Cli to generate protocol buffers - protoc

Question

In my test.proto file I have as below, i.e. no field inside message HTML, how do I set a value for the _html field of message Page?
message HTML{
enum Type {
NO_TYPE = 0;
HTML5 = 1;
XHTML = 2;
}
}
message Page{
optional HTML _html = 1;
}
How can I set the values?
echo _html : **???** | protoc --encode=Page test.proto > binary.data
https://medium.com/#at_ishikawa/cli-to-generate-protocol-buffers-c2cfdf633dce

Answer 1

How can I set the values?
you can't when it is defined like you have shown. The message HTML only contains a definition of an enum but no actual fields. You can either add a field in the message HTML, or define the type in Page as HTML.Type instead of just HTML:
test.proto:
message HTML{
enum Type {
NO_TYPE = 0;
HTML5 = 1;
XHTML = 2;
}
}
message Page{
optional HTML.Type _html = 1;
}
and then create a file test.txt:
_html: HTML5
you can create a binary file like this:
protoc --experimental_allow_proto3_optional --encode Page test.proto < test.txt > binary.data
and decode it :
protoc --experimental_allow_proto3_optional --decode Page test.proto < binary.data
The last command prints:
_html: HTML5
Apart from the enum definition, the HTML message is an Empty message, which even exists as a predefined message:
// A generic empty message that you can re-use to avoid defining duplicated
// empty messages in your APIs. A typical example is to use it as the request
// or the response type of an API method.
// The JSON representation for Empty is empty JSON object {}.
message Empty {}