THttpServer.cxx

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// $Id$
// Author: Sergey Linev   21/12/2013
 
/*************************************************************************
 * Copyright (C) 1995-2013, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#include "THttpServer.h"
 
#include "TThread.h"
#include "TTimer.h"
#include "TSystem.h"
#include "TROOT.h"
#include "TUrl.h"
#include "TEnv.h"
#include "TError.h"
#include "TClass.h"
#include "RConfigure.h"
#include "TRegexp.h"
#include "TObjArray.h"
 
#include "THttpEngine.h"
#include "THttpLongPollEngine.h"
#include "THttpWSHandler.h"
#include "TRootSniffer.h"
#include "TRootSnifferStore.h"
#include "TCivetweb.h"
#include "TFastCgi.h"
 
#include <chrono>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <memory>
#include <string>
#include <thread>
 
class THttpTimer : public TTimer {
   Long_t fNormalTmout{0};
   Bool_t fSlow{kFALSE};
   Int_t fSlowCnt{0};
 
public:
   THttpServer &fServer; ///!< server processing requests
 
   /// constructor
   THttpTimer(Long_t milliSec, Bool_t mode, THttpServer &serv) : TTimer(milliSec, mode), fNormalTmout(milliSec), fServer(serv) {}
 
   void SetSlow(Bool_t flag)
   {
      fSlow = flag;
      fSlowCnt = 0;
      Long_t ms = fNormalTmout;
      if (fSlow) {
         if (ms < 100)
            ms = 500;
         else if (ms < 500)
            ms = 3000;
         else
            ms = 10000;
      }
 
      SetTime(ms);
   }
   Bool_t IsSlow() const { return fSlow; }
 
   /// timeout handler
   /// used to process http requests in main ROOT thread
   void Timeout() override
   {
      Int_t nprocess = fServer.ProcessRequests();
 
      if (nprocess > 0) {
         fSlowCnt = 0;
         if (IsSlow())
            SetSlow(kFALSE);
      } else if (!IsSlow() && (fSlowCnt++ > 10)) {
           SetSlow(kTRUE);
      }
   }
};
 
 
/** \class THttpServer
\ingroup http
 
Online http server for arbitrary ROOT application
 
Idea of THttpServer - provide remote http access to running
ROOT application and enable HTML/JavaScript user interface.
Any registered object can be requested and displayed in the browser.
There are many benefits of such approach:
 
1. standard http interface to ROOT application
2. no any temporary ROOT files when access data
3. user interface running in all browsers
 
To start http server simply create instance
of the THttpServer class like:
 
    serv = new THttpServer("http:8080");
 
This will starts civetweb-based http server with http port 8080.
Than one should be able to open address "http://localhost:8080"
in any modern web browser (Firefox, Chrome, Opera, ...) and browse objects,
created in ROOT application. By default, server can access files,
canvases and histograms via `gROOT` pointer. All such objects
can be displayed with JSROOT graphics.
 
At any time one could register other objects with the command:
 
    TGraph* gr = new TGraph(10);
    gr->SetName("gr1");
    serv->Register("graphs/subfolder", gr);
 
If objects content is changing in the application, one could
enable monitoring flag in the browser - than objects view
will be regularly updated.
 
More information: https://root.cern/root/htmldoc/guides/HttpServer/HttpServer.html
*/
 
ClassImp(THttpServer);
 
////////////////////////////////////////////////////////////////////////////////
/// constructor
///
/// As argument, one specifies engine kind which should be
/// created like "http:8080". One could specify several engines
/// at once, separating them with semicolon (";"). Following engines are supported:
///
///     http     - TCivetweb, civetweb-based implementation of http protocol
///     fastcgi  - TFastCgi, special protocol for communicating with web servers
///
/// For each created engine one should provide socket port number like "http:8080" or "fastcgi:9000".
/// Additional engine-specific options can be supplied with URL syntax like "http:8080?thrds=10".
/// Full list of supported options should be checked in engines docu.
///
/// One also can configure following options, separated by semicolon:
///
///     readonly, ro   - set read-only mode (default)
///     readwrite, rw  - allows methods execution of registered objects
///     global         - scans global ROOT lists for existing objects (default)
///     noglobal       - disable scan of global lists
///     cors           - enable CORS header with origin="*"
///     cors=domain    - enable CORS header with origin="domain"
///     basic_sniffer  - use basic sniffer without support of hist, gpad, graph classes
///
/// For example, create http server, which allows cors headers and disable scan of global lists,
/// one should provide "http:8080;cors;noglobal" as parameter
///
/// THttpServer uses JavaScript ROOT (https://root.cern/js) to implement web clients UI.
/// Normally JSROOT sources are used from $ROOTSYS/js directory,
/// but one could set JSROOTSYS shell variable to specify alternative location
 
THttpServer::THttpServer(const char *engine) : TNamed("http", "ROOT http server")
{
   const char *jsrootsys = gSystem->Getenv("JSROOTSYS");
   if (!jsrootsys)
      jsrootsys = gEnv->GetValue("HttpServ.JSRootPath", jsrootsys);
 
   if (jsrootsys && *jsrootsys) {
      if ((strncmp(jsrootsys, "http://", 7)==0) || (strncmp(jsrootsys, "https://", 8)==0))
         fJSROOT = jsrootsys;
      else
         fJSROOTSYS = jsrootsys;
   }
 
   if (fJSROOTSYS.Length() == 0) {
      TString jsdir = TString::Format("%s/js", TROOT::GetDataDir().Data());
      if (gSystem->ExpandPathName(jsdir)) {
         ::Warning("THttpServer::THttpServer", "problems resolving '%s', set JSROOTSYS to proper JavaScript ROOT location",
                 jsdir.Data());
         fJSROOTSYS = ".";
      } else {
         fJSROOTSYS = jsdir;
      }
   }
 
   Bool_t basic_sniffer = strstr(engine, "basic_sniffer") != nullptr;
 
   AddLocation("jsrootsys/", fJSROOTSYS.Data());
 
   if (!basic_sniffer) {
      AddLocation("currentdir/", ".");
      AddLocation("rootsys/", TROOT::GetRootSys());
   }
 
   fDefaultPage = fJSROOTSYS + "/files/online.htm";
   fDrawPage = fJSROOTSYS + "/files/draw.htm";
 
