A4格式的Selenium打印PDF

Question

我有以下代码打印到PDF(它可以工作)，我只使用谷歌浏览器进行打印。

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

正如我们所看到的，我正在使用Page.printToPDF打印到base64，并将"A4"作为format传递到params参数上。

不幸的是，这个参数似乎被忽略了。我看到一些使用木偶师的代码使用它(格式 A4)，我认为这对我有帮助。

即使使用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.six 验证原始代码的输出

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]

当我将这些磅大小转换为英寸时，我感到震惊。 尺寸为 8.5 x 11，不等于 8.27 x 11.69 的 A4 纸张尺寸。 当我看到这个时，我决定通过查看铬和硒源代码来更多地探索这个问题。

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++双精度是一种通用数据类型，在内部用于编译器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。

这些参数具有默认值，这些值在 Chrome DevTools 协议中定义：

纸张宽度

• ：纸张宽度(以英寸为单位)。默认为 8.5 英寸。
纸张高度
• ：纸张高度(以英寸为单位)。默认为 11 英寸

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

• paper_widthchromium源代码
• 纸张宽度在Chrome DevTools Protocol

根据chromium源代码，命令Page.printToPDF的调用方式为SendCommandAndGetResultWithTimeout.

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);
}

在我的原始答案中，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;

查看硒源代码后，不清楚如何正确地将命令传递send_command_and_get_result或send_command_and_get_result_with_timeout.

我确实在webdriver硒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']

经过一些研究和测试，我发现此功能可用于实现您的用例。

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 纸张大小。

原始帖子 07-13-2021

---

调用函数时可以传递多个参数Page.printToPDF.其中两个参数是：

• paper_width
• paper_height

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
----------------------------------------