How do I encode and decode the map type in proto properly?

[litcc]

How do I encode and decode the map type in proto properly?

syntax = "proto3";
import "google/protobuf/wrappers.proto";
message DefaultMessage{
  google.protobuf.StringValue address = 1;
  google.protobuf.StringValue replay = 2;
  map<string, string> headers = 3;
  google.protobuf.BytesValue body = 4;
}

Code generated using prost_build :

#[derive(Clone, PartialEq, ::prost::Message)]
pub struct DefaultMessage {
    #[prost(message, optional, tag="1")]
    pub address: ::core::option::Option<::prost::alloc::string::String>,
    #[prost(message, optional, tag="2")]
    pub replay: ::core::option::Option<::prost::alloc::string::String>,
    #[prost(map="string, string", tag="3")]
    pub headers: ::std::collections::HashMap<::prost::alloc::string::String, ::prost::alloc::string::String>,
    #[prost(message, optional, tag="4")]
    pub body: ::core::option::Option<::prost::alloc::vec::Vec<u8>>,
}

Manually written code:

impl TryFrom<DefaultMessage>  for BytesMut{
    type Error = EncodeError;
    fn try_from(value: DefaultMessage) -> Result<Self, Self::Error> {
        let mut bytes11 = BytesMut::new();
        Message::encode(&value,&mut bytes11)?;
        Ok(bytes11)
    }
}

impl TryFrom<BytesMut>  for DefaultMessage{
    type Error = DecodeError;

    fn try_from(value: BytesMut) -> Result<DefaultMessage, DecodeError> {
        let data: DefaultMessage = Message::decode(value)?;
        Ok(data)
    }
}

Manually written call test code:

let kk: DefaultMessage = DefaultMessage::new();
let bytes11 = BytesMut::try_from(kk);
println!("{:?}", bytes11);
let kkk = bytes11.unwrap();
let data1 = DefaultMessage::try_from(kkk);
println!("{:?}", data1);

Error reporting:

error[E0433]: failed to resolve: could not find `hash_map` in `encoding`
  --> /mnt/work/code/Me/Rust/EventBus/target/debug/build/event_bus-080bae14922086fd/out/event_bus.message.rs:32:28
   |
32 | #[derive(Clone, PartialEq, ::prost::Message)]
   |                            ^^^^^^^^^^^^^^^^ could not find `hash_map` in `encoding`
   |
   = note: this error originates in the derive macro `::prost::Message` (in Nightly builds, run with -Z macro-backtrace for more info)

When I remove the map type, the program executes normally

[LucioFranco]

I'm not sure what is going on here, could you provide a reproducible set of code I can run locally?

[litcc]

Reproduction code:

https://github.com/litcc/prost-issue-reproduce

Compiler environment.
stable-x86_64-unknown-linux-gnu (default)
rustc 1.63.0 (4b91a6ea7 2022-08-08)

[LucioFranco]

Your problem is that you turned off default features which includes no enabling the std feature which is required to use HashMap's since that type only exists if you use std. The fix is this:

prost = { version = "0.11", default-features = false, features = ["prost-derive", "std"] }

Or by just enabling default features.

[litcc]

thank you for your reply! 👍