How to check if a URL is downloadable in requests

Question

I am making this downloader app using tkinter and requests and I recently found a bug in my program. Basically I want my program to check whether the given URL is downloadable or not before starting the download of the content of the URL. I used to do this by getting the headers of the URL and checking if 'Content-Length' exists and it works for some URLs (like: https://www.google.com) but for the others (like the link to a youtube video) it does not and it makes my program crash. I saw that someone said one stackoverflow that I could check for 'attachment' in 'Content-Disposition' of the headers but it didn't work for me and returned the same thing for a downloadable and a non-downloadable URL. What is the best way to do this? The code mentioned in the other stackoverflow issue that I tried and did not work:

import requests
url = 'https://www.google.com'
headers=requests.head(url).headers
downloadable = 'attachment' in headers.get('Content-Disposition', '')

My former code:

headers = requests.head(url, headers={'accept-encoding': ''}).headers
try:
    print(type(headers['Content-Length']))
    file_size = int(headers['Content-Length'])
except KeyError:
    # Just a class that I defined to raise an exception if the URL was not downloadable
    raise NotDownloadable()

UPDATE: URL: https://aspb1.cdn.asset.aparat.com/aparat-video/a5e07b7f62ffaad0c104763c23d7393215613675-360p.mp4?wmsAuthSign=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ0b2tlbiI6IjUzMGU0Mzc3ZjRlZjVlYWU0OTFkMzdiOTZkODgwNGQ2IiwiZXhwIjoxNjExMzMzMDQxLCJpc3MiOiJTYWJhIElkZWEgR1NJRyJ9.FjMi_dkdLCUkt25dfGqPLcehpaC32dBBUNDC9cLNiu0 This URL is the one I used for testing. If you open the URL it directly leads you to a video which you can download but when checking for the 'Content-Disposition' it returned 'None' just like the majority of the downloadable and non-downloadable URLs I have tried.

Answer 1

According to Request for Comment (RFC) 6266 the Content-Disposition Header Field:

is not part of the HTTP standard, but since it is widely implemented, we are documenting its use and risks for implementers.

Since the Content-Disposition header is not always available, you could use a solution that not only looks for that specific header, but also looks at the individual file types within the Content-Type header

Here is a list of Content-Types.

The code below checks the headers for Content-Disposition, but it also checks the headers for some of the Content-Type that are commonly downloadable.

I also added a check for the Content-Length, because it could be useful in chunking the file being downloaded.

Have you considered creating sub-download folders?

• download_folder/text_files
• download_folder/pdf_files

or

• download_folder/01242021/text_files
• download_folder/01242021/pdf_files

import requests

urls = ['https://www.stats.govt.nz/assets/Uploads/Annual-enterprise-survey/Annual-enterprise-survey-2019-financial'
        '-year-provisional/Download-data/annual-enterprise-survey-2019-financial-year-provisional-csv.csv',
        'http://www.pdf995.com/samples/pdf.pdf', 'https://jeroen.github.io/files/sample.rtf',
        'https://www.cnn.com/2021/01/23/opinions/biden-climate-change-gillette-wyoming-coal-sutter/index.html',
        'https://www.google.com',
        'https://thumbs-prod.si-cdn.com/d4e3zqOM5KUq8m0m-AFVxuqa5ZM=/800x600/filters:no_upscale():focal(554x699:555x700)/https://public-media.si-cdn.com/filer/a4/04/a404c799-7118-459a-8de4-89e4a44b124f/img_1317.jpg',
        'https://www.blank.org']

for url in urls:
    headers = requests.head(url).headers
    Content_Length = [value for key, value in headers.items() if key == 'Content-Length']
    if len(Content_Length) > 0:
        Content_Size = ''.join(map(str, Content_Length))
    else:
        Content_Size = 'The content size was not available.'


    Content_Disposition_Exists = bool({key: value for key, value in headers.items() if key == 'Content_Disposition'})
    if Content_Disposition_Exists is True:
        # do something with the file
       pass
    else:
        Content_Type = {value for key, value in headers.items() if key == 'Content-Type'}

        compression_formats = ['application/gzip', 'application/vnd.rar', 'application/x-7z-compressed',
                               'application/zip', 'application/x-tar']
        compressed_file = bool([file_format for file_format in compression_formats if file_format in Content_Type])

        image_formats = ['image/bmp', 'image/gif', 'image/jpeg', 'image/png', 'image/svg+xml', 'image/tiff',
                         'image/webp']
        image_file = bool([file_format for file_format in image_formats if file_format in Content_Type])

        text_formats = ['application/rtf', 'text/plain']
        text_file = bool([file_format for file_format in text_formats if file_format in Content_Type])

        if compressed_file is True:
            print('Compressed file')
            print(Content_Size)
        elif image_file is True:
            print('Image file')
            print(Content_Size)
        elif text_file is True:
            print('Text file')
             print(Content_Size)
        elif 'application/pdf' in Content_Type:
            print('PDF file')
            print(Content_Size)
        elif 'text/csv' in Content_Type:
            print('CSV File')
            print(Content_Size)

