Improve prometheus metrics generation reliability

That means it shouldn't crash with multiple request types to the same
URI anymore.

Additional changes:
 * Add esptherm_version header containing the current commit hash
 * Add constexpr uint to str utility
 * Add esptherm_build_info metric to metrics page
   * This metrics has the labels esptherm_commit, mcu_type,
arduino_version, sdk_version, and cpp_std_version.

.gitignore

@@ -19,3 +19,6 @@ wifipass.txt
 otapass.txt
 mqttuser.txt
 mqttpass.txt
+
+# This file changes every commit.
+src/generated/esptherm_version.h

TODO.md

@@ -33,7 +33,7 @@ Not all of these are necessarily going to be implemented at all.
  * Add MQTT discovery support(https://www.home-assistant.io/docs/mqtt/discovery/)
  * Dynamically gzip compress metrics page?
  * Implement actual prometheus library as external project
- * Add prometheus info metrics esptherm_build_info, esptherm_network_info, esptherm_module_info, and esptherm_sensor_info
+ * Add prometheus info metrics esptherm_network_info, esptherm_module_info, and esptherm_sensor_info
  * Add MQTT metrics to prometheus
  * Add prometheus metrics for HTTP response times and sizes
  * Add prometheus metrics for push statistics, if DSM is disabled

lib/utils/include/utils.h

@@ -76,9 +76,62 @@ constexpr size_t strlen(const char *str) {
 #endif
 
 /**
- * EXPAND_MACRO is a utility macro to expand a macro to its string form.
+ * MACRO_TO_STRING is a utility macro to convert a macro to its string form.
  */
-#define EXPAND_MACRO(macro) #macro
+#define MACRO_TO_STRING(macro) #macro
+
+/**
+ * EXPAND_MACRO is a utility macro to expand a macro value to its string form.
+ */
+#define EXPAND_MACRO(macro) MACRO_TO_STRING(macro)
+
+namespace utils {
+/**
+ * A helper struct to convert a set of digits to a C string.
+ *
+ * @tparam digits	The digits to convert to a string.
+ */
+template<uint8_t... digits>
+struct digits_to_chars { static const char value[]; };
+
+/**
+ * A helper struct to convert a set of digits to a C string.
+ *
+ * @tparam digits	The digits to convert to a string.
+ */
+template<uint8_t... digits>
+const char digits_to_chars<digits...>::value[] = {('0' + digits)..., 0};
+
+/**
+ * A helper struct separating a number into separate digits.
+ *
+ * @tparam rem		The remainder that is yet to be separated.
+ * @tparam digits	The digits to convert to a string.
+ */
+template<uint64_t rem, uint8_t... digits>
+struct explode : explode<rem / 10, rem % 10, digits...> {};
+
+/**
+ * A helper struct separating a number into separate digits.
+ *
+ * @tparam digits	The digits to convert to a string.
+ */
+template<uint8_t... digits>
+struct explode<0, digits...> : digits_to_chars<digits...> {};
+
+/**
+ * A helper struct converting an unsigned number to a string.
+ *
+ * @tparam num	The digits to convert to a string.
+ */
+template<uint64_t num>
+struct unsigned_to_string : explode<num / 10, num % 10> {};
+} /* namespace utils */
+
+/**
+ * UNSIGNED_TO_STRING is a helper macro converting an unsigned number to a constexpr string.
+ */
+#define UNSIGNED_TO_STRING(exp) utils::unsigned_to_string<exp>::value
 
 namespace utils {
 /**

platformio.ini

@@ -31,6 +31,7 @@ upload_speed = 921600
 extra_scripts =
 	pre:shared/compress_web.py
 	pre:shared/generate_hash_header.py
+	pre:shared/generate_version_header.py
 lib_deps =
 	ArduinoOTA
 	ESPAsyncWebServer = https://github.com/me-no-dev/ESPAsyncWebServer.git
@@ -52,6 +53,7 @@ board_build.embed_files =
 	data/gzip/favicon.ico.gz
 	data/gzip/favicon.png.gz
 	data/gzip/favicon.svg.gz
+; The C++ version is a default for platforms that don't specify one.
 build_flags =
 	-std=c++11
 	-Wall
@@ -126,7 +128,7 @@ build_flags =
 [env:esp_wroom_02_ota]
 extends = env:esp_wroom_02
 upload_protocol = espota
-upload_port = esp-wifi-Thermometer.local
+upload_port = esp-wifi-thermometer.local
 extra_scripts =
     ${env.extra_scripts}
     post:shared/read_ota_pass.py

shared/generate_hash_header.py

@@ -62,14 +62,15 @@ def generate_hash_header(hashes: Dict[str, str]) -> None:
     """Generates the header file containing the hashes of the static files.
 
