From be83bc717db0375e19431fe38c0490ff1a9e40ec Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 26 Apr 2017 05:57:37 -0700
Subject: ffi: support buf objects.

* buf.c (make_duplicate_buf, buf_get, buf_fill): New
functions.

* buf.h (make_duplicate_buf, buf_get, buf_fill): Declared.

* ffi.c (struct txr_ffi_type): New member, nelem.
Keeps track of number of elements, for types that are
FFI pointers. This lets us support the get method so that
a buf can be a C function return value, if its size is
declared in our FFI type system.
(ffi_buf_put, ffi_buf_get, ffi_buf_fill): New functions.
(ffi_type_compile): Handle two new cases of syntax for
buffers: (buf <size>) and buf.
---
 buf.c | 24 ++++++++++++++++++++++++
 buf.h |  3 +++
 ffi.c | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/buf.c b/buf.c
index 0c1ecf18..58cd4177 100644
--- a/buf.c
+++ b/buf.c
@@ -107,6 +107,18 @@ val make_borrowed_buf(val len, mem_t *data)
   return obj;
 }
 
+val make_duplicate_buf(val len, mem_t *data)
+{
+  val obj = make_obj();
+
+  obj->b.type = BUF;
+  obj->b.data = chk_copy_obj(data, c_num(len));
+  obj->b.len = len;
+  obj->b.size = nil;
+
+  return obj;
+}
+
 static struct buf *buf_handle(val buf, val ctx)
 {
   if (type(buf) == BUF)
@@ -186,6 +198,18 @@ val length_buf(val buf)
   return b->len;
 }
 
+mem_t *buf_get(val buf, val self)
+{
+  struct buf *b = buf_handle(buf, self);
+  return b->data;
+}
+
+void buf_fill(val buf, mem_t *src, val self)
+{
+  struct buf *b = buf_handle(buf, self);
+  memcpy(b->data, src, c_num(b->len));
+}
+
 static void buf_put_bytes(val buf, val pos, mem_t *ptr, cnum size, val self)
 {
   struct buf *b = buf_handle(buf, self);
diff --git a/buf.h b/buf.h
index 56a04c7e..8102fff8 100644
--- a/buf.h
+++ b/buf.h
@@ -27,9 +27,12 @@
 
 val make_buf(val len, val init_val, val alloc_size);
 val make_borrowed_buf(val len, mem_t *data);
+val make_duplicate_buf(val len, mem_t *data);
 val buf_trim(val buf);
 val buf_set_length(val obj, val len, val init_val);
 val length_buf(val buf);
+mem_t *buf_get(val buf, val self);
+void buf_fill(val buf, mem_t *src, val self);
 
 #if HAVE_I8
 val buf_put_i8(val buf, val pos, val num);
diff --git a/ffi.c b/ffi.c
index 4c5c5399..00143b87 100644
--- a/ffi.c
+++ b/ffi.c
@@ -83,6 +83,7 @@ struct txr_ffi_type {
   val mnames;
   val mtypes;
   cnum size, align;
+  cnum nelem;
   void (*put)(struct txr_ffi_type *, val obj, mem_t *dst, val self);
   val (*get)(struct txr_ffi_type *, mem_t *src, val self);
   void (*fill)(struct txr_ffi_type *, mem_t *src, val obj, val self);
@@ -587,6 +588,28 @@ static val ffi_wstr_get(struct txr_ffi_type *tft, mem_t *src, val self)
   return string(p);
 }
 
+static void ffi_buf_put(struct txr_ffi_type *tft,
+                        val buf, mem_t *dst, val self)
+{
+  mem_t *b = buf_get(buf, self);
+  *coerce(const mem_t **, dst) = b;
+}
+
+static val ffi_buf_get(struct txr_ffi_type *tft, mem_t *src, val self)
+{
+  (void) tft;
+  (void) self;
+  mem_t *p = *coerce(mem_t **, src);
+  return make_duplicate_buf(num(tft->nelem), p);
+}
+
+static void ffi_buf_fill(struct txr_ffi_type *tft, mem_t *src,
+                         val buf, val self)
+{
+  (void) tft;
+  buf_fill(buf, src, self);
+}
+
 static void ffi_ptr_in_put(struct txr_ffi_type *tft,
                            val s, mem_t *dst, val self)
 {
@@ -866,6 +889,15 @@ val ffi_type_compile(val syntax)
                                    &ffi_type_pointer,
                                    ffi_ptr_in_out_put, ffi_ptr_out_get,
                                    target_type);
+    } else if (sym == buf_s) {
+      cnum nelem = c_num(cadr(syntax));
+      val type = make_ffi_type_builtin(syntax, cptr_s, sizeof (mem_t *),
+                                       &ffi_type_pointer,
+                                       ffi_buf_put, ffi_buf_get);
+      struct txr_ffi_type *tft = ffi_type_struct(type);
+      tft->fill = ffi_buf_fill;
+      tft->nelem = nelem;
+      return type;
     }
 
     uw_throwf(error_s, lit("~a: unimplemented case"), self, nao);
@@ -965,6 +997,13 @@ val ffi_type_compile(val syntax)
     return make_ffi_type_builtin(syntax, cptr_s, sizeof (mem_t *),
                                  &ffi_type_pointer,
                                  ffi_wstr_put, ffi_wstr_get);
+  } else if (syntax == buf_s) {
+    val type = make_ffi_type_builtin(syntax, cptr_s, sizeof (mem_t *),
+                                     &ffi_type_pointer,
+                                     ffi_buf_put, ffi_void_get);
+    struct txr_ffi_type *tft = ffi_type_struct(type);
+    tft->fill = ffi_buf_fill;
+    return type;
   } else if (syntax == void_s) {
     return make_ffi_type_builtin(syntax, nil, 0, &ffi_type_void,
                                  ffi_void_put, ffi_void_get);
-- 
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