.c_str()

esphome/components/image/__init__.py

@@ -665,15 +665,10 @@ async def write_image(config, all_frames=False):
         if is_svg_file(path):
             import resvg_py
 
-            if resize:
-                width, height = resize
-                # resvg-py allows rendering by width/height directly
-                image_data = resvg_py.svg_to_bytes(
-                    svg_path=str(path), width=int(width), height=int(height)
-                )
-            else:
-                # Default size
-                image_data = resvg_py.svg_to_bytes(svg_path=str(path))
+            resize = resize or (None, None)
+            image_data = resvg_py.svg_to_bytes(
+                svg_path=str(path), width=resize[0], height=resize[1], dpi=100
+            )
 
             # Convert bytes to Pillow Image
             image = Image.open(io.BytesIO(image_data))

esphome/components/mqtt/mqtt_client.cpp

@@ -635,7 +635,8 @@ void MQTTClientComponent::set_log_message_template(MQTTMessage &&message) { this
 const MQTTDiscoveryInfo &MQTTClientComponent::get_discovery_info() const { return this->discovery_info_; }
 void MQTTClientComponent::set_topic_prefix(const std::string &topic_prefix, const std::string &check_topic_prefix) {
   if (App.is_name_add_mac_suffix_enabled() && (topic_prefix == check_topic_prefix)) {
-    this->topic_prefix_ = str_sanitize(App.get_name());
+    char buf[ESPHOME_DEVICE_NAME_MAX_LEN + 1];
+    this->topic_prefix_ = str_sanitize_to(buf, App.get_name().c_str());
   } else {
     this->topic_prefix_ = topic_prefix;
   }

esphome/components/mqtt/mqtt_component.cpp

@@ -48,7 +48,8 @@ void MQTTComponent::set_subscribe_qos(uint8_t qos) { this->subscribe_qos_ = qos;
 void MQTTComponent::set_retain(bool retain) { this->retain_ = retain; }
 
 std::string MQTTComponent::get_discovery_topic_(const MQTTDiscoveryInfo &discovery_info) const {
-  std::string sanitized_name = str_sanitize(App.get_name());
+  char sanitized_name[ESPHOME_DEVICE_NAME_MAX_LEN + 1];
+  str_sanitize_to(sanitized_name, App.get_name().c_str());
   const char *comp_type = this->component_type();
   char object_id_buf[OBJECT_ID_MAX_LEN];
   StringRef object_id = this->get_default_object_id_to_(object_id_buf);
@@ -60,7 +61,7 @@ std::string MQTTComponent::get_discovery_topic_(const MQTTDiscoveryInfo &discove
   p = append_char(p, '/');
   p = append_str(p, comp_type, strlen(comp_type));
   p = append_char(p, '/');
-  p = append_str(p, sanitized_name.data(), sanitized_name.size());
+  p = append_str(p, sanitized_name, strlen(sanitized_name));
   p = append_char(p, '/');
   p = append_str(p, object_id.c_str(), object_id.size());
   p = append_str(p, "/config", 7);

esphome/core/helpers.cpp

@@ -199,11 +199,22 @@ std::string str_snake_case(const std::string &str) {
   }
   return result;
 }
-std::string str_sanitize(const std::string &str) {
-  std::string result = str;
-  for (char &c : result) {
-    c = to_sanitized_char(c);
+char *str_sanitize_to(char *buffer, size_t buffer_size, const char *str) {
+  if (buffer_size == 0) {
+    return buffer;
   }
+  size_t i = 0;
+  while (*str && i < buffer_size - 1) {
+    buffer[i++] = to_sanitized_char(*str++);
+  }
+  buffer[i] = '\0';
+  return buffer;
+}
+
+std::string str_sanitize(const std::string &str) {
+  std::string result;
+  result.resize(str.size());
+  str_sanitize_to(&result[0], str.size() + 1, str.c_str());
   return result;
 }
 std::string str_snprintf(const char *fmt, size_t len, ...) {

esphome/core/helpers.h

@@ -545,7 +545,25 @@ std::string str_snake_case(const std::string &str);
 constexpr char to_sanitized_char(char c) {
   return (c == '-' || c == '_' || (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) ? c : '_';
 }
+
+/** Sanitize a string to buffer, keeping only alphanumerics, dashes, and underscores.
+ *
+ * @param buffer Output buffer to write to.
+ * @param buffer_size Size of the output buffer.
+ * @param str Input string to sanitize.
+ * @return Pointer to buffer.
+ *
+ * Buffer size needed: strlen(str) + 1.
+ */
+char *str_sanitize_to(char *buffer, size_t buffer_size, const char *str);
+
+/// Sanitize a string to buffer. Automatically deduces buffer size.
+template<size_t N> inline char *str_sanitize_to(char (&buffer)[N], const char *str) {
+  return str_sanitize_to(buffer, N, str);
+}
+
 /// Sanitizes the input string by removing all characters but alphanumerics, dashes and underscores.
+/// @warning Allocates heap memory. Use str_sanitize_to() with a stack buffer instead.
 std::string str_sanitize(const std::string &str);
 
