Refuse non-finite floats instead of publishing nan or inf

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to `cpp-sdk` are recorded here. Format follows [Keep a Chang
 
 ## [Unreleased]
 
+### Fixed
+
+- `Property::setValue(float)` published `nan`, `inf` or `-inf`, which the float payload grammar does not allow. `homie_format_float()` and `homie_format_double()` now return `false` with an empty string for a NaN or infinity, and `setValue()` logs and keeps the previous value. ([#27](https://github.com/electrification-bus/cpp-sdk/issues/27))
+
+### Added
+
+- `test_homie_float_vectors`: the 434 float32 vectors shared with python-sdk and rust-sdk.
+
 ## [0.7.0] - 2026-10-10
 
 ### Changed

homie/include/ebus/homie/homie_datatype.h

@@ -95,9 +95,9 @@ bool homie_validate_number(double value, const char* format, double* coerced);
 // Format a float payload: the shortest decimal that reads back as the same float, laid
 // out like Python's repr() without the exponent '+' (fixed notation with at least one
 // fraction digit for exponents -4..15, else d.ddde-XX), so "21.4", "40.0", "1e-05",
-// "1e16". This is python-sdk's float text. Writes NUL-terminated text to out (n >= 32);
-// a non-finite value is written as "nan", "inf" or "-inf", which is not a valid payload.
-void homie_format_float(float value, char* out, size_t n);
+// "1e16". This is python-sdk's float text. Writes NUL-terminated text to out (n >= 32)
+// and returns true. A NaN or infinity has no float payload: returns false, out is "".
+bool homie_format_float(float value, char* out, size_t n);
 
 // The same for a double: the shortest decimal that reads back as the same double.
-void homie_format_double(double value, char* out, size_t n);
+bool homie_format_double(double value, char* out, size_t n);

homie/src/Property.cpp

@@ -81,8 +81,14 @@ void Property::setValue(int64_t value) {
     _has_value = true;
 }
 void Property::setValue(float value) {
+    char text[32];
+    if (!homie_format_float(value, text, sizeof(text))) {
+        homie_logf("Property: '%s' - %f is not a float payload; keeping the previous value\n",
+                   _id, (double)value);
+        return;
+    }
     _floatValue = value;
-    homie_format_float(value, _value, sizeof(_value));
+    snprintf(_value, sizeof(_value), "%s", text);
     _has_value = true;
 }
 void Property::setValue(const char* value) {

homie/src/homie_datatype.cpp

@@ -295,10 +295,10 @@ bool homie_validate_duration(const char* payload) {
 // Shortest round trip: the fewest significant digits whose text reads back as `value`,
 // through strtof() for a float (nine digits always suffice) or strtod() for a double
 // (seventeen).
-static void format_shortest(double value, bool is_float, char* out, size_t n) {
+static bool format_shortest(double value, bool is_float, char* out, size_t n) {
     if (!isfinite(value)) {
-        snprintf(out, n, "%g", value);
-        return;
+        if (n > 0) out[0] = '\0';
+        return false;
     }
     char sci[32];
     const int max_prec = is_float ? 8 : 16;
@@ -346,12 +346,13 @@ static void format_shortest(double value, bool is_float, char* out, size_t n) {
         snprintf(buf + len, sizeof(buf) - len, "e%s%02d", exp10 < 0 ? "-" : "", abs(exp10));
     }
     snprintf(out, n, "%s", buf);
+    return true;
 }
 
-void homie_format_float(float value, char* out, size_t n) {
-    format_shortest(value, true, out, n);
+bool homie_format_float(float value, char* out, size_t n) {
+    return format_shortest(value, true, out, n);
 }
 
-void homie_format_double(double value, char* out, size_t n) {
-    format_shortest(value, false, out, n);
+bool homie_format_double(double value, char* out, size_t n) {
+    return format_shortest(value, false, out, n);
 }