   TRootSniffer *sniff = nullptr;
   if (basic_sniffer) {
      sniff = new TRootSniffer();
      sniff->SetScanGlobalDir(kFALSE);
      sniff->CreateOwnTopFolder(); // use dedicated folder
   } else {
      static const TClass *snifferClass = TClass::GetClass("TRootSnifferFull");
      sniff = (TRootSniffer *)snifferClass->New();
   }
 
   SetSniffer(sniff);
 
   // start timer
   SetTimer(20, kTRUE);
 
   if (strchr(engine, ';') == 0) {
      CreateEngine(engine);
   } else {
      TObjArray *lst = TString(engine).Tokenize(";");
 
      for (Int_t n = 0; n <= lst->GetLast(); n++) {
         const char *opt = lst->At(n)->GetName();
         if ((strcmp(opt, "readonly") == 0) || (strcmp(opt, "ro") == 0)) {
            GetSniffer()->SetReadOnly(kTRUE);
         } else if ((strcmp(opt, "readwrite") == 0) || (strcmp(opt, "rw") == 0)) {
            GetSniffer()->SetReadOnly(kFALSE);
         } else if (strcmp(opt, "global") == 0) {
            GetSniffer()->SetScanGlobalDir(kTRUE);
         } else if (strcmp(opt, "noglobal") == 0) {
            GetSniffer()->SetScanGlobalDir(kFALSE);
         } else if (strncmp(opt, "cors=", 5) == 0) {
            SetCors(opt + 5);
         } else if (strcmp(opt, "cors") == 0) {
            SetCors("*");
         } else
            CreateEngine(opt);
      }
 
      delete lst;
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// destructor
///
/// delete all http engines and sniffer
 
THttpServer::~THttpServer()
{
   StopServerThread();
 
   if (fTerminated) {
      TIter iter(&fEngines);
      while (auto engine = dynamic_cast<THttpEngine *>(iter()))
         engine->Terminate();
   }
 
   fEngines.Delete();
 
   SetSniffer(nullptr);
 
   SetTimer(0);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set TRootSniffer to the server
///
/// Server takes ownership over sniffer
 
void THttpServer::SetSniffer(TRootSniffer *sniff)
{
   fSniffer.reset(sniff);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set termination flag,
///
/// No any further requests will be processed, server only can be destroyed afterwards
 
void THttpServer::SetTerminate()
{
   fTerminated = kTRUE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// returns read-only mode
 
Bool_t THttpServer::IsReadOnly() const
{
   return fSniffer ? fSniffer->IsReadOnly() : kTRUE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set read-only mode for the server (default on)
///
/// In read-only server is not allowed to change any ROOT object, registered to the server
/// Server also cannot execute objects method via exe.json request
 
void THttpServer::SetReadOnly(Bool_t readonly)
{
   if (fSniffer)
      fSniffer->SetReadOnly(readonly);
}
 
////////////////////////////////////////////////////////////////////////////////
/// returns true if only websockets are handled by the server
///
/// Typically used by WebGui
 
Bool_t THttpServer::IsWSOnly() const
{
   return fWSOnly;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set websocket-only mode.
///
/// If true, server will only handle websockets connection
/// plus serving file requests to access jsroot/ui5 scripts
 
void THttpServer::SetWSOnly(Bool_t on)
{
   fWSOnly = on;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Add files location, which could be used in the server
///
/// One could map some system folder to the server like
///
///     serv->AddLocation("mydir/", "/home/user/specials");
///
/// Than files from this directory could be addressed via server like `http://localhost:8080/mydir/myfile.root`
 
void THttpServer::AddLocation(const char *prefix, const char *path)
{
   if (!prefix || (*prefix == 0))
      return;
 
   if (!path)
      fLocations.erase(fLocations.find(prefix));
   else
      fLocations[prefix] = path;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set location of JSROOT to use with the server
///
/// One could specify address like:
///
/// * https://root.cern/js/7.6.0/
/// * https://jsroot.gsi.de/7.6.0/
///
/// This allows to get new JSROOT features with old server,
/// reduce load on THttpServer instance, also startup time can be improved
/// When empty string specified (default), local copy of JSROOT is used (distributed with ROOT)
 
void THttpServer::SetJSROOT(const char *location)
{
   fJSROOT = location ? location : "";
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set default HTML page
///
/// Sets file name, delivered by the server when http address is opened in the browser.
///
/// By default, $ROOTSYS/js/files/online.htm page is used
/// When empty filename is specified, default page will be used
 
void THttpServer::SetDefaultPage(const std::string &filename)
{
   if (!filename.empty())
      fDefaultPage = filename;
   else
      fDefaultPage = fJSROOTSYS + "/files/online.htm";
 
   // force to read page content next time again
   fDefaultPageCont.clear();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set drawing HTML page
///
/// Set file name of HTML page, delivered by the server when
/// objects drawing page is requested from the browser
/// By default, $ROOTSYS/js/files/draw.htm page is used
/// When empty filename is specified, default page will be used
 
void THttpServer::SetDrawPage(const std::string &filename)
{
   if (!filename.empty())
      fDrawPage = filename;
   else
      fDrawPage = fJSROOTSYS + "/files/draw.htm";
 
   // force to read page content next time again
   fDrawPageCont.clear();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Factory method to create different http engines
///
/// At the moment two engine kinds are supported:
///
/// * civetweb or http (default)
/// * fastcgi
///
/// Examples:
///
///     // creates civetweb web server with http port 8080
///     serv->CreateEngine("http:8080");
///     serv->CreateEngine("civetweb:8080");
///     serv->CreateEngine(":8080");
///     // creates fastcgi server with port 9000
///     serv->CreateEngine("fastcgi:9000");
///
/// One could apply additional parameters, using URL syntax:
///
///     serv->CreateEngine("http:8080?thrds=10");
 
Bool_t THttpServer::CreateEngine(const char *engine)
{
   if (!engine)
      return kFALSE;
 
   const char *arg = strchr(engine, ':');
   if (!arg)
      return kFALSE;
 
