source: Evidence/Config/Config.cc @ 127

/********************************************************************\

  Configuration server for the Evidence Control System

  - The configuration file is opened without buffering to catch changes
    without closing/opening.
  - If a configuration file change is detected through inotify, the service "Config/Modified"
    is updated (it contains no data) to inform applications. 
  - The employed line buffer has conservatively at least the size of the configuration file. If
    needed, it will be enlarged.
         
  Oliver Grimm, November 2009

\********************************************************************/

#define CONFIG_FILE "configuration.txt"
#define SERVER_NAME "Config"

#include "../Evidence.h"
#include <sys/stat.h>
#include <sys/inotify.h>

//
// Class derived from DimRpc
//
class EvidenceConfig: public DimRpc, public EvidenceServer {

  private:
    FILE *File; 
    char *Buffer;
    unsigned int BufferLength;
    DimService *ConfigModified;

    void rpcHandler();
  
  public:
    EvidenceConfig(const char *);
    ~EvidenceConfig();
        
        void ConfigChanged(); 
};

// Constructor
EvidenceConfig::EvidenceConfig(const char *Filename):
        DimRpc("ConfigRequest", "C", "C"), EvidenceServer(SERVER_NAME) {

  // Create DIM service to indicate changes of configuration file
  ConfigModified = new DimService (SERVER_NAME"/Modified", (char *) "");

  // Open configuration file
  if ((File = fopen(Filename, "r")) == NULL) {
    Msg(FATAL, "Could not open configuration file '%s' (%s)\n", Filename, strerror(errno));
  }

  // Disable buffering, so file modifications are immediately seen
  if(setvbuf(File, NULL, _IONBF, 0) != 0) {
    Msg(WARN, "Error setting configuration file '%s' to unbuffered mode.\n", Filename);
  }
    
  Buffer = NULL;    // Will be allocated in rpcHandler()
  BufferLength = 0;
}

// Destructor
EvidenceConfig::~EvidenceConfig() {

  if (File != NULL) fclose(File);  
  delete[] Buffer;
}

// Implementation of response to configuration request
void EvidenceConfig::rpcHandler() {

  char *Token1,*Token2,*Token3, *Request = getString();
  struct stat FileStatus;
  
  // Check if Buffer[] is large enough to hold full file, enlarge if necessary
  if (fstat(fileno(File), &FileStatus) == -1) {
     Msg(ERROR, "Could not determine size of configuration file to allocate buffer (%s)\n", strerror(errno));
  }
  else if(BufferLength < FileStatus.st_size) {
    delete[] Buffer;
    Buffer = new char [FileStatus.st_size];
    BufferLength = FileStatus.st_size;   
  }
  
  // Search for configuration item
  rewind(File);
  while (fgets(Buffer, BufferLength, File) != NULL) {
    
    // Combine lines that end with '+'
    while (Buffer[strlen(Buffer)-2] == '+') {
      if (fgets(Buffer+strlen(Buffer)-2, BufferLength-(strlen(Buffer)-2), File) == NULL) break;
    }
    
    // Ignore comments
    for (int i=0; i<strlen(Buffer); i++) if (Buffer[i] == '#') Buffer[i] = '\0';
    
    // Extract tokens
    Token1 = strtok(Buffer, " \t:");
    Token2 = strtok(NULL, " \t:");
    Token3 = strtok(NULL, "\n");
    
    // Check if all tokens existing
    if(Token1==NULL || Token2==NULL || Token3==NULL) continue;

    // Check for match and then send data
    if (strstr(Request, Token1)!=NULL && strstr(Request, Token2)!=NULL) {
      setData(Token3);
      break;
    }
  }
  Msg(INFO, "Client '%s' (ID %d) requested '%s'. Send '%s'.",
                DimServer::getClientName(),
                DimServer::getClientId(), 
                Request, feof(File)!=0 ? "n/a" : Token3);
}

// Signalisation of configuration change
void EvidenceConfig::ConfigChanged() {

  ConfigModified->updateService();
}

//          
// Declaring class static ensures destructor is called when exit() is invoked 
//
int main() {
        
  static EvidenceConfig Config(CONFIG_FILE);

  int Notify;
  struct inotify_event Event;
  
  if ((Notify = inotify_init()) == -1) {
    Config.Msg(EvidenceConfig::WARN, "inotify_init() failed, cannot monitor changes of configuration file (%s)\n", strerror(errno));
  }
  else if (inotify_add_watch(Notify, CONFIG_FILE, IN_MODIFY) == -1) { 
      Config.Msg(EvidenceConfig::WARN, "Could not set inotify watch on configuration file (%s)\n", strerror(errno));
          close(Notify);
          Notify = -1;
  }

  // Sleep until file changes or signal caught 
  while (!EvidenceServer::ExitRequest) {
    if (Notify != -1) {
          read(Notify, &Event, sizeof(Event));
          Config.ConfigChanged();
        }
    else pause();         
  }
  
  if (Notify != -1) close(Notify);
}