Assume you defined a object named Foo,
message Foo {
...
}
If you want to send a list of Foo, you can make it a repeated field in another message,
message FooList {
repeated Foo foos = 1;
}
You can check the language guide ,
You specify that message fields are one of the following:
required: a well-formed message must have exactly one of this field.
optional: a well-formed message can have zero or one of this field (but not more than one).
repeated: this field can be repeated any number of times (including zero) in a well-formed message. The order of the repeated values will be preserved.