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Clean up Base* code

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Make it separate from Hash, since other things can be base-encoded too.

This isn't really needed for Nix, but it makes the code easier to read
e.g. for someone reimplementing this stuff in a different language. (Of
course, Base16/Base64 should be gotten off-the-shelf, but now the hash
code, which is more bespoke, is less cluttered with the parts that would
be from some library.)

Many reimplementations of "Nix32" and our hash type already exist, so
this cleanup is coming years too late, but I say better late than never
/ it is always good to nudge the code in the direction of being a
"living spec".

Co-authored-by: Sergei Zimmerman <sergei@zimmerman.foo>
This commit is contained in:
John Ericson 2025-08-05 14:12:00 -04:00
parent 664f06c94c
commit 991831227e
18 changed files with 357 additions and 244 deletions
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64
src/libutil/util.cc
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@ -204,70 +204,6 @@ void ignoreExceptionExceptInterrupt(Verbosity lvl)
}
}
constexpr char base64Chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
std::string base64Encode(std::string_view s)
{
std::string res;
res.reserve((s.size() + 2) / 3 * 4);
int data = 0, nbits = 0;
for (char c : s) {
data = data << 8 | (unsigned char) c;
nbits += 8;
while (nbits >= 6) {
nbits -= 6;
res.push_back(base64Chars[data >> nbits & 0x3f]);
}
}
if (nbits)
res.push_back(base64Chars[data << (6 - nbits) & 0x3f]);
while (res.size() % 4)
res.push_back('=');
return res;
}
std::string base64Decode(std::string_view s)
{
constexpr char npos = -1;
constexpr std::array<char, 256> base64DecodeChars = [&] {
std::array<char, 256> result{};
for (auto & c : result)
c = npos;
for (int i = 0; i < 64; i++)
result[base64Chars[i]] = i;
return result;
}();
std::string res;
// Some sequences are missing the padding consisting of up to two '='.
// vvv
res.reserve((s.size() + 2) / 4 * 3);
unsigned int d = 0, bits = 0;
for (char c : s) {
if (c == '=')
break;
if (c == '\n')
continue;
char digit = base64DecodeChars[(unsigned char) c];
if (digit == npos)
throw FormatError("invalid character in Base64 string: '%c'", c);
bits += 6;
d = d << 6 | digit;
if (bits >= 8) {
res.push_back(d >> (bits - 8) & 0xff);
bits -= 8;
}
}
return res;
}
std::string stripIndentation(std::string_view s)
{
size_t minIndent = 10000;