/* splice.c   by Michael Thorpe   2009-02-02 */
/* We could replace a few lines with ftruncate if it always extended */

#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include "splice.h"

#define BUFLEN 8192

static size_t readall(int fd,void *buf,size_t count) {
	size_t i;

	while(count) {
		i=read(fd,buf,count);
		if(i==-1) {
			if(errno==EAGAIN)
				continue;
			break;
		}
		if(i==0)
			break;
		buf=i+(char *)buf;
		count-=i;
	}
	return(count);
}

static size_t writeall(int fd,void *buf,size_t count) {
	size_t i;

	while(count) {
		i=write(fd,buf,count);
		if(i==-1) {
			if(errno==EAGAIN)
				continue;
			break;
		}
		if(i==0)
			break;
		buf=(char *)buf+i;
		count-=i;
	}
	return(count);
}

int splice(int f,off_t pos,void *old,size_t oldlen,void *new,size_t newlen) {
	void *buf;
	size_t l,m,r,w;
	int retval=1;

	if(!oldlen && !newlen)
		return(0);
	if(old && oldlen) {
		if(-1==lseek(f,pos,SEEK_SET))
			return(1);
		if(readall(f,old,oldlen))
			return(1);
	}
	if(!new)
		return(0);
	if(oldlen==newlen) {
		if(-1==lseek(f,pos,SEEK_SET))
			return(1);
		m=writeall(f,new,newlen);
		return(m?m==newlen?1:-1:0);
	}
	buf=malloc(BUFLEN);
	if(!buf)
		return(1);
	if(oldlen<newlen) {
		oldlen=newlen-oldlen;
		if(-1==(r=lseek(f,0,SEEK_END)))
			goto fail;
		w=r+oldlen;
		if(w<=r)
			goto fail;
		while(r>pos) {
			l=r-pos<BUFLEN?r-pos:BUFLEN;
			r-=l;
			w-=l;
			if(-1==lseek(f,r,SEEK_SET))
				goto fail;
			if(readall(f,buf,l))
				goto fail;
			if(r+l != w)
				if(-1==lseek(f,w,SEEK_SET))
					goto fail;
			m=writeall(f,buf,l);
			if(l != m)
				retval=-1;
			if(m)
				goto fail;
		}
		if(-1==lseek(f,pos,SEEK_SET))
			goto fail;
		m=writeall(f,new,newlen);
		if(m != newlen)
			retval=-1;
		if(m)
			goto fail;
	} else {
		if(-1==lseek(f,pos,SEEK_SET))
			goto fail;
		m=writeall(f,new,newlen);
		if(m != newlen)
			retval=-1;
		if(m)
			goto fail;
		pos+=newlen;
		oldlen=oldlen-newlen;
		if(-1==lseek(f,pos+oldlen,SEEK_SET))
			goto fail;
		while(0<(r=read(f,buf,BUFLEN))) {
			if(0>lseek(f,pos,SEEK_SET))
				goto fail;
			m=writeall(f,buf,r);
			if(m != r)
				retval=-1;
			if(m)
				goto fail;
			pos+=r;
			if(-1==lseek(f,pos+oldlen,SEEK_SET))
				goto fail;
		}
		retval=-1;
		if(-1==ftruncate(f,pos))
			goto fail;
	}
	retval=0;
fail:
	free(buf);
	return(retval);
}