 /// Calculate FNV-1 hash of a string while applying snake_case + sanitize transformations.

script/ci-custom.py

@@ -687,6 +687,7 @@ HEAP_ALLOCATING_HELPERS = {
     "format_mac_address_pretty": "format_mac_addr_upper() with a stack buffer",
     "get_mac_address": "get_mac_address_into_buffer() with a stack buffer",
     "get_mac_address_pretty": "get_mac_address_pretty_into_buffer() with a stack buffer",
+    "str_sanitize": "str_sanitize_to() with a stack buffer",
     "str_truncate": "removal (function is unused)",
     "str_upper_case": "removal (function is unused)",
     "str_snake_case": "removal (function is unused)",
@@ -704,6 +705,7 @@ HEAP_ALLOCATING_HELPERS = {
     r"format_mac_address_pretty|"
     r"get_mac_address_pretty(?!_)|"
     r"get_mac_address(?!_)|"
+    r"str_sanitize(?!_)|"
     r"str_truncate|"
     r"str_upper_case|"
     r"str_snake_case"

tests/component_tests/image/config/mm_dimensions.svg

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" width="10mm" height="10mm" viewBox="0 0 100 100">
+  <rect x="0" y="0" width="100" height="100" fill="#00FF00"/>
+  <circle cx="50" cy="50" r="30" fill="#0000FF"/>
+</svg>

tests/component_tests/image/test_init.py

@@ -5,17 +5,21 @@ from __future__ import annotations
 from collections.abc import Callable
 from pathlib import Path
 from typing import Any
+from unittest.mock import MagicMock, patch
 
 import pytest
 
 from esphome import config_validation as cv
 from esphome.components.image import (
+    CONF_INVERT_ALPHA,
+    CONF_OPAQUE,
     CONF_TRANSPARENCY,
     CONFIG_SCHEMA,
     get_all_image_metadata,
     get_image_metadata,
+    write_image,
 )
-from esphome.const import CONF_ID, CONF_RAW_DATA_ID, CONF_TYPE
+from esphome.const import CONF_DITHER, CONF_FILE, CONF_ID, CONF_RAW_DATA_ID, CONF_TYPE
 from esphome.core import CORE
 
 
@@ -350,3 +354,52 @@ def test_get_all_image_metadata_empty() -> None:
         "get_all_image_metadata should always return a dict"
     )
     # Length could be 0 or more depending on what's in CORE at test time
+
+
+@pytest.fixture
+def mock_progmem_array():
+    """Mock progmem_array to avoid needing a proper ID object in tests."""
+    with patch("esphome.components.image.cg.progmem_array") as mock_progmem:
+        mock_progmem.return_value = MagicMock()
+        yield mock_progmem
+
+
+@pytest.mark.asyncio
+async def test_svg_with_mm_dimensions_succeeds(
+    component_config_path: Callable[[str], Path],
+    mock_progmem_array: MagicMock,
+) -> None:
+    """Test that SVG files with dimensions in mm are successfully processed."""
+    # Create a config for write_image without CONF_RESIZE
+    config = {
+        CONF_FILE: component_config_path("mm_dimensions.svg"),
+        CONF_TYPE: "BINARY",
+        CONF_TRANSPARENCY: CONF_OPAQUE,
+        CONF_DITHER: "NONE",
+        CONF_INVERT_ALPHA: False,
+        CONF_RAW_DATA_ID: "test_raw_data_id",
+    }
+
+    # This should succeed without raising an error
+    result = await write_image(config)
+
+    # Verify that write_image returns the expected tuple
+    assert isinstance(result, tuple), "write_image should return a tuple"
+    assert len(result) == 6, "write_image should return 6 values"
+
+    prog_arr, width, height, image_type, trans_value, frame_count = result
+
+    # Verify the dimensions are positive integers
+    # At 100 DPI, 10mm = ~39 pixels (10mm * 100dpi / 25.4mm_per_inch)
+    assert isinstance(width, int), "Width should be an integer"
+    assert isinstance(height, int), "Height should be an integer"
+    assert width > 0, "Width should be positive"
+    assert height > 0, "Height should be positive"
+    assert frame_count == 1, "Single image should have frame_count of 1"
+    # Verify we got reasonable dimensions from the mm-based SVG
+    assert 30 < width < 50, (
+        f"Width should be around 39 pixels for 10mm at 100dpi, got {width}"
+    )
+    assert 30 < height < 50, (
+        f"Height should be around 39 pixels for 10mm at 100dpi, got {height}"
+    )