtr,
 							boost::multi_index::indexed_by<
 								boost::multi_index::ordered_non_unique<boost::multi_index::member<Plugin, const std::string, &Plugin::name>>,
diff --git a/libadhocutil/unittests/testPluginsRuntime.cpp b/libadhocutil/unittests/testPluginsRuntime.cpp
index 2b13913..aa1dcf1 100644
--- a/libadhocutil/unittests/testPluginsRuntime.cpp
+++ b/libadhocutil/unittests/testPluginsRuntime.cpp
@@ -13,7 +13,9 @@ auto variant	= selfExe.parent_path().leaf();
 auto toolset	= selfExe.parent_path().parent_path().leaf();
 auto lib = rootDir / "bin" / toolset / variant / "libutilTestClasses.so";
 
-static boost::optional<std::string> resolver(const std::type_info &, const std::string &);
+static boost::optional<std::string> nullResolver(const std::type_info &, const std::string &);
+static boost::optional<std::string> badResolver(const std::type_info &, const std::string &);
+static boost::optional<std::string> goodResolver(const std::type_info &, const std::string &);
 
 BOOST_AUTO_TEST_CASE( ready )
 {
@@ -36,20 +38,58 @@ BOOST_AUTO_TEST_CASE( loadAndUnloadlib )
 }
 
 boost::optional<std::string>
-resolver(const std::type_info &, const std::string &)
+nullResolver(const std::type_info &, const std::string &)
 {
-	return std::string();
+	return nullptr;
+}
+
+boost::optional<std::string>
+badResolver(const std::type_info &, const std::string &)
+{
+	return std::string("dontexist");
+}
+
+boost::optional<std::string>
+goodResolver(const std::type_info & t, const std::string & n)
+{
+	BOOST_REQUIRE_EQUAL(typeid(BaseThing), t);
+	BOOST_REQUIRE_EQUAL("ImplOfThing", n);
+	return lib.string();
 }
 
 BOOST_AUTO_TEST_CASE( addAndRemoveResolver )
 {
 	auto pm = AdHoc::PluginManager::getDefault();
 	BOOST_REQUIRE_EQUAL(0, pm->countResolvers());
-	pm->addResolver<BaseThing>(resolver);
+	pm->addResolver<BaseThing>(nullResolver);
 	BOOST_REQUIRE_EQUAL(1, pm->countResolvers());
-	BOOST_REQUIRE_THROW(pm->addResolver<BaseThing>(resolver), DuplicateResolverException);
+	BOOST_REQUIRE_THROW(pm->addResolver<BaseThing>(nullResolver), DuplicateResolverException);
 	BOOST_REQUIRE_EQUAL(1, pm->countResolvers());
 	pm->removeResolver<BaseThing>();
 	BOOST_REQUIRE_EQUAL(0, pm->countResolvers());
 }
 
+BOOST_AUTO_TEST_CASE( null )
+{
+	auto pm = AdHoc::PluginManager::getDefault();
+	pm->addResolver<BaseThing>(nullResolver);
+	BOOST_REQUIRE_THROW(pm->get<BaseThing>("ImplOfThing"), AdHoc::NoSuchPluginException);
+	pm->removeResolver<BaseThing>();
+}
+
+BOOST_AUTO_TEST_CASE( bad )
+{
+	auto pm = AdHoc::PluginManager::getDefault();
+	pm->addResolver<BaseThing>(badResolver);
+	BOOST_REQUIRE_THROW(pm->get<BaseThing>("ImplOfThing"), AdHoc::LoadLibraryException);
+	pm->removeResolver<BaseThing>();
+}
+
+BOOST_AUTO_TEST_CASE( good )
+{
+	auto pm = AdHoc::PluginManager::getDefault();
+	pm->addResolver<BaseThing>(goodResolver);
+	BOOST_REQUIRE(pm->get<BaseThing>("ImplOfThing"));
+	pm->removeResolver<BaseThing>();
+}
+
-- 
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