How to Build a Command-Line Barcode Reader with Rust and C++ Barcode SDK

Rust's popularity is increasing rapidly. This article aims to integrate Rust with the Dynamsoft C++ Barcode Reader SDK. We will walk through the process of building a command-line barcode reader for Windows and Linux.

Prerequisites

Rust: A systems programming language renowned for speed, safety, and concurrency.
bindgen: A Rust tool that generates Rust FFI bindings to C and C++ libraries. You can install it with the following command:
```
cargo install bindgen-cli
```
Dynamsoft Barcode Reader Trial License: You will receive a 30-day free trial license by email.
Dynamsoft C++ Barcode SDK v9.x: A ZIP package that contains the shared library and header files for Windows and Linux.

Step 1: Setting Up the Rust Project

Use Cargo to initialize the project:

cargo new barcode_reader
cd barcode_reader

Modify Cargo.toml to include the required dependencies:
```
[package]
name = "hello_world"
version = "0.1.0"
edition = "2018"

[build-dependencies]
cc = "1.0"
walkdir = "2.5.0"
```
The cc crate is used to compile the C++ code. The walkdir crate is used to traverse the directory to find the shared library.

Step 2: Configuring the C++ Barcode SDK

Extract the downloaded Dynamsoft C++ Barcode SDK, and copy the headers and platform-specific libraries to the Rust project directory structure as follows:

|- include
    |- DynamsoftBarcodeReader.h
    |- DynamsoftCommon.h
|- platforms
    |- linux
        |- libDynamicPdf.so
        |- libDynamsoftLicenseClient.so
        |- libDynamsoftBarcodeReader.so
    |- win
        |- bin
            |- DynamicPdfx64.dll
            |- DynamsoftBarcodeReaderx64.dll
            |- DynamsoftLicenseClientx64.dll
            |- vcomp110.dll
        |- lib
            |- DBRx64.lib

Create a lib directory within your project. In the lib folder, create two files: bridge.cpp and bridge.h. These files will handle communication between Rust and the C++ SDK.

Edit build.rs to build the C++ code and link the shared libraries.

Determine the target operating system (Windows/Linux). When running cargo build, the println!() function won't output anything to the console unless you add cargo:warning to the message.

use std::env;
use cc::Build;

use std::fs;
use walkdir::WalkDir;
use std::path::{Path, PathBuf};

fn main() {
    // Determine the target operating system
    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
    println!("cargo:warning=OS: {}..............................................", target_os);
}

Link the shared libraries based on the target operating system, and copy the shared libraries to the output path.

fn get_out_dir() -> PathBuf {
    let out_dir = env::var("OUT_DIR").unwrap();
    let debug_offset = out_dir.find("debug").unwrap_or(0);
    let release_offset = out_dir.find("release").unwrap_or(0);
    let mut path = String::from("");

    if debug_offset > 0 {
        println!(">>> where is debug {}", debug_offset);
        path.push_str(&format!("{}", &out_dir[..debug_offset]));
        path.push_str("debug");
        println!("{}", path);
    }

    if release_offset > 0 {
        println!(">>> where is release {}", release_offset);
        path.push_str(&format!("{}", &out_dir[..release_offset]));
        path.push_str("release");
        println!("{}", path);
    }

    PathBuf::from(path)
}

fn copy_shared_libs_from_dir_to_out_dir(src_dir: &Path, out_dir: &Path, extension: &str) {
    for entry in WalkDir::new(src_dir).into_iter().filter_map(|e| e.ok()) {
        if entry.path().extension().and_then(|ext| ext.to_str()) == Some(extension) {
            let lib_path = entry.path();
            let file_name = lib_path.file_name().unwrap();
            let dest_path = out_dir.join(file_name);

            fs::copy(lib_path, dest_path.clone()).expect("Failed to copy shared library");
            println!("Copied {} to {}", lib_path.display(), dest_path.display());
        }
    }
}

match target_os.as_str() {
    "windows" => {
        // Link Dynamsoft Barcode Reader for Windows
        println!("cargo:rustc-link-search=../../../platforms/win/lib");
        println!("cargo:rustc-link-lib=static=DBRx64");

        // Copy *.dll files to the output path for Windows
        let src_dir = Path::new("../../../platforms/win/bin");
        copy_shared_libs_from_dir_to_out_dir(src_dir, &get_out_dir(), "dll");
    },
    "linux" => {
        // Link Dynamsoft Barcode Reader for Linux
        println!("cargo:rustc-link-search=../../../platforms/linux");
        println!("cargo:rustc-link-lib=dylib=DynamsoftBarcodeReader");

        // Set rpath for Linux
        println!("cargo:rustc-link-arg=-Wl,-rpath,../../../platforms/linux");

        // Copy *.so files to the output path for Linux
        let src_dir = Path::new("../../../platforms/linux/bin");
        copy_shared_libs_from_dir_to_out_dir(src_dir, &get_out_dir(), "so");
    },
}

Compile the C++ code that exposes some C functions to Rust.

