fix: Handle STDIN reads without a body

runtime/src/http_parser_settings.c

@@ -192,7 +192,12 @@ http_parser_settings_on_header_end(http_parser *parser)
 #endif
 
 	http_request->header_end = true;
+
+	if (parser->method == HTTP_PUT || parser->method == HTTP_POST) {
 		http_request->body_length = parser->content_length;
+	} else {
+		http_request->body_length = 0;
+	}
 
 	return 0;
 }

runtime/src/libc/wasi_impl_serverless.c

@@ -663,6 +663,8 @@ wasi_snapshot_preview1_backing_fd_read(wasi_context_t *context, __wasi_fd_t fd,
 		int                  old_read        = current_request->cursor;
 		int                  bytes_to_read   = current_request->body_length - old_read;
 
+		assert(current_request->body_length >= 0);
+
 		for (int i = 0; i < iovs_len; i++) {
 			if (bytes_to_read == 0) goto done;