Replace use of locale dependent atoi(…) with locale-independent std::from_chars(…) (C++17)

test: Add test cases for LocaleIndependentAtoi

fuzz: Assert legacy atoi(s) == LocaleIndependentAtoi<int>(s)

fuzz: Assert legacy atoi64(s) == LocaleIndependentAtoi<int64_t>(s)

src/util/strencodings.h

@@ -11,6 +11,7 @@
 
 #include <attributes.h>
 #include <span.h>
+#include <util/string.h>
 
 #include <charconv>
 #include <cstdint>
@@ -68,8 +69,33 @@ std::string EncodeBase32(Span<const unsigned char> input, bool pad = true);
 std::string EncodeBase32(const std::string& str, bool pad = true);
 
 void SplitHostPort(std::string in, uint16_t& portOut, std::string& hostOut);
-int64_t atoi64(const std::string& str);
-int atoi(const std::string& str);
+
+// LocaleIndependentAtoi is provided for backwards compatibility reasons.
+//
+// New code should use the ParseInt64/ParseUInt64/ParseInt32/ParseUInt32 functions
+// which provide parse error feedback.
+//
+// The goal of LocaleIndependentAtoi is to replicate the exact defined behaviour
+// of atoi and atoi64 as they behave under the "C" locale.
+template <typename T>
+T LocaleIndependentAtoi(const std::string& str)
+{
+    static_assert(std::is_integral<T>::value);
+    T result;
+    // Emulate atoi(...) handling of white space and leading +/-.
+    std::string s = TrimString(str);
+    if (!s.empty() && s[0] == '+') {
+        if (s.length() >= 2 && s[1] == '-') {
+            return 0;
+        }
+        s = s.substr(1);
+    }
+    auto [_, error_condition] = std::from_chars(s.data(), s.data() + s.size(), result);
+    if (error_condition != std::errc{}) {
+        return 0;
+    }
+    return result;
+}
 
 /**
  * Tests if the given character is a decimal digit.