You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: convert.rs
    path of file: ./repos/rust-teos/watchtower-plugin/src
    
    the code of the file until where you have to start completion: use std::fmt;
use std::{convert::TryFrom, str::FromStr};

use hex::FromHex;
use serde::{Deserialize, Serialize};
use serde_json::json;

use bitcoin::{Transaction, Txid};

use teos_common::appointment::Locator;
use teos_common::TowerId;

/// Errors related to the `registertower` command.
#[derive(Debug)]
pub enum RegisterError {
    InvalidId(String),
    InvalidHost(String),
    InvalidPort(String),
    InvalidFormat(String),
}

impl std::fmt
    
    fn try_from(value: serde_json::Value) -> Result<Self, Self::Error> {
        match value {
            serde_json::Value::Array(a) => {
                let param_count = a.len();
                if param_count != 2 {
                    Err(GetAppointmentError::InvalidFormat(format!(
                        "Unexpected request format. The request needs 2 parameter. Received: {param_count}"
                    )))
                } else {
                    let tower_id = if let Some(s) = a.get(0).unwrap().as_str() {
                        TowerId::from_str(s).map_err(|_| {
                            GetAppointmentError::InvalidId("Invalid tower id".to_owned())
                        })
                    } else {
                        Err(GetAppointmentError::InvalidId(
                            "tower_id must be a hex encoded string".to_owned(),
                        ))
                    }?;

                    let locator = if let Some(s) = a.get(1).unwrap().as_str() {
                        Locator::from_hex(s).map_err(|_| {
                            GetAppointmentError::InvalidLocator("Invalid locator".to_owned())
                        })
                    } else {
                        Err(GetAppointmentError::InvalidLocator(
                            "locator must be a hex encoded string".to_owned(),
                        ))
                    }?;

                    Ok(Self { tower_id, locator })
                }
            }
            serde_json::Value::Object(mut m) => {
                let allowed_keys = ["tower_id", "locator"];

                if m.len() > allowed_keys.len() {
                    return Err(GetAppointmentError::InvalidFormat(
                        "Invalid named argument found in request".to_owned(),
                    ));
                }

                // DISCUSS: There may be a more idiomatic way of doing this
                for k in allowed_keys.iter() {
                    if !m.contains_key(*k) {
                        return Err(GetAppointmentError::InvalidFormat(format!(
                            "{k} is mandatory"
                        )));
                    }
                }

                let mut params = Vec::with_capacity(allowed_keys.len());
                for k in allowed_keys {
                    if let Some(v) = m.remove(k) {
                        params.push(v);
                    }
                }
                GetAppointmentParams::try_from(json!(params))
            }
            _ => Err(GetAppointmentError::InvalidFormat(format!(
                "Unexpected request format. Expected: tower_id locator. Received: '{value}'"
            ))),
        }
    }