Add a buffered writer to stdlib _io module.

src/lib/_io.rs

@@ -2,6 +2,10 @@ type buf_reader = unsafe obj {
   fn read() -> vec[u8];
 };
 
+type buf_writer = unsafe obj {
+  fn write(vec[u8] v);
+};
+
 fn default_bufsz() -> uint {
   ret 4096u;
 }
@@ -10,7 +14,7 @@ fn new_buf() -> vec[u8] {
   ret _vec.alloc[u8](default_bufsz());
 }
 
-fn new_buf_reader(str s) -> buf_reader {
+fn new_buf_reader(str path) -> buf_reader {
 
   unsafe obj fd_buf_reader(int fd, mutable vec[u8] buf) {
 
@@ -39,11 +43,45 @@ fn new_buf_reader(str s) -> buf_reader {
     }
   }
 
-  auto fd = os.libc.open(_str.buf(s), 0);
+  auto fd = os.libc.open(_str.buf(path), 0);
   if (fd < 0) {
-    log "error opening file";
+    log "error opening file for reading";
     log sys.rustrt.last_os_error();
     fail;
   }
   ret fd_buf_reader(fd, new_buf());
 }
+
+fn new_buf_writer(str path) -> buf_writer {
+
+  unsafe obj fd_buf_writer(int fd) {
+
+    fn write(vec[u8] v) {
+      auto len = _vec.len[u8](v);
+      auto count = 0u;
+      auto vbuf;
+      while (count < len) {
+        vbuf = _vec.buf_off[u8](v, count);
+        auto nout = os.libc.write(fd, vbuf, len);
+        if (nout < 0) {
+          log "error dumping buffer";
+          log sys.rustrt.last_os_error();
+          fail;
+        }
+        count += nout as uint;
+      }
+    }
+
+    drop {
+      os.libc.close(fd);
+    }
+  }
+
+  auto fd = os.libc.open(_str.buf(path), 0);
+  if (fd < 0) {
+    log "error opening file for writing";
+    log sys.rustrt.last_os_error();
+    fail;
+  }
+  ret fd_buf_writer(fd);
+}

src/lib/_vec.rs

@@ -3,7 +3,7 @@ import op = util.operator;
 
 native "rust" mod rustrt {
   type vbuf;
-  fn vec_buf[T](vec[T] v) -> vbuf;
+  fn vec_buf[T](vec[T] v, uint offset) -> vbuf;
   fn vec_len[T](vec[T] v) -> uint;
   /* The T in vec_alloc[T, U] is the type of the vec to allocate.  The
    * U is the type of an element in the vec.  So to allocate a vec[U] we
@@ -50,7 +50,12 @@ fn len[T](vec[T] v) -> uint {
 }
 
 fn buf[T](vec[T] v) -> vbuf {
-  ret rustrt.vec_buf[T](v);
+  ret rustrt.vec_buf[T](v, 0u);
+}
+
+fn buf_off[T](vec[T] v, uint offset) -> vbuf {
+  check (offset < len[T](v));
+  ret rustrt.vec_buf[T](v, offset);
 }
 
 // Returns elements from [start..end) from v.

src/rt/rust_builtin.cpp

@@ -116,9 +116,9 @@ str_buf(rust_task *task, rust_str *s)
 }
 
 extern "C" CDECL void *
-vec_buf(rust_task *task, type_desc *ty, rust_vec *v)
+vec_buf(rust_task *task, type_desc *ty, rust_vec *v, size_t offset)
 {
-    return (void *)&v->data[0];
+    return (void *)&v->data[ty->size * offset];
 }
 
 extern "C" CDECL size_t