runtime/evm: add tests for JSON round trip

analyzer/evmnfts/evm_nfts.go

@@ -118,7 +118,11 @@ func (p *processor) ProcessItem(ctx context.Context, batch *storage.QueryBatch,
 		staleNFT.DownloadRound,
 		storage.SanitizeStringP(nftData.MetadataURI),
 		nftData.MetadataAccessed,
-		// If SanitizeString can affect JSON validity, we're doomed.
+		// Metadata has already gone through a round trip of JSON Unmarshal
+		// and Marshal, which should already make it safe for PostgreSQL. But
+		// for consistency, pass it through SanitizeString as well. This
+		// shouldn't have any effect, and if it does, it shouldn't affect the
+		// JSON syntax.
 		storage.SanitizeStringP(nftData.Metadata),
 		storage.SanitizeStringP(nftData.Name),
 		storage.SanitizeStringP(nftData.Description),

analyzer/runtime/evm/erc721_test.go

@@ -0,0 +1,42 @@
+package evm
+
+import (
+	"encoding/json"
+	"testing"
+	"unicode/utf8"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestJSONRoundTrip(t *testing.T) {
+	for _, s := range []string{
+		// Invalid UTF-8.
+		"{\"a\": \"\xff\"}",
+		"{\"\xff\": \"a\"}",
+		// NUL bytes.
+		"{\"a\": \"\x00\"}",
+		"{\"\x00\": \"a\"}",
+		// Codepoint zero.
+		"{\"a\": \"\\u0000\"}",
+		"{\"\\u0000\": \"a\"}",
+	} {
+		var parsed any
+		err := json.Unmarshal([]byte(s), &parsed)
+		if err != nil {
+			// Erroring out while unmarshalling is fine.
+			t.Logf("%#v -> parsing: %v\n", s, err)
+			continue
+		}
+		roundTripBuf, err := json.Marshal(parsed)
+		if err != nil {
+			// Erroring out while marshalling is uncool, but not a showstopper.
+			t.Logf("%#v -> stringifying: %v\n", s, err)
+			continue
+		}
+		roundTrip := string(roundTripBuf)
+		// If it gets through the round trip, it'd better be clean.
+		require.True(t, utf8.ValidString(roundTrip), "%#v -> invalid UTF-8 %#v", s, roundTrip)
+		require.NotContains(t, roundTrip, 0x0, "%#v -> contains NUL byte %#v", s, roundTrip)
+		t.Logf("%#v -> %#v\n", s, roundTrip)
+	}
+}