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Error Messages

4ward produces actionable, specific error messages for every P4Runtime operation. Every error tells you what went wrong, shows the value you sent, and lists the valid options.

Examples

Unknown table ID: 

NOT_FOUND: unknown table ID 99999 (valid tables: 'port_table' (44171635))

Wrong action for a table: 

INVALID_ARGUMENT: unknown action ID 99999 in table 'port_table'
  (valid actions: 'MyIngress.forward' (29683729),
   'MyIngress.drop' (25652968), 'NoAction' (21257015))

Match field type mismatch: 

INVALID_ARGUMENT: match field 'hdr.ethernet.etherType' expects EXACT but got TERNARY

Table full: 

RESOURCE_EXHAUSTED: table 'port_table' is full (1024 entries)

@refers_to violation: 

INVALID_ARGUMENT: @refers_to violation: no entry in 'target_table'
  with 'id' = 0xaabbccddeeff

Constraint violation (with source location from @entry_restriction): 

INVALID_ARGUMENT: All entries must satisfy:

In @entry_restriction of table 'MyIngress.acl'; at offset line 2, columns 9 to 58:
  |
2 |         ipv4_dst::mask != 0 -> ether_type::value == 0x0800;
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

But your entry does not.

Simulator error (with P4 source location): 

INTERNAL: undefined variable: x (at my_program.p4:42:3)

Design principles

  • What, not just that. Every error includes the entity name, the value that caused the problem, and the constraint that was violated.
  • How to fix it. "Unknown" errors list valid options with their numeric IDs. Enum errors list valid values.
  • Where in the P4 source. Simulator errors include the P4 file, line, and column from the IR source info.
  • Proper gRPC status codes. NOT_FOUND for missing entities, INVALID_ARGUMENT for malformed requests, RESOURCE_EXHAUSTED for capacity limits, FAILED_PRECONDITION for state requirements, PERMISSION_DENIED for arbitration, UNIMPLEMENTED for unsupported features.
  • Structured error details. Batch writes include per-update status with space and code fields per P4Runtime spec section 12.3.
  • Golden-tested. All 75 error paths are locked down by golden tests. Messages cannot silently degrade. Update with: 
    bazel test //grpc:GoldenErrorTest --test_env=UPDATE_GOLDEN=1

All error messages

See grpc/golden_errors/ for the complete list of golden-tested error messages.