zmq_fileserver.c

#include <czmq.h>
#define CHUNK_SIZE 4096
#define PIPELINE 10

static void
free_chunk (void *data, void *arg)
{
  free (data);
}

int main (void)
{
  zctx_t *ctx = zctx_new ();

  FILE *file = fopen ("TestFiles/100K.bin", "r");
  assert (file);

  void *router = zsocket_new (ctx, ZMQ_ROUTER);
  zsocket_set_hwm (router, PIPELINE);
  zsocket_bind (router, "tcp://*:6000");
  while (true) {
    // First frame in each message is the sender identity
    zframe_t *identity = zframe_recv (router);
    if (!identity)
      break; // Shutting down, quit

    // Second frame is "fetch" command
    char *command = zstr_recv (router);
    assert (streq (command, "fetch"));
    free (command);

    // Third frame is chunk offset in file
    char *offset_str = zstr_recv (router);
    size_t offset = atoi (offset_str);
    free (offset_str);

    // Fourth frame is maximum chunk size
    char *chunksz_str = zstr_recv (router);
    size_t chunksz = atoi (chunksz_str);
    free (chunksz_str);

    // Read chunk of data from file
    fseek (file, offset, SEEK_SET);
    byte *data = malloc (chunksz);
    assert (data);

    // Send resulting chunk to client
    size_t size = fread (data, 1, chunksz, file);
    zframe_t *chunk = zframe_new_zero_copy (data, size, free_chunk, NULL);
    zframe_send (&identity, router, ZFRAME_MORE);
    zframe_send (&chunk, router, 0);
  }
  fclose (file);

  zctx_destroy (&ctx);
  return 0;
}