Refused to get unsafe header 'Accept-Ranges' Error from PDF.js with Amazon URLs: What it is and How to Fix it

Refused to get unsafe header “Accept-Ranges” Error from PDF.js with Amazon URLs: What it is and How to Fix it

From a data scientist or software engineer’s perspective, pdf.js is an incredibly useful tool for rendering PDF files in a browser. However, when working with Amazon URLs, you may encounter the “Refused to get unsafe header ‘Accept-Ranges’” error. This article aims to help you understand this error and its solution.

Understanding the Error: Refused to get unsafe header “Accept-Ranges”

This error message is thrown by the browser when it tries to access a resource, such as a PDF file stored on Amazon S3, but is blocked due to the server’s CORS (Cross-Origin Resource Sharing) policy. This policy prevents JavaScript from accessing certain headers, including ‘Accept-Ranges’, from a different origin for security reasons.

Amazon S3, by default, does not include ‘Accept-Ranges’ in its ‘Access-Control-Allow-Headers’ response, which means pdf.js is unable to fetch the range of bytes it needs to render the PDF.

Why is ‘Accept-Ranges’ Important?

pdf.js uses ‘Accept-Ranges’ to request specific parts of the PDF file, allowing it to render the file progressively. Without access to this header, pdf.js is unable to provide this feature, leading to a less efficient rendering process.

How to Fix the Error

To resolve this issue, you need to modify the CORS configuration for your S3 bucket to allow the ‘Accept-Ranges’ header.

Step 1: Modify S3 CORS Configuration

Go to the Amazon S3 Console and select the bucket that contains the PDF files. Click on Permissions, then CORS Configuration.

Replace the existing CORS configuration with the following:

[
    {
        "AllowedHeaders": [
            "*"
        ],
        "AllowedMethods": [
            "GET",
            "HEAD"
        ],
        "AllowedOrigins": [
            "*"
        ],
        "ExposeHeaders": [
            "Accept-Ranges",
            "Content-Encoding",
            "Content-Length",
            "Content-Range"
        ],
        "MaxAgeSeconds": 3000
    }
]

Click Save.

This configuration allows all headers ('*'), permits GET and HEAD methods, and exposes the ‘Accept-Ranges’ header, among others, to JavaScript.

Step 2: Confirm the Configuration

To confirm the CORS configuration was successful, you can use curl to send a preflight request:

curl -X OPTIONS -H "Origin: http://yourdomain.com" -H "Access-Control-Request-Method: GET" -H "Access-Control-Request-Headers: Accept-Ranges" https://your-bucket-name.s3.amazonaws.com/your-file.pdf

Replace http://yourdomain.com with your website’s domain and https://your-bucket-name.s3.amazonaws.com/your-file.pdf with your PDF file’s S3 URL. If set up correctly, you’ll see ‘Accept-Ranges’ in the ‘Access-Control-Allow-Headers’ response.

Conclusion

The “Refused to get unsafe header ‘Accept-Ranges’” error from pdf.js with Amazon URLs arises due to the CORS policy of Amazon S3. By adjusting the CORS configuration of your S3 bucket, you can allow pdf.js to access the ‘Accept-Ranges’ header, enabling efficient, progressive rendering of PDF files.

The world of data science and software engineering is full of such quirks. Understanding them not only improves your problem-solving skills but also enhances the end-user experience by ensuring seamless operation of your applications.

Keywords: Refused to get unsafe header, Accept-Ranges error, pdf.js, Amazon URLs, CORS configuration, S3 bucket, data science, software engineering, problem-solving

About Saturn Cloud

Saturn Cloud is your all-in-one solution for data science & ML development, deployment, and data pipelines in the cloud. Spin up a notebook with 4TB of RAM, add a GPU, connect to a distributed cluster of workers, and more. Join today and get 150 hours of free compute per month.