如何检查请求中的 URL 是否可下载

Question

我正在使用 tkinter 和 requests 制作这个下载器应用程序，我最近在我的程序中发现了一个错误。基本上我希望我的程序在开始下载 URL 的内容之前检查给定的 URL 是否可下载。我曾经通过获取 URL 的标头并检查“Content-Length”是否存在来做到这一点，它适用于某些 URL（如：https://www.google.com），但适用于其他 URL（如指向一个 youtube 视频）它没有，它使我的程序崩溃。我看到有人说一个stackoverflow，我可以在标题的“Content-Disposition”中检查“附件”，但它对我不起作用，并且对于可下载和非- 可下载的网址。做这个的最好方式是什么？ 我尝试过但没有工作的另一个stackoverflow问题中提到的代码：

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

我以前的代码：

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()

更新：网址： https://aspb1.cdn.asset.aparat.com/aparat-video/a5e07b7f62ffaad0c104763c23d7393215613675-360p.mp4?wmsAuthSign=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ0b2tlbiI6IjUzMGU0Mzc3ZjRlZjVlYWU0OTFkMzdiOTZkODgwNGQ2IiwiZXhwIjoxNjExMzMzMDQxLCJpc3MiOiJTYWJhIElkZWEgR1NJRyJ9.FjMi_dkdLCUkt25dfGqPLcehpaC32dBBUNDC9cLNiu0 这个网址是我用来测试的。如果您打开 URL，它会直接将您带到可以下载的视频，但是在检查“内容处置”时，它返回“无”，就像我尝试过的大多数可下载和不可下载的 URL 一样。

Answer 1

根据Request for Comment (RFC) 6266Content-Disposition Header Field：

不是 HTTP 标准的一部分，但由于它被广泛实施， 我们正在为实施者记录它的使用和风险。

由于 Content-Disposition 标头并不总是可用，您可以使用一种解决方案，不仅查找该特定标头，还查看 Content-Type 标头中的各个文件类型

这是Content-Types的列表。

下面的代码检查 Content-Disposition 的标头，但它也检查一些通常可下载的 Content-Type 的标头。

我还添加了对 Content-Length 的检查， 因为它可能有助于对正在下载的文件进行分块。

您是否考虑过创建子下载文件夹？

• download_folder/text_files
• download_folder/pdf_files

或

• 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)

---

这是另一个带有函数的版本

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

如果 url 中没有给出文件名信息，Content-Disposition 会提供它。但这些信息并不总是存在，就像您的网址一样。一种解决方案是按内容类型进行过滤，请参见下面的示例。如果您想下载特定的内容类型，例如video/mp4，您可以添加过滤器。

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)

Answer 3

我认为您以前的代码可以工作，但稍作修改。它正在尝试下载完整的文件，因此每次运行时它都会被挂起

import requests
url = 'https://aspb1.cdn.asset.aparat.com/aparat-video/a5e07b7f62ffaad0c104763c23d7393215613675-360p.mp4?wmsAuthSign=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ0b2tlbiI6IjUzMGU0Mzc3ZjRlZjVlYWU0OTFkMzdiOTZkODgwNGQ2IiwiZXhwIjoxNjExMzMzMDQxLCJpc3MiOiJTYWJhIElkZWEgR1NJRyJ9.FjMi_dkdLCUkt25dfGqPLcehpaC32dBBUNDC9cLNiu0'
r = requests.get(url,stream=True)


try:
    print(r.headers)
    #if "Content-Length" in r.headers:
    file_size = int(r.headers["Content-Length"])
except KeyError:
    # Just a class that I defined to raise an exception if the URL was not downloadable
    raise NotDownloadable()

使用stream=True

r = requests.get(url,stream=True)

这在用户文档中没有解释。但是通过猜测我们可以说，分块传输编码正在进行，数据流被分成一系列不重叠的“块”。这些块由服务器相互独立地发送出去。

Answer 4

您可以检查content-type 响应标头。此标头定义所请求资源的媒体类型。最常见的类型显示为here。

content-type 标头由type "/" subtype 定义，有些还包含一个参数，格式为type "/" subtype ";" parameter，参数格式为attribute "=" value。参数值不是强制性的，但类型和子类型是强制性的。

RFC 134定义的当前有7种类型：

文本 多部分 应用 信息 图片 声音的 视频

您要查找的标头因您期望的资源而异，但您可以使用一些示例。

示例

下载图片

import requests

response = requests.head(url)
response_headers = response.headers
response_content_type = response_headers.get("content-type")

# you could use this code to search for all images using just the type

if response_content_type.lower().split("/")[0] == "image":
    is_image = True
else:
    is_image = False

# alternatively you could specify your expected content-types including the subtype

CONTENT_TYPES = ["image/gif", "image/jpeg", "image/png", "image/tiff", "image.svg+xml"...]

if response_content_type.lower() in CONTENT_TYPES:
    is_image = True
else:
    is_image = False

if is_image:
    # code to download image

此代码可以很容易地适应不同的类型和子类型。

注意

值得注意的是类型是固定的，你不能定义一个新的子类型但是你可以定义一个新的子类型。