/* ProcFS - buf.c - by Alen Stojanov and David van Moolenbroek */

#include "inc.h"

#include <stdarg.h>

#define BUF_SIZE 4096

static char buf[BUF_SIZE + 1];

static size_t off, left, used;

static off_t skip;

/*===========================================================================*

* buf_init *

*===========================================================================*/

void buf_init(off_t start, size_t len)

{

/* Initialize the buffer for fresh use. The first 'start' bytes of the

* produced output are to be skipped. After that, up to a total of

* 'len' bytes are requested.

*/

skip = start;

left = MIN(len, BUF_SIZE);

off = 0;

used = 0;

}

/*===========================================================================*

* buf_printf *

*===========================================================================*/

void buf_printf(char *fmt, ...)

{

/* Add formatted text to the end of the buffer.

*/

va_list args;

ssize_t len, max;

if (left == 0)

return;

/* There is no way to estimate how much space the result will take, so

* we need to produce the string even when skipping part of the start.

* If part of the result is to be skipped, do not memcpy; instead, save

* the offset of where the result starts within the buffer.

*

* The null terminating character is not part of the result, so room

* must be given for it to be stored after completely filling up the

* requested part of the buffer.

*/

max = MIN(skip + left, BUF_SIZE);

va_start(args, fmt);

len = vsnprintf(&buf[off + used], max + 1, fmt, args);

va_end(args);

if (skip > 0) {

assert(off == 0);

assert(used == 0);

if (skip >= len) {

skip -= len;

return;

}

off = skip;

if (left > BUF_SIZE - off)

left = BUF_SIZE - off;

len -= off;

skip = 0;

}

assert(skip == 0);

assert(len >= 0);

assert((long) left >= 0);

if (len > (ssize_t) left)

len = left;

used += len;

left -= len;

}

/*===========================================================================*

* buf_append *

*===========================================================================*/

void buf_append(char *data, size_t len)

{

/* Add arbitrary data to the end of the buffer.

*/

if (left == 0)

return;

if (skip > 0) {

if (skip >= (ssize_t) len) {

skip -= len;

return;

}

data += skip;

len -= skip;

skip = 0;

}

if (len > left)

len = left;

memcpy(&buf[off + used], data, len);

used += len;

left -= len;

}

/*===========================================================================*

* buf_get *

*===========================================================================*/

size_t buf_get(char **ptr)

{

/* Return the buffer's starting address and the length of the used

* part, not counting the trailing null character for the latter.

*/

*ptr = &buf[off];

return used;

}