problem: no response from proxy if upstream returned error

fix: #35

testing/simple-upstream/src/main/groovy/testing/BlocksHandler.groovy

@@ -0,0 +1,39 @@
+package testing
+
+import com.fasterxml.jackson.databind.ObjectMapper
+
+class BlocksHandler implements CallHandler {
+
+    ObjectMapper objectMapper
+
+    BlocksHandler(ObjectMapper objectMapper) {
+        this.objectMapper = objectMapper
+    }
+
+    @Override
+    Result handle(String method, List<Object> params) {
+        if (method == "eth_blockNumber") {
+            return Result.ok("0x100001")
+        }
+        if (method == "eth_getBlockByNumber") {
+            String blockId = params[0]
+            println("get block $blockId")
+            def result = getResource("block-${blockId}.json")
+            return Result.ok(result)
+        }
+        if (method == "eth_getTransactionByHash") {
+            String txId = params[0]
+            def result = getResource("tx-${txId}.json")
+            return Result.ok(result)
+        }
+        return null
+    }
+
+    Object getResource(String name) {
+        String json = BlocksHandler.class.getResourceAsStream("/" + name)?.text
+        if (json == null) {
+            return null
+        }
+        return objectMapper.readValue(json, Map)
+    }
+}

testing/simple-upstream/src/main/groovy/testing/CallHandler.groovy

@@ -0,0 +1,42 @@
+package testing
+
+interface CallHandler {
+
+    Result handle(String method, List<Object> params)
+
+    static class Result {
+        private Object result
+        private Integer errorCode
+        private String errorMessage
+
+        Result(Object result, Integer errorCode, String errorMessage) {
+            this.result = result
+            this.errorCode = errorCode
+            this.errorMessage = errorMessage
+        }
+
+        static Result ok(Object result) {
+            return new Result(result, null, null)
+        }
+
+        static Result error(int errorCode, String errorMessage) {
+            return new Result(null, errorCode, errorMessage)
+        }
+
+        boolean isResult() {
+            return errorCode == null
+        }
+
+        Object getResult() {
+            return result
+        }
+
+        int getErrorCode() {
+            return errorCode
+        }
+
+        String getErrorMessage() {
+            return errorMessage
+        }
+    }
+}

testing/simple-upstream/src/main/groovy/testing/CommonHandlers.groovy

@@ -0,0 +1,13 @@
+package testing
+
+class CommonHandlers implements CallHandler {
+
+
+    @Override
+    Result handle(String method, List<Object> params) {
+        if (method == "eth_syncing") {
+            return Result.ok(false)
+        }
+        return null
+    }
+}

testing/simple-upstream/src/main/groovy/testing/InvalidCallHandler.groovy

@@ -0,0 +1,8 @@
+package testing
+
+class InvalidCallHandler implements CallHandler {
+    @Override
+    Result handle(String method, List<Object> params) {
+        return Result.error(-32000, "Call is not supported")
+    }
+}

testing/simple-upstream/src/main/groovy/testing/SimpleUpstream.groovy

@@ -0,0 +1,62 @@
+package testing
+
+import com.fasterxml.jackson.databind.ObjectMapper
+import spark.Spark
+
+class SimpleUpstream {
+
+    private int port = 18545
+    private ObjectMapper objectMapper
+
+    private List<CallHandler> handlers = []
+
+    void prepare() {
+        objectMapper = new ObjectMapper()
+
+        handlers << new TestcaseHandler()
+        handlers << new CommonHandlers()
+        handlers << new BlocksHandler(objectMapper)
+        handlers << new InvalidCallHandler()
+    }
+
+    void start() {
+        println("Starting upstream on 0.0.0.0:$port")
+        Spark.port(port)
+        Spark.post("/") { req, resp ->
+            println("request")
+            try {
+                Map json = objectMapper.readValue(req.body(), Map)
+                def id = json["id"]
+                String method = json["method"].toString()
+                List<Object> params = json.containsKey("params") ? json["params"] as List<Object> : []
+
+                CallHandler.Result result = handlers.findResult { h ->
+                    return h.handle(method, params)
+                }
+                Map resultJson = [
+                        id     : id,
+                        jsonrpc: "2.0"
+                ]
+                if (result.isResult()) {
+                    resultJson["result"] = result.result
+                } else {
+                    resultJson["error"] = [
+                            code   : result.getErrorCode(),
+                            message: result.getErrorMessage()
+                    ]
+                }
+                resp.status(200)
+                resp.header("content-type", "application/json")
+                return objectMapper.writeValueAsString(resultJson)
+            } catch (Throwable t) {
+                t.printStackTrace()
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        def server = new SimpleUpstream()
+        server.prepare()
+        server.start()
+    }
+}

testing/simple-upstream/src/main/groovy/testing/TestcaseHandler.groovy

@@ -0,0 +1,14 @@
+package testing
+
+class TestcaseHandler implements CallHandler {
+
+    @Override
+    Result handle(String method, List<Object> params) {
+        // https://github.com/emeraldpay/dshackle/issues/35
+        if (method == "eth_call"
+                && params[0].to?.toLowerCase() == "0x542156d51D10Db5acCB99f9Db7e7C91B74E80a2c".toLowerCase()) {
+            return Result.error(-32015, "VM execution error.")
+        }
+        return null
+    }
+}