diff options
| -rw-r--r-- | src/stdio/vsnprintf.c | 63 |
1 files changed, 38 insertions, 25 deletions
diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c index be2c44eb..b3510a63 100644 --- a/src/stdio/vsnprintf.c +++ b/src/stdio/vsnprintf.c @@ -4,39 +4,52 @@ #include <errno.h> #include <stdint.h> +struct cookie { + char *s; + size_t n; +}; + +#define MIN(a, b) ((a) < (b) ? (a) : (b)) + static size_t sn_write(FILE *f, const unsigned char *s, size_t l) { - size_t k = f->wend - f->wpos; - if (k > l) k = l; - memcpy(f->wpos, s, k); - f->wpos += k; - /* pretend to succeed, but discard extra data */ + struct cookie *c = f->cookie; + size_t k = MIN(c->n, f->wpos - f->wbase); + if (k) { + memcpy(c->s, f->wbase, k); + c->s += k; + c->n -= k; + } + k = MIN(c->n, l); + if (k) { + memcpy(c->s, s, k); + c->s += k; + c->n -= k; + } + *c->s = 0; + f->wpos = f->wbase = f->buf; + /* pretend to succeed, even if we discarded extra data */ return l; } int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap) { - int r; - char b; - FILE f = { .lbf = EOF, .write = sn_write, .lock = -1 }; + unsigned char buf[1]; + char dummy[1]; + struct cookie c = { .s = n ? s : dummy, .n = n ? n-1 : 0 }; + FILE f = { + .lbf = EOF, + .write = sn_write, + .lock = -1, + .buf = buf, + .cookie = &c, + }; - if (n-1 > INT_MAX-1) { - if (n) { - errno = EOVERFLOW; - return -1; - } - s = &b; - n = 1; + if (n > INT_MAX) { + errno = EOVERFLOW; + return -1; } - /* Ensure pointers don't wrap if "infinite" n is passed in */ - if (n > (char *)0+SIZE_MAX-s-1) n = (char *)0+SIZE_MAX-s-1; - f.buf_size = n; - f.buf = f.wpos = (void *)s; - f.wbase = f.wend = (void *)(s+n); - r = vfprintf(&f, fmt, ap); - - /* Null-terminate, overwriting last char if dest buffer is full */ - if (n) f.wpos[-(f.wpos == f.wend)] = 0; - return r; + *c.s = 0; + return vfprintf(&f, fmt, ap); } |