buf: implement fill_buf operation for buf streams.

* buf.c (buf_strm_fill_buf): New function.
(buf_strm_ops): Wire in buf_strm_fill_buf operation.

* tests/018/streams.tl: New tests.

2 files changed, 38 insertions, 1 deletions

diff --git a/buf.c b/buf.c
index c14f68b3..360d5bec 100644
--- a/buf.c
+++ b/buf.c
@@ -52,6 +52,8 @@
 #include "txr.h"
 #include "buf.h"
 
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
 static struct buf *buf_handle(val buf, val ctx);
 
 static cnum buf_check_len(val len, val self)
@@ -1196,6 +1198,28 @@ static val buf_strm_unget_byte(val stream, int byte)
   return num_fast(byte);
 }
 
+static ucnum buf_strm_fill_buf(val stream, mem_t *ptr, ucnum len, ucnum pos)
+{
+  val self = lit("fill-buf");
+  struct buf_strm *s = coerce(struct buf_strm *, stream->co.handle);
+  struct buf *b = us_buf_handle(s->buf);
+
+  if (convert(size_t, len) != len || len > INT_PTR_MAX)
+    uw_throwf(error_s, lit("~a: buffer too large"), self, nao);
+  if (pos >= len) {
+    return len;
+  } else {
+    size_t index = c_unum(s->pos, self);
+    size_t room = len - pos;
+    size_t avail = c_u(b->size) - index;
+    size_t copy = min(room, avail);
+    memcpy(ptr + pos, b->data + index, copy);
+    s->pos = plus(s->pos, unum(copy));
+    return pos + copy;
+  }
+}
+
+
 static val buf_strm_seek(val stream, val offset, enum strm_whence whence)
 {
   val self = lit("seek-stream");
@@ -1307,7 +1331,7 @@ static struct strm_ops buf_strm_ops =
                 buf_strm_unget_char,
                 buf_strm_unget_byte,
                 0,
-                0,
+                buf_strm_fill_buf,
                 0,
                 0,
                 buf_strm_seek,
diff --git a/tests/018/streams.tl b/tests/018/streams.tl
index 3bdab5bd..f82bc06e 100644
--- a/tests/018/streams.tl
+++ b/tests/018/streams.tl
@@ -236,3 +236,16 @@
     (seek-stream s 0 :from-current) 0
     (truncate-stream s 0) t
     (get-buf-from-stream s) #b''))
+
+(with-in-buf-stream (s #b'00112233445566778899AABCCCDDEEFF')
+  (let ((b (make-buf 0)))
+    (mtest
+      (fill-buf-adjust b 0 s) 0
+      b #b''
+      (seek-stream s 0 :from-current) 0
+      (buf-set-length b 5) 0
+      (fill-buf-adjust b 0 s) 5
+      b #b'0011223344'
+      (seek-stream s -3 :from-end) t
+      (fill-buf-adjust b 0 s) 3
+      b #b'DDEEFF')))