fix(util): avoid sign extension in base64 encodesr

Author: gjasny

util/include/prometheus/detail/base64.h

@@ -37,9 +37,9 @@ inline std::string base64_encode(const std::string& input) {
  auto it = input.begin();
 
  for (std::size_t i = 0; i < input.size() / 3; ++i) {
- temp = (*it++) << 16;
- temp += (*it++) << 8;
- temp += (*it++);
+ temp = static_cast<std::uint8_t>(*it++) << 16;
+ temp += static_cast<std::uint8_t>(*it++) << 8;
+ temp += static_cast<std::uint8_t>(*it++);
  encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
  encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
  encoded.append(1, kEncodeLookup[(temp & 0x00000FC0) >> 6]);
@@ -48,14 +48,14 @@ inline std::string base64_encode(const std::string& input) {
 
  switch (input.size() % 3) {
  case 1:
- temp = (*it++) << 16;
+ temp = static_cast<std::uint8_t>(*it++) << 16;
  encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
  encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
  encoded.append(2, kPadCharacter);
  break;
  case 2:
- temp = (*it++) << 16;
- temp += (*it++) << 8;
+ temp = static_cast<std::uint8_t>(*it++) << 16;
+ temp += static_cast<std::uint8_t>(*it++) << 8;
  encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
  encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
  encoded.append(1, kEncodeLookup[(temp & 0x00000FC0) >> 6]);
@@ -118,7 +118,7 @@ inline std::string base64_decode(const std::string& input) {
 
  decoded.push_back((temp >> 16) & 0x000000FF);
  decoded.push_back((temp >> 8) & 0x000000FF);
- decoded.push_back((temp)&0x000000FF);
+ decoded.push_back((temp) & 0x000000FF);
  }
 
  return decoded;

util/tests/unit/base64_test.cc

@@ -13,13 +13,29 @@ struct TestVector {
 };
 
 const TestVector testVector[] = {
+ // RFC 3548 examples
+ {"\x14\xfb\x9c\x03\xd9\x7e", "FPucA9l+"},
+ {"\x14\xfb\x9c\x03\xd9", "FPucA9k="},
+ {"\x14\xfb\x9c\x03", "FPucAw=="},
+
+ // RFC 4648 examples
  {"", ""},
  {"f", "Zg=="},
  {"fo", "Zm8="},
  {"foo", "Zm9v"},
  {"foob", "Zm9vYg=="},
  {"fooba", "Zm9vYmE="},
  {"foobar", "Zm9vYmFy"},
+
+ // Wikipedia examples
+ {"sure.", "c3VyZS4="},
+ {"sure", "c3VyZQ=="},
+ {"sur", "c3Vy"},
+ {"su", "c3U="},
+ {"leasure.", "bGVhc3VyZS4="},
+ {"easure.", "ZWFzdXJlLg=="},
+ {"asure.", "YXN1cmUu"},
+ {"sure.", "c3VyZS4="},
 };
 
 using namespace testing;