AT-Parser-RS

A lightweight, no_std AT command parser library for embedded Rust applications.

Overview

AT-Parser-RS provides a flexible framework for implementing AT command interfaces in embedded systems. It supports the standard AT command syntax including execution, query, test, and set operations.

Features

• no_std compatible - suitable for bare-metal and embedded environments
• Fixed-size response buffers via Bytes<SIZE> — no heap allocation
• Support for all AT command forms:
  • AT+CMD - Execute command
  • AT+CMD? - Query current value
  • AT+CMD=? - Test supported values
  • AT+CMD=<args> - Set new value(s)
• Type-safe command registration via traits
• Static command definitions (suitable for embedded/RTOS)

Feature Flags

The library supports the following optional features:

• osal_rs - Enables integration with FreeRTOS through the osal-rs library for RTOS-based applications. Provides synchronization primitives like Mutex for thread-safe command handling.
• enable_panic - Enables a custom panic handler for no_std environments, providing a minimal panic implementation for embedded targets.

By default, no features are enabled, providing pure no_std compatibility without external dependencies.

# Build with FreeRTOS support
cargo build --features="osal_rs"

# Build with custom panic handler
cargo build --features="enable_panic"

# Build with both features
cargo build --features="osal_rs,enable_panic"

Command Forms

The parser supports four standard AT command forms:

Form	Syntax	Purpose	Example
Execute	AT+CMD	Execute an action	AT+RST
Query	AT+CMD?	Get current setting	AT+ECHO?
Test	AT+CMD=?	Get supported values	AT+ECHO=?
Set	AT+CMD=<args>	Set new value(s)	AT+ECHO=1

Note: All commands must start with the AT prefix (e.g., AT+CMD, not just +CMD). The parser expects the full AT command syntax.

Core Types

AtContext<SIZE> Trait

The main trait for implementing command handlers. The const generic SIZE defines the response buffer size in bytes. Override only the methods your command needs:

pub trait AtContext<const SIZE: usize> {
    fn exec(&self) -> AtResult<'_, SIZE>;
    fn query(&mut self) -> AtResult<'_, SIZE>;
    fn test(&mut self) -> AtResult<'_, SIZE>;
    fn set(&mut self, args: Args) -> AtResult<'_, SIZE>;
}

All methods return Err(AtError::NotSupported) by default.

AtResult<'a, SIZE> and AtError<'a>

pub type AtResult<'a, const SIZE: usize> = Result<Bytes<SIZE>, AtError<'a>>;

pub enum AtError<'a> {
    UnknownCommand,        // Command not found
    NotSupported,          // Operation not implemented
    InvalidArgs,           // Invalid argument(s)
    Unhandled(&'a str),    // Error with a borrowed description
    UnhandledOwned(String) // Error with an owned description
}

Use Unhandled when you have a static or borrowed string literal, and UnhandledOwned when you need to construct an error message dynamically at runtime.

Bytes<SIZE>

Bytes<SIZE> is a fixed-size byte buffer from osal-rs (re-exported by this crate) used to return responses without heap allocation:

use at_parser_rs::Bytes;

// Create from a string slice (truncated to SIZE if longer)
let response = Bytes::<64>::from_str("OK");

AtParser<T, SIZE>

The parser is generic over both the handler type T and the response buffer size SIZE:

pub struct AtParser<'a, T, const SIZE: usize>
where
    T: AtContext<SIZE> + ?Sized;

Args Structure

Provides access to comma-separated arguments:

pub struct Args<'a> {
    pub raw: &'a str,
}

impl<'a> Args<'a> {
    pub fn get(&self, index: usize) -> Option<&'a str>;
}

Usage Examples

1. Define Command Modules

Implement the AtContext<SIZE> trait for your command handlers. Choose a buffer size that fits your largest response string:

use at_parser_rs::context::AtContext;
use at_parser_rs::{AtResult, AtError, Args, Bytes};

const SIZE: usize = 64;

/// Echo command - returns/sets echo state
pub struct EchoModule {
    pub echo: bool,
}

impl AtContext<SIZE> for EchoModule {
    // Execute: return current echo state
    fn exec(&self) -> AtResult<'_, SIZE> {
        if self.echo {
            Ok(Bytes::from_str("ECHO: ON"))
        } else {
            Ok(Bytes::from_str("ECHO: OFF"))
        }
    }

    // Query: return current echo value
    fn query(&mut self) -> AtResult<'_, SIZE> {
        if self.echo { Ok(Bytes::from_str("1")) } else { Ok(Bytes::from_str("0")) }
    }

