Piping from http to sd card results in OOM error

Not sure why I get this error:

ERROR: Out of Memory!
done piping
at line 1 col 106
...str(0,b);f[a]=f[a].substr(b)}else d=f[a],f[a]="","DataClose"...
in function called from system

(highlighted piece of code is the substr() call)
Simplified code is:

http.request(httpOptions, function(requestResult) {
  requestResult.pipe(f, {
    chunkSize: 512,
    complete: function() {
      console.log('done piping');
    }
  });

}).end();