Fixing Image URL Redirects On Kobo Aura ONE With BYOS

Aug 15, 2025 by Luna Greco 54 views

Redirects are not followed by script for image URLs

Introduction

Hey guys! Today, we're diving deep into an interesting issue encountered while setting up a BYOS (Bring Your Own Server) with a Kobo Aura ONE. Specifically, we're talking about how redirects for image URLs aren't being followed by the script, which can be a real head-scratcher if you're not sure where to look. This article will break down the problem, explain why it happens, and offer a solution to get your Kobo working smoothly with your BYOS setup. So, if you've been struggling with image display issues on your Kobo, you're in the right place!

The Problem: Redirects and Image URLs

When setting up a BYOS like usetrmnl/byos_laravel for your Kobo Aura ONE, you might expect everything to work seamlessly. However, sometimes things don't go as planned. One common issue is that image URLs, particularly HTTP URLs that redirect to HTTPS, aren't being followed by the script. This means that the images aren't displayed on your Kobo as expected. Let's dig into the details to understand why this happens. The core of the problem lies in how the curl command is used to fetch images. If the -L flag is missing, curl won't follow redirects, leading to failed image loads. This can be especially tricky to diagnose because the server might return a valid Location header, making it seem like everything is fine, even though the image isn't actually being fetched. The initial symptom of this issue is that your Kobo device isn't displaying images correctly, or at all, when connected to your BYOS setup. You might see placeholders or broken image icons instead of the actual content. This can be particularly frustrating because everything else might seem to be working fine – the device connects to the server, retrieves data, but fails specifically when it comes to displaying images. To truly understand the issue, it's essential to dive into the logs. The logs provide a detailed record of what's happening behind the scenes, and they can reveal the exact point of failure. In this case, examining the logs can show that the image URLs are being accessed over HTTP and that the server is responding with a redirect to HTTPS. However, without the -L flag in the curl command, this redirect is not followed, and the image retrieval process stops there. This issue is more common in setups where a reverse proxy is used to handle HTTPS connections. The BYOS might be configured to serve content over HTTP internally, while the reverse proxy handles the secure HTTPS connection for external access. This setup is efficient and secure, but it relies on redirects to ensure that all traffic is eventually routed over HTTPS. Therefore, if the client (in this case, the Kobo device) doesn't follow redirects, the images won't load correctly. The difficulty in diagnosing this problem stems from the fact that the redirect itself doesn't trigger an error in the logs. The server is behaving correctly by issuing the redirect, and the client (the curl command) is receiving this response. However, because curl is not configured to follow redirects, it doesn't proceed to fetch the image from the HTTPS URL. This means that the logs might not show a clear error message, making it harder to pinpoint the root cause of the problem. In the provided debug logs, you can see lines like TRMNL fetch image from http://[redacted]/storage/images/generated/34a060ce-542a-4ae7-bd26-2f282b52f44a.png returned 0. This indicates that the initial HTTP request was made, but there's no subsequent log entry showing a successful image retrieval. This is a key clue that a redirect might be the issue. The logs also highlight that the API is returning an image URL with the http prefix, which is another important piece of the puzzle. This confirms that the BYOS is configured to serve images over HTTP, at least initially, and that redirects are necessary to switch to HTTPS. Recognizing this pattern in the logs is crucial for understanding the problem and implementing the correct solution.

