From 97828a8e4e297a5bf64bb58d92bf4deee2159887 Mon Sep 17 00:00:00 2001
From: Julian Smith <jules@op59.net>
Date: Thu, 18 Feb 2021 23:12:01 +0000
Subject: [PATCH] simgear/io/HTTPFileRequest.*: Use fnptr rather than
 std::function to avoid SEGVs with g++ on Linux.

Previous code sometimes gave a SEGV in _callback's destructor when
setCallback() was called; this is on Linux with g++-8.3.0. Have tried various
alternative ways to initialise _callback but the problem persistend.

So have switched to an old-style function-pointer plus void* approach.
---
 simgear/io/HTTPFileRequest.cxx | 11 ++++++-----
 simgear/io/HTTPFileRequest.hxx | 15 +++++++++++----
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/simgear/io/HTTPFileRequest.cxx b/simgear/io/HTTPFileRequest.cxx
index 018e06da..22b25b16 100644
--- a/simgear/io/HTTPFileRequest.cxx
+++ b/simgear/io/HTTPFileRequest.cxx
@@ -26,13 +26,13 @@ namespace simgear
 {
 namespace HTTP
 {
-
   //----------------------------------------------------------------------------
   FileRequest::FileRequest(const std::string& url, const std::string& path, bool append):
     Request(url, "GET"),
     _filename(path),
     _append(append),
-    _callback()
+    _callback(nullptr),
+    _callback_ref(nullptr)
   {
     if (append && _filename.isFile()) {
       size_t size = _filename.sizeInBytes();
@@ -45,9 +45,10 @@ namespace HTTP
     }
   }
 
-  void FileRequest::setCallback(std::function<void(const void* data, size_t numbytes)> callback)
+  void FileRequest::setCallback(Callback callback, void* ref)
   {
     _callback = callback;
+    _callback_ref = ref;
   }
 
   //----------------------------------------------------------------------------
@@ -115,7 +116,7 @@ namespace HTTP
 
     _file.write(s, n);
     if (_callback) {
-      _callback(s, n);
+      _callback(_callback_ref, s, n);
     }
   }
 
@@ -124,7 +125,7 @@ namespace HTTP
   {
     _file.close();
     if (_callback) {
-      _callback(nullptr, 0);
+      _callback(_callback_ref, nullptr, 0);
     }
   }
 
diff --git a/simgear/io/HTTPFileRequest.hxx b/simgear/io/HTTPFileRequest.hxx
index 94ebecf2..3c9c463e 100644
--- a/simgear/io/HTTPFileRequest.hxx
+++ b/simgear/io/HTTPFileRequest.hxx
@@ -53,16 +53,23 @@ namespace HTTP
       FileRequest(const std::string& url, const std::string& path, bool append=false);
       
       /*
-       * Set callback for each chunk of data we receive. Called with (nullptr,
-       * 0) when download has completed (successfully or unsuccesfully).
+       * Function pointer type for use with setCallback().
        */
-      void setCallback(std::function<void (const void* data, size_t numbytes)> callback);
+      typedef void (*Callback)(void* ref, const void* data, size_t numbytes);
+      
+      /*
+       * Set callback for each chunk of data we receive. Called with
+       * (ref, nullptr, 0) when download has completed (successfully or
+       * unsuccesfully).
+       */
+      void setCallback(Callback callback, void* ref);
 
     protected:
       SGPath _filename;
       sg_ofstream _file;
       bool _append;
-      std::function<void(const void* data, size_t numbytes)> _callback;
+      Callback _callback;
+      void* _callback_ref;
 
       virtual void responseHeadersComplete();
       virtual void gotBodyData(const char* s, int n);