add-explorer

name	add-explorer
description	Add support for a new blockchain explorer API to diffyscan. Use when a new chain or explorer type needs to be supported.
disable-model-invocation	true
argument-hint	["explorer-name"]

Guide through adding support for a new blockchain explorer to diffyscan.

Decision tree: do you need code changes?

Most new chains need NO code changes. Work through this list in order:

1. Etherscan v2 API (preferred) -- If the chain is listed on Etherscan's v2 supported chains, create a config with "explorer_hostname": "api.etherscan.io" and "explorer_chain_id": <chain-id>. Done. No code changes. This uses the endpoint https://api.etherscan.io/v2/api?chainid=<id>&module=contract&action=getsourcecode&address=<addr>.

2. Legacy Etherscan-compatible hostname -- If the chain has its own Etherscan-style API (e.g. api.basescan.org, api-optimistic.etherscan.io), create a config with just "explorer_hostname" (no explorer_chain_id). The default fetcher handles it. No code changes.

3. Existing Blockscout domain -- If the chain uses a Blockscout instance whose domain already ends with one of the recognized suffixes (see dispatcher below), create a config with that hostname. No code changes.

4. New Blockscout domain -- If the chain uses Blockscout but with an unrecognized domain, add the domain suffix to _get_explorer_fetcher(). One-line change.

5. Entirely new API format -- Only if the explorer has a non-Etherscan, non-Blockscout API do you need a new fetcher function.

Architecture: diffyscan/utils/explorer.py

All explorer logic lives in one file. The call flow is:

get_contract_from_explorer()          # public entry point, handles caching
  -> _get_explorer_fetcher()          # dispatcher: hostname -> (fetcher_fn, requires_token)
  -> fetcher(...)                     # one of the four fetchers below
  -> _validate_contract_name()        # verify name matches config

The dispatcher: _get_explorer_fetcher(explorer_hostname)

This function maps hostnames to fetcher functions using prefix/suffix matching. It returns a tuple of (fetcher_function, requires_token: bool).

Current routing rules (checked in order):

Condition	Fetcher	Token required?
hostname.startswith("zksync")	_get_contract_from_zksync	No
hostname.endswith("mantle.xyz")	_get_contract_from_mantle	No
hostname.endswith("lineascan.build")	_get_contract_from_etherscan (token forced to None)	No
hostname.endswith(...) any of: mode.network, blockscout.com, swellnetwork.io, lisk.com, inkonchain.com, routescan.io, monadvision.com	_get_contract_from_blockscout	No
Default (everything else)	_get_contract_from_etherscan	Yes

When requires_token is True, the caller passes (token, hostname, address, chain_id). When False, the caller passes (hostname, address) only.

Fetcher 1: _get_contract_from_etherscan(token, hostname, address, chain_id=None)

Handles both Etherscan v2 and legacy Etherscan APIs.

• v2 endpoint (when chain_id is set): https://{hostname}/v2/api?chainid={chain_id}&module=contract&action=getsourcecode&address={address}&apikey={token}
• Legacy endpoint (when chain_id is None): https://{hostname}/api?module=contract&action=getsourcecode&address={address}&apikey={token}
• Has built-in rate-limit retry logic (up to 5 retries with linear backoff)
• Response format: {"message": "OK", "result": [{"ContractName": ..., "SourceCode": ..., "CompilerVersion": ..., ...}]}
• If SourceCode starts with {{, it is treated as a JSON solc standard input (stripped of outer braces and parsed)
• Otherwise, _build_source_files() + _build_solc_input() construct the solc input from flat source
• Limitation: Flattened (single-file) contracts and contracts verified without standard JSON input may produce incomplete solc inputs. The flat-source path creates a minimal solc input from the single source file plus any AdditionalSources, but without the original compiler settings (e.g. remappings, via-IR). This can cause bytecode mismatches even when source diffs are clean.

Fetcher 2: _get_contract_from_blockscout(hostname, address)

• Endpoint: https://{hostname}/api/v2/smart-contracts/{address}
• No API token needed
• Response is a flat JSON object with fields: name, file_path, source_code, additional_sources (list of {file_path, source_code}), compiler_version, compiler_settings, optimization_enabled, optimization_runs, constructor_args, evm_version, external_libraries (list of {name, address, ...})
• Note: the response uses both optimization_runs and optimizations_runs (typo in some Blockscout versions); the code checks both

Fetcher 3: _get_contract_from_zksync(hostname, address)

• Endpoint: https://{hostname}/contract_verification/info/{address}
• No API token needed
• Response: {"verifiedAt": ..., "request": {"ContractName": ..., "CompilerVersion": ..., "sourceCode": {"sources": ...}}}
• Returns a minimal contract dict with name, sources, compiler -- does NOT go through _build_contract_payload or _attach_contract_metadata
• Outlier: Unlike the other fetchers, this does not return solcInput. Downstream code (run_source_diff, run_bytecode_diff) expects contract["solcInput"], so zkSync contracts use a different code path. New fetchers should follow the standard shape returned by _build_contract_payload (name, compiler, solcInput, plus optional constructor_arguments, evm_version, libraries).

