+namespace detail {
+// Map from character code to escape mode:
+// 0 = pass through
+// 1 = unused
+// 2 = pass through in PATH mode
+// 3 = space, replace with '+' in QUERY mode
+// 4 = percent-encode
+extern const unsigned char uriEscapeTable[];
+} // namespace detail
+
+template <class String>
+void uriEscape(StringPiece str, String& out, UriEscapeMode mode) {
+ static const char hexValues[] = "0123456789abcdef";
+ char esc[3];
+ esc[0] = '%';
+ // Preallocate assuming that 25% of the input string will be escaped
+ out.reserve(out.size() + str.size() + 3 * (str.size() / 4));
+ auto p = str.begin();
+ auto last = p; // last regular character
+ // We advance over runs of passthrough characters and copy them in one go;
+ // this is faster than calling push_back repeatedly.
+ unsigned char minEncode = static_cast<unsigned char>(mode);
+ while (p != str.end()) {
+ char c = *p;
+ unsigned char v = static_cast<unsigned char>(c);
+ unsigned char discriminator = detail::uriEscapeTable[v];
+ if (LIKELY(discriminator <= minEncode)) {
+ ++p;
+ } else if (mode == UriEscapeMode::QUERY && discriminator == 3) {
+ out.append(&*last, p - last);
+ out.push_back('+');
+ ++p;
+ last = p;
+ } else {
+ out.append(&*last, p - last);
+ esc[1] = hexValues[v >> 4];
+ esc[2] = hexValues[v & 0x0f];
+ out.append(esc, 3);
+ ++p;
+ last = p;
+ }
+ }
+ out.append(&*last, p - last);
+}
+
+template <class String>
+void uriUnescape(StringPiece str, String& out, UriEscapeMode mode) {
+ out.reserve(out.size() + str.size());
+ auto p = str.begin();
+ auto last = p;
+ // We advance over runs of passthrough characters and copy them in one go;
+ // this is faster than calling push_back repeatedly.
+ while (p != str.end()) {
+ char c = *p;
+ unsigned char v = static_cast<unsigned char>(v);
+ switch (c) {
+ case '%':
+ {
+ if (UNLIKELY(std::distance(p, str.end()) < 3)) {
+ throw std::invalid_argument("incomplete percent encode sequence");
+ }
+ auto h1 = detail::hexTable[static_cast<unsigned char>(p[1])];
+ auto h2 = detail::hexTable[static_cast<unsigned char>(p[2])];
+ if (UNLIKELY(h1 == 16 || h2 == 16)) {
+ throw std::invalid_argument("invalid percent encode sequence");
+ }
+ out.append(&*last, p - last);
+ out.push_back((h1 << 4) | h2);
+ p += 3;
+ last = p;
+ break;
+ }
+ case '+':
+ if (mode == UriEscapeMode::QUERY) {
+ out.append(&*last, p - last);
+ out.push_back(' ');
+ ++p;
+ last = p;
+ break;
+ }
+ // else fallthrough
+ default:
+ ++p;
+ break;
+ }
+ }
+ out.append(&*last, p - last);
+}
+