Read Binary File

// File Path of downloaded dafsa.bin in firefox stable - Ubuntu:
// file:///home/arpit/.cache/mozilla/firefox/843zsjle.default/settings/main/public-suffix-list/dafsa.bin

// File Path of downloaded dafsa.bin in firefox nightly -  Ubuntu:
// file:///home/arpit/Development/moz/mozilla-central/obj-x86_64-pc-linux-gnu/tmp/profile-default/settings/main/public-suffix-list/dafsa.bin

// File Path of downloaded dafsa.bin in firefox stable - Windows:
// file://C:/Users/rpitt/AppData/Local/Mozilla/Firefox/Profiles/6fm1js29.default-1564744451242/settings/main/public-suffix-list/dafsa.bin

I considered using IFstream instead of fopen.
- IFstream handles char16_t* natively, fopen does not.


Current Method:

#include "mozilla/FStream.h"

NS_IMETHODIMP nsEffectiveTLDService::Observe(nsISupports* aSubject,
                                             const char* aTopic,
                                             const char16_t* aData) {
// aData is like one of the examples mentioned above

  if (nsCRT::strcmp(aTopic, "public-suffix-list-updated") == 0) {

    const char16_t* fileURI = (char16_t*)((char*)aData + 7); // cut "file://" from aData
    IFstream dafsaFile;

    dafsaFile.open(fileName, ifstream::binary | ifstream::ate);
    if (dafsaFile.is_open()) {
        unsigned int length = dafsaFile.tellg();
        dafsaFile.seekg(ifstream::beg);
        unsigned char kDafsaRemote[length];
        dafsaFile.read((char*)kDafsaRemote, length);

        mGraph = mozilla::Dafsa(kDafsaRemote);

    }
    dafsaFile.close();
  return NS_OK;
}

Previous Method:

NS_IMETHODIMP nsEffectiveTLDService::Observe(nsISupports* aSubject,
                                             const char* aTopic,
                                             const char16_t* aData) {

  if (nsCRT::strcmp(aTopic, "public-suffix-list-updated") == 0) {

    const char* fileURI = (char*) aData +7;  // cut "file://" from aData
    FILE* fp = fopen(fileURI, "rb");
    if(fp){
      fseek(fp, 0, SEEK_END);
      unsigned int size = ftell(fp);
      rewind(fp);

      // Initialise kDafsaRemote with the data read from dafsa.bin
      unsigned char kDafsaRemote[size];
      fread(kDafsaRemote, size, 1, fp);

     nsEffectiveTLDService:: mGraph = mozilla::Dafsa(kDafsaRemote);
    }

    fclose(fp);

  return NS_OK;
}