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NFC: Improve URI decoding in NDEF parser (#267)

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* add decode_char

* Skip double malloc(), can just tell printf() how long the string is

* Decode URI within the same buffer

* Only decode if next 2 chars are valid hex

* Update changelog

* Clearer code for hex decode

Co-authored-by: jaylikesbunda <jaylikesbunda@users.noreply.github.com>

---------

Co-authored-by: Willy-JL <49810075+Willy-JL@users.noreply.github.com>
Co-authored-by: jaylikesbunda <jaylikesbunda@users.noreply.github.com>
This commit is contained in:
jay candel
2024-10-20 13:28:10 +08:00
committed by GitHub
parent 3e17d6588a
commit 7ebbadfbf8
2 changed files with 41 additions and 15 deletions
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55
applications/main/nfc/plugins/supported_cards/ndef.c
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@@ -27,11 +27,7 @@ static void
print_data(FuriString* str, const char* prefix, const uint8_t* buf, size_t len, bool force_hex) {
if(prefix) furi_string_cat_printf(str, "%s: ", prefix);
if(!force_hex && is_text(buf, len)) {
char* tmp = malloc(len + 1);
memcpy(tmp, buf, len);
tmp[len] = '\0';
furi_string_cat_printf(str, "%s", tmp);
free(tmp);
furi_string_cat_printf(str, "%.*s", len, buf);
} else {
for(uint8_t i = 0; i < len; i++) {
furi_string_cat_printf(str, "%02X ", buf[i]);
@@ -40,6 +36,17 @@ static void
furi_string_cat(str, "\n");
}
static inline uint8_t hex_to_int(char c) {
if(c >= '0' && c <= '9') return c - '0';
if(c >= 'A' && c <= 'F') return c - 'A' + 10;
if(c >= 'a' && c <= 'f') return c - 'a' + 10;
return 0;
}
static char decode_char(const char* str) {
return (hex_to_int(str[1]) << 4) | hex_to_int(str[2]);
}
static void parse_ndef_uri(FuriString* str, const uint8_t* payload, uint32_t payload_len) {
// https://learn.adafruit.com/adafruit-pn532-rfid-nfc/ndef#uri-records-0x55-slash-u-607763
const char* prepends[] = {
@@ -88,26 +95,44 @@ static void parse_ndef_uri(FuriString* str, const uint8_t* payload, uint32_t pay
size_t prepend_len = strlen(prepend);
size_t uri_len = prepend_len + (payload_len - 1);
char* const uri_buf = malloc(uri_len);
char* const uri_buf = malloc(uri_len); // const to keep the original pointer to free later
memcpy(uri_buf, prepend, prepend_len);
memcpy(uri_buf + prepend_len, payload + 1, payload_len - 1);
char* uri = uri_buf;
char* uri = uri_buf; // cursor we can iterate and shift freely
// Encoded chars take 3 bytes (%AB), decoded chars take 1 byte
// We can decode by iterating and overwriting the same buffer
size_t decoded_len = 0;
for(size_t encoded_idx = 0; encoded_idx < uri_len; encoded_idx++) {
if(uri[encoded_idx] == '%' && encoded_idx + 2 < uri_len) {
char hi = toupper(uri[encoded_idx + 1]);
char lo = toupper(uri[encoded_idx + 2]);
if(((hi >= 'A' && hi <= 'F') || (hi >= '0' && hi <= '9')) &&
((lo >= 'A' && lo <= 'F') || (lo >= '0' && lo <= '9'))) {
uri[decoded_len++] = decode_char(&uri[encoded_idx]);
encoded_idx += 2;
continue;
}
}
uri[decoded_len++] = uri[encoded_idx];
}
const char* type = "URI";
if(strncmp(uri, "http", strlen("http")) == 0) {
if(strncmp(uri, "http", 4) == 0) {
type = "URL";
} else if(strncmp(uri, "tel:", strlen("tel:")) == 0) {
} else if(strncmp(uri, "tel:", 4) == 0) {
type = "Phone";
uri += strlen("tel:");
uri_len -= strlen("tel:");
} else if(strncmp(uri, "mailto:", strlen("mailto:")) == 0) {
uri += 4;
decoded_len -= 4;
} else if(strncmp(uri, "mailto:", 7) == 0) {
type = "Mail";
uri += strlen("mailto:");
uri_len -= strlen("mailto:");
uri += 7;
decoded_len -= 7;
}
furi_string_cat_printf(str, "%s\n", type);
print_data(str, NULL, (uint8_t*)uri, uri_len, false);
print_data(str, NULL, (uint8_t*)uri, decoded_len, false);
free(uri_buf);
}