Make major improvements to stdio

Buffering now has optimal performance, bugs have been fixed, and some
missing apis have been introduced. This implementation is also now more
production worthy since it's less brittle now in terms of system errors.
That's going to help redbean since lua i/o is all based on stdio.

See #97

libc/stdio/fread.c

@@ -16,12 +16,19 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/calls/struct/iovec.h"
 #include "libc/errno.h"
 #include "libc/fmt/conv.h"
+#include "libc/macros.internal.h"
 #include "libc/runtime/runtime.h"
+#include "libc/sock/sock.h"
 #include "libc/stdio/internal.h"
 #include "libc/stdio/stdio.h"
 #include "libc/str/internal.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/o.h"
+#include "libc/sysv/errfuns.h"
 
 /**
  * Reads data from stream.
@@ -31,17 +38,62 @@
  * @return count on success, [0,count) on eof, or 0 on error or count==0
  */
 size_t fread(void *buf, size_t stride, size_t count, FILE *f) {
-  int c;
-  size_t i, n;
-  unsigned char *p;
-  for (n = stride * count, p = buf, i = 0; i < n; ++i) {
-    if ((c = getc(f)) != -1) {
-      p[i] = c & 0xff;
-    } else if (!(i % stride)) {
-      return i / stride;
-    } else {
-      return __fseterr(f, EOVERFLOW);
-    }
+  char *p;
+  ssize_t rc;
+  size_t n, m;
+  struct iovec iov[2];
+  if ((f->iomode & O_ACCMODE) == O_WRONLY) {
+    f->state = errno = EBADF;
+    return 0;
+  }
+  if (f->beg > f->end) {
+    f->state = errno = EINVAL;
+    return 0;
+  }
+  p = buf;
+  n = stride * count;
+  m = f->end - f->beg;
+  memcpy(p, f->buf + f->beg, MIN(n, m));
+  if (n < m) {
+    f->beg += n;
+    return count;
+  }
+  if (n == m) {
+    f->beg = f->end = 0;
+    return count;
+  }
+  if (f->fd == -1) {
+    f->beg = 0;
+    f->end = 0;
+    f->state = -1;
+    return m / stride;
+  }
+  iov[0].iov_base = p + m;
+  iov[0].iov_len = n - m;
+  if (f->bufmode != _IONBF && n < f->size) {
+    iov[1].iov_base = f->buf;
+    if (f->size > PUSHBACK) {
+      iov[1].iov_len = f->size - PUSHBACK;
+    } else {
+      iov[1].iov_len = f->size;
+    }
+  } else {
+    iov[1].iov_base = NULL;
+    iov[1].iov_len = 0;
+  }
+  if ((rc = readv(f->fd, iov, 2)) == -1) {
+    f->state = errno;
+    return 0;
+  }
+  n = rc;
+  f->beg = 0;
+  f->end = 0;
+  if (n > iov[0].iov_len) {
+    f->end += n - iov[0].iov_len;
+    return count;
+  } else {
+    n = (m + n) / stride;
+    if (n < count) f->state = -1;
+    return n;
   }
-  return count;
 }