dex-sdk 0.0.2

Strongly typed Rust SDK for Dex
Documentation 
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// Copyright (c) 2026 Super Durable, Inc.
//
// Licensed under the Super Durable Source License 1.0.
// You may not use this file except in compliance with the License.
// See the LICENSE file in the repository root.
//
// SPDX-License-Identifier: LicenseRef-Super-Durable-1.0

use std::error::Error;
use std::fmt::{Display, Formatter};

/// Result returned by application Step and RPC handlers.
pub type HandlerResult<T> = Result<T, HandlerError>;

#[derive(Clone, Debug, Eq, PartialEq)]
/// Reports an application-defined Step or RPC failure to Dex.
///
/// Return this error from [`crate::Step::wait_for`], [`crate::Step::execute`], or an RPC handler.
/// Dex records the message and applies the configured retry or failure policy.
pub struct HandlerError {
    message: String,
    error_type: String,
}

impl HandlerError {
    /// Creates a handler error with a developer-facing message.
    pub fn new(message: impl Into<String>) -> Self {
        Self {
            message: message.into(),
            error_type: std::any::type_name::<Self>().to_string(),
        }
    }

    pub(crate) fn invalid_step_result(
        flow_type: &str,
        step_type: Option<&str>,
        method: &str,
        detail: impl std::fmt::Display,
    ) -> Self {
        let target = step_type.map_or_else(
            || format!("RPC in Flow {flow_type}"),
            |step_type| format!("Flow {flow_type} Step {step_type}"),
        );
        Self {
            message: format!("{target} {method} returned an invalid result: {detail}"),
            error_type: "dex_sdk::SdkError::InvalidStepResult".to_string(),
        }
    }

    pub(crate) fn error_type(&self) -> &str {
        &self.error_type
    }
}

impl Display for HandlerError {
    fn fmt(&self, formatter: &mut Formatter<'_>) -> std::fmt::Result {
        formatter.write_str(&self.message)
    }
}

impl Error for HandlerError {}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn invalid_step_result_has_stable_context_and_type() {
        let error = HandlerError::invalid_step_result(
            "OrderFlow",
            Some("ApproveOrder"),
            "execute",
            "missing movement",
        );
        assert_eq!("dex_sdk::SdkError::InvalidStepResult", error.error_type());
        assert!(
            error
                .to_string()
                .contains("Flow OrderFlow Step ApproveOrder")
        );
    }
}