/*
 * tailf -- Monitor the end of one or more log files.
 *
 * (C) 1997 Pharos IP Pty Ltd
 * $Id: tailf.c,v 1.2 1997-12-30 17:50:11+10 mbp Exp $
 * $Source: /fn/cvsroot/pip/tools/tailf/tailf.c,v $
 */

/* This uses polling, which is a bit ugly, but I can't seem to work
 * out how select() works -- it seems to always return immediately.
 * Anyhow, this is smaller and more friendly than 'tail -f'. 
 * <mbp 19971128> */

#include <fcntl.h>
#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#define MAX_FILES 64

int nMonitored;
int afdMonitored[MAX_FILES];

#define BUF_SIZE 4<<10

char abBuf[BUF_SIZE];

#define FD_STDOUT 1

#define SLEEP_SEC 0
#define SLEEP_USEC 100000

int fOpenFiles(int nArgs, char const * const * const apszArgs)
{
    int iArg;
    int fd;
    char const * pszFile;

    nMonitored = 0;
    /* For each argument */
    for (iArg = 1; iArg < nArgs; iArg++) {
	if (nMonitored >= MAX_FILES) {
	    fputs("warning: too many files\n", stderr);
	    break;
	}

	/* Try to open the file for reading */
	pszFile = apszArgs[iArg];
	fd = open(pszFile, O_RDONLY);
	if (fd < 0) {
	    perror(pszFile);
	    continue;
	}

	/* Seek to the end of the file */
	if (lseek(fd, +1, SEEK_END) == -1) {
	    perror(pszFile);
	    continue;
	}
	
	/* If it was opened OK, add to the monitoring set */
	afdMonitored[nMonitored++] = fd;
    }

    if (nMonitored == 0) {
	fputs("no files\n", stderr);
	return 0;
    }

    return 1;
}

int fMonitorFiles(void)
{
    int rc;
    int i;
    int nbRead, nbWritten;
    int fd;
    struct timeval tvWait;

    /* Wait for a little while. */
    tvWait.tv_sec = SLEEP_SEC;
    tvWait.tv_usec = SLEEP_USEC;

    rc = select(0, 0, 0, 0, &tvWait);
    if (rc < 0) {
	perror("select");
	return 0;
    }

    /* Check all file descriptors for new data. */
    for (i = 0; i < nMonitored; i++) {
	fd = afdMonitored[i];
	nbRead = read(fd, abBuf, BUF_SIZE);
	if (nbRead < 0  ||  nbRead > BUF_SIZE) {
	    perror("read");
	    return 0;
	}
	if (nbRead == 0) {	/* eof */
	    continue;
	}
	
	nbWritten = write(1, abBuf, nbRead);
	if (nbWritten < 0  ||  nbWritten != nbRead) {
	    perror("write");
	    return 0;
	}
    }

    return 1;
}


int main(int argc, char const * const * const argv)
{
    if (!fOpenFiles(argc, argv))
	return 1;

    while(fMonitorFiles())
	;

    return 1;
}

/* 
 * Local variables:
 * c-basic-offset: 4
 * End:
 */