    // Set: enable/disable echo
    fn set(&mut self, args: Args) -> AtResult<'_, SIZE> {
        let v = args.get(0).ok_or(AtError::InvalidArgs)?;
        match v {
            "0" => {
                self.echo = false;
                Ok(Bytes::from_str("ECHO OFF"))
            }
            "1" => {
                self.echo = true;
                Ok(Bytes::from_str("ECHO ON"))
            }
            _ => Err(AtError::InvalidArgs),
        }
    }

    // Test: show valid values and usage
    fn test(&mut self) -> AtResult<'_, SIZE> {
        Ok(Bytes::from_str("Valid values: 0 (OFF), 1 (ON)"))
    }
}

/// Reset command - executes system reset
pub struct ResetModule;

impl AtContext<SIZE> for ResetModule {
    fn exec(&self) -> AtResult<'_, SIZE> {
        // Trigger hardware reset
        // reset_system();
        Ok(Bytes::from_str("OK - System reset"))
    }

    fn test(&mut self) -> AtResult<'_, SIZE> {
        Ok(Bytes::from_str("Reset the system"))
    }
}

2. Create Module Instances

For standard applications, create instances on the stack:

let mut echo = EchoModule { echo: false };
let mut reset = ResetModule;

For embedded/no_std environments with static mut (single-threaded only):

static mut ECHO: EchoModule = EchoModule { echo: false };
static mut RESET: ResetModule = ResetModule;

Note: static mut requires unsafe blocks and is only safe in single-threaded contexts. For RTOS or multi-threaded applications, use proper synchronization primitives.

3. Initialize Parser and Register Commands

use at_parser_rs::parser::AtParser;
use at_parser_rs::context::AtContext;

const SIZE: usize = 64;

let mut parser: AtParser<dyn AtContext<SIZE>, SIZE> = AtParser::new();

let commands: &mut [(&str, &mut dyn AtContext<SIZE>)] = &mut [
    ("AT+ECHO", &mut echo),
    ("AT+RST", &mut reset),
];

parser.set_commands(commands);

4. Execute Commands

// Execute: show current state
match parser.execute("AT+ECHO") {
    Ok(response) => println!("Response: {}", response),  // "ECHO: OFF"
    Err(e) => println!("Error: {:?}", e),
}

// Test: show valid values
match parser.execute("AT+ECHO=?") {
    Ok(response) => println!("Valid: {}", response),     // "Valid values: 0 (OFF), 1 (ON)"
    Err(e) => println!("Error: {:?}", e),
}

// Set: enable echo
match parser.execute("AT+ECHO=1") {
    Ok(response) => println!("Response: {}", response),  // "ECHO ON"
    Err(e) => println!("Error: {:?}", e),
}

// Query: get current value
match parser.execute("AT+ECHO?") {
    Ok(response) => println!("Echo: {}", response),      // "1"
    Err(e) => println!("Error: {:?}", e),
}

// Execute reset
match parser.execute("AT+RST") {
    Ok(response) => println!("Response: {}", response),  // "OK - System reset"
    Err(e) => println!("Error: {:?}", e),
}

// Unknown command
match parser.execute("AT+UNKNOWN") {
    Ok(_) => {},
    Err(AtError::UnknownCommand) => println!("Command not found"),
    Err(_) => {}
}

Bytes<SIZE> implements Display, so it can be printed directly with {} or converted to a string via .to_string().

Advanced Example: UART Module

use at_parser_rs::{AtResult, AtError, Args, Bytes};
use at_parser_rs::context::AtContext;

const SIZE: usize = 64;

pub struct UartModule {
    pub baudrate: u32,
    pub data_bits: u8,
}

impl AtContext<SIZE> for UartModule {
    // Query: return current configuration
    fn query(&mut self) -> AtResult<'_, SIZE> {
        Ok(Bytes::from_str("115200,8"))
    }

    // Set: configure UART
    fn set(&mut self, args: Args) -> AtResult<'_, SIZE> {
        let baudrate = args.get(0)
            .ok_or(AtError::InvalidArgs)?
            .parse::<u32>()
            .map_err(|_| AtError::InvalidArgs)?;
        
        let data_bits = args.get(1)
            .ok_or(AtError::InvalidArgs)?
            .parse::<u8>()
            .map_err(|_| AtError::InvalidArgs)?;

        if ![7, 8].contains(&data_bits) {
            return Err(AtError::InvalidArgs);
        }

        self.baudrate = baudrate;
        self.data_bits = data_bits;
        
        // Apply configuration to hardware
        // configure_uart(baudrate, data_bits);
        
