Merge pull request #127 from ethereum/evmc-query

EVM-C: Simplify callbacks

examples/capi.c

@@ -24,28 +24,12 @@ static void print_address(const struct evm_uint160be* address)
         printf("%x", address->bytes[i] & 0xff);
 }
 
-static void query(union evm_variant* result,
+static int account_exists(struct evm_env* env,
-                  struct evm_env* env,
+                           const struct evm_uint160be* address) {
-                  enum evm_query_key key,
+    printf("EVM-C: EXISTS @");
-                  const struct evm_uint160be* address) {
+    print_address(address);
-    printf("EVM-C: QUERY %d\n", key);
+    printf("\n");
-    switch (key) {
+    return 0;
-    case EVM_CODE_BY_ADDRESS:
-        result->data = NULL;
-        result->data_size = 0;
-        break;
-
-    case EVM_BALANCE:
-        result->uint256be = balance(env, address);
-        break;
-
-    case EVM_ACCOUNT_EXISTS:
-        result->int64 = 0;
-        break;
-
-    default:
-        result->int64 = 0;
-    }
 }
 
 static void get_storage(struct evm_uint256be* result,
@@ -68,6 +52,26 @@ static void set_storage(struct evm_env* env,
     printf("\n");
 }
 
+static void get_balance(struct evm_uint256be* result,
+                        struct evm_env* env,
+                        const struct evm_uint160be* address)
+{
+    printf("EVM-C: BALANCE @");
+    print_address(address);
+    printf("\n");
+    *result = balance(env, address);
+}
+
+static size_t get_code(const uint8_t** code,
+                       struct evm_env* env,
+                       const struct evm_uint160be* address)
+{
+    printf("EVM-C: CODE @");
+    print_address(address);
+    printf("\n");
+    return 0;
+}
+
 static void selfdestruct(struct evm_env* env,
                          const struct evm_uint160be* address,
                          const struct evm_uint160be* beneficiary)
@@ -109,9 +113,11 @@ static void evm_log(struct evm_env* env, const struct evm_uint160be* address,
 }
 
 static const struct evm_host example_host = {
-    query,
+    account_exists,
     get_storage,
     set_storage,
+    get_balance,
+    get_code,
     selfdestruct,
     call,
     get_tx_context,

include/evm.h

@@ -183,73 +183,16 @@ struct evm_result {
     } reserved;
 };
 
-/// The query callback key.
+/// Check account existence callback function
-enum evm_query_key {
-    EVM_CODE_BY_ADDRESS = 10, ///< Code by an address for EXTCODECOPY.
-    EVM_CODE_SIZE = 11,       ///< Code size by an address for EXTCODESIZE.
-    EVM_BALANCE = 12,         ///< Balance of a given address for BALANCE.
-    EVM_ACCOUNT_EXISTS = 14,  ///< Check if an account exists.
-};
-
-
-/// Variant type to represent possible types of values used in EVM.
 ///
-/// Type-safety is lost around the code that uses this type. We should have
+/// This callback function is used by the EVM to check if
-/// complete set of unit tests covering all possible cases.
+/// there exists an account at given address.
-/// The size of the type is 64 bytes and should fit in single cache line.
+/// @param      env      Pointer to execution environment managed by the host
-union evm_variant {
+///                      application.
-    /// A host-endian 64-bit integer.
-    int64_t int64;
-
-    /// A big-endian 256-bit integer or hash.
-    struct evm_uint256be uint256be;
-
-    /// A memory reference.
-    struct {
-        /// Pointer to the data.
-        uint8_t const* data;
-
-        /// Size of the referenced memory/data.
-        size_t data_size;
-    };
-};
-
-/// Query callback function.
-///
-/// This callback function is used by the EVM to query the host application
-/// about additional information about accounts in the state required to
-/// execute EVM code.
-/// @param[out] result  The result of the query.
-/// @param      env     Pointer to execution environment managed by the host
-///                     application.
-/// @param      key     The kind of the query. See evm_query_key
-///                     and details below.
 /// @param      address  The address of the account the query is about.
-///
+/// @return              1 if exists, 0 otherwise.
-/// ## Types of queries
+typedef int (*evm_account_exists_fn)(struct evm_env* env,
-///
+                                     const struct evm_uint160be* address);
-/// - ::EVM_CODE_BY_ADDRESS
-///   @result evm_variant::data       The appropriate code for the given address or NULL if not found.
-///
-/// - ::EVM_CODE_SIZE
-///   @result evm_variant::int64      The appropriate code size for the given address or 0 if not found.
-///
-/// - ::EVM_BALANCE
-///   @result evm_variant::uint256be  The appropriate balance for the given address or 0 if not found.
-///
-/// - ::EVM_ACCOUNT_EXISTS
-///   @result evm_variant::int64      1 if exists, 0 if not.
-///
-///
-/// @todo
-/// - Consider swapping key and address arguments,
-///   e.g. `query(result, env, addr, EVM_SLOAD, k)`.
-/// - Consider renaming key argument to something else. Key is confusing
-///   especially for SSTORE and SLOAD. Maybe "kind"?
-typedef void (*evm_query_state_fn)(union evm_variant* result,
-                                   struct evm_env* env,
-                                   enum evm_query_key key,
-                                   const struct evm_uint160be* address);
 
 /// Get storage callback function.
 ///
@@ -279,6 +222,32 @@ typedef void (*evm_set_storage_fn)(struct evm_env* env,
                                    const struct evm_uint256be* key,
                                    const struct evm_uint256be* value);
 
+/// Get balance callback function.
+///
+/// This callback function is used by an EVM to query the balance of the given
+/// address.
+/// @param[out] result   The returned balance value.
+/// @param      env      Pointer to execution environment managed by the host
+///                      application.
+/// @param      address  The address.
+typedef void (*evm_get_balance_fn)(struct evm_uint256be* result,
+                                   struct evm_env* env,
+                                   const struct evm_uint160be* address);
+
+/// Get code callback function.
+///
+/// This callback function is used by an EVM to get the code of a contract of
+/// given address.
+/// @param[out] result_code  The pointer to the contract code. This argument is
+///                          optional. If NULL is provided, the host MUST only
+///                          return the code size.
+/// @param      env          Pointer to execution context managed by the Host.
+/// @param      address      The address of the contract.
+/// @return                  The size of the code.
+typedef size_t (*evm_get_code_fn)(const uint8_t** result_code,
+                                  struct evm_env* env,
+                                  const struct evm_uint160be* address);
+
 /// Selfdestruct callback function.
 ///
 /// This callback function is used by an EVM to SELFDESTRUCT given contract.
@@ -327,10 +296,14 @@ typedef void (*evm_call_fn)(
 /// realisation of OOP interface (only virtual methods, no data).
 /// Host implementations SHOULD create constant singletons of this (similar
 /// to vtables) to lower the maintenance and memory management cost.
+///
+/// @todo Merge evm_host with evm_env?
 struct evm_host {
-    evm_query_state_fn query;
+    evm_account_exists_fn account_exists;
     evm_get_storage_fn get_storage;
     evm_set_storage_fn set_storage;
+    evm_get_balance_fn get_balance;
+    evm_get_code_fn get_code;
     evm_selfdestruct_fn selfdestruct;
     evm_call_fn call;
     evm_get_tx_context_fn get_tx_context;