Fetcher 4: _get_contract_from_mantle(hostname, address)

• Endpoint: https://{hostname}/api?module=contract&action=getsourcecode&address={address}
• No API token needed
• Etherscan-like response but uses FileName (not ContractName) as primary path, and AdditionalSources list uses Filename/SourceCode keys (note capitalization differences)

Shared helpers

• _build_source_files(primary_path, primary_source, additional_sources, *, path_key, content_key) -- Assembles a {path: {"content": source}} dict. The path_key and content_key parameters handle the field name differences between explorers.
• _build_solc_input(source_files, *, optimizer_enabled, optimizer_runs, settings=None) -- Wraps source files into a standard solc JSON input with optimizer config and output selection.
• _build_contract_payload(name, compiler, solc_input, *, constructor_arguments, evm_version, libraries) -- Assembles the final contract dict and calls _attach_contract_metadata().
• _attach_contract_metadata(contract, source_files, constructor_arguments, evm_version, libraries) -- Normalizes and attaches constructor args (hex string without 0x prefix), EVM version (None if "default"), and libraries (resolved to {path: {name: address}} format). Libraries can come from explorer response OR from solcInput.settings.libraries; both are merged.

Steps: adding a new Etherscan v2 chain (no code changes)

1. Find the chain ID (e.g. from chainlist.org)
2. Create config_samples/<chain>/<config>.json:

   {
     "contracts": { ... },
     "explorer_hostname": "api.etherscan.io",
     "explorer_token_env_var": "ETHERSCAN_EXPLORER_TOKEN",
     "explorer_chain_id": <chain-id>,
     "github_repo": { ... }
   }
   

3. Test: uv run diffyscan <config> --yes --cache-explorer

Steps: adding a new Blockscout domain

1. Add the domain suffix to the tuple in _get_explorer_fetcher() in diffyscan/utils/explorer.py (the any(explorer_hostname.endswith(domain) for domain in [...]) block)
2. Create a config with "explorer_hostname": "<blockscout-hostname>"
3. Test: uv run diffyscan <config> --yes --cache-explorer

Steps: adding a completely new explorer type

1. Understand the API: Document the endpoint URL, response shape, and which fields map to contract name, source code, compiler version, optimizer settings, constructor args, EVM version, and libraries.

2. Add hostname detection in _get_explorer_fetcher(): Add a new elif branch with startswith() or endswith() matching. Return (your_fetcher, False) -- most non-Etherscan explorers do not use API tokens.

3. Implement the fetcher _get_contract_from_<name>(hostname, address):

   • Call the explorer API via fetch(url).json()
   • Validate response (check for verification status, required fields)
   • Use _build_source_files() to assemble sources (pass the correct path_key/content_key for the response format)
   • Use _build_solc_input() to wrap into solc input
   • Return via _build_contract_payload() to get normalized metadata
   • If the fetcher does not need a token, its signature should be (hostname, address) (two args). If it does need a token, use (token, hostname, address, chain_id=None) (four args) and set requires_token=True in the dispatcher.

4. Add tests in tests/test_explorer_utils.py -- follow the existing pattern: monkeypatch fetch to return a DummyResponse, call get_contract_from_explorer(), assert the result.

5. Add a config sample in config_samples/<chain>/.

Config fields reference

Field	Required	Description
explorer_hostname	Yes	API hostname (e.g. api.etherscan.io, explorer.mode.network)
explorer_chain_id	No	Chain ID for Etherscan v2 API; omit for legacy or non-Etherscan explorers
explorer_token_env_var	No	Env var name holding the API key (e.g. ETHERSCAN_EXPLORER_TOKEN)

Testing

• Unit tests: tests/test_explorer_utils.py -- monkeypatch diffyscan.utils.explorer.fetch and CACHE_DIR
• Integration: uv run diffyscan <config> --yes --cache-explorer
• The --cache-explorer flag caches responses to .diffyscan_cache/ so repeated runs do not hit the API

Checklist

• Determined whether code changes are actually needed (most chains: no)
• If Etherscan v2: config-only with explorer_hostname + explorer_chain_id
• If new Blockscout domain: added suffix to _get_explorer_fetcher() tuple
• If new API type: implemented fetcher, added dispatcher rule, used shared helpers
• Config sample created in config_samples/<chain>/
• Tests added in tests/test_explorer_utils.py
• .env.example updated if a new token env var is needed