test: Fuzz Base32/Base58/Base64 roundtrip conversions

This commit introduces symmetric encode-decode roundtrips for all bases.
Minor refactors were also included:
• Split each base into a separate fuzz target.
• Added symmetric encode-decode roundtrip tests for all bases.
• Removed trim testing for encoded_string, as Base58 does not use whitespace padding.
• Made comparisons stricter by removing unnecessary lowercase conversions for bases that have mixed-case alphabets.

Co-authored-by: Hodlinator <172445034+hodlinator@users.noreply.github.com>

src/test/fuzz/base_encode_decode.cpp

@@ -6,49 +6,90 @@
 
 #include <base58.h>
 #include <psbt.h>
+#include <test/fuzz/FuzzedDataProvider.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 
 #include <cassert>
-#include <cstdint>
 #include <string>
 #include <vector>
+#include <ranges>
 
-using util::TrimString;
 using util::TrimStringView;
 
-FUZZ_TARGET(base_encode_decode)
+FUZZ_TARGET(base58_encode_decode)
 {
-    const std::string random_encoded_string(buffer.begin(), buffer.end());
+    FuzzedDataProvider provider(buffer.data(), buffer.size());
+    const std::string random_string{provider.ConsumeRandomLengthString(1000)};
 
+    // Decode/Encode roundtrip
     std::vector<unsigned char> decoded;
-    if (DecodeBase58(random_encoded_string, decoded, 100)) {
-        const std::string encoded_string = EncodeBase58(decoded);
-        assert(encoded_string == TrimStringView(encoded_string));
-        assert(ToLower(encoded_string) == ToLower(TrimString(random_encoded_string)));
+    if (DecodeBase58(random_string, decoded, 100)) {
+        const auto encoded_string{EncodeBase58(decoded)};
+        assert(encoded_string == TrimStringView(random_string));
+        assert(encoded_string.empty() || !DecodeBase58(encoded_string, decoded, provider.ConsumeIntegralInRange<int>(0, decoded.size() - 1)));
     }
+    // Encode/Decode roundtrip
+    const auto encoded{EncodeBase58(buffer)};
+    std::vector<unsigned char> roundtrip_decoded;
+    assert(DecodeBase58(encoded, roundtrip_decoded, buffer.size())
+        && std::ranges::equal(roundtrip_decoded, buffer));
+}
 
-    if (DecodeBase58Check(random_encoded_string, decoded, 100)) {
-        const std::string encoded_string = EncodeBase58Check(decoded);
-        assert(encoded_string == TrimString(encoded_string));
-        assert(ToLower(encoded_string) == ToLower(TrimString(random_encoded_string)));
-    }
+FUZZ_TARGET(base58check_encode_decode)
+{
+    FuzzedDataProvider provider(buffer.data(), buffer.size());
+    const std::string random_string{provider.ConsumeRandomLengthString(1000)};
 
-    auto result = DecodeBase32(random_encoded_string);
-    if (result) {
-        const std::string encoded_string = EncodeBase32(*result);
-        assert(encoded_string == TrimStringView(encoded_string));
-        assert(ToLower(encoded_string) == ToLower(TrimString(random_encoded_string)));
+    // Decode/Encode roundtrip
+    std::vector<unsigned char> decoded;
+    if (DecodeBase58Check(random_string, decoded, 100)) {
+        const auto encoded_string{EncodeBase58Check(decoded)};
+        assert(encoded_string == TrimStringView(random_string));
+        assert(encoded_string.empty() || !DecodeBase58Check(encoded_string, decoded, provider.ConsumeIntegralInRange<int>(0, decoded.size() - 1)));
     }
+    // Encode/Decode roundtrip
+    const auto encoded{EncodeBase58Check(buffer)};
+    std::vector<unsigned char> roundtrip_decoded;
+    assert(DecodeBase58Check(encoded, roundtrip_decoded, buffer.size())
+        && std::ranges::equal(roundtrip_decoded, buffer));
+}
 
-    result = DecodeBase64(random_encoded_string);
-    if (result) {
-        const std::string encoded_string = EncodeBase64(*result);
-        assert(encoded_string == TrimString(encoded_string));
-        assert(ToLower(encoded_string) == ToLower(TrimString(random_encoded_string)));
+FUZZ_TARGET(base32_encode_decode)
+{
+    const std::string random_string{buffer.begin(), buffer.end()};
+
+    // Decode/Encode roundtrip
+    if (auto result{DecodeBase32(random_string)}) {
+        const auto encoded_string{EncodeBase32(*result)};
+        assert(encoded_string == ToLower(TrimStringView(random_string)));
     }
+    // Encode/Decode roundtrip
+    const auto encoded{EncodeBase32(buffer)};
+    const auto decoded{DecodeBase32(encoded)};
+    assert(decoded && std::ranges::equal(*decoded, buffer));
+}
+
+FUZZ_TARGET(base64_encode_decode)
+{
+    const std::string random_string{buffer.begin(), buffer.end()};
+
+    // Decode/Encode roundtrip
+    if (auto result{DecodeBase64(random_string)}) {
+        const auto encoded_string{EncodeBase64(*result)};
+        assert(encoded_string == TrimStringView(random_string));
+    }
+    // Encode/Decode roundtrip
+    const auto encoded{EncodeBase64(buffer)};
+    const auto decoded{DecodeBase64(encoded)};
+    assert(decoded && std::ranges::equal(*decoded, buffer));
+}
+
+FUZZ_TARGET(psbt_base64_decode)
+{
+    const std::string random_string{buffer.begin(), buffer.end()};
 
     PartiallySignedTransaction psbt;
     std::string error;
-    (void)DecodeBase64PSBT(psbt, random_encoded_string, error);
+    assert(DecodeBase64PSBT(psbt, random_string, error) == error.empty());
 }