Add config component with hostname setting

components/config/CMakeLists.txt

@@ -0,0 +1,5 @@
+idf_component_register(
+  SRCS "config.c"
+  INCLUDE_DIRS "."
+  REQUIRES fatal nvs_flash
+)

components/config/config.c

@@ -0,0 +1,159 @@
+/*
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Copyright (c) Camden Dixie O'Brien
+ */
+
+#include "config.h"
+
+#include "fatal.h"
+
+#include "esp_log.h"
+#include "nvs_flash.h"
+#include <stdbool.h>
+#include <string.h>
+
+#define TAG "Config"
+
+#define NAMESPACE "config"
+#define MAX_CONSUMERS 8
+
+#define DEFAULT_HOSTNAME "bedside-clock"
+#define HOSTNAME_KEY "hostname"
+
+typedef struct {
+	char hostname[MAX_HOSTNAME_SIZE];
+} Config;
+
+typedef struct {
+	ConfigStringCallback callbacks[MAX_CONSUMERS];
+	unsigned count;
+} StringConsumers;
+
+typedef struct {
+	Config config;
+	StringConsumers hostname_consumers;
+} State;
+
+static State state;
+
+static bool load_hostname()
+{
+	esp_err_t error;
+
+	nvs_handle_t handle;
+	error = nvs_open(NAMESPACE, NVS_READONLY, &handle);
+	if (error == ESP_ERR_NVS_NOT_FOUND)
+		return false;
+	if (error != ESP_OK) {
+		ESP_LOGE(TAG, "Error opening NVS: %04x", error);
+		return false;
+	}
+
+	size_t size = MAX_HOSTNAME_SIZE;
+	error = nvs_get_str(handle, HOSTNAME_KEY, state.config.hostname, &size);
+	if (error != ESP_OK) {
+		ESP_LOGE(TAG, "Error loading hostname from storage: %04x", error);
+		nvs_close(handle);
+		return false;
+	}
+
+	nvs_close(handle);
+	return true;
+}
+
+static void save_hostname()
+{
+	esp_err_t error;
+
+	nvs_handle_t handle;
+	error = nvs_open(NAMESPACE, NVS_READWRITE, &handle);
+	if (error == ESP_ERR_NVS_NOT_FOUND)
+		return;
+	if (error != ESP_OK) {
+		ESP_LOGE(TAG, "Error opening NVS: %04x", error);
+		return;
+	}
+
+	error = nvs_set_str(handle, HOSTNAME_KEY, state.config.hostname);
+	if (error != ESP_OK) {
+		ESP_LOGE(TAG, "Error loading hostname from storage: %04x", error);
+		nvs_close(handle);
+		return;
+	}
+
+	error = nvs_commit(handle);
+	if (error != ESP_OK)
+		ESP_LOGE(TAG, "Error commiting NVS update: %04x", error);
+
+	nvs_close(handle);
+}
+
+void config_init()
+{
+	esp_err_t error;
+
+	error = nvs_flash_init();
+	if (error == ESP_ERR_NVS_NO_FREE_PAGES
+	    || error == ESP_ERR_NVS_NEW_VERSION_FOUND) {
+		ESP_LOGI(TAG, "NVS partition full or outdated; erasing");
+		(void)nvs_flash_erase();
+		error = nvs_flash_init();
+	}
+	if (error != ESP_OK) {
+		ESP_LOGE(TAG, "Error initializing NVS store: %04x", error);
+		FATAL();
+	}
+
+	memset(&state, 0, sizeof(state));
+
+	if (!load_hostname()) {
+		config_set_hostname(DEFAULT_HOSTNAME);
+		save_hostname();
+	}
+}
+
+void config_set_hostname(const char *hostname)
+{
+	if (hostname == NULL) {
+		ESP_LOGW(TAG, "Null pointer passed to %s(); ignored", __func__);
+		return;
+	}
+	size_t len = strlen(hostname);
+	if (len >= MAX_HOSTNAME_SIZE) {
+		ESP_LOGW(
+		    TAG, "Hostname \"%s\" exceeds maximum size; truncated",
+		    hostname);
+		len = MAX_HOSTNAME_SIZE - 1;
+	}
+
+	memcpy(state.config.hostname, hostname, len);
+	state.config.hostname[len] = '\0';
+
+	save_hostname();
+
+	for (unsigned i = 0; i < state.hostname_consumers.count; ++i)
+		state.hostname_consumers.callbacks[i](state.config.hostname);
+}
+
+size_t config_get_hostname(char *buffer, size_t buffer_size)
+{
+	size_t len = strlen(state.config.hostname);
+	if (len < buffer_size) {
+		memcpy(buffer, state.config.hostname, len);
+		buffer[len] = '\0';
+	}
+	return len;
+}
+
+void config_add_hostname_consumer(ConfigStringCallback callback)
+{
+	if (callback == NULL) {
+	} else if (state.hostname_consumers.count >= MAX_CONSUMERS) {
+		ESP_LOGE(
+		    TAG, "Max consumers exceeded for hostname; callback discarded");
+	} else {
+		state.hostname_consumers.callbacks[state.hostname_consumers.count]
+		    = callback;
+		++state.hostname_consumers.count;
+	}
+}

components/config/config.h

@@ -0,0 +1,54 @@
+/*
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Copyright (c) Camden Dixie O'Brien
+ */
+
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#include <stddef.h>
+
+#define MAX_HOSTNAME_SIZE 32
+
+/**
+ * Callback type for consumers of string settings.
+ */
+typedef void (*ConfigStringCallback)(const char *value);
+
+/**
+ * Initialize the configuration module.
+ *
+ * If there is a saved configuration, it will be loaded. Otherwise,
+ * the default configuration will be loaded and saved.
+ */
+void config_init();
+
+/**
+ * Set the device's hostname.
+ *
+ * The argument should be a null-terminated string. If the maximum
+ * length is exceeded, the value will still be used, but will be
+ * truncated.
+ */
+void config_set_hostname(const char *hostname);
+
+/**
+ * Write the device's hostname into the given buffer.
+ *
+ * The length of the hostname is returned. If the value's size exceeds
+ * the size of the buffer, nothing will be written to the buffer but
+ * the length is still returned.
+ */
+size_t config_get_hostname(char *buffer, size_t buffer_size);
+
+/**
+ * Add a callback for hostname updates.
+ *
+ * The function specified in the argument will be invoked whenever a
+ * the hostname is updated, with the new value as its argument. The
+ * lifetime of the passed argument will be static, but the value may
+ * be modified once the callback returns.
+ */
+void config_add_hostname_callback(ConfigStringCallback callback);
+
+#endif

main/CMakeLists.txt

@@ -1,5 +1,5 @@
 idf_component_register(
   SRCS "main.c"
   INCLUDE_DIRS "."
-  REQUIRES fatal
+  REQUIRES config
 )

main/main.c

@@ -3,9 +3,9 @@
  * Copyright (c) Camden Dixie O'Brien
  */
 
-#include "fatal.h"
+#include "config.h"
 
 void app_main(void)
 {
-	FATAL();
+	config_init();
 }