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util: Support dynamic width & precision in ConstevalFormatString

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This is needed in the next commit to add compile-time checking to strprintf
calls, because bitcoin-cli.cpp uses dynamic width in many format strings.

This change is easiest to review ignoring whitespace.

Co-authored-by: MarcoFalke <*~=`'#}+{/-|&$^_@721217.xyz>
Co-authored-by: Hodlinator <172445034+hodlinator@users.noreply.github.com>
Co-authored-by: l0rinc <pap.lorinc@gmail.com>
This commit is contained in:
Ryan Ofsky
2024-10-28 19:11:16 -04:00
parent da10e0bab4
commit 184f34f2d0
2 changed files with 82 additions and 40 deletions
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78
src/util/string.h
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@@ -25,53 +25,65 @@ namespace util {
* strings, to reduce the likelihood of tinyformat throwing exceptions at
* run-time. Validation is partial to try and prevent the most common errors
* while avoiding re-implementing the entire parsing logic.
*
* @note Counting of `*` dynamic width and precision fields (such as `%*c`,
* `%2$*3$d`, `%.*f`) is not implemented to minimize code complexity as long as
* they are not used in the codebase. Usage of these fields is not counted and
* can lead to run-time exceptions. Code wanting to use the `*` specifier can
* side-step this struct and call tinyformat directly.
*/
template <unsigned num_params>
struct ConstevalFormatString {
const char* const fmt;
consteval ConstevalFormatString(const char* str) : fmt{str} { Detail_CheckNumFormatSpecifiers(fmt); }
constexpr static void Detail_CheckNumFormatSpecifiers(std::string_view str)
constexpr static void Detail_CheckNumFormatSpecifiers(const char* str)
{
unsigned count_normal{0}; // Number of "normal" specifiers, like %s
unsigned count_pos{0}; // Max number in positional specifier, like %8$s
for (auto it{str.begin()}; it < str.end();) {
if (*it != '%') {
++it;
continue;
}
for (auto it{str}; *it != '\0'; ++it) {
if (*it != '%' || *++it == '%') continue; // Skip escaped %%
if (++it >= str.end()) throw "Format specifier incorrectly terminated by end of string";
if (*it == '%') {
// Percent escape: %%
++it;
continue;
}
auto add_arg = [&] {
unsigned maybe_num{0};
while ('0' <= *it && *it <= '9') {
maybe_num *= 10;
maybe_num += *it - '0';
++it;
}
unsigned maybe_num{0};
while ('0' <= *it && *it <= '9') {
maybe_num *= 10;
maybe_num += *it - '0';
++it;
if (*it == '$') {
++it;
// Positional specifier, like %8$s
if (maybe_num == 0) throw "Positional format specifier must have position of at least 1";
count_pos = std::max(count_pos, maybe_num);
} else {
// Non-positional specifier, like %s
++count_normal;
}
};
if (*it == '$') {
// Positional specifier, like %8$s
if (maybe_num == 0) throw "Positional format specifier must have position of at least 1";
count_pos = std::max(count_pos, maybe_num);
if (++it >= str.end()) throw "Format specifier incorrectly terminated by end of string";
} else {
// Non-positional specifier, like %s
++count_normal;
// Increase argument count and consume positional specifier, if present.
add_arg();
// Consume flags.
while (*it == '#' || *it == '0' || *it == '-' || *it == ' ' || *it == '+') ++it;
auto parse_size = [&] {
if (*it == '*') {
++it;
add_arg();
} else {
while ('0' <= *it && *it <= '9') ++it;
}
};
// Consume dynamic or static width value.
parse_size();
// Consume dynamic or static precision value.
if (*it == '.') {
++it;
parse_size();
}
// The remainder "[flags][width][.precision][length]type" of the
// specifier is not checked. Parsing continues with the next '%'.
if (*it == '\0') throw "Format specifier incorrectly terminated by end of string";
// Length and type in "[flags][width][.precision][length]type"
// is not checked. Parsing continues with the next '%'.
}
if (count_normal && count_pos) throw "Format specifiers must be all positional or all non-positional!";
unsigned count{count_normal | count_pos};