Fix: Decline non-object JSON bodies as foreign traffic in the JSON-RPC parsers

authbridge/authlib/plugins/a2aparser/plugin.go

@@ -43,10 +43,19 @@ func (p *A2AParser) OnRequest(_ context.Context, pctx *pipeline.Context) pipelin
 		return pipeline.Action{Type: pipeline.Continue}
 	}
 
+	// A top-level non-object body (array, string, number, null) is not
+	// JSON-RPC; peek the first byte so it takes the calm skip path below
+	// rather than logging as malformed.
+	trimmed := bytes.TrimLeft(pctx.Body, " \t\r\n")
+	isObject := len(trimmed) > 0 && trimmed[0] == '{'
+
 	var rpc parsercommon.JSONRPCRequest
-	if err := json.Unmarshal(pctx.Body, &rpc); err != nil {
-		slog.Debug("a2a-parser: invalid JSON-RPC", "error", err, "bodyLen", len(pctx.Body))
-		return pipeline.Action{Type: pipeline.Continue}
+	if isObject {
+		if err := json.Unmarshal(pctx.Body, &rpc); err != nil {
+			slog.Debug("a2a-parser: invalid JSON-RPC", "error", err, "bodyLen", len(pctx.Body),
+				"host", pctx.Host, "path", pctx.Path)
+			return pipeline.Action{Type: pipeline.Continue}
+		}
 	}
 
 	// Claim only A2A-namespace methods. Both A2A and MCP ride JSON-RPC 2.0
@@ -58,8 +67,9 @@ func (p *A2AParser) OnRequest(_ context.Context, pctx *pipeline.Context) pipelin
 	// (which unmarshals into JSONRPCRequest with an empty Method). Without
 	// it, abctl showed a phantom a2a-parser match on both MCP and inference
 	// traffic. mcp-parser has the mirror guard for its own namespace.
-	if !isA2AMethod(rpc.Method) {
-		slog.Debug("a2a-parser: not an A2A-namespace method, skipping", "method", rpc.Method, "bodyLen", len(pctx.Body))
+	if !isObject || !isA2AMethod(rpc.Method) {
+		slog.Debug("a2a-parser: not an A2A-namespace method, skipping", "method", rpc.Method,
+			"bodyLen", len(pctx.Body), "host", pctx.Host, "path", pctx.Path)
 		return pipeline.Action{Type: pipeline.Continue}
 	}
 

authbridge/authlib/plugins/a2aparser/plugin_test.go

@@ -345,6 +345,12 @@ func TestA2AParser_NonJSONRPCBody_NoMatch(t *testing.T) {
 		{"openai chat completions", `{"model":"gpt-4","messages":[{"role":"user","content":"hi"}],"stream":true}`},
 		{"empty object", `{}`},
 		{"explicit empty method", `{"jsonrpc":"2.0","id":1,"method":"","params":{}}`},
+		// Non-object JSON: declined on shape, before any method check. The
+		// array wraps a real A2A method on purpose — it would match
+		// isA2AMethod if it were an object.
+		{"top-level array", `[{"jsonrpc":"2.0","id":1,"method":"message/send"}]`},
+		{"top-level string", `"hello"`},
+		{"top-level number", `42`},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {

authbridge/authlib/plugins/mcpparser/plugin.go

@@ -209,10 +209,19 @@ func (p *MCPParser) OnRequest(_ context.Context, pctx *pipeline.Context) pipelin
 		return pipeline.Action{Type: pipeline.Continue}
 	}
 
+	// A top-level non-object body (array, string, number, null) is not
+	// JSON-RPC; peek the first byte so it takes the calm skip path below
+	// rather than logging as malformed.
+	trimmed := bytes.TrimLeft(pctx.Body, " \t\r\n")
+	isObject := len(trimmed) > 0 && trimmed[0] == '{'
+
 	var rpc parsercommon.JSONRPCRequest
-	if err := json.Unmarshal(pctx.Body, &rpc); err != nil {
-		slog.Debug("mcp-parser: body is not valid JSON-RPC", "error", err, "bodyLen", len(pctx.Body))
-		return pipeline.Action{Type: pipeline.Continue}
+	if isObject {
+		if err := json.Unmarshal(pctx.Body, &rpc); err != nil {
+			slog.Debug("mcp-parser: body is not valid JSON-RPC", "error", err, "bodyLen", len(pctx.Body),
+				"host", pctx.Host, "path", pctx.Path)
+			return pipeline.Action{Type: pipeline.Continue}
+		}
 	}
 	// Claim only MCP-namespace methods. Both MCP and A2A ride JSON-RPC 2.0
 	// over HTTP, so "the method is non-empty" cannot tell them apart — the
@@ -223,8 +232,9 @@ func (p *MCPParser) OnRequest(_ context.Context, pctx *pipeline.Context) pipelin
 	// JSONRPCRequest with an empty Method) — which would otherwise show a
 	// phantom "mcp: {}" on every such event. a2a-parser has the mirror
 	// guard for its own namespace.
-	if !isMCPMethod(rpc.Method) {
-		slog.Debug("mcp-parser: not an MCP-namespace method, skipping", "method", rpc.Method, "bodyLen", len(pctx.Body))
+	if !isObject || !isMCPMethod(rpc.Method) {
+		slog.Debug("mcp-parser: not an MCP-namespace method, skipping", "method", rpc.Method,
+			"bodyLen", len(pctx.Body), "host", pctx.Host, "path", pctx.Path)
 		return pipeline.Action{Type: pipeline.Continue}
 	}
 

authbridge/authlib/plugins/mcpparser/plugin_test.go

@@ -186,6 +186,26 @@ func TestMCPParser_SkipsJSONThatIsNotJSONRPC(t *testing.T) {
 	}
 }
 
+// A top-level JSON array is not JSON-RPC, so it is declined on shape
+// before any method check — the body here wraps a real MCP method that
+// would match isMCPMethod if it were an object.
+func TestMCPParser_TopLevelArray_NoMatch(t *testing.T) {
+	p := NewMCPParser()
+	pctx := &pipeline.Context{
+		Body: []byte(`[{"jsonrpc":"2.0","id":1,"method":"tools/list"}]`),
+	}
+	action := p.OnRequest(context.Background(), pctx)
+	if action.Type != pipeline.Continue {
+		t.Fatalf("expected Continue, got %v", action.Type)
+	}
+	if pctx.Extensions.MCP != nil {
+		t.Errorf("MCP should remain nil for a top-level array, got %+v", pctx.Extensions.MCP)
+	}
+	if pctx.Extensions.Invocations != nil {
+		t.Errorf("expected no Invocation recorded, got %+v", pctx.Extensions.Invocations)
+	}
+}
+
 // MCP and A2A both ride JSON-RPC 2.0, so mcp-parser must NOT claim A2A
 // methods just because they carry a non-empty JSON-RPC method. Gating on
 // the MCP namespace makes it decline A2A traffic (message/*, tasks/*,