如何使用 RSelenium 从网页下载嵌入的 PDF 文件？

Question

编辑：从我目前收到的 cmets 中，我设法使用 RSelenium 访问我正在寻找的 PDF 文件，使用以下代码：

library(RSelenium)
driver <- rsDriver(browser = "firefox")
remote_driver <- driver[["client"]]
remote_driver$navigate("https://www.rad.cvm.gov.br/enetconsulta/frmGerenciaPaginaFRE.aspx?CodigoTipoInstituicao=1&NumeroSequencialDocumento=62398")
# It needs some time to load the page
option <- remote_driver$findElement(using = 'xpath', "//select[@id='cmbGrupo']/option[@value='PDF|412']")
option$clickElement()

现在，我需要 R 来单击下载按钮，但我无法做到。我试过了：

button <- remote_driver$findElement(using = "xpath", "//*[@id='download']")
button$clickElement()

但我收到以下错误：

Selenium message:Unable to locate element: //*[@id="download"]
For documentation on this error, please visit: https://www.seleniumhq.org/exceptions/no_such_element.html
Build info: version: '4.0.0-alpha-2', revision: 'f148142cf8', time: '2019-07-01T21:30:10'

Erro:    Summary: NoSuchElement
 Detail: An element could not be located on the page using the given search parameters.
 class: org.openqa.selenium.NoSuchElementException
 Further Details: run errorDetails method

有人能说出这里出了什么问题吗？ 谢谢！

原问题：

我有几个网页需要下载嵌入的 PDF 文件，我正在寻找一种使用 R 实现自动化的方法。这是其中一个网页：https://www.rad.cvm.gov.br/enetconsulta/frmGerenciaPaginaFRE.aspx?CodigoTipoInstituicao=1&NumeroSequencialDocumento=62398 这是 CVM（Comissão de Valores Mobiliários，巴西相当于美国证券交易委员会 - SEC）的网页，用于下载财务报表附注（Notas Explicativas）巴西公司。

我尝试了几个选项，但该网站的构建方式似乎难以提取直接链接。 我尝试了Downloading all PDFs from URL 中的建议，但html_nodes(".ms-vb2 a") %>% html_attr("href") 产生了一个空字符向量。 同样，当我在这里尝试https://www.samuelworkman.org/blog/scraping-up-bits-of-helpfulness/ 中的方法时，html_attr("href") 会生成一个空向量。

我不习惯在 R 中使用网页 scraping 代码，所以我无法弄清楚发生了什么。 感谢您的帮助！

Answer 1

如果有人遇到与我相同的问题，我将发布我使用的解决方案：

# set Firefox profile to download PDFs automatically
pdfprof <- makeFirefoxProfile(list(
  "pdfjs.disabled" = TRUE,
  "plugin.scan.plid.all" = FALSE,
  "plugin.scan.Acrobat" = "99.0",
  "browser.helperApps.neverAsk.saveToDisk" = 'application/pdf'))

driver <- rsDriver(browser = "firefox", extraCapabilities = pdfprof)
remote_driver <- driver[["client"]]
remote_driver$navigate("https://www.rad.cvm.gov.br/enetconsulta/frmGerenciaPaginaFRE.aspx?CodigoTipoInstituicao=1&NumeroSequencialDocumento=62398")
Sys.sleep(3) # It needs some time to load the page (set to 3 seconds)

option <- remote_driver$findElement(using = 'xpath', "//select[@id='cmbGrupo']/option[@value='PDF|412']") # select the option to open PDF file
option$clickElement()

# Find iframes in the webpage
web.elem <- remote_driver$findElements(using = "css", "iframe") # get all iframes in the webpage
sapply(web.elem, function(x){x$getElementAttribute("id")}) # see their names
remote_driver$switchToFrame(web.elem[[1]]) # Move to the first iframe (Formularios Filho)
web.elem.2 <- remote_driver$findElements(using = "css", "iframe") # get all iframes in the webpage
sapply(web.elem.2, function(x){x$getElementAttribute("id")}) # see their names
# The pdf Viewer iframe is the only one inside Formularios Filho
remote_driver$switchToFrame(web.elem.2[[1]]) # Move to the first iframe (pdf Viewer)
Sys.sleep(3) # It needs some time to load the page (set to 3 seconds)

# Download the PDF file
button <- remote_driver$findElement(using = "xpath", "//*[@id='download']")
button$clickElement() # download
Sys.sleep(3) # Need sometime to finish download and then close the window
remote_driver$close() # Close the window