   TString clname, sarg;
   if (arg != engine)
      clname.Append(engine, arg - engine);
   arg++; // skip first :
 
   THttpEngine *eng = nullptr;
 
   if ((clname.Length() == 0) || (clname == "http") || (clname == "civetweb")) {
      eng = new TCivetweb(kFALSE);
#ifndef R__WIN32
   } else if (clname == "socket") {
      eng = new TCivetweb(kFALSE);
      sarg = "x"; // civetweb require x before socket name
      sarg.Append(arg);
      arg = sarg.Data();
#endif
   } else if (clname == "https") {
      eng = new TCivetweb(kTRUE);
   } else if (clname == "fastcgi") {
      eng = new TFastCgi();
   }
 
   if (!eng) {
      // ensure that required engine class exists before we try to create it
      TClass *engine_class = gROOT->LoadClass(clname.Data());
      if (!engine_class)
         return kFALSE;
 
      eng = (THttpEngine *)engine_class->New();
      if (!eng)
         return kFALSE;
   }
 
   eng->SetServer(this);
 
   if (!eng->Create(arg)) {
      delete eng;
      return kFALSE;
   }
 
   fEngines.Add(eng);
 
   return kTRUE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create timer which will invoke ProcessRequests() function periodically
///
/// Timer is required to perform all actions in main ROOT thread
/// Method arguments are the same as for TTimer constructor
/// By default, sync timer with 100 ms period is created
///
/// It is recommended to always use sync timer mode and only change period to
/// adjust server reaction time. Use of async timer requires, that application regularly
/// calls gSystem->ProcessEvents(). It happens automatically in ROOT interactive shell.
/// If milliSec == 0, no timer will be created.
/// In this case application should regularly call ProcessRequests() method.
///
/// Async timer allows to use THttpServer in applications, which does not have explicit
/// gSystem->ProcessEvents() calls. But be aware, that such timer can interrupt any system call
/// (like malloc) and can lead to dead locks, especially in multi-threaded applications.
 
void THttpServer::SetTimer(Long_t milliSec, Bool_t mode)
{
   if (fTimer) {
      fTimer->Stop();
      fTimer.reset();
   }
   if (milliSec > 0) {
      if (fOwnThread) {
         Error("SetTimer", "Server runs already in special thread, therefore no any timer can be created");
      } else {
         fTimer = std::make_unique<THttpTimer>(milliSec, mode, *this);
         fTimer->TurnOn();
      }
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// Creates special thread to process all requests, directed to http server
///
/// Should be used with care - only dedicated instance of TRootSniffer is allowed
/// By default THttpServer allows to access global lists pointers gROOT or gFile.
/// To be on the safe side, all kind of such access performed from the main thread.
/// Therefore usage of specialized thread means that no any global pointers will
/// be accessible by THttpServer
 
void THttpServer::CreateServerThread()
{
   if (fOwnThread)
      return;
 
   SetTimer(0);
   fMainThrdId = 0;
   fOwnThread = true;
 
   std::thread thrd([this] {
      int nempty = 0;
      while (fOwnThread && !fTerminated) {
         int nprocess = ProcessRequests();
         if (nprocess > 0)
            nempty = 0;
         else
            nempty++;
         if (nempty > 1000) {
            nempty = 0;
            std::this_thread::sleep_for(std::chrono::milliseconds(1));
         }
      }
   });
 
   fThrd = std::move(thrd);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Stop server thread
///
/// Normally called shortly before http server destructor
 
void THttpServer::StopServerThread()
{
   if (!fOwnThread)
      return;
 
   fOwnThread = false;
   fThrd.join();
   fMainThrdId = 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Checked that filename does not contains relative path below current directory
///
/// Used to prevent access to files below current directory
 
Bool_t THttpServer::VerifyFilePath(const char *fname)
{
   if (!fname || (*fname == 0))
      return kFALSE;
 
   Int_t level = 0;
 
   while (*fname) {
 
      // find next slash or backslash
      const char *next = strpbrk(fname, "/\\");
      if (next == 0)
         return kTRUE;
 
      // most important - change to parent dir
      if ((next == fname + 2) && (*fname == '.') && (*(fname + 1) == '.')) {
         fname += 3;
         level--;
         if (level < 0)
            return kFALSE;
         continue;
      }
 
      // ignore current directory
      if ((next == fname + 1) && (*fname == '.')) {
         fname += 2;
         continue;
      }
 
      // ignore slash at the front
      if (next == fname) {
         fname++;
         continue;
      }
 
      fname = next + 1;
      level++;
   }
 
   return kTRUE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Verifies that request is just file name
///
/// File names typically contains prefix like "jsrootsys/"
/// If true, method returns real name of the file,
/// which should be delivered to the client
/// Method is thread safe and can be called from any thread
 
Bool_t THttpServer::IsFileRequested(const char *uri, TString &res) const
{
   if (!uri || (*uri == 0))
      return kFALSE;
 
   TString fname(uri);
 
   for (auto &entry : fLocations) {
      Ssiz_t pos = fname.Index(entry.first.c_str());
      if (pos == kNPOS)
         continue;
      fname.Remove(0, pos + (entry.first.length() - 1));
      if (!VerifyFilePath(fname.Data()))
         return kFALSE;
      res = entry.second.c_str();
      if ((fname[0] == '/') && (res[res.Length() - 1] == '/'))
         res.Resize(res.Length() - 1);
      res.Append(fname);
      return kTRUE;
   }
 
   return kFALSE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Executes http request, specified in THttpCallArg structure
///
/// Method can be called from any thread
/// Actual execution will be done in main ROOT thread, where analysis code is running.
 
