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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/base64.h"
#include <stddef.h>
#include <string_view>
#include "base/check.h"
#include "base/numerics/checked_math.h"
#include "base/strings/string_util.h"
#include "third_party/modp_b64/modp_b64.h"
namespace base {
namespace {
ModpDecodePolicy GetModpPolicy(Base64DecodePolicy policy) {
switch (policy) {
case Base64DecodePolicy::kStrict:
return ModpDecodePolicy::kStrict;
case Base64DecodePolicy::kForgiving:
return ModpDecodePolicy::kForgiving;
}
}
} // namespace
std::string Base64Encode(span<const uint8_t> input) {
std::string output;
Base64EncodeAppend(input, &output);
return output;
}
void Base64EncodeAppend(span<const uint8_t> input, std::string* output) {
// Ensure `modp_b64_encode_data_len` will not overflow.
CHECK_LE(input.size(), MODP_B64_MAX_INPUT_LEN);
size_t encode_data_len = modp_b64_encode_data_len(input.size());
const size_t after_size =
base::CheckAdd(encode_data_len, output->size()).ValueOrDie();
output->resize(after_size);
span<const char> read = base::as_chars(input);
span<char> write = base::span(*output).last(encode_data_len);
const size_t written_size = modp_b64_encode_data(
write.data(), // This must point to `encode_data_len` many chars.
read.data(), read.size());
// If this failed it would indicate we wrote OOB or left bytes uninitialized.
// It's possible for this to be elided by the compiler, since writing OOB is
// UB.
CHECK_EQ(written_size, write.size());
}
std::string Base64Encode(std::string_view input) {
return Base64Encode(base::as_byte_span(input));
}
bool Base64Decode(std::string_view input,
std::string* output,
Base64DecodePolicy policy) {
std::string decode_buf;
decode_buf.resize(modp_b64_decode_len(input.size()));
// Does not NUL-terminate result since result is binary data!
size_t written_size = modp_b64_decode(decode_buf.data(), input.data(),
input.size(), GetModpPolicy(policy));
// Forgiving mode requires whitespace to be stripped prior to decoding.
// We don't do that in the above code to ensure that the "happy path" of
// input without whitespace is as fast as possible. Since whitespace in input
// will always cause `modp_b64_decode` to fail, just handle whitespace
// stripping on failure. This is not much slower than just scanning for
// whitespace first, even for input with whitespace.
if (written_size == MODP_B64_ERROR &&
policy == Base64DecodePolicy::kForgiving) {
// We could use `output` here to avoid an allocation when decoding is done
// in-place, but it violates the API contract that `output` is only modified
// on success.
std::string input_without_whitespace;
RemoveChars(input,
std::string_view(std::begin(kInfraAsciiWhitespace),
std::end(kInfraAsciiWhitespace)),
&input_without_whitespace);
// This means that the required size to decode is at most what was needed
// above, which means `decode_buf` will fit the decoded bytes at its current
// size and we don't need to call `modp_b64_decode_len()` again.
CHECK_LE(input_without_whitespace.size(), input.size());
written_size =
modp_b64_decode(decode_buf.data(), input_without_whitespace.data(),
input_without_whitespace.size(), GetModpPolicy(policy));
}
if (written_size == MODP_B64_ERROR) {
return false;
}
// If this failed it would indicate we wrote OOB. It's possible for this to be
// elided by the compiler, since writing OOB is UB.
CHECK_LE(written_size, decode_buf.size());
// Shrinks the buffer and makes it NUL-terminated.
decode_buf.resize(written_size);
*output = std::move(decode_buf);
return true;
}
std::optional<std::vector<uint8_t>> Base64Decode(std::string_view input) {
std::vector<uint8_t> write_buf(modp_b64_decode_len(input.size()));
span<char> write = base::as_writable_chars(base::span(write_buf));
size_t written_size =
modp_b64_decode(write.data(), input.data(), input.size());
if (written_size == MODP_B64_ERROR) {
return std::nullopt;
}
// If this failed it would indicate we wrote OOB. It's possible for this to be
// elided by the compiler, since writing OOB is UB.
CHECK_LE(written_size, write.size());
write_buf.resize(written_size);
return write_buf;
}
} // namespace base
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