AAPT2: Encode 4-byte strings in Modified UTF-8
Codepoints that are encoded to 4 bytes in UTF-8 are not allowed in
Modified UTF-8. They instead should be encoded as surrogate pairs in the
same way that CESU-8 allows for surrogate pairs. This will also cause 4
byte UTF-8 codes to be represented in 6 bytes.
Bug: 37140916
Test: aapt2_tests
Change-Id: I155dc24f166139d1d36a16bac088dcfcd59eb321
diff --git a/tools/aapt2/util/Util.cpp b/tools/aapt2/util/Util.cpp
index d1c9ca1..9bef54e5 100644
--- a/tools/aapt2/util/Util.cpp
+++ b/tools/aapt2/util/Util.cpp
@@ -297,6 +297,53 @@
return true;
}
+std::string Utf8ToModifiedUtf8(const std::string& utf8) {
+ // Java uses Modified UTF-8 which only supports the 1, 2, and 3 byte formats of UTF-8. To encode
+ // 4 byte UTF-8 codepoints, Modified UTF-8 allows the use of surrogate pairs in the same format
+ // of CESU-8 surrogate pairs. Calculate the size of the utf8 string with all 4 byte UTF-8
+ // codepoints replaced with 2 3 byte surrogate pairs
+ size_t modified_size = 0;
+ const size_t size = utf8.size();
+ for (size_t i = 0; i < size; i++) {
+ if (((uint8_t) utf8[i] >> 4) == 0xF) {
+ modified_size += 6;
+ i += 3;
+ } else {
+ modified_size++;
+ }
+ }
+
+ // Early out if no 4 byte codepoints are found
+ if (size == modified_size) {
+ return utf8;
+ }
+
+ std::string output;
+ output.reserve(modified_size);
+ for (size_t i = 0; i < size; i++) {
+ if (((uint8_t) utf8[i] >> 4) == 0xF) {
+ auto codepoint = (char32_t) utf32_from_utf8_at(utf8.data(), size, i, nullptr);
+
+ // Calculate the high and low surrogates as UTF-16 would
+ char32_t high = ((codepoint - 0x10000) / 0x400) + 0xD800;
+ char32_t low = ((codepoint - 0x10000) % 0x400) + 0xDC00;
+
+ // Encode each surrogate in UTF-8
+ output.push_back((char) (0xE4 | ((high >> 12) & 0xF)));
+ output.push_back((char) (0x80 | ((high >> 6) & 0x3F)));
+ output.push_back((char) (0x80 | (high & 0x3F)));
+ output.push_back((char) (0xE4 | ((low >> 12) & 0xF)));
+ output.push_back((char) (0x80 | ((low >> 6) & 0x3F)));
+ output.push_back((char) (0x80 | (low & 0x3F)));
+ i += 3;
+ } else {
+ output.push_back(utf8[i]);
+ }
+ }
+
+ return output;
+}
+
std::u16string Utf8ToUtf16(const StringPiece& utf8) {
ssize_t utf16_length = utf8_to_utf16_length(
reinterpret_cast<const uint8_t*>(utf8.data()), utf8.length());