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Sending a message is the most frequent action that a smart contract performs during the action phase. It can get into the out action list by: The sending message action consists of:
  • an 8-bit bitmask mode specifying the way of sending;
  • a cell containing the message to send, which is serialized as MessageRelaxed type.

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Message normalization

During the process of sending, the original message is normalized. In the final message that is sent to the destination address, the following changes are applied to the fields of the CommonMsgInfoRelaxed type:
  • ihr_disabled is set to true;
  • bounced is set to false;
  • fwd_fee is set to actual forward fee dedicated to the validators of the destination address shard;
  • src address is set to address of the sender smart contract;
  • created_at is set to the current Unix timestamp;
  • created_lt is set to the logical time of that action.
As a result, when composing a message cell, it is acceptable to:
  • fill the ihr_disabled, bounced, fwd_fee, created_at, and created_lt fields with any values;
  • fill the src field with addr_none.
If the message cell does not fit into the maximum allowed size (1023 bits) after the normalization, the process is repeated with different ways to pack it:
  • with init packed in a separate cell, referred from the root cell;
  • with init and body packed in separate cells.
If after the second attempt the message is still too large, the exception is thrown in the action phase. This can lead to rejecting the whole action phase, sending a bounce message, or skipping this action. The exact behavior depends on the mode bitmask of the action.

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Serialization

action_send_msg#0ec3c86d mode:(## 8) 
    out_msg:^(MessageRelaxed Any) = OutAction;

out_list_node$_ prev:^Cell action:OutAction = OutListNode;

message$_ {X:Type} info:CommonMsgInfoRelaxed
    init:(Maybe (Either StateInit ^StateInit))
    body:(Either X ^X) = MessageRelaxed X;

int_msg_info$0 ihr_disabled:Bool bounce:Bool bounced:Bool
    src:MsgAddress dest:MsgAddressInt 
    value:CurrencyCollection extra_flags:(VarUInteger 16) fwd_fee:Grams
    created_lt:uint64 created_at:uint32 = CommonMsgInfoRelaxed;

ext_out_msg_info$11 src:MsgAddress dest:MsgAddressExt
    created_lt:uint64 created_at:uint32 = CommonMsgInfoRelaxed;