io: add alternative to sendflie

io.c

@@ -57,6 +57,39 @@ io_nwrite(int fd, const void* buf, size_t n) {
 }
 
 
+int
+io_ncopy(int fd_in, int fd_out, size_t size) {
+  size_t copied = 0;
+  void* buf;
+  ssize_t n;
+
+  if(!(buf=malloc(IO_COPY_BUFSIZE))) {
+    return -1;
+  }
+
+  while(copied < size) {
+    n = size - copied;
+    if(n > IO_COPY_BUFSIZE) {
+      n = IO_COPY_BUFSIZE;
+    }
+
+    if(io_nread(fd_in, buf, n)) {
+      free(buf);
+      return -1;
+    }
+    if(io_nwrite(fd_out, buf, n)) {
+      free(buf);
+      return -1;
+    }
+
+    copied += n;
+  }
+
+  free(buf);
+  return 0;
+}
+
+
 int
 io_pread(int fd, void* buf, size_t n, off_t off) {
   int r;

io.h

@@ -37,6 +37,12 @@ int io_nread(int fd, void* buf, size_t n);
 int io_nwrite(int fd, const void* buf, size_t n);
 
 
+/**
+ * Copy exactly N bytes from one file descriptor to another.
+ **/
+int io_ncopy(int fd_in, int fd_out, size_t size);
+
+
 /**
  * Copy exactly N bytes from a file descriptor to a socket.
  **/