Logo ROOT   6.14/05
Reference Guide
httptextlog.C File Reference

Detailed Description

This macro demonstrates custom access and custom drawing for TMsgList class Main motivation for this example - demonstrate how traffic between server and client can be minimized and how one could build custom UI in the browser.

TMsgList in this tutorial keep last N messages, numbering each with unique identifier There is TMsgList::Select() method which selects messages from the list If one specifies identifier, only messages newer than this identifier are selected In the selection list (TList object of TObjString) first item always identifier for the latest message in the list

In JavaScript code (httptextlog.js) one uses Select() method to receive latest messages, which not yet been seen in the browser and display them as text At maximum, 1000 elements are preserved in the browser.

Macro should always be started in compiled mode, otherwise Select() method is not accessible via TClass instance. One also requires comments after ClassDef to correctly configure behavior of the JavaScript ROOT code

After macro started, one could open in browser address


One could either click item again or enable monitoring to always receive latest messages Or one could open only this output and nothing else:


In last case it could be used in iframe, also it requires less code to load on the page

#include <stdio.h>
#include <string.h>
#include "TNamed.h"
#include "TList.h"
#include "TObjString.h"
#include "TH1.h"
#include "TH2.h"
#include "TRandom3.h"
#include "TSystem.h"
#include "THttpServer.h"
#include "TRootSniffer.h"
#include "TDatime.h"
#include "TClass.h"
Bool_t bRun = kTRUE;
class TMsgList : public TNamed {
TList fMsgs; // list messages, stored as TObjString
Int_t fLimit; // max number of stored messages
Long64_t fCounter; // current message id
TList fSelect; //! temporary list used for selection
TObjString fStrCounter; //! current id stored in the string
TMsgList(const char* name = "log", Int_t limit = 1000) :
TNamed(name,"list of log messages"),
// counter initialized from current time
// if application restarted, id will be bigger and request from browser
// will not lead to messages lost. Of course, if more than 1000 messages
// per second are generated, one could have mismatch
fCounter = ((Long64_t) TDatime().Get()) * 1000;
virtual ~TMsgList() { fMsgs.Clear(); }
void AddMsg(const char* msg)
// add message to the list
// if number of stored messages bigger than configured, old messages will be removed
// zero (msg==0) messages will not be add to the list
while (fMsgs.GetSize() >= fLimit) {
TObject* last = fMsgs.Last();
delete last;
if (msg==0) return;
fMsgs.AddFirst(new TObjString(msg));
TList* Select(Int_t max = 0, Long64_t id = 0)
// Central method to select new messages
// Current id stored as first item and used on the client to request new portion
// One could limit number of returned messages
TIter iter(&fMsgs);
TObject* obj = 0;
Long64_t curr = fCounter;
if (max == 0) max = fMsgs.GetLast()+1;
// add current id as first string in the list
fStrCounter.SetString(TString::LLtoa(fCounter, 10));
while (((obj = iter()) != 0) && (--curr >= id) && (--max>=0)) fSelect.Add(obj);
return &fSelect;
ClassDef(TMsgList, 1); // Custom messages list
void httptextlog()
// create logging instance
TMsgList* log = new TMsgList("log", 200);
if ((TMsgList::Class()->GetMethodAllAny("Select") == 0) || (strcmp(log->ClassName(), "TMsgList")!=0)) {
printf("Most probably, macro runs in interpreter mode\n");
printf("To access new methods from TMsgList class,\n");
printf("one should run macro with ACLiC like:\n");
printf(" shell> root -b httpextlog.C+\n");
if (gSystem->AccessPathName("httptextlog.js")!=0) {
printf("Please start macro from directory where httptextlog.js is available\n");
printf("Only in this case web interface can work\n");
// create histograms, just for fun
TH1D *hpx = new TH1D("hpx","This is the px distribution",100,-4,4);
TH2F *hpxpy = new TH2F("hpxpy","py vs px",40,-4,4,40,-4,4);
// start http server
THttpServer* serv = new THttpServer("http:8080");
// One could specify location of newer version of JSROOT
// serv->SetJSROOT("https://root.cern.ch/js/latest/");
// serv->SetJSROOT("http://jsroot.gsi.de/latest/");
// let always load httptextlog.js script in the browser
// register histograms
serv->Register("/", hpx);
serv->Register("/", hpxpy);
// register log instance
serv->Register("/", log);
// while server runs in read-only mode, we should allow methods execution
serv->Restrict("/log", "allow_method=Select,GetTitle");
// register exit command
serv->RegisterCommand("/Stop","bRun=kFALSE;", "rootsys/icons/ed_delete.png");
serv->RegisterCommand("/ExitRoot","gSystem->Exit(1);", "rootsys/icons/ed_delete.png");
// Fill histograms randomly
TRandom3 random;
Float_t px, py;
const Long_t kUPDATE = 1000;
Long_t cnt = 0;
while (bRun) {
// IMPORTANT: one should regularly call ProcessEvents
if (cnt++ % kUPDATE == 0) {
if (gSystem->ProcessEvents()) break;
Long_t loop = cnt / kUPDATE;
// make messages not very often
if (loop % 1000 == 0) {
loop = loop/1000;
int shift = loop % 40;
// make a 'stairs' with spaces
log->AddMsg(TString::Format("%*s Message %ld", shift, "", loop));
delete serv; // delete http server
Sergey Linev

Definition in file httptextlog.C.