Why This Happens: The Missing `-L` Flag

The root cause of this issue lies in the curl command used to fetch the images. Specifically, the -L flag, which tells curl to follow HTTP 3xx redirects, is missing. Without this flag, curl will not follow redirects, and the image will not be fetched if the URL redirects from HTTP to HTTPS. Let's break this down further to understand the technical details and why this flag is so important. The curl command is a powerful tool used to transfer data from or to a server, using various protocols like HTTP, HTTPS, FTP, and more. It's a command-line utility that's commonly used in scripts and applications to automate data transfers. When curl encounters a redirect (a server response with a status code in the 3xx range, such as 301 or 302), it needs to know whether to follow that redirect to the new URL or to stop the process. By default, curl does not follow redirects for security reasons. This is to prevent malicious redirects that could lead to unexpected or harmful outcomes. However, in many legitimate scenarios, redirects are a normal part of the web infrastructure. For example, a website might use redirects to move content to a new URL, to enforce HTTPS, or to balance traffic across multiple servers. In these cases, it's essential for curl to be able to follow the redirects to access the intended content. The -L flag, which stands for --location, tells curl to follow these redirects. When this flag is included in the curl command, curl will automatically make a new request to the URL specified in the Location header of the redirect response. This process continues until curl reaches a final URL that doesn't return a redirect, or until it reaches a maximum number of redirects (to prevent infinite loops). In the context of the TRMNL-Kobo project, the script uses curl to fetch images from the BYOS. The relevant line of code in trmnlloop.sh is: bash curl -s -m 10 "$image_url" > "$image_path" As you can see, the -L flag is missing from this command. This means that if the $image_url returns a redirect (e.g., from HTTP to HTTPS), curl will not follow it, and the image will not be fetched correctly. The logs provided in the issue confirm this behavior. The logs show that the API returns an image URL with the http prefix, and curl attempts to fetch the image from this URL. The server responds with a redirect to the HTTPS version of the URL, but because curl is not configured to follow redirects, it stops there. This results in an empty or incomplete image file being saved, which then causes the image to not display correctly on the Kobo device. The reason this issue wasn't immediately apparent is that the server's response, including the Location header, is technically a valid response. curl receives the response, but it doesn't proceed to follow the redirect. This means that there are no explicit error messages in the logs that would immediately point to the missing -L flag as the culprit. Instead, the logs show a successful connection and response, but the absence of a subsequent image retrieval indicates the problem. To summarize, the missing -L flag in the curl command is the key reason why redirects are not being followed for image URLs. This is particularly relevant in setups where a reverse proxy is used to handle HTTPS connections, as the BYOS might serve content over HTTP internally and rely on redirects to switch to HTTPS. Adding the -L flag to the curl command will resolve this issue by instructing curl to follow redirects and fetch the image from the final HTTPS URL.

The Solution: Adding the `-L` Flag

The fix for this issue is straightforward: add the -L flag to the curl command in the trmnlloop.sh script. This tells curl to follow redirects, ensuring that images are fetched correctly even if they require a redirect from HTTP to HTTPS. Let's walk through the steps to implement this solution and understand why it's the most effective approach. The first step is to locate the relevant line of code in the trmnlloop.sh script. As mentioned earlier, the problematic line is: bash curl -s -m 10 "$image_url" > "$image_path" This command is responsible for fetching the image from the URL specified by $image_url and saving it to the path specified by $image_path. The -s flag tells curl to run in silent mode, suppressing progress meter and error messages, and the -m 10 flag sets a maximum time of 10 seconds for the transfer. To fix the redirect issue, you need to add the -L flag to this command. The corrected line should look like this: bash curl -L -s -m 10 "$image_url" > "$image_path" By adding -L, you're instructing curl to follow any HTTP 3xx redirects that the server might send. This means that if the server responds with a redirect from HTTP to HTTPS, curl will automatically make a new request to the HTTPS URL and fetch the image from there. This simple change ensures that images are fetched correctly, even if they require a redirect. Now, let's discuss why this solution is the most effective approach. There are other ways to address the redirect issue, but adding the -L flag is the most direct and reliable method. For example, you could try to configure the BYOS to always serve images over HTTPS directly, eliminating the need for redirects. However, this might not always be feasible or desirable, especially if you're using a reverse proxy for handling HTTPS connections. Another approach might be to modify the BYOS to return HTTPS URLs instead of HTTP URLs. While this could also solve the problem, it would require changes to the server-side code, which might be more complex and time-consuming. Adding the -L flag, on the other hand, is a simple, targeted fix that addresses the root cause of the issue without requiring significant changes to the BYOS or the overall setup. It's a small change with a big impact, ensuring that curl behaves as expected in the presence of redirects. Furthermore, adding the -L flag is a more robust solution because it handles redirects in general, not just HTTP to HTTPS redirects. This means that if the server ever uses redirects for other reasons (e.g., content moved to a new URL), curl will still be able to fetch the image correctly. In addition to adding the -L flag, it's also worth considering setting the FORCE_HTTPS environment variable in the BYOS configuration, as suggested in the original issue. This can help ensure that the BYOS always returns HTTPS URLs, which can further reduce the likelihood of redirect-related issues. However, even with FORCE_HTTPS enabled, adding the -L flag is a good practice because it provides an extra layer of protection against redirect problems. To implement this solution, you'll need to access the trmnlloop.sh script on your Kobo device or the server where the script is running. You can use a text editor to modify the script, making sure to save the changes after adding the -L flag. After making the change, you'll need to restart the TRMNL service or reboot your Kobo device for the changes to take effect. Once the service is restarted, the curl command will follow redirects, and your images should display correctly.

