Resp Result

Help data structure for web framework response

Why

• Result will become 500 using as a web framework response type when Err(_), the action usually not I expect
• using a non-Result type as a web framework response type cannot use ?, the code will fill with if let or match

that why I need a RespResult, which can

• control respond code or other messages when it becomes RespResult::Err, not always 500
• impl the Try thus can use friendly ? to simplify code

note: because the Try not stable yet, this crate need Nightly rust

Usage

Install

add resp-result into your crate

[dependencies]
resp-result = "*"

feature flags

• extra-error: enable extra error message in trait RespError
• log: make tracing also logger to the log
• tracing : enable recorder using tracing
• nightly_try_v2 : impl Try for RespResult making it can use ?, it will enable feature try_trait_v2 and require Nightly rust compiler

Define an Error

RespResult<T,E> require the E impl the RespError

for example

use resp_result::{RespError, RespResult};
use std::borrow::Cow;
use http::StatusCode;

pub struct PlainError(String);

impl RespError for PlainError{
    fn log_message(&self) -> Cow<'_, str> {
        Cow::Owned(format!("PlainError: {}", self.0))
    }

    fn resp_message(&self) -> Cow<'_, str> {
        "PlainError".into()
    }

    fn http_code(&self) -> StatusCode {
        StatusCode::BAD_REQUEST
    }

    type ExtraMessage = String;

    fn extra_message(&self) -> Self::ExtraMessage {
            self.0.clone()
    }
}
/// this can be used as a handler return type
type PlainRResult<T> = RespResult<T, PlainError>;

Bound of T in RespResult<T, E>

The T require implement Serialize and has 'static lifetime

Using it

the following is an example for using [RespResult]

use resp_result::{RespError, RespResult};
use std::borrow::Cow;
use http::StatusCode;

pub struct PlainError(String);

impl RespError for PlainError{
    fn log_message(&self) -> Cow<'_, str> {
        Cow::Owned(format!("PlainError: {}", self.0))
    }

    type ExtraMessage = String;

    fn extra_message(&self) -> Self::ExtraMessage {
            self.0.clone()
    }
}
/// this can be used as a handler return type
type PlainRResult<T> = RespResult<T, PlainError>;

pub async fn welcome_short_name(name: String) -> PlainRResult<String>{
    if name.len() >= 8{
        // you can use `?` just like the function that returns `Result`
        Err(PlainError("the name size great then 8".to_string()))?;
    }

    if name.len() >= 4 {
        // `Result::Ok` can convert into `RespResult::Success` just using `into`
        Ok(format!("welcome! {name} with size great then 4")).into()
    }else{
        // or just direct using `RespResult::ok`
        RespResult::ok(format!("welcome! {name}"))
    }
}

ExtraFlag and ExtraFlags

In general the RespResult::Success is always generate response with status code 200 OK and using serde_json serialize the body into json. But sometimes we want to return an 304 Not Modified with empty body to tell the client the resource does not change. To support above using a situation, comes out the ExtraFlag and ExtraFlags

Extra Flag

extra flag have 4 different types can bring different effects on response

• empty_body: this flag will stop RespResult perform serialize into response body
• status: this flag will overwrite StatusCode of response
• set-header: this flag will insert or append provide header into the response header map
• remove-header: this flag will remove header from the response header map

different extra flags can use + to combine effect or += to adding effect

Extra Flags

extra flags is a set of extra flag

FlagWrap

flag wrap provides a wrap to send the extra flag

when using the extra flag, you need changing the return type from RespResult<T, E> to RespResult<FlagWrap<T>, E>

the follow example change Status Code to 404 Not Found

use resp_result::{RespError, RespResult, FlagWrap, ExtraFlag};
use std::borrow::Cow;
use http::StatusCode;

pub struct PlainError(String);

impl RespError for PlainError{
    fn log_message(&self) -> Cow<'_, str> {
        Cow::Owned(format!("PlainError: {}", self.0))
    }

    type ExtraMessage = String;

    fn extra_message(&self) -> Self::ExtraMessage {
            self.0.clone()
    }
}
/// this can be used as the handler return type
type PlainRResult<T> = RespResult<T, PlainError>;

pub async fn welcome_short_name(
    name: String,
    ) -> PlainRResult<FlagWrap<String>>{
        if name.len() >= 8{
            RespResult::ok(
                format!("welcome! {name} your name size is {}",name.len()))
                // using `with_flags` to covert RespResult<T, E>
                // to `RespResult<FlagWrap<T>, E>`
                // using `()` for no extra flags
                .with_flags(())
        }else{
            // using `flag_ok` directly construct a flag with the resp result
            RespResult::flag_ok(
                format!("Welcome! {name}"),
                ExtraFlag::status(StatusCode::NOT_FOUND)
            )
        }
    }

Effect RespResult behavior

by default the RespResult will serialize the response body like that

{
  "is-ok": true,
  "error-message": "...",
  "extra-msg": "...",
  "body": null
}

the default behavior can be changed by using set_config to set global configuration

for example, by config, we can change the response body into following

{
  "status": "fail",
  "reterror": 10001,
  "message": "something wrong",
  "body": null
}

See the doc of ConfigTrait for more information

Help Macros

resp_result attribute macro

This macro is used on the function. It will convert the original Result<T,E> into the RespResult, this makes writing handler more convenience.

Note: require E in Result implement the RespError

• example

// the `rresult` is an alias of `resp_result`
// the function `test` now will return a `RespResult`
#[rresult]
fn test((a, b): (i32, i64), foo: String) -> Result<(), PlainError> {
    println!("{a},{b},{foo}");
    let a = foo.parse::<i32>()?;
    println!("{a:?}");
    Ok(())
}

RespError derive macro

Using this macro while implement RespError for the enum, usually using with thiserror

It now has 2 arg on each variant of enum

1. err_msg : the message return to the client, usually need to erase the sensitive message compare with log_message. if not provided it will using log_message
2. err_code: the Http Status Code returned by this kind of error. If not provide, will be 500

Here is an example

    use std::num::ParseIntError;

    use axum::extract::rejection::PathRejection;
    use axum_resp_result::RespError;
    #[derive(Debug, thiserror::Error, RespError)]
    pub(super) enum PlainError {
        #[error("Parse Request Path Error: {0}")]
        #[resp_result(
            err_msg = "Parse Request Path Error", 
            // the error_code can either the code number or the code name
            err_code = 400
        )]
        Path(#[from] PathRejection),
        #[error("Parse Int Error: {0}")]
        #[resp_result(err_msg = "Invalid Input Integer", err_code = "Bad Request")]
        ParseInt(#[from] ParseIntError),
    }