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Merge pull request #5887 from pennae/avoid-streams

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avoid std::?stream overhead when it's not helpful
This commit is contained in:
Théophane Hufschmitt 2022-01-12 10:52:40 +01:00 • committed by GitHub
commit e61c4bc25a
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4 changed files with 112 additions and 37 deletions
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42
src/libutil/json.cc
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@ -7,16 +7,38 @@ namespace nix {
void toJSON(std::ostream & str, const char * start, const char * end)
{
str << '"';
for (auto i = start; i != end; i++)
if (*i == '\"' || *i == '\\') str << '\\' << *i;
else if (*i == '\n') str << "\\n";
else if (*i == '\r') str << "\\r";
else if (*i == '\t') str << "\\t";
else if (*i >= 0 && *i < 32)
str << "\\u" << std::setfill('0') << std::setw(4) << std::hex << (uint16_t) *i << std::dec;
else str << *i;
str << '"';
constexpr size_t BUF_SIZE = 4096;
char buf[BUF_SIZE + 7]; // BUF_SIZE + largest single sequence of puts
size_t bufPos = 0;
const auto flush = [&] {
str.write(buf, bufPos);
bufPos = 0;
};
const auto put = [&] (char c) {
buf[bufPos++] = c;
};
put('"');
for (auto i = start; i != end; i++) {
if (bufPos >= BUF_SIZE) flush();
if (*i == '\"' || *i == '\\') { put('\\'); put(*i); }
else if (*i == '\n') { put('\\'); put('n'); }
else if (*i == '\r') { put('\\'); put('r'); }
else if (*i == '\t') { put('\\'); put('t'); }
else if (*i >= 0 && *i < 32) {
const char hex[17] = "0123456789abcdef";
put('\\');
put('u');
put(hex[(uint16_t(*i) >> 12) & 0xf]);
put(hex[(uint16_t(*i) >> 8) & 0xf]);
put(hex[(uint16_t(*i) >> 4) & 0xf]);
put(hex[(uint16_t(*i) >> 0) & 0xf]);
}
else put(*i);
}
put('"');
flush();
}
void toJSON(std::ostream & str, const char * s)

30
src/libutil/util.hh
View file

@ -11,6 +11,8 @@
#include <unistd.h>
#include <signal.h>
#include <boost/lexical_cast.hpp>
#include <atomic>
#include <functional>
#include <map>
@ -419,21 +421,21 @@ bool statusOk(int status);
/* Parse a string into an integer. */
template<class N>
std::optional<N> string2Int(const std::string & s)
std::optional<N> string2Int(const std::string_view s)
{
if (s.substr(0, 1) == "-" && !std::numeric_limits<N>::is_signed)
return std::nullopt;
std::istringstream str(s);
N n;
str >> n;
if (str && str.get() == EOF) return n;
return std::nullopt;
try {
return boost::lexical_cast<N>(s.data(), s.size());
} catch (const boost::bad_lexical_cast &) {
return std::nullopt;
}
}
/* Like string2Int(), but support an optional suffix 'K', 'M', 'G' or
'T' denoting a binary unit prefix. */
template<class N>
N string2IntWithUnitPrefix(std::string s)
N string2IntWithUnitPrefix(std::string_view s)
{
N multiplier = 1;
if (!s.empty()) {
@ -444,7 +446,7 @@ N string2IntWithUnitPrefix(std::string s)
else if (u == 'G') multiplier = 1ULL << 30;
else if (u == 'T') multiplier = 1ULL << 40;
else throw UsageError("invalid unit specifier '%1%'", u);
s.resize(s.size() - 1);
s.remove_suffix(1);
}
}
if (auto n = string2Int<N>(s))
@ -454,13 +456,13 @@ N string2IntWithUnitPrefix(std::string s)
/* Parse a string into a float. */
template<class N>
std::optional<N> string2Float(const string & s)
std::optional<N> string2Float(const std::string_view s)
{
std::istringstream str(s);
N n;
str >> n;
if (str && str.get() == EOF) return n;
return std::nullopt;
try {
return boost::lexical_cast<N>(s.data(), s.size());
} catch (const boost::bad_lexical_cast &) {
return std::nullopt;
}
}