[Base64] Add validation

Garbage/Include/Garbage/Base64.hpp

@@ -138,6 +138,33 @@ namespace Garbage::Base64
 
         return result;
     }
+
+    [[nodiscard]] constexpr
+    bool Validate(std::string_view data)
+    {
+        // Technically superfluous - the decoder can deal with unpadded data.
+        if (data.size() % 4 != 0) {
+            return false;
+        }
+
+        std::size_t i = 0;
+        for (char ch : data) {
+            bool condition = (ch == '+') ||
+                             (ch >= '/' && ch <= '9') ||
+                             (ch >= 'A' && ch <= 'Z') ||
+                             (ch >= 'a' && ch <= 'z');
+            if (!condition) {
+                // Allow '=' for the last two character
+                if (i >= data.size() - 2 && ch == '=') {
+                    continue;
+                }
+                return false;
+            }
+            ++i;
+        }
+
+        return true;
+    }
 }
 
 #endif // GARBAGE_BASE64_HPP

Tests/Base64/Tests.cpp

@@ -10,6 +10,8 @@ TEST_CASE("Base64 encoding/decoding tests")
         std::string encoded = Garbage::Base64::Encode(data);
         REQUIRE(encoded.size() == 0);
 
+        REQUIRE(Garbage::Base64::Validate(encoded));
+
         std::vector<std::uint8_t> decoded = Garbage::Base64::Decode(encoded);
         REQUIRE(encoded.size() == 0);
     }
@@ -21,12 +23,15 @@ TEST_CASE("Base64 encoding/decoding tests")
 
         std::string encoded = Garbage::Base64::Encode(data);
         REQUIRE(encoded == "TWFueSBoYW5kcyBtYWtlIGxpZ2h0IHdvcmsu");
+        REQUIRE(Garbage::Base64::Validate(encoded));
     }
 
     SECTION("Decoding short data")
     {
         std::string data("TWFueSBoYW5kcyBtYWtlIGxpZ2h0IHdvcmsu");
 
+        REQUIRE(Garbage::Base64::Validate(data));
+
         std::vector<std::uint8_t> decoded = Garbage::Base64::Decode(data);
         std::string destination(decoded.begin(), decoded.end());
         REQUIRE(destination == "Many hands make light work.");
@@ -39,12 +44,15 @@ TEST_CASE("Base64 encoding/decoding tests")
 
         std::string encoded = Garbage::Base64::Encode(data);
         REQUIRE(encoded == "V2l0aCBhIHBhZGRpbmc=");
+        REQUIRE(Garbage::Base64::Validate(encoded));
     }
 
     SECTION("Decoding with a padding char")
     {
         std::string data("V2l0aCBhIHBhZGRpbmc=");
 
+        REQUIRE(Garbage::Base64::Validate(data));
+
         std::vector<std::uint8_t> decoded = Garbage::Base64::Decode(data);
         std::string destination(decoded.begin(), decoded.end());
         REQUIRE(destination == "With a padding");
@@ -57,12 +65,15 @@ TEST_CASE("Base64 encoding/decoding tests")
 
         std::string encoded = Garbage::Base64::Encode(data);
         REQUIRE(encoded == "V2l0aCB0d28gcGFkZGluZw==");
+        REQUIRE(Garbage::Base64::Validate(encoded));
     }
 
     SECTION("Decoding with two padding chars")
     {
         std::string data("V2l0aCB0d28gcGFkZGluZw==");
 
+        REQUIRE(Garbage::Base64::Validate(data));
+
         std::vector<std::uint8_t> decoded = Garbage::Base64::Decode(data);
         std::string destination(decoded.begin(), decoded.end());
         REQUIRE(destination == "With two padding");