+/* non-copying interface: provide pointer to region to write to
+ * bio_nwrite0: check how much space is available
+ * bio_nwrite: also increase length
+ * (example usage: bio_nwrite0(), write to buffer, bio_nwrite()
+ * or just bio_nwrite(), write to buffer)
+ */
+static size_t bio_nwrite0(BIO *bio, char **buf)
+ {
+ struct bio_bio_st *b;
+ size_t num;
+ size_t write_offset;
+
+ BIO_clear_retry_flags(bio);
+
+ if (!bio->init)
+ return 0;
+
+ b = bio->ptr;
+ assert(b != NULL);
+ assert(b->peer != NULL);
+ assert(b->buf != NULL);
+
+ b->request = 0;
+ if (b->closed)
+ {
+ BIOerr(BIO_F_BIO_NWRITE0, BIO_R_BROKEN_PIPE);
+ return -1;
+ }
+
+ assert(b->len <= b->size);
+
+ if (b->len == b->size)
+ {
+ BIO_set_retry_write(bio);
+ return -1;
+ }
+
+ num = b->size - b->len;
+ write_offset = b->offset + b->len;
+ if (write_offset >= b->size)
+ write_offset -= b->size;
+ if (write_offset + num > b->size)
+ /* no ring buffer wrap-around for non-copying interface
+ * (to fulfil the promise by BIO_ctrl_get_write_guarantee,
+ * BIO_nwrite may have to be called twice) */
+ num = b->size - write_offset;
+
+ if (buf != NULL)
+ *buf = b->buf + write_offset;
+ assert(write_offset + num <= b->size);
+
+ return num;
+ }
+
+static size_t bio_nwrite(BIO *bio, char **buf, size_t num)
+ {
+ struct bio_bio_st *b;
+ size_t space;
+
+ space = bio_nwrite0(bio, buf);
+ if (num > space)
+ num = space;
+ if (num <= 0)
+ return num;
+ b->len += num;
+ assert(b->len <= b->size);
+
+ return num;
+ }
+