Provide a JID for IRC users, and add a stringprep dependency for this

src/xmpp/jid.cpp

@@ -1,4 +1,12 @@
 #include <xmpp/jid.hpp>
+#include <config.h>
+#include <cstring>
+
+#ifdef LIBIDN_FOUND
+ #include <stringprep.h>
+#endif
+
+#include <logger/logger.hpp>
 
 Jid::Jid(const std::string& jid)
 {
@@ -19,3 +27,41 @@ Jid::Jid(const std::string& jid)
 
   this->domain = jid.substr(at, slash - at);
 }
+
+#include <iostream>
+
+static constexpr size_t max_jid_part_len = 1023;
+
+std::string jidprep(const std::string& original)
+{
+#ifdef LIBIDN_FOUND
+  // TODO: cache the result
+  const std::string error_msg("Failed to convert " + original + " into a valid JID:");
+  Jid jid(original);
+
+  char local[max_jid_part_len] = {};
+  memcpy(local, jid.local.data(), jid.local.size());
+  Stringprep_rc rc = static_cast<Stringprep_rc>(::stringprep(local, max_jid_part_len,
+                     static_cast<Stringprep_profile_flags>(0), stringprep_xmpp_nodeprep));
+  if (rc != STRINGPREP_OK)
+  {
+    log_error(error_msg + stringprep_strerror(rc));
+    return "";
+  }
+
+  char domain[max_jid_part_len] = {};
+  memcpy(domain, jid.domain.data(), jid.domain.size());
+  rc = static_cast<Stringprep_rc>(::stringprep(domain, max_jid_part_len,
+       static_cast<Stringprep_profile_flags>(0), stringprep_nameprep));
+  if (rc != STRINGPREP_OK)
+  {
+    log_error(error_msg + stringprep_strerror(rc));
+    return "";
+  }
+
+  return std::string(local) + "@" + domain;
+#else
+  (void)original;
+  return "";
+#endif
+}