/src/abseil-cpp/absl/strings/internal/append_and_overwrite.h
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1 | | // Copyright 2025 The Abseil Authors |
2 | | // |
3 | | // Licensed under the Apache License, Version 2.0 (the "License"); |
4 | | // you may not use this file except in compliance with the License. |
5 | | // You may obtain a copy of the License at |
6 | | // |
7 | | // https://www.apache.org/licenses/LICENSE-2.0 |
8 | | // |
9 | | // Unless required by applicable law or agreed to in writing, software |
10 | | // distributed under the License is distributed on an "AS IS" BASIS, |
11 | | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
12 | | // See the License for the specific language governing permissions and |
13 | | // limitations under the License. |
14 | | |
15 | | #ifndef ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_ |
16 | | #define ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_ |
17 | | |
18 | | #include "absl/base/config.h" |
19 | | #include "absl/base/internal/hardening.h" |
20 | | #include "absl/base/macros.h" |
21 | | #include "absl/base/optimization.h" |
22 | | #include "absl/base/throw_delegate.h" |
23 | | #include "absl/strings/resize_and_overwrite.h" |
24 | | |
25 | | namespace absl { |
26 | | ABSL_NAMESPACE_BEGIN |
27 | | namespace strings_internal { |
28 | | |
29 | | // An internal-only variant similar to `absl::StringResizeAndOverwrite()` |
30 | | // optimized for repeated appends to a string that uses exponential growth so |
31 | | // that the amortized complexity of increasing the string size by a small amount |
32 | | // is O(1), in contrast to O(str.size()) in the case of precise growth. Use of |
33 | | // this function is subtle; see https://reviews.llvm.org/D102727 to understand |
34 | | // the tradeoffs. |
35 | | // |
36 | | // Appends at most `append_n` characters to `str`, using the user-provided |
37 | | // operation `append_op` to modify the possibly indeterminate |
38 | | // contents. `append_op` must return the length of the buffer appended to `str`. |
39 | | // |
40 | | // Invalidates all iterators, pointers, and references into `str`, regardless |
41 | | // of whether reallocation occurs. |
42 | | // |
43 | | // `append_op(value_type* buf, size_t buf_size)` is allowed to write |
44 | | // `value_type{}` to `buf[buf_size]`, which facilitiates interoperation with |
45 | | // functions that write a trailing NUL. |
46 | | template <typename T, typename Op> |
47 | | void StringAppendAndOverwrite(T& str, typename T::size_type append_n, |
48 | 0 | Op append_op) { |
49 | 0 | if (ABSL_PREDICT_FALSE(append_n > str.max_size() - str.size())) { |
50 | 0 | ThrowStdLengthError("absl::strings_internal::StringAppendAndOverwrite"); |
51 | 0 | } |
52 | |
|
53 | 0 | auto old_size = str.size(); |
54 | 0 | auto resize = old_size + append_n; |
55 | |
|
56 | 0 | if (resize > str.capacity()) { |
57 | | // Make sure to always grow by at least a factor of 2x. |
58 | 0 | const auto min_growth = str.capacity(); |
59 | 0 | if (ABSL_PREDICT_FALSE(str.capacity() > str.max_size() - min_growth)) { |
60 | 0 | str.reserve(str.max_size()); |
61 | 0 | } else if (resize < str.capacity() + min_growth) { |
62 | 0 | str.reserve(str.capacity() + min_growth); |
63 | 0 | } |
64 | 0 | } |
65 | | |
66 | | // Avoid calling StringResizeAndOverwrite() here since it does an MSAN |
67 | | // verification on the entire string. StringResizeAndOverwriteImpl() is |
68 | | // StringResizeAndOverwrite() without the MSAN verification. |
69 | 0 | StringResizeAndOverwriteImpl( |
70 | 0 | str, resize, |
71 | 0 | [old_size, append_n, do_append = std::move(append_op)]( |
72 | 0 | typename T::value_type* data_ptr, typename T::size_type) mutable { |
73 | 0 | typename T::size_type num_appended = static_cast<typename T::size_type>( |
74 | 0 | std::move(do_append)(data_ptr + old_size, append_n)); |
75 | 0 | absl::base_internal::HardeningAssertGE(num_appended, |
76 | 0 | typename T::size_type{0}); |
77 | 0 | absl::base_internal::HardeningAssertLE(num_appended, append_n); |
78 | 0 | return old_size + num_appended; |
79 | 0 | }); Unexecuted instantiation: str_cat.cc:absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::strings_internal::AppendPieces(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, std::initializer_list<std::__1::basic_string_view<char, std::__1::char_traits<char> > >)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::strings_internal::AppendPieces(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, std::initializer_list<std::__1::basic_string_view<char, std::__1::char_traits<char> > >)::$_0)::{lambda(char*, unsigned long)#1}::operator()(char*, unsigned long)Unexecuted instantiation: str_cat.cc:absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&)::$_0)::{lambda(char*, unsigned long)#1}::operator()(char*, unsigned long)Unexecuted instantiation: str_cat.cc:absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&)::$_0)::{lambda(char*, unsigned long)#1}::operator()(char*, unsigned long)Unexecuted instantiation: str_cat.cc:absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0)::{lambda(char*, unsigned long)#1}::operator()(char*, unsigned long)Unexecuted instantiation: str_cat.cc:absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0)::{lambda(char*, unsigned long)#1}::operator()(char*, unsigned long) |
80 | |
|
81 | | #if defined(ABSL_HAVE_MEMORY_SANITIZER) |
82 | | // Only check the region appended to. Checking the entire string would cause |
83 | | // pathological quadratic verfication on repeated small appends. |
84 | | __msan_check_mem_is_initialized(str.data() + old_size, str.size() - old_size); |
85 | | #endif |
86 | 0 | } Unexecuted instantiation: str_cat.cc:void absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::strings_internal::AppendPieces(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, std::initializer_list<std::__1::basic_string_view<char, std::__1::char_traits<char> > >)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::strings_internal::AppendPieces(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, std::initializer_list<std::__1::basic_string_view<char, std::__1::char_traits<char> > >)::$_0) Unexecuted instantiation: str_cat.cc:void absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&)::$_0) Unexecuted instantiation: str_cat.cc:void absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&)::$_0) Unexecuted instantiation: str_cat.cc:void absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0) Unexecuted instantiation: str_cat.cc:void absl::strings_internal::StringAppendAndOverwrite<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size_type, absl::StrAppend(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&, absl::AlphaNum const&)::$_0) |
87 | | |
88 | | } // namespace strings_internal |
89 | | ABSL_NAMESPACE_END |
90 | | } // namespace absl |
91 | | |
92 | | |
93 | | #endif // ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_ |