File compression using bzip2 library doesn't work - c

Question

I just wrote a C function that compress a file using bzip2 library APIs. The compression is not working fine. When I decompress the output file using an archiving utility, I'm getting some garbage value along with the actual data. I have done everything as per the instructions in the bzip2 library manual. Can someone tell me what went wrong?
The code may not be well structured. This is just an attempt to understand the usage of libzip2 library.
#define BUFSIZE 512
int main(int argc, char *argv[])
{
char file_name[64];
if(argc != 2)
{
printf("usage: compr <file name>");
return -1;
}
strncpy(file_name,argv[1],64);
return file_compress(file_name);
}
int file_compress(char * arg)
{
int input_fd, output_fd;
ssize_t ret_in ;
char buffer[BUFSIZE];
char buffout[BUFSIZE];
struct stat fileStat;
int insize;
int st;
bz_stream strm;
strm.bzalloc= NULL;
strm.bzfree= NULL;
strm.opaque= NULL;
st = BZ2_bzCompressInit (&strm,1,0,30 );
if(st != BZ_OK)
{
return 1;
}
else
{
input_fd = open (arg, O_RDONLY);
if (input_fd < 0)
{
return 1;
}
if(fstat(input_fd,&fileStat) < 0)
return 1;
insize = fileStat.st_size;
printf("File Size: \t%d bytes\n",insize);
strcat(arg,".bz2");
output_fd = open(arg, O_WRONLY | O_CREAT, 0644);
if(output_fd == -1)
{
return 1;
}
strm.avail_in = 0;
while(1)
{
if(insize > 0 && strm.avail_in == 0)
ret_in = read (input_fd, buffer, BUFSIZE);
else
ret_in = 0;
strm.next_in=buffer;
strm.avail_in=ret_in;
strm.next_out=buffout;
strm.avail_out=BUFSIZE;
if(insize == 0)
{
st= BZ2_bzCompress ( &strm,BZ_FINISH);
}
else if(insize <= BUFSIZE)
{
st= BZ2_bzCompress ( &strm,BZ_FINISH);
}
else
{
st=BZ2_bzCompress ( &strm,BZ_RUN);
}
insize -= ret_in;
if(BUFSIZE - strm.avail_out > 0)
{
int ret_out=write (output_fd, buffout, BUFSIZE - strm.avail_out);
printf("retout%d \n",ret_out);
}
if(st == BZ_STREAM_END)
break;
if(st < 0 )
{
return 1;
}
}
close (input_fd);
close (output_fd);
}
st = BZ2_bzCompressEnd (&strm );
if(st != BZ_OK)
{
// perror("ERROR BZ2_bzCompressEnd\n");
return 1;
}
return 0;
}