diff --git a/logging.c b/logging.c
index 8f46500d..a04ca633 100644
--- a/logging.c
+++ b/logging.c
@@ -256,15 +256,18 @@ void logevent_and_free(LogContext *ctx, char *event)
     sfree(event);
 }
 
+void logeventvf(LogContext *ctx, const char *fmt, va_list ap)
+{
+    logevent_and_free(ctx, dupvprintf(fmt, ap));
+}
+
 void logeventf(LogContext *ctx, const char *fmt, ...)
 {
     va_list ap;
-    char *buf;
 
     va_start(ap, fmt);
-    buf = dupvprintf(fmt, ap);
+    logeventvf(ctx, fmt, ap);
     va_end(ap);
-    logevent_and_free(ctx, buf);
 }
 
 /*
diff --git a/misc.c b/misc.c
index f360eebb..274f8aa8 100644
--- a/misc.c
+++ b/misc.c
@@ -1259,6 +1259,24 @@ int ptrlen_eq_string(ptrlen pl, const char *str)
     return (pl.len == len && !memcmp(pl.ptr, str, len));
 }
 
+int ptrlen_eq_ptrlen(ptrlen pl1, ptrlen pl2)
+{
+    return (pl1.len == pl2.len && !memcmp(pl1.ptr, pl2.ptr, pl1.len));
+}
+
+int ptrlen_startswith(ptrlen whole, ptrlen prefix, ptrlen *tail)
+{
+    if (whole.len >= prefix.len &&
+        !memcmp(whole.ptr, prefix.ptr, prefix.len)) {
+        if (tail) {
+            tail->ptr = (const char *)whole.ptr + prefix.len;
+            tail->len = whole.len - prefix.len;
+        }
+        return TRUE;
+    }
+    return FALSE;
+}
+
 char *mkstr(ptrlen pl)
 {
     char *p = snewn(pl.len + 1, char);
diff --git a/misc.h b/misc.h
index fd63b335..90322092 100644
--- a/misc.h
+++ b/misc.h
@@ -100,6 +100,8 @@ ptrlen make_ptrlen(const void *ptr, size_t len);
 ptrlen ptrlen_from_asciz(const char *str);
 ptrlen ptrlen_from_strbuf(strbuf *sb);
 int ptrlen_eq_string(ptrlen pl, const char *str);
+int ptrlen_eq_ptrlen(ptrlen pl1, ptrlen pl2);
+int ptrlen_startswith(ptrlen whole, ptrlen prefix, ptrlen *tail);
 char *mkstr(ptrlen pl);
 int string_length_for_printf(size_t);
 /* Derive two printf arguments from a ptrlen, suitable for "%.*s" */
diff --git a/putty.h b/putty.h
index 492d87e1..46b8be54 100644
--- a/putty.h
+++ b/putty.h
@@ -1484,6 +1484,8 @@ void logtraffic(LogContext *logctx, unsigned char c, int logmode);
 void logflush(LogContext *logctx);
 void logevent(LogContext *logctx, const char *event);
 void logeventf(LogContext *logctx, const char *fmt, ...);
+void logeventvf(LogContext *logctx, const char *fmt, va_list ap);
+
 /*
  * Pass a dynamically allocated string to logevent and immediately
  * free it. Intended for use by wrapper macros which pass the return