        Ok(Bytes::from_str("OK"))
    }

    // Test: show valid configurations and usage
    fn test(&mut self) -> AtResult<'_, SIZE> {
        Ok(Bytes::from_str("AT+UART=<baudrate>,<data_bits> where baudrate: 9600-115200, data_bits: 7|8"))
    }
}

Usage:

parser.execute("AT+UART=?");        // "AT+UART=<baudrate>,<data_bits> where..."
parser.execute("AT+UART=115200,8"); // "OK"
parser.execute("AT+UART?");         // "115200,8"

Parsing Arguments

The Args structure provides a simple interface for accessing comma-separated arguments:

fn set(&mut self, args: Args) -> AtResult<'_, SIZE> {
    let arg0 = args.get(0).ok_or(AtError::InvalidArgs)?;
    let arg1 = args.get(1).ok_or(AtError::InvalidArgs)?;
    let arg2 = args.get(2); // Optional argument
    
    // Process arguments...
    Ok(Bytes::from_str("OK"))
}

Important: Args::get() uses 0-based indexing. For a command like AT+CMD=foo,bar,baz:

• args.get(0) returns Some("foo")
• args.get(1) returns Some("bar")
• args.get(2) returns Some("baz")
• args.get(3) returns None

For numeric arguments:

let value = args.get(0)
    .ok_or(AtError::InvalidArgs)?
    .parse::<i32>()
    .map_err(|_| AtError::InvalidArgs)?;

Thread Safety

Single-threaded (bare-metal)

static mut MODULE: MyModule = MyModule::new();
// Safe in single-threaded context

Multi-threaded (RTOS)

use core::cell::RefCell;
use osal_rs::sync::Mutex;

static MODULE: Mutex<RefCell<MyModule>> = Mutex::new(RefCell::new(MyModule::new()));

Using the at_modules! Macro

The library provides an at_modules! macro for defining static command arrays. The first argument is the SIZE const:

use at_parser_rs::at_modules;
use at_parser_rs::context::AtContext;

const SIZE: usize = 64;

static mut ECHO: EchoModule = EchoModule { echo: false };
static mut RESET: ResetModule = ResetModule;

at_modules! {
    SIZE;
    "AT+ECHO" => ECHO,
    "AT+RST" => RESET,
}

Limitations and Considerations

⚠️ Important: This macro has significant limitations:

1. Unsafe: The macro creates mutable references to static data, requiring unsafe blocks
2. Single-threaded only: Not suitable for multi-threaded or RTOS environments
3. Limited flexibility: Cannot mix different command handler types

Recommended Alternative

For most applications, the manual approach shown in the examples is preferred:

use at_parser_rs::context::AtContext;
use at_parser_rs::parser::AtParser;

const SIZE: usize = 64;

let mut echo = EchoModule { echo: false };
let mut reset = ResetModule;

let commands: &mut [(&str, &mut dyn AtContext<SIZE>)] = &mut [
    ("AT+ECHO", &mut echo),
    ("AT+RST", &mut reset),
];

parser.set_commands(commands);

This approach is safer, more flexible, and works in all contexts (stack, heap, RTOS).

Best Practices

1. Choose an appropriate SIZE: Pick a buffer size that fits your largest response string; responses longer than SIZE are silently truncated
2. Validate arguments: Always check argument count and validity before processing
3. Handle errors gracefully: Use appropriate AtError variants for different failure modes. Use AtError::Unhandled("msg") for static string descriptions and AtError::UnhandledOwned(string) for dynamically constructed messages
4. Document test responses: Use test() to provide clear usage information
5. Minimize state: Keep module state simple and thread-safe

Examples

The library includes several example files demonstrating different usage patterns:

Standard Examples

• complete_usage.rs - Complete demonstration with multiple command types (Echo, Reset, Info, LED)
• basic_parser.rs - Shows direct usage of the AtParser with comprehensive test cases

Embedded/no_std Examples

These examples demonstrate code patterns suitable for no_std environments:

• embedded_basic.rs - Basic patterns and error handling for no_std/embedded environments
• embedded_error_handling.rs - Patterns for custom error handling and type conversions
• embedded_uart_config.rs - UART and device configuration patterns with AtContext implementation

Note: The embedded examples are designed to show code patterns and best practices rather than being fully functional standalone programs. They demonstrate how to structure code for embedded/no_std contexts.

Run examples with:

# Standard examples (fully functional)
cargo run --example complete_usage
cargo run --example basic_parser

# Embedded examples (demonstrate patterns)
cargo run --example embedded_basic --no-default-features
cargo run --example embedded_error_handling --no-default-features
cargo run --example embedded_uart_config --no-default-features

License

This project is licensed under the GNU Lesser General Public License v2.1 or later (LGPL-2.1-or-later) - see the LICENSE file for details.