add a new function recv_at_least() to socket stream (#224)

add new functions recv_at_least() and recv_at_least_mutable() to socket stream

net/basic_socket.cpp

@@ -262,6 +262,33 @@ bool ISocketStream::skip_read(size_t count) {
  return true;
 }
 
+ssize_t ISocketStream::recv_at_least(void* buf, size_t count, size_t least, int flags) {
+ size_t n = 0;
+ do {
+ ssize_t ret = this->recv(buf, count, flags);
+ if (ret < 0) return ret;
+ if (ret == 0) break; // EOF
+ if ((n += ret) >= least) break;
+ count -= ret;
+ } while (count);
+ return n;
+}
+
+ssize_t ISocketStream::recv_at_least_mutable(struct iovec *iov, int iovcnt,
+ size_t least, int flags /*=0*/) {
+ size_t n = 0;
+ iovector_view v(iov, iovcnt);
+ do {
+ ssize_t ret = this->recv(v.iov, v.iovcnt, flags);
+ if (ret < 0) return ret;
+ if (ret == 0) break; // EOF
+ if ((n += ret) >= least) break;
+ auto r = v.extract_front(ret);
+ assert(r == ret); (void)r;
+ } while (v.iovcnt && v.iov->iov_len);
+ return n;
+}
+
 int do_get_name(int fd, Getter getter, EndPoint& addr) {
  sockaddr_storage storage;
  socklen_t len = storage.get_max_socklen();

net/socket.h

@@ -217,6 +217,10 @@ namespace net {
  virtual ssize_t recv(void *buf, size_t count, int flags = 0) = 0;
  virtual ssize_t recv(const struct iovec *iov, int iovcnt, int flags = 0) = 0;
 
+ // recv at `least` bytes to buffer (`buf`, `count`)
+ ssize_t recv_at_least(void* buf, size_t count, size_t least, int flags = 0);
+ ssize_t recv_at_least_mutable(struct iovec *iov, int iovcnt, size_t least, int flags = 0);
+
  // read count bytes and drop them
  // return true/false for success/failure
  bool skip_read(size_t count);