From d349a797ba044d10344d83375bbc85ca4c78afbc Mon Sep 17 00:00:00 2001
From: Hampus Eriksson <hampus.eriksson09@gmail.com>
Date: Tue, 26 Sep 2023 08:53:22 +0200
Subject: [PATCH] Correctly encode structs without members

The JSON RPC API specification for 'eth_signTypedData_v4' does not
explicitly state that the required struct 'EIP712Domain' has to define
any members [1]. The current implementation cannot correctly encode
such a structure, as it assumes that at least one member has been
parsed and added to the struct's string representation.

This commit refactors the struct encoding function such that it now
accepts structures that does not define any members.

[1] https://eips.ethereum.org/EIPS/eip-712#specification-of-the-eth_signtypeddata-json-rpc
---
 .../org/web3j/crypto/StructuredDataEncoder.java    |  9 +++------
 .../java/org/web3j/crypto/StructuredDataTest.java  | 14 ++++++++++++++
 .../ValidMinimalStructuredData.json                |  8 ++++++++
 3 files changed, 25 insertions(+), 6 deletions(-)
 create mode 100644 crypto/src/test/resources/structured_data_json_files/ValidMinimalStructuredData.json

diff --git a/crypto/src/main/java/org/web3j/crypto/StructuredDataEncoder.java b/crypto/src/main/java/org/web3j/crypto/StructuredDataEncoder.java
index ff9e3369e..143fcfdb1 100644
--- a/crypto/src/main/java/org/web3j/crypto/StructuredDataEncoder.java
+++ b/crypto/src/main/java/org/web3j/crypto/StructuredDataEncoder.java
@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.StringJoiner;
 import java.util.TreeSet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -120,14 +121,10 @@ public Set<String> getDependencies(String primaryType) {
     public String encodeStruct(String structName) {
         HashMap<String, List<StructuredData.Entry>> types = jsonMessageObject.getTypes();
 
-        StringBuilder structRepresentation = new StringBuilder(structName + "(");
+        StringJoiner structRepresentation = new StringJoiner(",", structName + "(", ")");
         for (StructuredData.Entry entry : types.get(structName)) {
-            structRepresentation.append(String.format("%s %s,", entry.getType(), entry.getName()));
+            structRepresentation.add(String.format("%s %s", entry.getType(), entry.getName()));
         }
-        structRepresentation =
-                new StringBuilder(
-                        structRepresentation.substring(0, structRepresentation.length() - 1));
-        structRepresentation.append(")");
 
         return structRepresentation.toString();
     }
diff --git a/crypto/src/test/java/org/web3j/crypto/StructuredDataTest.java b/crypto/src/test/java/org/web3j/crypto/StructuredDataTest.java
index 5f15636b7..970f933a7 100644
--- a/crypto/src/test/java/org/web3j/crypto/StructuredDataTest.java
+++ b/crypto/src/test/java/org/web3j/crypto/StructuredDataTest.java
@@ -113,6 +113,20 @@ public void testEncodeType() throws IOException, RuntimeException {
                 expectedTypeEncoding);
     }
 
+    @Test
+    public void testMinimalEncodeType() throws IOException, RuntimeException {
+        String validMinimalStructuredDataJSONFilePath =
+                "build/resources/test/"
+                        + "structured_data_json_files/ValidMinimalStructuredData.json";
+        StructuredDataEncoder dataEncoder =
+                new StructuredDataEncoder(getResource(validMinimalStructuredDataJSONFilePath));
+        String expectedTypeEncoding = "EIP712Domain()";
+
+        assertEquals(
+                dataEncoder.encodeType(dataEncoder.jsonMessageObject.getPrimaryType()),
+                expectedTypeEncoding);
+    }
+
     @Test
     public void testTypeHash() throws IOException, RuntimeException {
         StructuredDataEncoder dataEncoder = new StructuredDataEncoder(jsonMessageString);
diff --git a/crypto/src/test/resources/structured_data_json_files/ValidMinimalStructuredData.json b/crypto/src/test/resources/structured_data_json_files/ValidMinimalStructuredData.json
new file mode 100644
index 000000000..6444e1ba2
--- /dev/null
+++ b/crypto/src/test/resources/structured_data_json_files/ValidMinimalStructuredData.json
@@ -0,0 +1,8 @@
+{
+  "types": {
+    "EIP712Domain": []
+  },
+  "primaryType": "EIP712Domain",
+  "domain": {},
+  "message": {}
+}
\ No newline at end of file