From 4464e464b6a7a23858fb199f62c2ab31997c2331 Mon Sep 17 00:00:00 2001 From: "J. Nick Koston" Date: Fri, 19 Dec 2025 10:48:52 -1000 Subject: [PATCH] safer --- esphome/core/helpers.cpp | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/esphome/core/helpers.cpp b/esphome/core/helpers.cpp index 18cef6e0dcb..64d313ab7b3 100644 --- a/esphome/core/helpers.cpp +++ b/esphome/core/helpers.cpp @@ -392,8 +392,12 @@ std::string value_accuracy_to_string(float value, int8_t accuracy_decimals) { size_t value_accuracy_to_buf(std::span buf, float value, int8_t accuracy_decimals) { normalize_accuracy_decimals(value, accuracy_decimals); + // snprintf returns chars that would be written (excluding null), or negative on error int len = snprintf(buf.data(), buf.size(), "%.*f", accuracy_decimals, value); - return len > 0 ? std::min(static_cast(len), buf.size() - 1) : 0; + if (len < 0) + return 0; // encoding error + // On truncation, snprintf returns would-be length; actual written is buf.size() - 1 + return static_cast(len) >= buf.size() ? buf.size() - 1 : static_cast(len); } size_t value_accuracy_with_uom_to_buf(std::span buf, float value, @@ -402,8 +406,12 @@ size_t value_accuracy_with_uom_to_buf(std::span bu return value_accuracy_to_buf(buf, value, accuracy_decimals); } normalize_accuracy_decimals(value, accuracy_decimals); + // snprintf returns chars that would be written (excluding null), or negative on error int len = snprintf(buf.data(), buf.size(), "%.*f %s", accuracy_decimals, value, unit_of_measurement.c_str()); - return len > 0 ? std::min(static_cast(len), buf.size() - 1) : 0; + if (len < 0) + return 0; // encoding error + // On truncation, snprintf returns would-be length; actual written is buf.size() - 1 + return static_cast(len) >= buf.size() ? buf.size() - 1 : static_cast(len); } int8_t step_to_accuracy_decimals(float step) {