--- a/src/context.cpp	Fri Nov 19 13:04:47 2010 -0800
+++ b/src/context.cpp	Mon Aug 15 21:08:11 2011 -0700
@@ -853,16 +853,20 @@
     string_map::iterator i = env_from.find(from);
     if (i != env_from.end()) rc = (*i).second;  // found user@domain key
     else {
-        char *x = strchr(from, '@');
+        const char *x = strchr(from, '@');
         if (x) {
+            char buf[200];
             x++;
             i = env_from.find(x);
+            size_t n = x - from;    // length of user name plus @
             if (i != env_from.end()) rc = (*i).second;  // found domain key
-            else {
-                char y = *x;
-                *x = '\0';
-                i = env_from.find(from);
-                *x = y;
+            else if (n < sizeof(buf)) {
+                // we only test reasonably short user names, since we need
+                // to copy them to a buffer to avoid a dup/free cycle on every
+                // test here.
+                strncpy(buf, from, n);
+                buf[n] = '\0';
+                i = env_from.find(buf);
                 if (i != env_from.end()) rc = (*i).second;  // found user@ key
             }
         }
@@ -879,17 +883,23 @@
 CONTEXTP CONTEXT::find_context(const char *from) {
     context_map::iterator i = env_from_context.find(from);
     if (i != env_from_context.end()) return (*i).second;        // found user@domain key
-    char *x = strchr(from, '@');
+    const char *x = strchr(from, '@');
     if (x) {
+        char buf[200];
         x++;
         i = env_from_context.find(x);
+        size_t n = x - from;    // length of user name plus @
         if (i != env_from_context.end()) return (*i).second;    // found domain key
-        char y = *x;
-        *x = '\0';
-        i = env_from_context.find(from);
-        *x = y;
+        else if (n < sizeof(buf)) {
+            // we only test reasonably short user names, since we need
+            // to copy them to a buffer to avoid a dup/free cycle on every
+            // test here.
+            strncpy(buf, from, n);
+            buf[n] = '\0';
+            i = env_from_context.find(buf);
         if (i != env_from_context.end()) return (*i).second;    // found user@ key
     }
+    }
     return this;
 }