faces/totp: improve memory usage

The TOTP face is working in the simulator but fails on the real hardware
when loaded with lots of codes, just like the LFS version.
This is likely caused by the recent refactoring of the TOTP face
which introduced a declarative credential interface for ease of use.
That's accomplished by decoding the secrets at runtime which increases
the RAM requirements. Users are likely hitting memory limits.

In order to mitigate this, the algorithm is changed from decoding
all of the secrets only once during initialization to on the fly
decoding of the secret for the current TOTP credential only.
This converts this face's dynamic memory usage from O(N) to O(1)
at the cost of memory management when switching faces and credentials
which could impact power consumption. Issue is confirmed fixed by
author of issue who has tested it on real hardware. Fixes #384.

Due to variable key sizes, the memory cannot be statically allocated.
Perhaps there's a maximum key size that can serve as worst case?

Also took this opportunity to restructure the code a bit.
Also added code to check for memory allocation failure.

Reported-by: madhogs <59648482+madhogs@users.noreply.github.com>
Fixed-by: Matheus Afonso Martins Moreira <matheus.a.m.moreira@gmail.com>
Tested-by: Matheus Afonso Martins Moreira <matheus.a.m.moreira@gmail.com>
Tested-on-hardware-by: madhogs <59648482+madhogs@users.noreply.github.com>
Signed-off-by: Matheus Afonso Martins Moreira <matheus.a.m.moreira@gmail.com>
GitHub-Issue: https://github.com/joeycastillo/Sensor-Watch/issues/384

2 files changed, 73 insertions, 34 deletions

diff --git a/movement/watch_faces/complication/totp_face.c b/movement/watch_faces/complication/totp_face.c
index 40b083dd..e8e37171 100644
--- a/movement/watch_faces/complication/totp_face.c
+++ b/movement/watch_faces/complication/totp_face.c
@@ -43,14 +43,14 @@ typedef struct {
     unsigned char labels[2];
     hmac_alg algorithm;
     uint32_t period;
-    size_t key_length;
-    unsigned char *key;
+    size_t encoded_key_length;
+    unsigned char *encoded_key;
 } totp_t;
 
 #define CREDENTIAL(label, key_array, algo, timestep) \
     (const totp_t) { \
-        .key = ((unsigned char *) key_array), \
-        .key_length = sizeof(key_array) - 1, \
+        .encoded_key = ((unsigned char *) key_array), \
+        .encoded_key_length = sizeof(key_array) - 1, \
         .period = (timestep), \
         .labels = (#label), \
         .algorithm = (algo), \
@@ -75,6 +75,46 @@ static inline size_t totp_total(void) {
     return sizeof(credentials) / sizeof(*credentials);
 }
 
+static void totp_face_free_current_secret(totp_state_t *totp_state) {
+    if (totp_state->current_decoded_key) {
+        free(totp_state->current_decoded_key);
+        totp_state->current_decoded_key = 0;
+    }
+}
+
+static void totp_face_decode_current_secret(totp_state_t *totp_state) {
+    totp_t *totp = totp_current(totp_state);
+
+    totp_state->current_decoded_key = malloc(UNBASE32_LEN(totp->encoded_key_length));
+    totp_state->current_decoded_key_length = base32_decode(totp->encoded_key, totp_state->current_decoded_key);
+
+    if (totp_state->current_decoded_key_length == 0) {
+        totp_face_free_current_secret(totp_state);
+    }
+}
+
+static bool totp_generate(totp_state_t *totp_state) {
+    if (!totp_state->current_decoded_key) {
+        totp_face_decode_current_secret(totp_state);
+    }
+
+    if (!totp_state->current_decoded_key) {
+        watch_display_string("ERROR", 4);
+        return false;
+    }
+
+    totp_t *totp = totp_current(totp_state);
+
+    TOTP(
+        totp_state->current_decoded_key,
+        totp_state->current_decoded_key_length,
+        totp->period,
+        totp->algorithm
+    );
+
+    return true;
+}
+
 static void totp_display(totp_state_t *totp_state) {
     char buf[14];
     div_t result;
@@ -92,46 +132,33 @@ static void totp_display(totp_state_t *totp_state) {
     watch_display_string(buf, 0);
 }
 
