Make Hint encoding safe for passing them as GET parameter in URLs

Thanks @TheMarex for flagging this!

src/engine/hint.cpp

@@ -4,6 +4,9 @@
 
 #include <boost/assert.hpp>
 
+#include <iterator>
+#include <algorithm>
+
 namespace osrm
 {
 namespace engine
@@ -18,13 +21,29 @@ bool Hint::IsValid(const util::Coordinate new_input_coordinates,
            facade.GetCheckSum() == data_checksum;
 }
 
-std::string Hint::ToBase64() const { return encodeBase64Bytewise(*this); }
+std::string Hint::ToBase64() const
+{
+    auto base64 = encodeBase64Bytewise(*this);
+
+    // Make safe for usage as GET parameter in URLs
+    std::replace(begin(base64), end(base64), '+', '-');
+    std::replace(begin(base64), end(base64), '/', '_');
+
+    return base64;
+}
 
 Hint Hint::FromBase64(const std::string &base64Hint)
 {
     BOOST_ASSERT_MSG(base64Hint.size() == ENCODED_HINT_SIZE, "Hint has invalid size");
 
-    return decodeBase64Bytewise<Hint>(base64Hint);
+    // We need mutability but don't want to change the API
+    auto encoded = base64Hint;
+
+    // Reverses above encoding we need for GET parameters in URL
+    std::replace(begin(encoded), end(encoded), '-', '+');
+    std::replace(begin(encoded), end(encoded), '_', '/');
+
+    return decodeBase64Bytewise<Hint>(encoded);
 }
 }
 }