There is a set of classes and functions in chain.hpp and contract_base.hpp for the interaction with the Echo chain.

chain interface includes:

Get balance

Member of class account.

You can get balance of account or contract in needed assets.

Parameters

Return

int64_t - requested balance.

Example

int64_t my_get_balance(string id, string asset_id)
{
    account other(id);
    return other.get_balance(asset_id);
}

Transfer

Member of class contract_base.

You can transfer assets from contract to the recipient.

Parameters

Return

void

Example

void my_transfer(string to, string asset_id, int64_t amount)
{
    transfer(to, asset_id, amount);
}

Get property of objects from echo chain

Member of class object.

You can get property of object from echo chain.

Parameters

Return

string - value of requested property.

Example

string my_get_property(string id, string request)
{
    object other(id);
    return other.get_property(request);
}

Get asset id for current contract call

Member of class contract_base.

You can get asset id with which the contract was called.

Return

uint64_t - asset id with which the contract was called.

Example

uint64_t my_get_call_asset_id()
{
    return get_call_asset_id();
}

Get block hash by number

Static member of class chain, in the namespace x86_64_contract.

You can get block hash by number.

Parameters

Return

string - block hash.

Example

string my_get_block_hash(uint32_t number)
{
    return chain::get_block_hash(number);
}

Get current head block author

Member of class contract_base.

You can get the author of current block.

Return

string - block author id.

Example

string my_get_block_author()
{
    return get_block_author();
}

Get current gas limit

Member of class contract_base.

You can get current gas limit.

Return

uint64_t int - current gas limit in 10^-8^ ECHO.

Example

uint64_t int my_get_gas_limit()
{
    return get_gas_limit();
}

Get current head block number

Member of class contract_base.

You can get current head block number.

Return

uint32_t - block number.

Example

uint32_t my_get_block_number()
{
    return get_block_number();
}

Get current head block timestamp

Member of class contract_base.

You can get current head block timestamp.

Return

uint32_t - block timestamp in seconds.

Example

uint32_t my_get_block_timestamp()
{
    return get_block_timestamp();
}

Get send value for current contract call

Member of class contract_base.

You can get send value for current contract call.

Return

int64_t - amount of send.

Example

int64_t my_get_send_value()
{
    return get_send_value();
}

Get sender for current contract call

Member of class contract_base.

You can get sender for current contract call.

Return

string - triplet id of sender.

Example

string my_get_sender()
{
    return get_sender();
}

Get origin sender for current contract call

Member of class contract_base.

You can get origin sender for current contract call.

Return

string - triplet id of sender.

Example

string my_get_origin_sender()
{
    return get_origin_sender();
}

Get called contract id

Static member of class chain, in the namespace x86_64_contract.

You can get called contract id.

Return

uint32_t - id of contract.

Example

uint32_t my_get_contract_id()
{
    return chain::get_contract_id();
}

Get called full contract id

Member of class contract_base.

You can get full contract id.

Return

string - triplet id of contract.

Example

string my_get_full_contract_id()
{
    return get_full_contract_id();
}

Get contract variable from another x86-64 contract

Member of class contract_object.

You can call get storage variable from another x86-64 contract. For the get, you will need to pass the amount by 0, count of gas by 0 and the variable name.

Parameters

Return

string - result of executing an internal contract call. First 4 bytes(8 characters) - size of output.

Example

void call_contract(string id, string var_name, uint64_t amount, uint64_t gas)
{
    contract_object c(id);
    string var_1 = c.call(amount, gas, var_name);
    string var_2 = c.call(amount, gas, string("var_name"));
}

Call x86-64 contract from another x86-64 contract with call line

Member of class contract_object.

You can call another x86-64 contract. For the call, you will need to pass the amount, count of gas to perform and the call line. If you do not want to limit the call to the gas, 0 is transmitted.

Parameters

Return

string - result of executing an internal contract call. First 4 bytes(8 characters) - size of output.

Example

string call_contract(string id, string call_line, uint64_t amount, uint64_t gas)
{
    contract_object c(id);
    return c.call(amount, gas, call_line);
}

Call x86-64 contract from another x86-64 contract with parameters

Member of class contract_object.

You can call another x86-64 contract. For the call, you will need to pass the amount, count of gas to perform, callee function name and the call params. If you do not want to limit the call to the gas, 0 is transmitted.

Parameters

Return

string - result of executing an internal contract call. First 4 bytes(8 characters) - size of output.

Example

string call_contract(string id, string var_1, unsigned int var_2, uint64_t amount, uint64_t gas)
{
    int var_local = 544;
    bool var_bool = true;
​
    contract_object c(id);
    return c.call(amount, gas, string("my_function"), var_1, var_2, var_local, var_bool, -45);
}

Echo interface contract example

#include "chain.hpp"
#include "contract_base.hpp"
#include "db_types.hpp"
#include "parameters.hpp"
#include "string.hpp"
​
namespace x86_64_contract {
​
class contract : public contract_base
{
public:
    void send_to_contract()
    {
        _value += get_send_value();
    }
​
    bool transfer(string to, string asset_id, uint64_t amount)
    {
        string sender = get_origin_sender();
        uint64_t send_with_call = get_send_value();
​
        object sender_obj(sender);
        string sender_name = sender_obj.get_property("name");
​
        if (sender != _owner && sender_name != "my_second_account")
        {
            if (send_with_call < amount)
                return false;
            else
            {
                transfer(to, asset_id, amount);
                _value += send_with_call - amount;
                return true;
            }
        }
​
        if (_value + send_with_call < amount)
            return false;
​
        transfer(to, asset_id, amount);
        _value += send_with_call - amount;        
        return true;
    }
​
    void constructor() override
    {
        _owner = get_origin_sender();
    }
​
private:
    string _name { "my_contract" };
    DB_STRING(_owner);
    DB_UINT64(_value);
};
​
MAIN(contract, FUNC(send_to_contract) FUNC(transfer))
​
}