-static void totp_face_decode_secrets(void) {
-    for (size_t n = totp_total(), i = 0; i < n; ++i) {
-        totp_t *totp = &credentials[i];
-        unsigned char *key = totp->key;
-
-        totp->key = malloc(UNBASE32_LEN(totp->key_length));
-        totp->key_length = base32_decode(key, totp->key);
-
-        if (totp->key_length == 0) {
-            free(totp->key);
-            continue;
-        }
-    }
-}
-
 void totp_face_setup(movement_settings_t *settings, uint8_t watch_face_index, void ** context_ptr) {
     (void) settings;
     (void) watch_face_index;
 
     if (*context_ptr == NULL) {
         totp_state_t *totp = malloc(sizeof(totp_state_t));
-        totp_face_decode_secrets();
         *context_ptr = totp;
     }
 }
 
 void totp_face_activate(movement_settings_t *settings, void *context) {
     (void) settings;
-    memset(context, 0, sizeof(totp_state_t));
-    totp_state_t *totp_state = (totp_state_t *)context;
-    totp_t *totp = totp_current(totp_state);
-    TOTP(totp->key, totp->key_length, totp->period, totp->algorithm);
+
+    totp_state_t *totp_state = (totp_state_t *) context;
+    memset(totp_state, 0, sizeof(*totp_state));
+
     totp_state->timestamp = watch_utility_date_time_to_unix_time(watch_rtc_get_date_time(), movement_timezone_offsets[settings->bit.time_zone] * 60);
-    totp_state->current_code = getCodeFromTimestamp(totp_state->timestamp);
+
+    if (totp_generate(totp_state)) {
+        totp_display(totp_state);
+    }
 }
 
 bool totp_face_loop(movement_event_t event, movement_settings_t *settings, void *context) {
     (void) settings;
-    totp_state_t *totp_state = (totp_state_t *)context;
-    totp_t *totp;
+
+    totp_state_t *totp_state = (totp_state_t *) context;
 
     switch (event.event_type) {
         case EVENT_TICK:
@@ -144,26 +171,34 @@ bool totp_face_loop(movement_event_t event, movement_settings_t *settings, void
             movement_move_to_face(0);
             break;
         case EVENT_ALARM_BUTTON_UP:
+            totp_face_free_current_secret(totp_state);
+
             if (totp_state->current_index + 1 < totp_total()) {
                 totp_state->current_index++;
             } else {
                 // wrap around to first key
                 totp_state->current_index = 0;
             }
-            totp = totp_current(totp_state);
-            TOTP(totp->key, totp->key_length, totp->period, totp->algorithm);
-            totp_display(totp_state);
+
+            if (totp_generate(totp_state)) {
+                totp_display(totp_state);
+            }
+
             break;
         case EVENT_LIGHT_BUTTON_UP:
+            totp_face_free_current_secret(totp_state);
+
             if (totp_state->current_index == 0) {
                 // Wrap around to the last credential.
                 totp_state->current_index = totp_total() - 1;
             } else {
                 totp_state->current_index--;
             }
-            totp = totp_current(totp_state);
-            TOTP(totp->key, totp->key_length, totp->period, totp->algorithm);
-            totp_display(totp_state);
+
+            if (totp_generate(totp_state)) {
+                totp_display(totp_state);
+            }
+
             break;
         case EVENT_ALARM_BUTTON_DOWN:
         case EVENT_ALARM_LONG_PRESS:
@@ -182,5 +217,7 @@ bool totp_face_loop(movement_event_t event, movement_settings_t *settings, void
 
 void totp_face_resign(movement_settings_t *settings, void *context) {
     (void) settings;
-    (void) context;
+
+    totp_state_t *totp_state = (totp_state_t *) context;
+    totp_face_free_current_secret(totp_state);
 }
diff --git a/movement/watch_faces/complication/totp_face.h b/movement/watch_faces/complication/totp_face.h
index af269e92..19a2cd45 100644
--- a/movement/watch_faces/complication/totp_face.h
+++ b/movement/watch_faces/complication/totp_face.h
@@ -70,6 +70,8 @@ typedef struct {
     uint8_t steps;
     uint32_t current_code;
     uint8_t current_index;
+    uint8_t *current_decoded_key;
+    size_t current_decoded_key_length;
 } totp_state_t;
 
 void totp_face_setup(movement_settings_t *settings, uint8_t watch_face_index, void ** context_ptr);