Alternative Solution: Setting `FORCE_HTTPS`

As mentioned earlier, an alternative solution is to set the FORCE_HTTPS environment variable in the usetrmnl/byos_laravel configuration. This ensures that the BYOS always serves URLs with the https prefix, potentially avoiding the need for redirects in the first place. However, it's important to understand the implications and trade-offs of this approach. Setting FORCE_HTTPS can be a convenient way to ensure that all URLs generated by the BYOS are secure. When this variable is enabled, the BYOS will generate URLs with the https scheme, regardless of the incoming request's scheme. This can help simplify the setup and reduce the likelihood of mixed content warnings or other issues related to insecure content. However, it's not a silver bullet, and there are several factors to consider before implementing this solution. First, setting FORCE_HTTPS requires that your BYOS is properly configured to handle HTTPS requests. This typically involves setting up a TLS/SSL certificate and configuring your web server (e.g., Apache or Nginx) to use the certificate. If your BYOS is not correctly configured for HTTPS, enabling FORCE_HTTPS could lead to errors or broken functionality. Second, even with FORCE_HTTPS enabled, redirects might still be necessary in some situations. For example, if you have existing HTTP URLs cached or linked from other sources, users might still access these URLs, which would then need to be redirected to the HTTPS versions. Additionally, if your reverse proxy or load balancer is configured to redirect HTTP traffic to HTTPS, setting FORCE_HTTPS might not completely eliminate the need for redirects. Third, setting FORCE_HTTPS can have performance implications. While HTTPS is generally more secure than HTTP, it also adds overhead due to the encryption and decryption processes. This overhead can impact the performance of your BYOS, especially if you're serving a large number of requests. Therefore, it's important to consider the performance implications and ensure that your server has sufficient resources to handle the additional load. Despite these considerations, setting FORCE_HTTPS can be a valuable tool in securing your BYOS and ensuring that all traffic is encrypted. It's particularly useful in environments where security is a top priority and where the performance overhead is acceptable. However, it's crucial to test the configuration thoroughly to ensure that everything works as expected. To implement this solution, you'll need to access the configuration file for your BYOS (e.g., the .env file in a Laravel application) and set the FORCE_HTTPS environment variable to true. The exact steps for doing this will vary depending on the specific BYOS you're using, so it's important to consult the documentation for your BYOS for detailed instructions. After setting the variable, you'll need to restart your BYOS for the changes to take effect. Once the BYOS is restarted, it should generate HTTPS URLs for all images and other content. It's important to verify that this is indeed the case by inspecting the URLs returned by the BYOS API. In summary, setting FORCE_HTTPS is a useful alternative solution for addressing the redirect issue, but it's not a complete solution on its own. It should be used in conjunction with other best practices for securing your BYOS, such as configuring HTTPS correctly and adding the -L flag to the curl command. By combining these approaches, you can ensure that your images are fetched correctly and that your BYOS is secure.

Conclusion

In conclusion, the issue of redirects not being followed by the script for image URLs can be a tricky one to diagnose, but the solution is relatively simple. By adding the -L flag to the curl command in the trmnlloop.sh script, you can ensure that redirects are followed, and images are fetched correctly. Additionally, setting the FORCE_HTTPS environment variable in your BYOS configuration can further mitigate this issue. Understanding the root cause of the problem and implementing these solutions will help you get your Kobo Aura ONE working seamlessly with your BYOS setup. Remember, debugging is a process of elimination. By carefully examining logs and understanding how different components interact, you can identify and resolve even the most complex issues. Happy reading, everyone!