apache/hadoop · error · IllegalStateException

The proxies specified for ${combinedProxyInterface} do not c

Error message

The proxies specified for ${combinedProxyInterface} do not cover method ${method}

What it means

ProxyCombiner.combine builds one dynamic proxy implementing combinedProxyInterface by delegating each method to one of the given backing proxies. Before creating it, it verifies coverage: every method declared on combinedProxyInterface must exist (by name and parameter types) on at least one backing proxy; the first uncovered method triggers IllegalStateException naming the interface and method. This is a fail-fast wiring check, usually hit while assembling HA-style composite proxies at startup.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/ProxyCombiner.java:75

   * @param combinedProxyInterface The interface of the combined proxy.
   * @param proxies The proxies which should be used as delegates.
   * @param <T> The type of the proxy that will be returned.
   * @return The combined proxy.
   */
  @SuppressWarnings("unchecked")
  public static <T> T combine(Class<T> combinedProxyInterface,
      Object... proxies) {
    methodLoop:
    for (Method m : combinedProxyInterface.getMethods()) {
      for (Object proxy : proxies) {
        try {
          proxy.getClass().getMethod(m.getName(), m.getParameterTypes());
          continue methodLoop; // go to the next method
        } catch (NoSuchMethodException nsme) {
          // Continue to try the next proxy
        }
      }
      throw new IllegalStateException("The proxies specified for "
          + combinedProxyInterface + " do not cover method " + m);
    }

    InvocationHandler handler =
        new CombinedProxyInvocationHandler(combinedProxyInterface, proxies);
    return (T) Proxy.newProxyInstance(combinedProxyInterface.getClassLoader(),
        new Class[] {combinedProxyInterface}, handler);
  }

  private static final class CombinedProxyInvocationHandler
      implements RpcInvocationHandler {

    private final Class<?> proxyInterface;
    private final Object[] proxies;

    private CombinedProxyInvocationHandler(Class<?> proxyInterface,
        Object[] proxies) {
      this.proxyInterface = proxyInterface;

View on GitHub (pinned to 2add963021)

Solutions

1. Ensure every method of the combined interface (exact name + parameter types) exists on at least one passed proxy.
2. Add or restore the missing method on the backing proxy/translator (keep signatures identical, including parameter types).
3. If the combined interface gained methods, update all constituent proxies in the same change.

Example fix

// before
interface Refresh extends RefreshProtocol, RefreshAdminProtocol {}
Refresh combined = (Refresh) ProxyCombiner.combine(Refresh.class,
    refreshProxy); // RefreshAdminProtocol methods uncovered -> IllegalStateException

// after
Refresh combined = (Refresh) ProxyCombiner.combine(Refresh.class,
    refreshProxy, refreshAdminProxy); // every method covered

// verify coverage before combine()
outer:
for (Method m : combinedInterface.getMethods()) {
  for (Object p : proxies) {
    try { p.getClass().getMethod(m.getName(), m.getParameterTypes()); continue outer; }
    catch (NoSuchMethodException ignored) { }
  }
  throw new IllegalStateException("No proxy covers " + m + " - add the missing backing proxy");
}
return ProxyCombiner.combine(combinedInterface, proxies);

When it happens

Trigger: Calling RPC.waitForProtocolProxy / combining proxies (e.g., HAServiceProtocol + ZKFC-style composites) where one backing proxy class lacks a method present on the combined interface; passing proxies in the wrong order for interfaces with overlapping names but different signatures; adding a method to the combined interface without updating a constituent translator.

Common situations: Custom HA client setups assembling combined protocol proxies; refactors of protocolPB translators where a method was renamed or dropped; tests stubbing one of the proxies with Mockito and losing the method.

Related errors

• Too many or few parameters for request. Method: [{}], Expect
• Too many or few parameters for request. Method: [{}], Expect
• ${theClass.getName()} could not be constructed.
• Call interrupted
• Failed to get connection for {}, {}: {} is already stopped

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/9239a8d6a19dccb3. Report an issue: GitHub.