From eed84b6cd6f7eca3fc5bf2ed6e2c3c48a25f63c8 Mon Sep 17 00:00:00 2001 From: pennam Date: Mon, 13 Jul 2026 15:50:01 +0200 Subject: [PATCH] WebSocketClient: fix undefined read order in frame length Multiple read() calls in one expression have unspecified evaluation order in C++, so the length bytes could be combined wrong. Read each byte into its own variable before combining them. --- src/WebSocketClient.cpp | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/src/WebSocketClient.cpp b/src/WebSocketClient.cpp index ab41b0a..437748d 100644 --- a/src/WebSocketClient.cpp +++ b/src/WebSocketClient.cpp @@ -213,18 +213,30 @@ int WebSocketClient::parseMessage() } else if (length == 126) { - iRxSize = (HttpClient::read() << 8) | HttpClient::read(); + // read each byte in a well-defined order (the evaluation order of + // multiple read() calls in a single expression is unspecified) + uint8_t b1 = HttpClient::read(); + uint8_t b0 = HttpClient::read(); + iRxSize = ((uint64_t)b1 << 8) | b0; } else { - iRxSize = ((uint64_t)HttpClient::read() << 56) | - ((uint64_t)HttpClient::read() << 48) | - ((uint64_t)HttpClient::read() << 40) | - ((uint64_t)HttpClient::read() << 32) | - ((uint64_t)HttpClient::read() << 24) | - ((uint64_t)HttpClient::read() << 16) | - ((uint64_t)HttpClient::read() << 8) | - (uint64_t)HttpClient::read(); + uint8_t b7 = HttpClient::read(); + uint8_t b6 = HttpClient::read(); + uint8_t b5 = HttpClient::read(); + uint8_t b4 = HttpClient::read(); + uint8_t b3 = HttpClient::read(); + uint8_t b2 = HttpClient::read(); + uint8_t b1 = HttpClient::read(); + uint8_t b0 = HttpClient::read(); + iRxSize = ((uint64_t)b7 << 56) | + ((uint64_t)b6 << 48) | + ((uint64_t)b5 << 40) | + ((uint64_t)b4 << 32) | + ((uint64_t)b3 << 24) | + ((uint64_t)b2 << 16) | + ((uint64_t)b1 << 8) | + (uint64_t)b0; } // read in the mask, if present