A4 格式的硒打印 PDF

Question

我有以下用于打印到 PDF 的代码（并且可以正常工作），并且我只使用 Google Chrome 进行打印。

def send_devtools(driver, command, params=None):
    # pylint: disable=protected-access
    if params is None:
        params = {}
    resource = "/session/%s/chromium/send_command_and_get_result" % driver.session_id
    url = driver.command_executor._url + resource
    body = json.dumps({"cmd": command, "params": params})
    resp = driver.command_executor._request("POST", url, body)
    return resp.get("value")


def export_pdf(driver):
    command = "Page.printToPDF"
    params = {"format": "A4"}
    result = send_devtools(driver, command, params)
    data = result.get("data")
    return data

如我们所见，我使用Page.printToPDF 打印到base64，并在params 参数上将“A4”作为format 传递。

不幸的是，这个参数似乎被忽略了。我看到了一些使用 puppeteer 的代码（格式 A4），我认为这对我有帮助。

即使是硬编码的宽度和高度（见下文），我也没有运气。

"paperWidth": 8.27,  # inches
"paperHeight": 11.69,  # inches

使用上面的代码，是否可以将页面设置为A4格式？

Answer 1

更新后 07-17-2021

---

我决定使用 Python 包 pdfminer.sixth 验证我的原始代码的输出

from pdfminer.pdfpage import PDFPage
from pdfminer.pdfpage import PDFParser
from pdfminer.pdfpage import PDFDocument

parser = PDFParser(open('test_1.pdf', 'rb'))
doc = PDFDocument(parser)
pageSizesList = []
for page in PDFPage.create_pages(doc):
    print(page.mediabox)
    # output
    [0, 0, 612, 792]

当我将这些磅值转换为英寸时，我感到很震惊。尺寸为 8.5 x 11，不等于 A4 纸张尺寸 8.27 x 11.69。当我看到这个时，我决定通过查看chromium 和selenium 源代码来进一步探索这个问题。

在chromium 源代码中，命令Page.printToPDF 位于文件page_handler.cc 中

void PageHandler::PrintToPDF(Maybe<bool> landscape,
                             Maybe<bool> display_header_footer,
                             Maybe<bool> print_background,
                             Maybe<double> scale,
                             Maybe<double> paper_width,
                             Maybe<double> paper_height,
                             Maybe<double> margin_top,
                             Maybe<double> margin_bottom,
                             Maybe<double> margin_left,
                             Maybe<double> margin_right,
                             Maybe<String> page_ranges,
                             Maybe<bool> ignore_invalid_page_ranges,
                             Maybe<String> header_template,
                             Maybe<String> footer_template,
                             Maybe<bool> prefer_css_page_size,
                             Maybe<String> transfer_mode,
                             std::unique_ptr<PrintToPDFCallback> callback)

此函数允许修改参数paper_width 和paper_height。这些参数采用double. C++ double 是一种通用数据类型，编译器在内部使用它来定义和保存任何数值数据类型，尤其是任何面向十进制的值。 C++ 双精度数据类型可以是小数，也可以是带值的整数。

这些参数有默认值，定义在Chrome DevTools Protocol:

• paperWidth：纸张宽度，以英寸为单位。默认为 8.5 英寸。
• paperHeight：纸张高度，以英寸为单位。默认为 11 英寸

注意参数格式之间的差异 chromium 源代码和Chrome DevTools Protocol 详细信息。

• chromium源代码中的paper_width
• Chrome DevTools Protocol 中的纸张宽度

根据chromium 源代码，命令Page.printToPDF 使用SendCommandAndGetResultWithTimeout. 调用

Status WebViewImpl::PrintToPDF(const base::DictionaryValue& params,
                               std::string* pdf) {
  // https://bugs.chromium.org/p/chromedriver/issues/detail?id=3517
  if (!browser_info_->is_headless) {
    return Status(kUnknownError,
                  "PrintToPDF is only supported in headless mode");
  }
  std::unique_ptr<base::DictionaryValue> result;
  Timeout timeout(base::TimeDelta::FromSeconds(10));
  Status status = client_->SendCommandAndGetResultWithTimeout(
      "Page.printToPDF", params, &timeout, &result);
  if (status.IsError()) {
    if (status.code() == kUnknownError) {
      return Status(kInvalidArgument, status);
    }
    return status;
  }
  if (!result->GetString("data", pdf))
    return Status(kUnknownError, "expected string 'data' in response");
  return Status(kOk);
}

在我原来的答案中，我使用了send_command_and_get_result,，即 类似于命令SendCommandAndGetResultWithTimeout.

