major stdio overhaul, using readv/writev, plus other changes

[musl] / src / stdio / vsnprintf.c

diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c
index 1f316ca..ba17bd7 100644 (file)
--- a/src/stdio/vsnprintf.c
+++ b/src/stdio/vsnprintf.c
@@ -2,33 +2,37 @@
 
 static size_t sn_write(FILE *f, const unsigned char *s, size_t l)
 {
-       /* pretend to succeed, but discard data */
+       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 */
        return l;
 }
 
 int vsnprintf(char *s, size_t n, const char *fmt, va_list ap)
 {
        int r;
-       FILE f;
-       unsigned char buf[1];
+       char b;
+       FILE f = { .lbf = EOF, .write = sn_write, .lock = -1 };
 
-       memset(&f, 0, sizeof(FILE));
-       f.lbf = EOF;
-       f.write = sn_write;
-       f.buf_size = 1;
-       f.buf = buf;
-       f.lock = -1;
-       if (n > INT_MAX) {
-               errno = EOVERFLOW;
-               return -1;
-       } else if (n > 0) {
-               if (n > (char *)0+SIZE_MAX-s) n = (char *)0+SIZE_MAX-s;
-               f.wpos = (void *)s;
-               f.wbase = f.wend = (void *)(s+n-1);
-               f.wstop = f.wend - 1;
+       if (n-1 > INT_MAX-1) {
+               if (n) {
+                       errno = EOVERFLOW;
+                       return -1;
+               }
+               s = &b;
+               n = 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);
-       /* wpos points just after last byte written, or to s+n-1 (wbase) */
-       *f.wpos = 0;
+
+       /* Null-terminate, overwriting last char if dest buffer is full */
+       if (n) f.wpos[-(f.wpos == f.wend)] = 0;
        return r;
 }