     Generates a header file, in src/generated, containing constant definitions with the hashes of the static files.
-    
+
     @param hashes: The filenames and hashes to generate the header for.
+    @raise IOError: If opening or writing the header file fails.
     """
 
     print("Generating " + path.relpath(hash_header_path, env.subst("$PROJECT_ROOT"))) # type: ignore[name-defined]
 
-    header = open(hash_header_path, 'w')
-    header.write(
+    with open(hash_header_path, 'w') as header:
+        header.write(
 """/*
  * web_file_hashes.h
  *
@@ -86,21 +87,21 @@ def generate_hash_header(hashes: Dict[str, str]) -> None:
 
 """)
 
-    for file, hash in hashes.items():
-        header.write(
+        for file, hash in hashes.items():
+            header.write(
 f"""/**
  * The md5 hash of the file "{file}".
  */
 """)
 
-        id: str = file.upper()
-        for c in ['.', '-', '/', ' ']:
-            id = id.replace(c, '_')
+            id: str = file.upper()
+            for c in ['.', '-', '/', ' ']:
+                id = id.replace(c, '_')
 
-        header.write(f"static constexpr const char {id}_HASH[] = \"{hash}\";")
-        header.write(os.linesep + os.linesep)
+            header.write(f"static constexpr const char {id}_HASH[] = \"{hash}\";")
+            header.write(os.linesep + os.linesep)
 
-    header.write("#endif /* SRC_GENERATED_WEB_FILE_HASHES_H_ */" + os.linesep)
+        header.write("#endif /* SRC_GENERATED_WEB_FILE_HASHES_H_ */" + os.linesep)
 
 
 def main() -> int:

shared/generate_version_header.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3 
+
+import os
+from os import path
+import subprocess
+import sys
+from typing import Final
+from subprocess import CalledProcessError
+
+try:
+    Import ("env")  # type: ignore[name-defined]
+except:
+    print("Failed to load platformio environment!", file=sys.stderr)
+    sys.exit(1)
+
+# The path of the header file to generated.
+version_header_path: Final[str] = path.join(env.subst('$PROJECT_SRC_DIR'), 'generated', 'esptherm_version.h')  # type: ignore[name-defined]
+
+
+def check_git():
+    """Checks whether the git command is available.
+    
+    Tries to run "git --version" and exits the script if it fails.
+    """
+    try:
+        subprocess.check_call(['git', '--version'])
+    except CalledProcessError:
+        print("Could not execute git. Is there a git executable on the PATH?", file=sys.stderr)
+        sys.exit(1)
+
+def get_short_hash() -> str:
+    """Gets the current commit short-hash.
+
+    Runs "git rev-parse --short HEAD" to get the current git commit short-hash.
+    @return The current commit hash.
+    @raise CalledProcessError: If the command returns a non-zero exit-code.
+    """
+    return subprocess.check_output(['git', 'rev-parse', '--short', 'HEAD'], text=True).strip()
+
+
+def generate_version_header(commit: str) -> None:
+    """Generates the header file containing the hashes of the static files.
+
+    Generates a header file, in src/generated, containing constant definitions with the hashes of the static files.
+
+    @raise IOError: If opening or writing the header file fails.
+    """
+
+    print("Generating " + path.relpath(version_header_path, env.subst("$PROJECT_ROOT")))  # type: ignore[name-defined]
+
+    with open(version_header_path, 'w') as header:
+        header.write(
+"""/*
+ * esptherm_version.h
+ *
+ * **Warning:** This file is automatically generated, and should not be edited manually.
+ *
+ * This file contains version information about the ESP-WiFi-Thermometer.
+ * At the moment it only contains the commit hash, but once there are versioned releases it will also contain the version numbers.
+ *
+ * This project is licensed under the MIT License.
+ * The MIT license can be found in the project root and at https://opensource.org/licenses/MIT.
+ */
+
+#ifndef SRC_GENERATED_ESPTHERM_VERSION_H_
+#define SRC_GENERATED_ESPTHERM_VERSION_H_
+
+""")
+
+        header.write(
+f"""/**
+ * The short hash of the ESP-WiFi-Thermometer git commit that was used for this build.
+ */
+static constexpr const char *ESPTHERM_COMMIT = "{commit}";
+
+""")
+
+        header.write("#endif /* SRC_GENERATED_ESPTHERM_VERSION_H_ */" + os.linesep)
+
+
+def main() -> int:
+    """The main entrypoint of this script.
+
+    The main function generating the version header file.
+
+    @return Zero if nothing goes wrong.
+    @raise IOError: If opening or reading the file fails.
+    """
+    check_git()
+    commit: str = ""
+    try:
+        commit = get_short_hash()
+    except CalledProcessError as e:
+        print(f"Failed to determine git hash. Process failed with exit code {e.returncode}.", file=sys.stderr)
+        return 1
+
+    generate_version_header(commit)
+
+    return 0
+
+
+if __name__ == '__main__' or __name__ == 'SCons.Script':
+    error: int = main()
+    if error != 0:
+        sys.exit(error)