Encode and Decode Base64 fields in JSON using Rust

Cargo.toml

[dependencies]
serde = { version = "1", features = ["derive"] }
serde_json = "1"
base64 = "0.22"

mod.rs

mod base64 {
    use base64::prelude::*;
    use serde::{Deserialize, Serialize};
    use serde::{Deserializer, Serializer};

    pub fn serialize<S: Serializer>(v: &Vec<u8>, s: S) -> Result<S::Ok, S::Error> {
        let base64 = BASE64_STANDARD.encode(v);
        String::serialize(&base64, s)
    }

    pub fn deserialize<'de, D: Deserializer<'de>>(d: D) -> Result<Vec<u8>, D::Error> {
        let base64 = String::deserialize(d)?;
        BASE64_STANDARD
            .decode(base64.as_bytes())
            .map_err(serde::de::Error::custom)
    }
}

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct Message {
    #[serde(with = "base64")]
    pub payload: Vec<u8>,
}

fn main() {
    let a = Message { payload: b"hello world".into() };
    println!("{:?}", a);
    let a_json = serde_json::to_string(&a).unwrap();
    println!("{}", a_json);
    let b: Message = serde_json::from_str(&a_json).unwrap();
    println!("{:?}", b);
    assert_eq!(a.payload, b.payload);
}

stdout

Message { payload: [104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100] }
{"payload":"aGVsbG8gd29ybGQ="}
Message { payload: [104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100] }