Bluetooth permission handling

Oct 13, 2025 by pinkandtrash.com 75 views

Introduction

Developing a Capacitor plugin for printing receipts can be a complex task, especially when it comes to handling Bluetooth connections and permissions. In this article, we will explore an issue where some printers fail to work in a Capacitor plugin, while they work perfectly in a native Android app.

Description

The issue arises when implementing printing using Printooth in a Capacitor plugin. Some printers fail to connect, resulting in the following error:

Connection failed: read failed, socket might be closed or timeout, read ret: -1

Even after trying to use BluetoothSocket directly instead of Printooth, the issue persists. The error message indicates that the Bluetooth connect permission is not granted.

Steps to Reproduce

Implement printing using Printooth in the Capacitor plugin.
Attempt to print with different Bluetooth printers.
Some printers fail with the following error:

Connection failed: read failed, socket might be closed or timeout, read ret: -1

Expected Behavior

All printers should work the same way they do in the native Android app.

Actual Behavior

Some printers fail to connect in the Capacitor plugin, while they work fine in a native Android app.

Additional Notes

The issue seems to be specific to the Capacitor plugin environment. Could this be related to how Capacitor handles Bluetooth permissions or connections?

Code Analysis

Let's take a closer look at the code to understand what might be causing the issue.

@CapacitorPlugin(
        name = "PrinterBridge",
        permissions = {
                @Permission(
                        alias = "bluetooth",
                        strings = {
                                // Basic Bluetooth permissions
                                Manifest.permission.BLUETOOTH,
                                Manifest.permission.BLUETOOTH_ADMIN,
                                // Android 12+ permissions
                                Manifest.permission.BLUETOOTH_CONNECT,
                                Manifest.permission.BLUETOOTH_SCAN,
                                // Android 14+ permission
                                Manifest.permission.NEARBY_WIFI_DEVICES
                        }
                )
        }
)
public class MyPlugin extends Plugin {
    // ...
}

In this code, we can see that the PrinterBridge plugin requires several Bluetooth permissions, including BLUETOOTH_CONNECT and BLUETOOTH_SCAN. However, the issue persists even after granting these permissions.

Possible Causes

Based on the code analysis, there are several possible causes for this issue:

Bluetooth permission handling: Capacitor might be handling Bluetooth permissions differently than the native Android app. This could lead to the issue where some printers fail to connect.
Bluetooth connection timeout: The connection timeout might be too short, causing the printer to fail to connect.
Printer-specific issues: Some printers might have specific issues that prevent them from connecting to the Capacitor plugin.

Solutions

To resolve this issue, we can try the following solutions:

Check Bluetooth permission handling: Verify that Capacitor is handling Bluetooth permissions correctly. Make sure to grant all required permissions and handle permission requests properly.
Increase connection timeout: Increase the connection timeout to give the printer more time to connect.
Test with different printers: Test the Capacitor plugin with different printers to identify any printer-specific issues.
Use a different Bluetooth library: Consider using a different Bluetooth library, such as BluetoothLeGatt, to see if it resolves the issue.

Conclusion

In conclusion, the issue where some printers fail to work in a Capacitor plugin is likely due to a combination of factors, including Bluetooth permission handling, connection timeout, and printer-specific issues. By analyzing the code and testing different solutions, we can resolve this issue and ensure that all printers work correctly in the Capacitor plugin.

Recommendations

Based on our analysis, we recommend the following:

Verify Bluetooth permission handling: Make sure that Capacitor is handling Bluetooth permissions correctly.
Increase connection timeout: Increase the connection timeout to give the printer more time to connect.
Test with different printers: Test the Capacitor plugin with different printers to identify any printer-specific issues.
Use a different Bluetooth library: Consider using a different Bluetooth library, such as BluetoothLeGatt, to see if it resolves the issue.

Q: What is the issue with some printers not working in Capacitor plugin?

A: The issue arises when implementing printing using Printooth in a Capacitor plugin. Some printers fail to connect, resulting in the following error:

Connection failed: read failed, socket might be closed or timeout, read ret: -1

Q: Why is this issue specific to the Capacitor plugin environment?

A: The issue seems to be specific to the Capacitor plugin environment. This could be related to how Capacitor handles Bluetooth permissions or connections.

Q: What are the possible causes of this issue?

A: Based on the code analysis, there are several possible causes for this issue:

Bluetooth permission handling: Capacitor might be handling Bluetooth permissions differently than the native Android app. This could lead to the issue where some printers fail to connect.
Bluetooth connection timeout: The connection timeout might be too short, causing the printer to fail to connect.
Printer-specific issues: Some printers might have specific issues that prevent them from connecting to the Capacitor plugin.

Q: How can I resolve this issue?

A: To resolve this issue, we can try the following solutions:

Check Bluetooth permission handling: Verify that Capacitor is handling Bluetooth permissions correctly. Make sure to grant all required permissions and handle permission requests properly.
Increase connection timeout: Increase the connection timeout to give the printer more time to connect.
Test with different printers: Test the Capacitor plugin with different printers to identify any printer-specific issues.
Use a different Bluetooth library: Consider using a different Bluetooth library, such as BluetoothLeGatt, to see if it resolves the issue.

Q: What are the recommendations for resolving this issue?

A: Based on our analysis, we recommend the following:

Verify Bluetooth permission handling: Make sure that Capacitor is handling Bluetooth permissions correctly.
Increase connection timeout: Increase the connection timeout to give the printer more time to connect.
Test with different printers: Test the Capacitor plugin with different printers to identify any printer-specific issues.
Use a different Bluetooth library: Consider using a different Bluetooth library, such as BluetoothLeGatt, to see if it resolves the issue.

Q: Can I use a different Bluetooth library to resolve this issue?

A: Yes, you can consider using a different Bluetooth library, such as BluetoothLeGatt, to see if it resolves the issue.

Q: How can I test with different printers to identify any printer-specific issues?

A: To test with different printers, you can try the following:

Use a different printer model: Try using a different printer model to see if the issue persists.
Check the printer's Bluetooth settings: Make sure that the printer's Bluetooth settings are correct and that it is discoverable.
Test with a different Bluetooth adapter: Try using a different Bluetooth adapter to see if the issue persists.

Q: What are the benefits of using a different Bluetooth library?

A: Using a different Bluetooth library, such as BluetoothLeGatt, can provide several benefits, including:

Improved connection stability: BluetoothLeGatt provides improved connection stability and reduces the likelihood of connection failures.
Better support for different printer models: BluetoothLeGatt provides better support for different printer models and can help to resolve printer-specific issues.
Enhanced security features: BluetoothLeGatt provides enhanced security features, including encryption and authentication, to help protect against unauthorized access.

Q: How can I implement a different Bluetooth library in my Capacitor plugin?

A: To implement a different Bluetooth library, such as BluetoothLeGatt, in your Capacitor plugin, you can follow these steps:

Add the BluetoothLeGatt library to your project: Add the BluetoothLeGatt library to your project by including it in your project's dependencies.
Import the BluetoothLeGatt library: Import the BluetoothLeGatt library in your plugin's code.
Use the BluetoothLeGatt library: Use the BluetoothLeGatt library to establish a connection with the printer and send print data.

By following these steps and recommendations, you can resolve the issue with some printers not working in your Capacitor plugin and ensure that all printers work correctly.