simulators/eth2/common: create client interfaces, update mock builder (…

…#738)

* simulators/eth2/common: refactor clients

* simulators/eth2/engine: fixes due to refactor

* simulators/eth2/common: builder: invalidate payloads

* simulators/eth2/common: builder readme

* simulators/eth2/common: builder: add option to build a payload on an outdated version

* simulators/eth2/withdrawals: add invalid built payload version test

* simulators/eth2/common: builder: remove check to build invalid payload

* simulators/eth2/withdrawals: Fix check

* simulators/eth2/withdrawals: test case validation

* simulators/eth2/common: builder: fix invalidation

* simulators/eth2/withdrawals: fix verifications again

simulators/eth2/common/builder/mock/README.md

@@ -2,6 +2,17 @@
 
 Instantiates a server that listens for Builder API (https://github.com/ethereum/builder-specs/) directives and responds with payloads built using an execution client.
 
+Currently, the builder will produce payloads with the following correct fields:
+- PrevRandao
+- Timestamp
+- SuggestedFeeRecipient
+- Withdrawals
+
+For the builder to function properly, the following parameters are necessary:
+- Execution client: Required to build the payloads
+- Beacon client: Required to fetch the state of the previous slot, and calculate, e.g., the prevrandao value
+
+## Mock Payload Building
 The builder can inject modifications into the built payloads at predefined slots by using configurable callbacks:
 - Before sending the ForkchoiceUpdated directive to the execution client, by modifying the payload attributes, using `WithPayloadAttributesModifier` option
 - Before responding with the build payload to the consensus client by modifying the any field in the payload, using `WithPayloadModifier` option
@@ -10,6 +21,23 @@ Both callbacks are supplied with either the `PayloadAttributesV1`/`PayloadAttrib
 
 The callbacks must respond with a boolean indicating whether any modification was performed, and an error, if any.
 
+Predefined invalidation can also be configured by using `WithPayloadInvalidatorAtEpoch`, `WithPayloadInvalidatorAtSlot`, `WithPayloadAttributesInvalidatorAtEpoch` or `WithPayloadAttributesInvalidatorAtSlot`.
+
+## Payload Invalidation Types
+- `state_root`: Inserts a random state root value in the built payload. Payload can only be deemed invalid after the payload has been unblinded
+- `parent_hash`: Inserts a random parent hash value in the built payload. Payload can be deemed invalid without needing to unblind
+- `coinbase`: Inserts a random address as coinbase in the built payload. Payload is not invalid
+- `base_fee`: Increases the base fee value by 1 in the built payload. Payload can only be deemed invalid after the payload has been unblinded
+- `uncle_hash`: Inserts a random uncle hash value in the built payload. Payload can be deemed invalid without needing to unblind
+- `receipt_hash`: Inserts a random receipt hash value in the built payload. Payload can only be deemed invalid after the payload has been unblinded
+
+## Payload Attributes Invalidation Types
+- `remove_withdrawal`: Removes a withdrawal from the correct list of expected withdrawals
+- `extra_withdrawal`: Inserts an extra withdrawal to the correct list of expected withdrawals
+- `withdrawal_address`, `withdrawal_amount`, `withdrawal_validator_index`, `withdrawal_index`: Invalidates a single withdrawal from the correct list of expected withdrawals
+- `timestamp`: Modifies the expected timestamp value of the block (-2 epochs)
+- `prevrandao`/`random`: Modifies the expected prevrandao
+
 The builder can also be configured to insert an error on:
 - `/eth/v1/builder/header/{slot}/{parent_hash}/{pubkey}` using `WithErrorOnHeaderRequest` option
 - `/eth/v1/builder/blinded_blocks` using `WithErrorOnPayloadReveal` option
@@ -18,13 +46,20 @@ Both callbacks are supplied with the beacon slot number of the payload/blinded b
 
 The callback can then use the slot number to determine whether to throw an error or not.
 
-Currently, the builder will produce payloads with the following correct fields:
-- PrevRandao
-- Timestamp
-- SuggestedFeeRecipient
-- Withdrawals
+## Mock Builder REST API
+### Mock Error
+- `DELETE` `/mock/errors/payload_request`: Disables errors on `/eth/v1/builder/header/...`
+- `POST` `/mock/errors/payload_request`: Enables errors on `/eth/v1/builder/header/...`
+- `POST` `/mock/errors/payload_request/<slot|epoch>/{slot/epoch number}`: Enables errors on `/eth/v1/builder/header/...` starting at the slot or epoch specified
+- `DELETE` `/mock/errors/payload_reveal`: Disables errors on `/eth/v1/builder/blinded_blocks`
+- `POST` `/mock/errors/payload_reveal`: Enables errors on `/eth/v1/builder/blinded_blocks`
+- `POST` `/mock/errors/payload_reveal/<slot|epoch>/{slot/epoch number}`: Enables errors on `/eth/v1/builder/blinded_blocks` starting at the slot or epoch specified
 
-For the builder to function properly, the following parameters are necessary:
-- Execution client: Required to build the payloads
-- Beacon client: Required to fetch the state of the previous slot, and calculate, e.g., the prevrandao value
-- Beacon Spec: Required so the builder is aware of fork specific changes in the built payloads, as well as the beacon blocks
+### Mock Built Payloads
+- `DELETE` `/mock/invalid/payload_attributes`: Disables any payload attributes modification
+- `POST` `/mock/invalid/payload_attributes/{type}`: Enables specified [type](#payload-attributes-invalidation-types) payload attributes modification
+- `POST` `/mock/invalid/payload_attributes/{type}/<slot|epoch>/{slot/epoch number}`: Enables specified [type](#payload-attributes-invalidation-types) payload attributes modification starting at the slot or epoch specified
+
+- `DELETE` `/mock/invalid/payload`: Disables any modification to payload built
+- `POST` `/mock/invalid/payload/{type}`: Enables specified [type](#payload-invalidation-types) of modification to payload built
+- `POST` `/mock/invalid/payload/{type}/<slot|epoch>/{slot/epoch number}`: Enables specified [type](#payload-invalidation-types) of modification to payload built starting at the slot or epoch specified