base: add base64.cc
Add a dedicated base64 translation unit for both encoding
and decoding. Will be used by follow-up CLs.
Also refactor existing code currently using base64
from string_utils.cc.
Bug: 205274609
Change-Id: I8ce97dd09fc1707c9989c0f148bd972b805d4b49
diff --git a/src/base/base64.cc b/src/base/base64.cc
new file mode 100644
index 0000000..437ad67
--- /dev/null
+++ b/src/base/base64.cc
@@ -0,0 +1,153 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "perfetto/ext/base/base64.h"
+
+namespace perfetto {
+namespace base {
+
+namespace {
+
+constexpr char kPadding = '=';
+
+constexpr char kEncTable[] =
+ "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+static_assert(sizeof(kEncTable) == (1u << 6) + sizeof('\0'), "Bad table size");
+
+// Maps an ASCII character to its 6-bit value. It only contains translations
+// from '+' to 'z'. Supports the standard (+/) and URL-safe (-_) alphabets.
+constexpr uint8_t kX = 0xff; // Value used for invalid characters
+constexpr uint8_t kDecTable[] = {
+ 62, kX, 62, kX, 63, 52, 53, 54, 55, 56, // 00 - 09
+ 57, 58, 59, 60, 61, kX, kX, kX, 0, kX, // 10 - 19
+ kX, kX, 0, 1, 2, 3, 4, 5, 6, 7, // 20 - 29
+ 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, // 30 - 39
+ 18, 19, 20, 21, 22, 23, 24, 25, kX, kX, // 40 - 49
+ kX, kX, 63, kX, 26, 27, 28, 29, 30, 31, // 50 - 59
+ 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, // 60 - 69
+ 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // 70 - 79
+};
+constexpr char kMinDecChar = '+';
+constexpr char kMaxDecChar = 'z';
+static_assert(kMaxDecChar - kMinDecChar <= sizeof(kDecTable), "Bad table size");
+
+inline uint8_t DecodeChar(char c) {
+ if (c < kMinDecChar || c > kMaxDecChar)
+ return kX;
+ return kDecTable[c - kMinDecChar];
+}
+
+} // namespace
+
+ssize_t Base64Encode(const void* src,
+ size_t src_size,
+ char* dst,
+ size_t dst_size) {
+ const size_t padded_dst_size = Base64EncSize(src_size);
+ if (dst_size < padded_dst_size)
+ return -1; // Not enough space in output.
+
+ const uint8_t* rd = static_cast<const uint8_t*>(src);
+ const uint8_t* const end = rd + src_size;
+ size_t wr_size = 0;
+ while (rd < end) {
+ uint8_t s[3]{};
+ s[0] = *(rd++);
+ dst[wr_size++] = kEncTable[s[0] >> 2];
+
+ uint8_t carry0 = static_cast<uint8_t>((s[0] & 0x03) << 4);
+ if (PERFETTO_LIKELY(rd < end)) {
+ s[1] = *(rd++);
+ dst[wr_size++] = kEncTable[carry0 | (s[1] >> 4)];
+ } else {
+ dst[wr_size++] = kEncTable[carry0];
+ dst[wr_size++] = kPadding;
+ dst[wr_size++] = kPadding;
+ break;
+ }
+
+ uint8_t carry1 = static_cast<uint8_t>((s[1] & 0x0f) << 2);
+ if (PERFETTO_LIKELY(rd < end)) {
+ s[2] = *(rd++);
+ dst[wr_size++] = kEncTable[carry1 | (s[2] >> 6)];
+ } else {
+ dst[wr_size++] = kEncTable[carry1];
+ dst[wr_size++] = kPadding;
+ break;
+ }
+
+ dst[wr_size++] = kEncTable[s[2] & 0x3f];
+ }
+ PERFETTO_DCHECK(wr_size == padded_dst_size);
+ return static_cast<ssize_t>(padded_dst_size);
+}
+
+std::string Base64Encode(const void* src, size_t src_size) {
+ std::string dst;
+ dst.resize(Base64EncSize(src_size));
+ auto res = Base64Encode(src, src_size, &dst[0], dst.size());
+ PERFETTO_CHECK(res == static_cast<ssize_t>(dst.size()));
+ return dst;
+}
+
+ssize_t Base64Decode(const char* src,
+ size_t src_size,
+ uint8_t* dst,
+ size_t dst_size) {
+ const size_t min_dst_size = Base64DecSize(src_size);
+ if (dst_size < min_dst_size)
+ return -1;
+
+ const char* rd = src;
+ const char* const end = src + src_size;
+ size_t wr_size = 0;
+
+ char s[4]{};
+ while (rd < end) {
+ uint8_t d[4];
+ for (uint32_t j = 0; j < 4; j++) {
+ // Padding is only feasible for the last 2 chars of each group of 4.
+ s[j] = rd < end ? *(rd++) : (j < 2 ? '\0' : kPadding);
+ d[j] = DecodeChar(s[j]);
+ if (d[j] == kX)
+ return -1; // Invalid input char.
+ }
+ dst[wr_size] = static_cast<uint8_t>((d[0] << 2) | (d[1] >> 4));
+ dst[wr_size + 1] = static_cast<uint8_t>((d[1] << 4) | (d[2] >> 2));
+ dst[wr_size + 2] = static_cast<uint8_t>((d[2] << 6) | (d[3]));
+ wr_size += 3;
+ }
+
+ PERFETTO_CHECK(wr_size <= dst_size);
+ wr_size -= (s[3] == kPadding ? 1 : 0) + (s[2] == kPadding ? 1 : 0);
+ return static_cast<ssize_t>(wr_size);
+}
+
+Optional<std::string> Base64Decode(const char* src, size_t src_size) {
+ std::string dst;
+ dst.resize(Base64DecSize(src_size));
+ auto res = Base64Decode(src, src_size, reinterpret_cast<uint8_t*>(&dst[0]),
+ dst.size());
+ if (res < 0)
+ return nullopt; // Decoding error.
+
+ PERFETTO_CHECK(res <= static_cast<ssize_t>(dst.size()));
+ dst.resize(static_cast<size_t>(res));
+ return make_optional(dst);
+}
+
+} // namespace base
+} // namespace perfetto
