Fix #1069 (#1070)

Author: yhirose

httplib.h

@@ -6997,7 +6997,30 @@ inline ssize_t SSLSocketStream::read(char *ptr, size_t size) {
 }
 
 inline ssize_t SSLSocketStream::write(const char *ptr, size_t size) {
-  if (is_writable()) { return SSL_write(ssl_, ptr, static_cast<int>(size)); }
+  if (is_writable()) {
+    auto ret = SSL_write(ssl_, ptr, static_cast<int>(size));
+    if (ret < 0) {
+      auto err = SSL_get_error(ssl_, ret);
+      int n = 1000;
+#ifdef _WIN32
+      while (--n >= 0 &&
+             (err == SSL_ERROR_WANT_WRITE ||
+              err == SSL_ERROR_SYSCALL && WSAGetLastError() == WSAETIMEDOUT)) {
+#else
+      while (--n >= 0 && err == SSL_ERROR_WANT_WRITE) {
+#endif
+        if (is_writable()) {
+          std::this_thread::sleep_for(std::chrono::milliseconds(1));
+          ret = SSL_write(ssl_, ptr, static_cast<int>(size));
+          if (ret >= 0) { return ret; }
+          err = SSL_get_error(ssl_, ret);
+        } else {
+          return -1;
+        }
+      }
+    }
+    return ret;
+  }
   return -1;
 }