Bool_t THttpServer::ExecuteHttp(std::shared_ptr<THttpCallArg> arg)
{
   if (fTerminated)
      return kFALSE;
 
   if ((fMainThrdId != 0) && (fMainThrdId == TThread::SelfId())) {
      // should not happen, but one could process requests directly without any signaling
 
      ProcessRequest(arg);
 
      return kTRUE;
   }
 
   if (fTimer && fTimer->IsSlow())
      fTimer->SetSlow(kFALSE);
 
   // add call arg to the list
   std::unique_lock<std::mutex> lk(fMutex);
   fArgs.push(arg);
   // and now wait until request is processed
   arg->fCond.wait(lk);
 
   return kTRUE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Submit http request, specified in THttpCallArg structure
///
/// Contrary to ExecuteHttp, it will not block calling thread.
/// User should implement THttpCallArg::HttpReplied() method
/// to react when HTTP request is executed.
 
/// Method can be called from any thread
/// Actual execution will be done in main ROOT thread, where analysis code is running.
/// When called from main thread and can_run_immediately==kTRUE, will be
/// executed immediately.
///
/// Returns kTRUE when was executed.
 
Bool_t THttpServer::SubmitHttp(std::shared_ptr<THttpCallArg> arg, Bool_t can_run_immediately)
{
   if (fTerminated)
      return kFALSE;
 
   if (can_run_immediately && (fMainThrdId != 0) && (fMainThrdId == TThread::SelfId())) {
      ProcessRequest(arg);
      arg->NotifyCondition();
      return kTRUE;
   }
 
   // add call arg to the list
   std::unique_lock<std::mutex> lk(fMutex);
   fArgs.push(arg);
   return kFALSE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Process requests, submitted for execution
///
/// Returns number of processed requests
///
/// Normally invoked by THttpTimer, when somewhere in the code
/// gSystem->ProcessEvents() is called.
/// User can call serv->ProcessRequests() directly, but only from main thread.
/// If special server thread is created, called from that thread
 
Int_t THttpServer::ProcessRequests()
{
   auto id = TThread::SelfId();
 
   if (fMainThrdId != id) {
      if (gDebug > 0 && fMainThrdId)
         Warning("ProcessRequests", "Changing main thread to %ld", (long)id);
      fMainThrdId = id;
   }
 
   Bool_t recursion = kFALSE;
 
   if (fProcessingThrdId) {
      if (fProcessingThrdId == id) {
         recursion = kTRUE;
      } else {
         Error("ProcessRequests", "Processing already running from %ld thread", (long) fProcessingThrdId);
         return 0;
      }
   }
 
   if (!recursion)
      fProcessingThrdId = id;
 
   Int_t cnt = 0;
 
   std::unique_lock<std::mutex> lk(fMutex, std::defer_lock);
 
   // first process requests in the queue
   while (true) {
      std::shared_ptr<THttpCallArg> arg;
 
      lk.lock();
      if (!fArgs.empty()) {
         arg = fArgs.front();
         fArgs.pop();
      }
      lk.unlock();
 
      if (!arg)
         break;
 
      if (arg->fFileName == "root_batch_holder.js") {
         ProcessBatchHolder(arg);
         continue;
      }
 
      auto prev = fSniffer->SetCurrentCallArg(arg.get());
 
      try {
         cnt++;
         ProcessRequest(arg);
         fSniffer->SetCurrentCallArg(prev);
      } catch (...) {
         fSniffer->SetCurrentCallArg(prev);
      }
 
      arg->NotifyCondition();
   }
 
   // regularly call Process() method of engine to let perform actions in ROOT context
   TIter iter(&fEngines);
   while (auto engine = static_cast<THttpEngine *>(iter())) {
      if (fTerminated)
         engine->Terminate();
      engine->Process();
   }
 
   if (!recursion)
      fProcessingThrdId = 0;
 
   return cnt;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Method called when THttpServer cannot process request
///
/// By default such requests replied with 404 code
/// One could overwrite with method in derived class to process all kinds of such non-standard requests
 
void THttpServer::MissedRequest(THttpCallArg *arg)
{
   arg->Set404();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Process special http request for root_batch_holder.js script
///
/// This kind of requests used to hold web browser running in headless mode
/// Intentionally requests does not replied immediately
 
void THttpServer::ProcessBatchHolder(std::shared_ptr<THttpCallArg> &arg)
{
   auto wsptr = FindWS(arg->GetPathName());
 
   if (!wsptr || !wsptr->ProcessBatchHolder(arg)) {
      arg->Set404();
      arg->NotifyCondition();
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create summary page with active WS handlers
 
std::string THttpServer::BuildWSEntryPage()
{
 
   std::string arr = "[";
 
   {
      std::lock_guard<std::mutex> grd(fWSMutex);
      for (auto &ws : fWSHandlers) {
         if (arr.length() > 1)
            arr.append(", ");
 
         arr.append(TString::Format("{ name: \"%s\", title: \"%s\" }", ws->GetName(), ws->GetTitle()).Data());
      }
   }
 
   arr.append("]");
 
   std::string res = ReadFileContent((TROOT::GetDataDir() + "/js/files/wslist.htm").Data());
 
   std::string arg = "\"$$$wslist$$$\"";
 
   auto pos = res.find(arg);
   if (pos != std::string::npos)
      res.replace(pos, arg.length(), arr);
 
   return res;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Replaces all references like "jsrootsys/..." or other pre-configured pathes
///
/// Either using pre-configured JSROOT installation from web or
/// redirect to jsrootsys from the main server path to benefit from browser caching
/// Creates appropriate importmap instead of <!--jsroot_importmap--> placeholder
 
void THttpServer::ReplaceJSROOTLinks(std::shared_ptr<THttpCallArg> &arg, const std::string &version)
{
   const std::string place_holder = "<!--jsroot_importmap-->";
 
   auto p = arg->fContent.find(place_holder);
 
   bool old_format = (p == std::string::npos);
 