---

Here is another version with Functions

import requests

urls = ['https://www.stats.govt.nz/assets/Uploads/Annual-enterprise-survey/Annual-enterprise-survey-2019-financial'
        '-year-provisional/Download-data/annual-enterprise-survey-2019-financial-year-provisional-csv.csv',
        'http://www.pdf995.com/samples/pdf.pdf', 'https://jeroen.github.io/files/sample.rtf',
        'https://www.cnn.com/2021/01/23/opinions/biden-climate-change-gillette-wyoming-coal-sutter/index.html',
        'https://www.google.com',
        'https://thumbs-prod.si-cdn.com/d4e3zqOM5KUq8m0m-AFVxuqa5ZM=/800x600/filters:no_upscale():focal(554x699:555x700)/https://public-media.si-cdn.com/filer/a4/04/a404c799-7118-459a-8de4-89e4a44b124f/img_1317.jpg',
        'https://www.blank.org']


def query_headers(webpage):
    response = requests.get(webpage, stream=True)
    headers = response.headers
    file_name = webpage.rsplit('/', 1)[-1]

    Content_Disposition_Exists = bool({key: value for key, value in headers.items() if key == 'Content_Disposition'})
    if Content_Disposition_Exists is True:
        # do something with the file
        pass
    else:
        Content_Type = {value for key, value in headers.items() if key == 'Content-Type'}

        compression_formats = ['application/gzip', 'application/vnd.rar', 'application/x-7z-compressed',
                               'application/zip', 'application/x-tar']
        compressed_file = bool([file_format for file_format in compression_formats if file_format in Content_Type])

        image_formats = ['image/bmp', 'image/gif', 'image/jpeg', 'image/png', 'image/svg+xml', 'image/tiff',
                         'image/webp']
        image_file = bool([file_format for file_format in image_formats if file_format in Content_Type])

        text_formats = ['application/rtf', 'text/plain']
        text_file = bool([file_format for file_format in text_formats if file_format in Content_Type])
        nl = '\n'

        if compressed_file is True:
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: Compressed file, File size: {content_size}, File name: {file_name}'
        elif image_file is True:
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: Image file, File size: {content_size}, File name: {file_name}'
        elif text_file is True:
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: Text file, File size: {content_size}, File name: {file_name}'
        elif 'application/pdf' in Content_Type:
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: PDF file, File size: {content_size}, File name: {file_name}'
        elif 'text/csv' in Content_Type:
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: CSV file, File size: {content_size}, File name: {file_name}'
        elif 'text/html' in "".join(str(Content_Type)):
            download_file(file_name, response)
            content_size = get_content_size(headers)
            return f'File Information: file_type: HTML file, File size: {content_size}, File name: {file_name}'
        else:
            content_size = get_content_size(headers)
            return f'File Information: file_type:  no file type found, File size: {content_size}, File name: {file_name}'


def get_content_size(headers):
    Content_Length = [value for key, value in headers.items() if key == 'Content-Length']
    if len(Content_Length) > 0:
        Content_Size = ''.join(map(str, Content_Length))
        return int(Content_Size)
    else:
        return 0


def download_file(filename, file_stream):
    with open(f'{filename}', 'wb') as f:
        f.write(file_stream.content)


for url in urls:
    download_info = query_headers(url)
    print(download_info)
    # output
    File Information: file_type: CSV file, File size: 253178, File name: annual-enterprise-survey-2019-financial-year-provisional-csv.csv
    File Information: file_type: PDF file, File size: 433994, File name: pdf.pdf
    File Information: file_type: Text file, File size: 9636, File name: sample.rtf
    File Information: file_type: HTML file, File size: 185243, File name: index.html
    File Information: file_type: HTML file, File size: 0, File name: www.google.com
    File Information: file_type: Image file, File size: 78868, File name: img_1317.jpg
    File Information: file_type: HTML file, File size: 170, File name: www.blank.org

Answer 2

Content-Disposition provides filename information if it is not given in the url. But this information is not always present, as is the case with your url. A solution is to filter by content type, see the example below. You can add filters if you wish to download specific content types such as video/mp4.

import requests

url = 'https://aspb1.cdn.asset.aparat.com/aparat-video/a5e07b7f62ffaad0c104763c23d7393215613675-360p.mp4?wmsAuthSign=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ0b2tlbiI6IjUzMGU0Mzc3ZjRlZjVlYWU0OTFkMzdiOTZkODgwNGQ2IiwiZXhwIjoxNjExMzMzMDQxLCJpc3MiOiJTYWJhIElkZWEgR1NJRyJ9.FjMi_dkdLCUkt25dfGqPLcehpaC32dBBUNDC9cLNiu0'
headers=requests.head(url, allow_redirects=True).headers
content_type = headers.get('content-type')

if 'text' in content_type.lower():
    downloadable = False
elif 'html' in content_type.lower():
    downloadable =  False
else:
    downloadable = True

print(downloadable)