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);