   // count slashes to handler relative paths to jsroot
   Int_t slash_cnt = 0;
   if (arg->fPathName.Length() > 0)
      slash_cnt++;
   for (Int_t n = 1; n < arg->fPathName.Length()-1; ++n)
      if (arg->fPathName[n] == '/') {
         if (arg->fPathName[n-1] != '/') {
            slash_cnt++; // normal slash in the middle, count it
         } else {
            slash_cnt = 0; // double slash, do not touch such path
            break;
         }
      }
 
 
   if (old_format) {
      // old functionality
 
      if (!version.empty()) {
         // replace link to JSROOT modules in import statements emulating new version for browser
         std::string search = "from './jsrootsys/";
         std::string replace = "from './" + version + "/jsrootsys/";
         arg->ReplaceAllinContent(search, replace);
         // replace link to ROOT ui5 modules in import statements emulating new version for browser
         search = "from './rootui5sys/";
         replace = "from './" + version + "/rootui5sys/";
         arg->ReplaceAllinContent(search, replace);
         // replace link on old JSRoot.core.js script - if still appears
         search = "jsrootsys/scripts/JSRoot.core.";
         replace = version + "/jsrootsys/scripts/JSRoot.core.";
         arg->ReplaceAllinContent(search, replace, true);
         arg->AddNoCacheHeader();
      }
 
      std::string repl;
 
      if (fJSROOT.Length() > 0) {
         repl = "=\"";
         repl.append(fJSROOT.Data());
         if (repl.back() != '/')
            repl.append("/");
      } else {
         if (slash_cnt > 0) {
            repl = "=\"";
            while (slash_cnt-- > 0) repl.append("../");
            repl.append("jsrootsys/");
         }
      }
 
      if (!repl.empty()) {
         arg->ReplaceAllinContent("=\"jsrootsys/", repl);
         arg->ReplaceAllinContent("from './jsrootsys/", TString::Format("from '%s", repl.substr(2).c_str()).Data());
      }
   } else {
      // new functionality creating importmap
 
      std::string path_prefix, jsroot_prefix;
      if (slash_cnt > 0) {
         path_prefix = "";
         while (slash_cnt-- > 0)
            path_prefix.append("../");
      } else {
         path_prefix = "./";
      }
 
      if (!version.empty())
         path_prefix.append(version + "/");
 
      if (fJSROOT.Length() > 0) {
         jsroot_prefix = fJSROOT.Data();
         if (jsroot_prefix.back() != '/')
            jsroot_prefix.append("/");
      } else {
         jsroot_prefix = path_prefix + "jsrootsys/";
      }
 
      static std::map<std::string, std::string> modules = {
         {"jsroot", "main.mjs"}, {"jsroot/core", "core.mjs"}, {"jsroot/io", "io.mjs"}, {"jsroot/tree", "tree.mjs"},
         {"jsroot/draw", "draw.mjs"}, {"jsroot/geom", "geom.mjs"}, {"jsroot/gui", "gui.mjs"}, {"jsroot/webwindow", "webwindow.mjs"}
      };
 
      if (std::string("qt5") == arg->GetWSPlatform()) {
         // Chromium in QWebEngine in Qt5.15 does not support importmap functionality and need to be workaround for some widgets
 
         arg->ReplaceAllinContent("from 'jsrootsys/modules/", "from '" + jsroot_prefix + "modules/");
 
         for (auto &entry : modules) {
            std::string search = "from '" + entry.first + "';";
            std::string replace = "from '" + jsroot_prefix + "modules/" + entry.second + "';";
            arg->ReplaceAllinContent(search, replace);
         }
 
      } else {
 
         bool first = true;
         TString importmap = "<script type=\"importmap\">\n{\n   \"imports\": ";
         for (auto &entry : modules) {
            importmap.Append(TString::Format("%s\n      \"%s\": \"%smodules/%s\"", first ? "{" : ",", entry.first.c_str(), jsroot_prefix.c_str(), entry.second.c_str()));
            first = false;
         }
         importmap.Append(TString::Format(",\n      \"jsrootsys/\": \"%s\"", jsroot_prefix.c_str()));
 
         for (auto &entry : fLocations)
            if (entry.first != "jsrootsys/")
               importmap.Append(TString::Format(",\n      \"%s\": \"%s%s\"", entry.first.c_str(), path_prefix.c_str(), entry.first.c_str()));
         importmap.Append("\n   }\n}\n</script>\n");
 
         arg->fContent.erase(p, place_holder.length());
 
         arg->fContent.insert(p, importmap.Data());
      }
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// Process single http request
///
/// Depending from requested path and filename different actions will be performed.
/// In most cases information is provided by TRootSniffer class
 
void THttpServer::ProcessRequest(std::shared_ptr<THttpCallArg> arg)
{
   if (fTerminated) {
      arg->Set404();
      return;
   }
 
   if ((arg->fFileName == "root.websocket") || (arg->fFileName == "root.longpoll")) {
      ExecuteWS(arg);
      return;
   }
 
   if (arg->fFileName.IsNull() || (arg->fFileName == "index.htm") || (arg->fFileName == "default.htm")) {
 
      std::string version;
 
      if (arg->fFileName == "default.htm") {
 
         if (!IsWSOnly())
            arg->fContent = ReadFileContent((fJSROOTSYS + "/files/online.htm").Data());
 
      } else {
         auto wsptr = FindWS(arg->GetPathName());
 
         auto handler = wsptr.get();
 
         if (!handler)
            handler = dynamic_cast<THttpWSHandler *>(fSniffer->FindTObjectInHierarchy(arg->fPathName.Data()));
 
         if (handler) {
 
            arg->fContent = handler->GetDefaultPageContent().Data();
 
            if (arg->fContent.find("file:") == 0) {
               const char *fname = arg->fContent.c_str() + 5;
               TString resolve;
               if (!IsFileRequested(fname, resolve)) resolve = fname;
               arg->fContent = ReadFileContent(resolve.Data());
            }
 
            version = handler->GetCodeVersion();
 
            handler->VerifyDefaultPageContent(arg);
         }
      }
 
      if (arg->fContent.empty() && arg->fFileName.IsNull() && arg->fPathName.IsNull() && IsWSOnly()) {
         // Creating page with list of available widgets is disabled now for security reasons
         // Later one can provide functionality back only if explicitly desired by the user
         //  BuildWSEntryPage();
 
         arg->SetContent("refused");
         arg->Set404();
      }
 
      if (arg->fContent.empty() && !IsWSOnly()) {
 
         if (fDefaultPageCont.empty())
            fDefaultPageCont = ReadFileContent(fDefaultPage);
 
         arg->fContent = fDefaultPageCont;
      }
 
      if (arg->fContent.empty()) {
 
         arg->Set404();
      } else if (!arg->Is404()) {
 
         ReplaceJSROOTLinks(arg, version);
 
         const char *hjsontag = "\"$$$h.json$$$\"";
 
