1 // Copyright 2023 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // 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, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14
15 #include <cpp-string/string_printf.h>
16 #include <errno.h>
17 #include <stdarg.h>
18 #include <stddef.h>
19 #include <stdio.h>
20
21 namespace bt_lib_cpp_string {
22 namespace {
23
StringVAppendfHelper(std::string * dest,const char * format,va_list ap)24 void StringVAppendfHelper(std::string* dest, const char* format, va_list ap) {
25 // Size of the small stack buffer to use. This should be kept in sync
26 // with the numbers in StringPrintfTest.
27 constexpr size_t kStackBufferSize = 1024u;
28
29 char stack_buf[kStackBufferSize];
30 // |result| is the number of characters that would have been written if
31 // kStackBufferSize were sufficiently large, not counting the terminating null
32 // character. |vsnprintf()| always null-terminates!
33 int result = vsnprintf(stack_buf, kStackBufferSize, format, ap);
34 if (result < 0) {
35 // As far as I can tell, we'd only get |EOVERFLOW| if the result is so large
36 // that it can't be represented by an |int| (in which case retrying would be
37 // futile), so Chromium's implementation is wrong.
38 return;
39 }
40
41 // Only append what fit into our stack buffer.
42 // Strings that are too long will be truncated.
43 size_t actual_len_excluding_null = result;
44 if (actual_len_excluding_null > kStackBufferSize - 1) {
45 actual_len_excluding_null = kStackBufferSize - 1;
46 }
47 dest->append(stack_buf, actual_len_excluding_null);
48 }
49
50 } // namespace
51
StringPrintf(const char * format,...)52 std::string StringPrintf(const char* format, ...) {
53 va_list ap;
54 va_start(ap, format);
55 std::string rv;
56 StringVAppendf(&rv, format, ap);
57 va_end(ap);
58 return rv;
59 }
60
StringVPrintf(const char * format,va_list ap)61 std::string StringVPrintf(const char* format, va_list ap) {
62 std::string rv;
63 StringVAppendf(&rv, format, ap);
64 return rv;
65 }
66
StringAppendf(std::string * dest,const char * format,...)67 void StringAppendf(std::string* dest, const char* format, ...) {
68 va_list ap;
69 va_start(ap, format);
70 StringVAppendf(dest, format, ap);
71 va_end(ap);
72 }
73
StringVAppendf(std::string * dest,const char * format,va_list ap)74 void StringVAppendf(std::string* dest, const char* format, va_list ap) {
75 int old_errno = errno;
76 StringVAppendfHelper(dest, format, ap);
77 errno = old_errno;
78 }
79
80 } // namespace bt_lib_cpp_string
81