be more robust to convert BS into valid NFC UTF-8.

src/headerparser.cc

@@ -3,6 +3,7 @@
 #include "parse_address.hh"
 #include "parse_timestamp.hh"
 #include "rules.hh"
+#include "to_utf8.hh"
 
 #include <pEp/pEp_string.h>
 #include <pEp/stringlist.h>
@@ -118,10 +119,22 @@ TRuleParser<T1, T2>* P(T2 message::* member, const qi::rule<std::string::const_i
 }
 
 
+std::string robust_to_utf8(const std::string& s)
+{
+    std::string ret;
+    try{
+        ret = toNFC(s);
+    }catch(illegal_utf8& e)
+    {
+        ret = to_utf8("ISO-8859-1", s);
+    }
+    return ret;
+}
+
 // make sure the C string is allocated on the correct heap, especially on MS Windows. *sigh*
 char* copy_string(const std::string& s)
 {
-    const std::string nfc = toNFC(s); // TODO: use views/ranges to avoid copying
+    const std::string nfc = robust_to_utf8(s); // TODO: use views/ranges to avoid copying
     return new_string(nfc.c_str(), nfc.size());
 }
 
@@ -129,7 +142,7 @@ char* copy_string(const std::string& s)
 const std::map<std::string, struct ParserBase*> parsers =
     {
         {"date",       P(&message::recv, &parse_timestamp) },
-        {"message-ID", P(&message::id, message_id, &copy_string) },
+        {"message-id", P(&message::id, message_id, &copy_string) },
         {"subject",    P(&message::shortmsg, phrase, &copy_string) },
         {"from",       P(&message::from, &parse_address) },
         {"to",         P(&message::to, &parse_address_list) },
@@ -155,8 +168,9 @@ void parse_header(message* msg, const HeaderSection& header)
         if(p == parsers.end())
         {
             // unknown header with no special parser: just dump it in opt_fields
-            const std::string nfc = toNFC(h.value); // TODO: use views/ranges to avoid copying
-            auto sp = new_stringpair( h.name.c_str(), nfc.c_str() );
+            const std::string nfc_name  = robust_to_utf8(h.name);  // TODO: use views/ranges to avoid copying
+            const std::string nfc_value = robust_to_utf8(h.value); // TODO: use views/ranges to avoid copying
+            auto sp = new_stringpair( nfc_name.c_str(), nfc_value.c_str() );
             auto f = stringpair_list_add( msg->opt_fields, sp);
             
             // the function above has a strange semantic: