Early return from asciistream file read if file is empty

Avoids a transitive vespalib::string append with nullptr buffer and
zero length, which in turn ends up passing nullptr to memmove, which
is undefined.

1 files changed, 3 insertions, 0 deletions

diff --git a/vespalib/src/vespa/vespalib/stllike/asciistream.cpp b/vespalib/src/vespa/vespalib/stllike/asciistream.cpp
index eb127c7051a..6b673363d2d 100644
--- a/vespalib/src/vespa/vespalib/stllike/asciistream.cpp
+++ b/vespalib/src/vespa/vespalib/stllike/asciistream.cpp
@@ -628,6 +628,9 @@ asciistream::createFromFile(stringref fileName)
         if (sz < 0) {
             throw IoException("Failed getting size of  file " + fileName + " : Error=" + file.getLastErrorString(), IoException::UNSPECIFIED, VESPA_STRLOC);
         }
+        if (sz == 0) {
+            return is;
+        }
         alloc::Alloc buf = alloc::Alloc::alloc(sz);
         ssize_t actual = file.Read(buf.get(), sz);
         if (actual != sz) {