Fix UTF-8 encoding in gpgdata write callback

This change associates the buffer allocated in the gpgme_data write
callback with the UTF-8 encoding. If there is a configured internal
encoding (e.g. Encoding.default_internal), then the string is exported
to that encoding.

ext/gpgme/gpgme_n.c

@@ -39,6 +39,7 @@
 #include "ruby.h"
 #ifdef HAVE_RUBY_ENCODING_H
 #include "ruby/encoding.h"
+static rb_encoding *utf8Encoding;
 #endif
 #include "gpgme.h"
 #include <errno.h>
@@ -346,6 +347,14 @@ write_cb (void *handle, const void *buffer, size_t size)
  vhook_value = RARRAY_PTR(vcb)[1];
  vbuffer = rb_str_new (buffer, size);
 
+#ifdef HAVE_RUBY_ENCODING_H
+ rb_encoding *default_internal_enc = rb_default_internal_encoding();
+ rb_enc_associate(vbuffer, utf8Encoding);
+ if (default_internal_enc) {
+ vbuffer = rb_str_export_to_enc(vbuffer, default_internal_enc);
+ }
+#endif
+
  vnwrite = rb_funcall (vcbs, rb_intern ("write"), 3,
  vhook_value, vbuffer, LONG2NUM(size));
  return NUM2LONG(vnwrite);
@@ -3068,4 +3077,8 @@ Init_gpgme_n (void)
  rb_define_const (mGPGME, "GPGME_EXPORT_MODE_PKCS12",
  INT2FIX(GPGME_EXPORT_MODE_PKCS12));
 #endif
+
+#ifdef HAVE_RUBY_ENCODING_H
+ utf8Encoding = rb_utf8_encoding();
+#endif
 }