 <p>Assume you defined a object named Foo,</p> <pre><code>message Foo { ... } </code></pre> <p>If you want to send a list of Foo, you can make it a repeated field in another message,</p> <pre><code>message FooList { repeated Foo foos = 1; } </code></pre> <p>You can check the <a href="https://developers.google.com/protocol-buffers/docs/proto" rel="nofollow">language guide</a> ,</p> <pre><code>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. </code></pre>