         // add h.json caching
         if (arg->fContent.find(hjsontag) != std::string::npos) {
            TString h_json;
            TRootSnifferStoreJson store(h_json, kTRUE);
            const char *topname = fTopName.Data();
            if (arg->fTopName.Length() > 0)
               topname = arg->fTopName.Data();
            fSniffer->ScanHierarchy(topname, arg->fPathName.Data(), &store);
 
            arg->ReplaceAllinContent(hjsontag, h_json.Data());
 
            arg->AddNoCacheHeader();
 
            if (arg->fQuery.Index("nozip") == kNPOS)
               arg->SetZipping();
         }
         arg->SetContentType("text/html");
      }
      return;
   }
 
   if ((arg->fFileName == "draw.htm") && !IsWSOnly()) {
      if (fDrawPageCont.empty())
         fDrawPageCont = ReadFileContent(fDrawPage);
 
      if (fDrawPageCont.empty()) {
         arg->Set404();
      } else {
         const char *rootjsontag = "\"$$$root.json$$$\"";
         const char *hjsontag = "\"$$$h.json$$$\"";
 
         arg->fContent = fDrawPageCont;
 
         ReplaceJSROOTLinks(arg);
 
         if ((arg->fQuery.Index("no_h_json") == kNPOS) && (arg->fQuery.Index("webcanvas") == kNPOS) &&
             (arg->fContent.find(hjsontag) != std::string::npos)) {
            TString h_json;
            TRootSnifferStoreJson store(h_json, kTRUE);
            const char *topname = fTopName.Data();
            if (arg->fTopName.Length() > 0)
               topname = arg->fTopName.Data();
            fSniffer->ScanHierarchy(topname, arg->fPathName.Data(), &store, kTRUE);
 
            arg->ReplaceAllinContent(hjsontag, h_json.Data());
         }
 
         if ((arg->fQuery.Index("no_root_json") == kNPOS) && (arg->fQuery.Index("webcanvas") == kNPOS) &&
             (arg->fContent.find(rootjsontag) != std::string::npos)) {
            std::string str;
            if (fSniffer->Produce(arg->fPathName.Data(), "root.json", "compact=23", str))
               arg->ReplaceAllinContent(rootjsontag, str);
         }
         arg->AddNoCacheHeader();
         if (arg->fQuery.Index("nozip") == kNPOS)
            arg->SetZipping();
         arg->SetContentType("text/html");
      }
      return;
   }
 
   if ((arg->fFileName == "favicon.ico") && arg->fPathName.IsNull()) {
      arg->SetFile(fJSROOTSYS + "/img/RootIcon.ico");
      return;
   }
 
   TString filename;
   if (IsFileRequested(arg->fFileName.Data(), filename)) {
      arg->SetFile(filename);
      return;
   }
 
   // check if websocket handler may serve file request
   if (!arg->fPathName.IsNull() && !arg->fFileName.IsNull()) {
      TString wsname = arg->fPathName, fname;
      auto pos = wsname.First('/');
      if (pos == kNPOS) {
         wsname = arg->fPathName;
      } else {
         wsname = arg->fPathName(0, pos);
         fname = arg->fPathName(pos + 1, arg->fPathName.Length() - pos);
         fname.Append("/");
      }
 
      fname.Append(arg->fFileName);
 
      if (VerifyFilePath(fname.Data())) {
 
         auto ws = FindWS(wsname.Data());
 
         if (ws && ws->CanServeFiles()) {
            TString fdir = ws->GetDefaultPageContent();
            // only when file is specified, can take directory, append prefix and file name
            if (fdir.Index("file:") == 0) {
               fdir.Remove(0, 5);
               auto separ = fdir.Last('/');
               if (separ != kNPOS)
                  fdir.Resize(separ + 1);
               else
                  fdir = "./";
 
               fdir.Append(fname);
               arg->SetFile(fdir);
               return;
            }
         }
      }
   }
 
   filename = arg->fFileName;
 
   Bool_t iszip = kFALSE;
   if (filename.EndsWith(".gz")) {
      filename.Resize(filename.Length() - 3);
      iszip = kTRUE;
   }
 
   if (IsWSOnly()) {
      if (arg->fContent.empty())
         arg->Set404();
   } else if ((filename == "h.xml") || (filename == "get.xml")) {
 
      Bool_t compact = arg->fQuery.Index("compact") != kNPOS;
 
      TString res;
 
      res.Form("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
      if (!compact)
         res.Append("\n");
      res.Append("<root>");
      if (!compact)
         res.Append("\n");
      {
         TRootSnifferStoreXml store(res, compact);
 
         const char *topname = fTopName.Data();
         if (arg->fTopName.Length() > 0)
            topname = arg->fTopName.Data();
         fSniffer->ScanHierarchy(topname, arg->fPathName.Data(), &store, filename == "get.xml");
      }
 
      res.Append("</root>");
      if (!compact)
         res.Append("\n");
 
      arg->SetContent(std::string(res.Data()));
 
      arg->SetXml();
   } else if (filename == "h.json") {
      TString res;
      TRootSnifferStoreJson store(res, arg->fQuery.Index("compact") != kNPOS);
      const char *topname = fTopName.Data();
      if (arg->fTopName.Length() > 0)
         topname = arg->fTopName.Data();
      fSniffer->ScanHierarchy(topname, arg->fPathName.Data(), &store);
      arg->SetContent(std::string(res.Data()));
      arg->SetJson();
   } else if (fSniffer->Produce(arg->fPathName.Data(), filename.Data(), arg->fQuery.Data(), arg->fContent)) {
      // define content type base on extension
      arg->SetContentType(GetMimeType(filename.Data()));
   } else {
      // miss request, user may process
      MissedRequest(arg.get());
   }
 
   if (arg->Is404())
      return;
 
   if (iszip)
      arg->SetZipping(THttpCallArg::kZipAlways);
 
   if (filename == "root.bin") {
      // only for binary data master version is important
      // it allows to detect if streamer info was modified
      const char *parname = fSniffer->IsStreamerInfoItem(arg->fPathName.Data()) ? "BVersion" : "MVersion";
      arg->AddHeader(parname, TString::Format("%u", (unsigned)fSniffer->GetStreamerInfoHash()).Data());
   }
 
