fix: explicitly throw an error for filter methods until subscriptions…

… is properly implemented

common/errors.go

@@ -459,6 +459,21 @@ func (e *ErrUnknownNetworkArchitecture) ErrorStatusCode() int {
 	return http.StatusBadRequest
 }
 
+type ErrNotImplemented struct{ BaseError }
+
+var NewErrNotImplemented = func(msg string) error {
+	return &ErrNotImplemented{
+		BaseError{
+			Code:    "ErrNotImplemented",
+			Message: msg,
+		},
+	}
+}
+
+func (e *ErrNotImplemented) ErrorStatusCode() int {
+	return http.StatusNotImplemented
+}
+
 type ErrInvalidEvmChainId struct{ BaseError }
 
 var NewErrInvalidEvmChainId = func(chainId any) error {

docs/pages/operation/directives.mdx

@@ -119,7 +119,7 @@ When sending requests to eRPC you can instruct to use only one specific upstream
 This will skip over any upstream that does not match the value you've provided.
 
 <Callout type="info">
-    You can use "*" as wildcard character to match a group of upstreams. e.g. "priv-*" will match any upstream IDs starting with "priv-"
+    You can use `*` as wildcard character to match a group of upstreams. e.g. "priv-*" will match any upstream IDs starting with "priv-"
 </Callout>
 
 For example if you want to make sure that request is sent to a specific upstream:

erpc/networks.go

@@ -147,6 +147,22 @@ func (n *Network) Forward(ctx context.Context, req *common.NormalizedRequest) (*
 		}
 	}
 
+	upsList, err := n.upstreamsRegistry.GetSortedUpstreams(n.NetworkId, method)
+	if err != nil {
+		if inf != nil {
+			inf.Close(nil, err)
+		}
+		return nil, err
+	}
+
+	// 3) Check if we should handle this method on this network
+	if err := n.shouldHandleMethod(method, upsList); err != nil {
+		if inf != nil {
+			inf.Close(nil, err)
+		}
+		return nil, err
+	}
+
 	// 3) Apply rate limits
 	if err := n.acquireRateLimitPermit(req); err != nil {
 		if inf != nil {
@@ -184,14 +200,7 @@ func (n *Network) Forward(ctx context.Context, req *common.NormalizedRequest) (*
 		return resp, err
 	}
 
-	upsList, err := n.upstreamsRegistry.GetSortedUpstreams(n.NetworkId, method)
-	if err != nil {
-		if inf != nil {
-			inf.Close(nil, err)
-		}
-		return nil, err
-	}
-
+	// 5) Actual forwarding logic
 	var execution failsafe.Execution[*common.NormalizedResponse]
 	var errorsByUpstream = map[string]error{}
 
@@ -369,6 +378,18 @@ func (n *Network) EvmChainId() (int64, error) {
 	return n.cfg.Evm.ChainId, nil
 }
 
+func (n *Network) shouldHandleMethod(method string, upsList []*upstream.Upstream) error {
+	if method == "eth_newFilter" ||
+		method == "eth_newBlockFilter" ||
+		method == "eth_newPendingTransactionFilter" {
+		if len(upsList) > 1 {
+			return common.NewErrNotImplemented("eth_newFilter, eth_newBlockFilter and eth_newPendingTransactionFilter are not supported yet when there are more than 1 upstream defined")
+		}
+	}
+
+	return nil
+}
+
 func (n *Network) enrichStatePoller(method string, req *common.NormalizedRequest, resp *common.NormalizedResponse) {
 	switch n.Architecture() {
 	case common.ArchitectureEvm: