Add-ons: add a simgear::ResourceProvider for add-on-specific lookup

A resource can be specified with the syntax:

  [addon=ADDON_ID]relative/path

Such a resource corresponds to the file $addon_base_path/relative/path
for the specific add-on whose identifier is ADDON_ID.

If the particular add-on isn't registered, looking up such a resource
throws sg_exception.

src/Add-ons/AddonResourceProvider.cxx

@@ -0,0 +1,80 @@
+// -*- coding: utf-8 -*-
+//
+// AddonResourceProvider.cxx --- ResourceProvider subclass for add-on files
+// Copyright (C) 2018  Florent Rougon
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+#include <string>
+
+#include <simgear/misc/ResourceManager.hxx>
+#include <simgear/misc/sg_path.hxx>
+#include <simgear/misc/strutils.hxx>
+
+#include <Main/util.hxx>
+
+#include "AddonManager.hxx"
+#include "AddonResourceProvider.hxx"
+
+namespace strutils = simgear::strutils;
+
+using std::string;
+
+namespace flightgear
+{
+
+namespace addons
+{
+
+ResourceProvider::ResourceProvider()
+  : simgear::ResourceProvider(simgear::ResourceManager::PRIORITY_NORMAL)
+{ }
+
+SGPath
+ResourceProvider::resolve(const string& resource, SGPath& context) const
+{
+  if (!strutils::starts_with(resource, "[addon=")) {
+    return SGPath();
+  }
+
+  string rest = resource.substr(7); // what follows '[addon='
+  auto endOfAddonId = rest.find(']');
+
+  if (endOfAddonId == string::npos) {
+    return SGPath();
+  }
+
+  string addonId = rest.substr(0, endOfAddonId);
+  // Extract what follows '[addon=ADDON_ID]'
+  string relPath = rest.substr(endOfAddonId + 1);
+
+  if (relPath.empty()) {
+    return SGPath();
+  }
+
+  const auto& addonMgr = AddonManager::instance();
+  SGPath addonDir = addonMgr->addonBasePath(addonId);
+  SGPath candidate = addonDir / relPath;
+
+  if (!candidate.isFile()) {
+    return SGPath();
+  }
+
+  return fgValidatePath(candidate, /* write */ false);
+}
+
+} // of namespace addons
+
+} // of namespace flightgear

src/Add-ons/AddonResourceProvider.hxx

@@ -0,0 +1,47 @@
+// -*- coding: utf-8 -*-
+//
+// AddonResourceProvider.hxx --- ResourceProvider subclass for add-on files
+// Copyright (C) 2018  Florent Rougon
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+#ifndef FG_ADDON_RESOURCE_PROVIDER_HXX
+#define FG_ADDON_RESOURCE_PROVIDER_HXX
+
+#include <string>
+
+#include <simgear/misc/ResourceManager.hxx>
+#include <simgear/misc/sg_path.hxx>
+
+namespace flightgear
+{
+
+namespace addons
+{
+
+class ResourceProvider : public simgear::ResourceProvider
+{
+public:
+  ResourceProvider();
+
+  virtual SGPath resolve(const std::string& resource, SGPath& context) const
+    override;
+};
+
+} // of namespace addons
+
+} // of namespace flightgear
+
+#endif  // of FG_ADDON_RESOURCE_PROVIDER_HXX

src/Add-ons/CMakeLists.txt

@@ -3,6 +3,7 @@ include(FlightGearComponent)
 set(SOURCES Addon.cxx
             AddonManager.cxx
             AddonMetadataParser.cxx
+            AddonResourceProvider.cxx
             AddonVersion.cxx
             contacts.cxx
             exceptions.cxx
@@ -12,6 +13,7 @@ set(HEADERS addon_fwd.hxx
             Addon.hxx
             AddonManager.hxx
             AddonMetadataParser.hxx
+            AddonResourceProvider.hxx
             AddonVersion.hxx
             contacts.hxx
             exceptions.hxx

src/Add-ons/addon_fwd.hxx

@@ -33,6 +33,7 @@ class Addon;
 class AddonManager;
 class AddonVersion;
 class AddonVersionSuffix;
+class ResourceProvider;
 
 enum class UrlType;
 class QualifiedUrl;

tests/CMakeLists.txt

@@ -10,6 +10,7 @@ set(sources
   Add-ons/Addon.cxx
   Add-ons/AddonManager.cxx
   Add-ons/AddonMetadataParser.cxx
+  Add-ons/AddonResourceProvider.cxx
   Add-ons/AddonVersion.cxx
   Add-ons/contacts.cxx
   Add-ons/exceptions.cxx