   // try to avoid caching on the browser
   arg->AddNoCacheHeader();
 
   // potentially add cors headers
   if (IsCors())
      arg->AddHeader("Access-Control-Allow-Origin", GetCors());
   if (IsCorsCredentials())
      arg->AddHeader("Access-Control-Allow-Credentials", GetCorsCredentials());
}
 
////////////////////////////////////////////////////////////////////////////////
/// Register object in folders hierarchy
///
/// See TRootSniffer::RegisterObject() for more details
 
Bool_t THttpServer::Register(const char *subfolder, TObject *obj)
{
   return fSniffer->RegisterObject(subfolder, obj);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Unregister object in folders hierarchy
///
/// See TRootSniffer::UnregisterObject() for more details
 
Bool_t THttpServer::Unregister(TObject *obj)
{
   return fSniffer->UnregisterObject(obj);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Register WS handler to the THttpServer
///
/// Only such handler can be used in multi-threaded processing of websockets
 
void THttpServer::RegisterWS(std::shared_ptr<THttpWSHandler> ws)
{
   std::lock_guard<std::mutex> grd(fWSMutex);
   fWSHandlers.emplace_back(ws);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Unregister WS handler to the THttpServer
 
void THttpServer::UnregisterWS(std::shared_ptr<THttpWSHandler> ws)
{
   std::lock_guard<std::mutex> grd(fWSMutex);
   for (int n = (int)fWSHandlers.size(); n > 0; --n)
      if ((fWSHandlers[n - 1] == ws) || fWSHandlers[n - 1]->IsDisabled())
         fWSHandlers.erase(fWSHandlers.begin() + n - 1);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Search WS handler with given name
///
/// Handler must be registered with RegisterWS() method
 
std::shared_ptr<THttpWSHandler> THttpServer::FindWS(const char *name)
{
   std::lock_guard<std::mutex> grd(fWSMutex);
   for (auto &ws : fWSHandlers) {
      if (strcmp(name, ws->GetName()) == 0)
         return ws;
   }
 
   return nullptr;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Execute WS related operation
 
Bool_t THttpServer::ExecuteWS(std::shared_ptr<THttpCallArg> &arg, Bool_t external_thrd, Bool_t wait_process)
{
   if (fTerminated) {
      arg->Set404();
      return kFALSE;
   }
 
   auto wsptr = FindWS(arg->GetPathName());
 
   auto handler = wsptr.get();
 
   if (!handler && !external_thrd)
      handler = dynamic_cast<THttpWSHandler *>(fSniffer->FindTObjectInHierarchy(arg->fPathName.Data()));
 
   if (external_thrd && (!handler || !handler->AllowMTProcess())) {
 
      if (fTimer && fTimer->IsSlow())
         fTimer->SetSlow(kFALSE);
 
      std::unique_lock<std::mutex> lk(fMutex);
      fArgs.push(arg);
      // and now wait until request is processed
      if (wait_process)
         arg->fCond.wait(lk);
 
      return kTRUE;
   }
 
   if (!handler)
      return kFALSE;
 
   Bool_t process = kFALSE;
 
   if (arg->fFileName == "root.websocket") {
      // handling of web socket
      process = handler->HandleWS(arg);
   } else if (arg->fFileName == "root.longpoll") {
      // ROOT emulation of websocket with polling requests
      if (arg->fQuery.BeginsWith("raw_connect") || arg->fQuery.BeginsWith("txt_connect")) {
         // try to emulate websocket connect
         // if accepted, reply with connection id, which must be used in the following communications
         arg->SetMethod("WS_CONNECT");
 
         bool israw = arg->fQuery.BeginsWith("raw_connect");
 
         // automatically assign engine to arg
         arg->CreateWSEngine<THttpLongPollEngine>(israw);
 
         if (handler->HandleWS(arg)) {
            arg->SetMethod("WS_READY");
 
            if (handler->HandleWS(arg))
               arg->SetTextContent(std::string(israw ? "txt:" : "") + std::to_string(arg->GetWSId()));
         } else {
            arg->TakeWSEngine(); // delete handle
         }
 
         process = arg->IsText();
      } else {
         TUrl url;
         url.SetOptions(arg->fQuery);
         url.ParseOptions();
         const char *connid = url.GetValueFromOptions("connection");
         if (connid)
            arg->SetWSId(std::stoul(connid));
         if (url.HasOption("close")) {
            arg->SetMethod("WS_CLOSE");
            arg->SetTextContent("OK");
         } else {
            arg->SetMethod("WS_DATA");
         }
 
         process = handler->HandleWS(arg);
      }
   }
 
   if (!process)
      arg->Set404();
 
   return process;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Restrict access to specified object
///
/// See TRootSniffer::Restrict() for more details
 
void THttpServer::Restrict(const char *path, const char *options)
{
   fSniffer->Restrict(path, options);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Register command which can be executed from web interface
///
/// As method one typically specifies string, which is executed with
/// gROOT->ProcessLine() method. For instance:
///
///     serv->RegisterCommand("Invoke","InvokeFunction()");
///
/// Or one could specify any method of the object which is already registered
/// to the server. For instance:
///
///     serv->Register("/", hpx);
///     serv->RegisterCommand("/ResetHPX", "/hpx/->Reset()");
///
/// Here symbols '/->' separates item name from method to be executed
///
/// One could specify additional arguments in the command with
/// syntax like %arg1%, %arg2% and so on. For example:
///
///     serv->RegisterCommand("/ResetHPX", "/hpx/->SetTitle(\"%arg1%\")");
///     serv->RegisterCommand("/RebinHPXPY", "/hpxpy/->Rebin2D(%arg1%,%arg2%)");
///
/// Such parameter(s) will be requested when command clicked in the browser.
///
/// Once command is registered, one could specify icon which will appear in the browser:
///
///     serv->SetIcon("/ResetHPX", "rootsys/icons/ed_execute.png");
///
/// One also can set extra property '_fastcmd', that command appear as
/// tool button on the top of the browser tree:
///
///     serv->SetItemField("/ResetHPX", "_fastcmd", "true");
///
/// Or it is equivalent to specifying extra argument when register command:
///
///     serv->RegisterCommand("/ResetHPX", "/hpx/->Reset()", "button;rootsys/icons/ed_delete.png");
 
