Expose libvips warnings via NODE_DEBUG env var

src/common.cc

@@ -16,6 +16,8 @@
 #include <string>
 #include <string.h>
 #include <vector>
+#include <queue>
+#include <mutex>
 
 #include <node.h>
 #include <node_buffer.h>
@@ -354,6 +356,33 @@ namespace sharp {
     }
   }
 
+  /*
+    Temporary buffer of warnings
+  */
+  std::queue<std::string> vipsWarnings;
+  std::mutex vipsWarningsMutex;
+
+  /*
+    Called with warnings from the glib-registered "VIPS" domain
+  */
+  void VipsWarningCallback(char const* log_domain, GLogLevelFlags log_level, char const* message, void* ignore) {
+    std::lock_guard<std::mutex> lock(vipsWarningsMutex);
+    vipsWarnings.emplace(message);
+  }
+
+  /*
+    Pop the oldest warning message from the queue
+  */
+  std::string VipsWarningPop() {
+    std::string warning;
+    std::lock_guard<std::mutex> lock(vipsWarningsMutex);
+    if (!vipsWarnings.empty()) {
+      warning = vipsWarnings.front();
+      vipsWarnings.pop();
+    }
+    return warning;
+  }
+
   /*
     Calculate the (left, top) coordinates of the output image
     within the input image, applying the given gravity.