chore: add string::fromHex

src/lib/base/String.cpp

@@ -219,6 +219,33 @@ int fromHexChar(char c)
 }
 // clang-format on
 
+std::vector<uint8_t> fromHex(const std::string &hexString)
+{
+  std::vector<uint8_t> result;
+  result.reserve(hexString.size() / 2);
+
+  size_t i = 0;
+  while (i < hexString.size()) {
+    if (hexString[i] == ':') {
+      i++;
+      continue;
+    }
+
+    if (i + 2 > hexString.size()) {
+      return {}; // uneven character count follows, it's unclear how to interpret it
+    }
+
+    auto high = fromHexChar(hexString[i]);
+    auto low = fromHexChar(hexString[i + 1]);
+    if (high < 0 || low < 0) {
+      return {};
+    }
+    result.push_back(high * 16 + low);
+    i += 2;
+  }
+  return result;
+}
+
 void uppercase(std::string &subject)
 {
   std::transform(subject.begin(), subject.end(), subject.begin(), ::toupper);

src/lib/base/String.h

@@ -82,6 +82,13 @@ std::string toHex(const std::string &subject, int width, const char fill = '0');
  */
 int fromHexChar(char c);
 
+/**
+ * @brief fromHex Turn the string into a std::vector<uint8_t>
+ * @param hexString a Hexidecimal string
+ * @return std::vector<uint8_t> version of the hex chars
+ */
+std::vector<uint8_t> fromHex(const std::string &hexString);
+
 //! Convert to all uppercase
 /*!
 Convert each character in \c subject to uppercase

src/test/unittests/base/StringTests.cpp

@@ -86,6 +86,13 @@ TEST(StringTests, fromHexChar_plaintext_hexString)
   EXPECT_EQ(15, string::fromHexChar('F'));
 }
 
+TEST(StringTests, fromHex_plaintext_hexString)
+{
+  EXPECT_EQ(255, string::fromHex("FF")[0]);
+  EXPECT_EQ(255, string::fromHex(":FF:EE")[0]);
+  EXPECT_EQ(238, string::fromHex(":FF:EE")[1]);
+}
+
 TEST(StringTests, uppercase_lowercaseInput_uppercaseOutput)
 {
   std::string subject = "12foo3BaR";