Bool_t THttpServer::RegisterCommand(const char *cmdname, const char *method, const char *icon)
{
   return fSniffer->RegisterCommand(cmdname, method, icon);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Hides folder or element from web gui
 
Bool_t THttpServer::Hide(const char *foldername, Bool_t hide)
{
   return SetItemField(foldername, "_hidden", hide ? "true" : (const char *)0);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set name of icon, used in browser together with the item
///
/// One could use images from $ROOTSYS directory like:
///    serv->SetIcon("/ResetHPX","/rootsys/icons/ed_execute.png");
 
Bool_t THttpServer::SetIcon(const char *fullname, const char *iconname)
{
   return SetItemField(fullname, "_icon", iconname);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create item in sniffer
 
Bool_t THttpServer::CreateItem(const char *fullname, const char *title)
{
   return fSniffer->CreateItem(fullname, title);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set item field in sniffer
 
Bool_t THttpServer::SetItemField(const char *fullname, const char *name, const char *value)
{
   return fSniffer->SetItemField(fullname, name, value);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Get item field from sniffer
 
const char *THttpServer::GetItemField(const char *fullname, const char *name)
{
   return fSniffer->GetItemField(fullname, name);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Returns MIME type base on file extension
 
const char *THttpServer::GetMimeType(const char *path)
{
   static const struct {
      const char *extension;
      int ext_len;
      const char *mime_type;
   } builtin_mime_types[] = {{".xml", 4, "text/xml"},
                             {".json", 5, "application/json"},
                             {".bin", 4, "application/x-binary"},
                             {".gif", 4, "image/gif"},
                             {".jpg", 4, "image/jpeg"},
                             {".png", 4, "image/png"},
                             {".html", 5, "text/html"},
                             {".htm", 4, "text/html"},
                             {".shtm", 5, "text/html"},
                             {".shtml", 6, "text/html"},
                             {".css", 4, "text/css"},
                             {".js", 3, "application/x-javascript"},
                             {".mjs", 4, "text/javascript"},
                             {".ico", 4, "image/x-icon"},
                             {".jpeg", 5, "image/jpeg"},
                             {".svg", 4, "image/svg+xml"},
                             {".txt", 4, "text/plain"},
                             {".torrent", 8, "application/x-bittorrent"},
                             {".wav", 4, "audio/x-wav"},
                             {".mp3", 4, "audio/x-mp3"},
                             {".mid", 4, "audio/mid"},
                             {".m3u", 4, "audio/x-mpegurl"},
                             {".ogg", 4, "application/ogg"},
                             {".ram", 4, "audio/x-pn-realaudio"},
                             {".xslt", 5, "application/xml"},
                             {".xsl", 4, "application/xml"},
                             {".ra", 3, "audio/x-pn-realaudio"},
                             {".doc", 4, "application/msword"},
                             {".exe", 4, "application/octet-stream"},
                             {".zip", 4, "application/x-zip-compressed"},
                             {".xls", 4, "application/excel"},
                             {".tgz", 4, "application/x-tar-gz"},
                             {".tar", 4, "application/x-tar"},
                             {".gz", 3, "application/x-gunzip"},
                             {".arj", 4, "application/x-arj-compressed"},
                             {".rar", 4, "application/x-arj-compressed"},
                             {".rtf", 4, "application/rtf"},
                             {".pdf", 4, "application/pdf"},
                             {".swf", 4, "application/x-shockwave-flash"},
                             {".mpg", 4, "video/mpeg"},
                             {".webm", 5, "video/webm"},
                             {".mpeg", 5, "video/mpeg"},
                             {".mov", 4, "video/quicktime"},
                             {".mp4", 4, "video/mp4"},
                             {".m4v", 4, "video/x-m4v"},
                             {".asf", 4, "video/x-ms-asf"},
                             {".avi", 4, "video/x-msvideo"},
                             {".bmp", 4, "image/bmp"},
                             {".ttf", 4, "application/x-font-ttf"},
                             {".woff", 5, "font/woff"},
                             {".woff2", 6, "font/woff2"},
                             {NULL, 0, NULL}};
 
   int path_len = strlen(path);
 
   for (int i = 0; builtin_mime_types[i].extension != NULL; i++) {
      if (path_len <= builtin_mime_types[i].ext_len)
         continue;
      const char *ext = path + (path_len - builtin_mime_types[i].ext_len);
      if (strcmp(ext, builtin_mime_types[i].extension) == 0) {
         return builtin_mime_types[i].mime_type;
      }
   }
 
   return "text/plain";
}
 
////////////////////////////////////////////////////////////////////////////////
/// Reads file content
///
/// @deprecated
 
char *THttpServer::ReadFileContent(const char *filename, Int_t &len)
{
   len = 0;
 
   std::ifstream is(filename, std::ios::in | std::ios::binary);
   if (!is)
      return nullptr;
 
   is.seekg(0, is.end);
   len = is.tellg();
   is.seekg(0, is.beg);
 
   char *buf = (char *)malloc(len);
   is.read(buf, len);
   if (!is) {
      free(buf);
      len = 0;
      return nullptr;
   }
 
   return buf;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Reads file content, using std::string as container
 
std::string THttpServer::ReadFileContent(const std::string &filename)
{
   std::ifstream is(filename, std::ios::in | std::ios::binary);
   std::string res;
   if (is) {
      is.seekg(0, std::ios::end);
      res.resize(is.tellg());
      is.seekg(0, std::ios::beg);
      is.read((char *)res.data(), res.length());
      if (!is)
         res.clear();
   }
   return res;
}