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[core] Extract base64_decode_quad_ to deduplicate base64 decode logic

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The base64 character-to-byte conversion and output copy loop were
duplicated in both the main decode loop and the tail/padding path.
Extract into a shared static helper to reduce flash usage (-64 bytes
on ESP32) and eliminate duplicated logic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
J. Nick Koston
2026-02-20 00:07:20 -06:00
co-authored by Claude Opus 4.6
parent 7a14f30710 9a028f37ba
commit 4b53f6ef2b
1 changed files with 25 additions and 31 deletions
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esphome/core/helpers.cpp
+25 -31
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@@ -597,13 +597,33 @@ size_t base64_decode(const std::string &encoded_string, uint8_t *buf, size_t buf
return base64_decode(reinterpret_cast<const uint8_t *>(encoded_string.data()), encoded_string.size(), buf, buf_len);
}
// Decode 4 base64 characters to up to 'count' output bytes, returns true if truncated
static inline bool base64_decode_quad_(uint8_t *char_array_4, int count, uint8_t *buf, size_t buf_len, size_t &out) {
for (int i = 0; i < 4; i++)
char_array_4[i] = base64_find_char(char_array_4[i]);
uint8_t char_array_3[3];
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
bool truncated = false;
for (int j = 0; j < count; j++) {
if (out < buf_len) {
buf[out++] = char_array_3[j];
} else {
truncated = true;
}
}
return truncated;
}
size_t base64_decode(const uint8_t *encoded_data, size_t encoded_len, uint8_t *buf, size_t buf_len) {
size_t in_len = encoded_len;
int i = 0;
int j = 0;
size_t in = 0;
size_t out = 0;
uint8_t char_array_4[4], char_array_3[3];
uint8_t char_array_4[4];
bool truncated = false;
// SAFETY: The loop condition checks is_base64() before processing each character.
@@ -613,42 +633,16 @@ size_t base64_decode(const uint8_t *encoded_data, size_t encoded_len, uint8_t *b
char_array_4[i++] = encoded_data[in];
in++;
if (i == 4) {
for (i = 0; i < 4; i++)
char_array_4[i] = base64_find_char(char_array_4[i]);
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
for (i = 0; i < 3; i++) {
if (out < buf_len) {
buf[out++] = char_array_3[i];
} else {
truncated = true;
}
}
truncated |= base64_decode_quad_(char_array_4, 3, buf, buf_len, out);
i = 0;
}
}
if (i) {
for (j = i; j < 4; j++)
for (int j = i; j < 4; j++)
char_array_4[j] = 0;
for (j = 0; j < 4; j++)
char_array_4[j] = base64_find_char(char_array_4[j]);
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
for (j = 0; j < i - 1; j++) {
if (out < buf_len) {
buf[out++] = char_array_3[j];
} else {
truncated = true;
}
}
truncated |= base64_decode_quad_(char_array_4, i - 1, buf, buf_len, out);
}
if (truncated) {