Build::new()
.cpp(true)
.include("../../../include")
.file("lib/bridge.cpp")
.compile("bridge");

println!("cargo:rustc-link-lib=static=bridge");

println!("cargo:rustc-link-search=native={}", env::var("OUT_DIR").unwrap());

Step3: Implementing the C/C++ Bridging Code

In this step, we will create the bridging code to enable Rust to interact with the C++ SDK. We will declare and implement the necessary structures and functions in C/C++.

Declaring Structures and Functions in bridge.h

In the directory, create a file named bridge.h and declare the C structures and functions that will be called by Rust.

#ifndef BRIDGE_H
#define BRIDGE_H

#include "DynamsoftBarcodeReader.h"

#ifdef __cplusplus
extern "C"
{
#endif

    typedef struct
    {
        const char *barcode_type;
        const char *barcode_value;
        int x1;
        int y1;
        int x2;
        int y2;
        int x3;
        int y3;
        int x4;
        int y4;
    } Barcode;

    typedef struct
    {
        Barcode *barcodes;
        int count;
    } BarcodeResults;

    Barcode *create_barcode(const char *type, const char *value, int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4);
    BarcodeResults *decode_barcode_file(void *instance, const char *filename);
    void free_barcode(BarcodeResults *results);
    int init_license(const char *license);

#ifdef __cplusplus
}
#endif

#endif // BRIDGE_H

The Barcode structure represents the barcode information.
The BarcodeResults structure contains an array of Barcode structures.
The create_barcode function creates a Barcode structure.
The decode_barcode_file function decodes barcodes from an image file.
The free_barcode function releases the memory allocated for the BarcodeResults structure.
The init_license function initializes the license.

Implementing the Functions in bridge.cpp

In the bridge.cpp file, implement the functions declared in bridge.h.

#include "bridge.h"
#include <cstring>
#include <cstdlib>

Barcode *create_barcode(const char *type, const char *value, int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4)
{
    Barcode *barcode = (Barcode *)std::malloc(sizeof(Barcode));
    barcode->barcode_type = strdup(type);
    barcode->barcode_value = strdup(value);
    barcode->x1 = x1;
    barcode->y1 = y1;
    barcode->x2 = x2;
    barcode->y2 = y2;
    barcode->x3 = x3;
    barcode->y3 = y3;
    barcode->x4 = x4;
    barcode->y4 = y4;
    return barcode;
}

void free_barcode(BarcodeResults *results)
{
    for (int i = 0; i < results->count; i++)
    {
        std::free((void *)results->barcodes[i].barcode_type);
        std::free((void *)results->barcodes[i].barcode_value);
    }
    std::free(results->barcodes);
    std::free(results);
}

int init_license(const char *license)
{
    char errorMsgBuffer[512];
    // Click https://www.dynamsoft.com/customer/license/trialLicense/?product=dbr to get a trial license.
    int ret = DBR_InitLicense(license, errorMsgBuffer, 512);
    return ret;
}

BarcodeResults *decode_barcode_file(void *instance, const char *filename)
{
    char errorMsgBuffer[512];
    TextResultArray *pResults = NULL;
    BarcodeResults *all_barcodes = NULL;
    int ret = DBR_DecodeFile(instance, filename, "");
    DBR_GetAllTextResults(instance, &pResults);
    if (pResults->resultsCount > 0)
    {
        all_barcodes = (BarcodeResults *)std::malloc(sizeof(BarcodeResults));
        all_barcodes->count = pResults->resultsCount;
        all_barcodes->barcodes = (Barcode *)std::malloc(sizeof(Barcode) * pResults->resultsCount);
        for (int iIndex = 0; iIndex < pResults->resultsCount; iIndex++)
        {
            LocalizationResult *localizationResult = pResults->results[iIndex]->localizationResult;
            Barcode *barcode = create_barcode(pResults->results[iIndex]->barcodeFormatString, pResults->results[iIndex]->barcodeText,
                                              localizationResult->x1, localizationResult->y1, localizationResult->x2, localizationResult->y2,
                                              localizationResult->x3, localizationResult->y3, localizationResult->x4, localizationResult->y4);
            all_barcodes->barcodes[iIndex] = *barcode;
        }
    }