# stub_devtools_client.h
 
Status SendCommandAndGetResult(
     const std::string& method,
     const base::DictionaryValue& params,
     std::unique_ptr<base::DictionaryValue>* result) override;

Status SendCommandAndGetResultWithTimeout(
     const std::string& method,
     const base::DictionaryValue& params,
     const Timeout* timeout,
     std::unique_ptr<base::DictionaryValue>* result) override;

查看selenium 源代码后，不清楚如何正确传递命令send_command_and_get_result 或send_command_and_get_result_with_timeout.

我确实在webdriverselenium源代码中注意到了这个函数：

def execute_cdp_cmd(self, cmd, cmd_args):
     """
     Execute Chrome Devtools Protocol command and get returned result

     The command and command args should follow chrome devtools protocol domains/commands, refer to link
     https://chromedevtools.github.io/devtools-protocol/

     :Args:
      - cmd: A str, command name
      - cmd_args: A dict, command args. empty dict {} if there is no command args

     :Usage:
         driver.execute_cdp_cmd('Network.getResponseBody', {'requestId': requestId})

     :Returns:
         A dict, empty dict {} if there is no result to return.
         For example to getResponseBody:

         {'base64Encoded': False, 'body': 'response body string'}

     """
     return self.execute("executeCdpCommand", {'cmd': cmd, 'params': cmd_args})['value']

在做了一些研究和测试后，我发现这个功能可以用来实现你的用例。

import base64
from selenium import webdriver
from selenium.webdriver.chrome.options import Options
from pdfminer.pdfpage import PDFPage
from pdfminer.pdfpage import PDFParser
from pdfminer.pdfpage import PDFDocument

chrome_options = Options()
chrome_options.add_argument("--disable-infobars")
chrome_options.add_argument("--disable-extensions")
chrome_options.add_argument("--disable-popup-blocking")
chrome_options.add_argument('--headless')

browser = webdriver.Chrome('/usr/local/bin/chromedriver', options=chrome_options)
browser.get('http://www.google.com')

# use can defined additional parameters if needed
params = {'landscape': False,
          'paperWidth': 8.27,
          'paperHeight': 11.69}

# call the function "execute_cdp_cmd" with the command "Page.printToPDF" with
# parameters defined above
data = browser.execute_cdp_cmd("Page.printToPDF", params)

# save the output to a file.
with open('file_name.pdf', 'wb') as file:
    file.write(base64.b64decode(data['data']))

browser.quit()

# verify the page size of the PDF file created
parser = PDFParser(open('file_name.pdf', 'rb'))
doc = PDFDocument(parser)
pageSizesList = []
for page in PDFPage.create_pages(doc):
    print(page.mediabox)
    # output 
    [0, 0, 594.95996, 840.95996]

输出以磅为单位，需要转换为英寸。

• 594.95996 点等于 8.263332777783 英寸
• 840.95996 点等于 11.6799994445 英寸

8.263332777783 x 11.6799994445 是 A4 纸张尺寸。

原帖 07-13-2021

---

调用函数Page.printToPDF.时可以传递多个parameters，其中两个参数是：

• 纸张宽度
• 纸张高度

以下代码将这些参数传递给Page.printToPDF.

import json
import base64
from selenium import webdriver
from selenium.webdriver.chrome.options import Options


def send_devtools(driver, command, params=None):
    if params is None:
        params = {}
    resource = "/session/%s/chromium/send_command_and_get_result" % driver.session_id
    url = driver.command_executor._url + resource
    body = json.dumps({"cmd": command, "params": params})
    resp = driver.command_executor._request("POST", url, body)
    return resp.get("value")


def create_pdf(driver, file_name):
    command = "Page.printToPDF"
    params = {'paper_width': '8.27', 'paper_height': '11.69'}
    result = send_devtools(driver, command,  params)
    save_pdf(result, file_name)
    return


def save_pdf(data, file_name):
    with open(file_name, 'wb') as file:
        file.write(base64.b64decode(data['data']))
    print('PDF created')


chrome_options = Options()
chrome_options.add_argument("--disable-infobars")
chrome_options.add_argument("--disable-extensions")
chrome_options.add_argument("--disable-popup-blocking")
chrome_options.add_argument('--headless')

browser = webdriver.Chrome('/usr/local/bin/chromedriver', options=chrome_options)
browser.get('http://www.google.com')

create_pdf(browser, 'test_pdf_1.pdf')

----------------------------------------
My system information
----------------------------------------
Platform:       maxOS
OS Version:     10.15.7
Python Version: 3.9
Selenium:       3.141.0
pdfminer.sixth: 20201018
----------------------------------------