Add return code to get_block_hash_fn

bindings/go/evmc/host.c

@@ -97,8 +97,8 @@ static inline void go_exported_functions_type_checks()
     tx_context = getTxContext(context);
 
     evmc_get_block_hash_fn get_block_hash_fn = NULL;
-    get_block_hash_fn(uint256be, context, number);
-    getBlockHash(uint256be, context, number);
+    status = get_block_hash_fn(uint256be, context, number);
+    status = getBlockHash(uint256be, context, number);
 
     evmc_emit_log_fn emit_log_fn = NULL;
     emit_log_fn(context, address, data, size, uint256be, size);

bindings/go/evmc/host.go

@@ -182,11 +182,21 @@ func getTxContext(pCtx unsafe.Pointer) C.struct_evmc_tx_context {
 }
 
 //export getBlockHash
-func getBlockHash(pResult *C.struct_evmc_uint256be, pCtx unsafe.Pointer, number int64) {
+func getBlockHash(pResult *C.struct_evmc_uint256be, pCtx unsafe.Pointer, number int64) C.int {
 	idx := int((*C.struct_extended_context)(pCtx).index)
 	ctx := getHostContext(idx)
 
-	*pResult = evmcUint256be(ctx.GetBlockHash(number))
+	blockhash := ctx.GetBlockHash(number)
+
+	*pResult = evmcUint256be(blockhash)
+
+	r := C.int(0)
+	if blockhash != (common.Hash{}) {
+		// All zeroes hash is considered a failure in lookup.
+		// FIXME: should we instead adjust `ctx.GetBlockHash`?
+		r = 1
+	}
+	return r
 }
 
 //export emitLog

examples/example_host.cpp

@@ -107,11 +107,12 @@ static evmc_tx_context get_tx_context(evmc_context* context)
     return result;
 }
 
-static void get_block_hash(evmc_uint256be* result, evmc_context* context, int64_t number)
+static int get_block_hash(evmc_uint256be* result, evmc_context* context, int64_t number)
 {
     (void)result;
     (void)context;
     (void)number;
+    return 0;
 }
 
 static void emit_log(evmc_context* context,

include/evmc/evmc.h

@@ -153,17 +153,19 @@ typedef struct evmc_tx_context (*evmc_get_tx_context_fn)(struct evmc_context* co
 /**
  * Get block hash callback function.
  *
- *  This callback function is used by an EVM to query the block hash of
- *  a given block.
+ *  This callback function is used by an VM to query the block hash of
+ *  a given block. If the requested block is not found, then an appropriate
+ *  result code is returned.
  *
- *  @param[out] result   The returned block hash value.
+ *  @param[out] result   The returned block hash value. Only written to
+ *                       if the return value is 1 (information is avialable).
  *  @param      context  The pointer to the Host execution context.
- *  @param      number   The block number. Must be a value between
- *                       (and including) 0 and 255.
+ *  @param      number   The block number.
+ *  @return              1 if the information is available, 0 otherwise.
  */
-typedef void (*evmc_get_block_hash_fn)(struct evmc_uint256be* result,
-                                       struct evmc_context* context,
-                                       int64_t number);
+typedef int (*evmc_get_block_hash_fn)(struct evmc_uint256be* result,
+                                      struct evmc_context* context,
+                                      int64_t number);
 
 /**
  * The execution status code.