    DBR_FreeTextResults(&pResults);
    return all_barcodes;
}

Step4: Generating Rust Bindings for C/C++ Code

To invoke the C/C++ functions from Rust, we need to generate Rust bindings for the C/C++ code. We can either write the bindings manually or use the bindgen tool to generate them automatically as follows:

bindgen ./lib/bridge.h -o bindings.rs

In addition to the methods implemented in bridge.cpp, we add two more functions contained in the C++ SDK: DBR_CreateInstance and DBR_DestroyInstance. The full bindings.rs file is as follows:

use std::ffi::c_void;
use std::os::raw::c_char;
use std::os::raw::c_int;

#[repr(C)]
pub struct Barcode {
    pub barcode_type: *const c_char,
    pub barcode_value: *const c_char,
    pub x1: c_int,
    pub y1: c_int,
    pub x2: c_int,
    pub y2: c_int,
    pub x3: c_int,
    pub y3: c_int,
    pub x4: c_int,
    pub y4: c_int,
}

#[repr(C)]
pub struct BarcodeResults {
    pub barcodes: *mut Barcode,
    pub count: c_int,
}

extern "C" {
    // Bridge functions
    pub fn free_barcode(barcode: *mut BarcodeResults);
    pub fn init_license(license: *const c_char) -> c_int;
    pub fn decode_barcode_file(instance: *mut c_void, filename: *const c_char) -> *mut BarcodeResults;

    // Dynamsoft C++ Barcode Reader SDK functions
    pub fn DBR_CreateInstance() -> *mut c_void;
    pub fn DBR_DestroyInstance(barcodeReader: *mut c_void); 
}

Step5: Writing Rust Code

The final step is to write Rust code in the main.rs file to implement the command-line barcode reader.

Import the generated bindings and other necessary libraries.

mod bindings;
use std::io::{self, Write};
use std::ffi::CString;
use bindings::*;

Activate the license of Dynamsoft Barcode Reader:

let license = "LICENSE-KEY";

let ret = unsafe {
    let license = CString::new(license).expect("CString::new failed");
    init_license(license.as_ptr())
};

println!("InitLicense: {}", ret);

Create an instance of Dynamsoft Barcode Reader:

let reader_ptr = unsafe { DBR_CreateInstance() };
if reader_ptr.is_null() {
    panic!("Failed to create barcode reader instance");
}

Prompt the user to enter a file name in a loop. If the user types exit, the program will exit.

loop {
    print!("Please enter the file name (or type 'exit' to quit): ");
    io::stdout().flush().unwrap(); 

    let mut file_name = String::new();
    io::stdin().read_line(&mut file_name).expect("Failed to read line");

    let file_name = file_name.trim();

    if file_name.to_lowercase() == "exit" {
        break;
    }

    println!("Processing file: {}", file_name);

    let path = CString::new(file_name).expect("CString::new failed");
}

Decode barcodes from the image file and print the results.

unsafe {
    let results_ptr = decode_barcode_file(reader_ptr, path.as_ptr());

    if results_ptr.is_null() {
        println!("No barcodes found.");
    } else {
        let results = &*results_ptr;
        let barcodes = std::slice::from_raw_parts(results.barcodes, results.count as usize);

        for (i, barcode) in barcodes.iter().enumerate() {
            let barcode_type = std::ffi::CStr::from_ptr(barcode.barcode_type).to_string_lossy();
            let barcode_value = std::ffi::CStr::from_ptr(barcode.barcode_value).to_string_lossy();

            println!("Barcode {}: type = {}, value = {}", i + 1, barcode_type, barcode_value);
            println!(
                "Coordinates: ({}, {}), ({}, {}), ({}, {}), ({}, {})",
                barcode.x1, barcode.y1, barcode.x2, barcode.y2,
                barcode.x3, barcode.y3, barcode.x4, barcode.y4
            );
        }

        free_barcode(results_ptr);
    }
}

Run the program.
```
cargo clean
cargo run
```

Source Code

https://github.com/yushulx/cmake-cpp-barcode-qrcode/tree/main/examples/9.x/rust

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