使用 wkhtmltopdf 库打印时如何接收 DOM 元素的高度？

Question

当我尝试使用 wkhtmltopdf 库打印时，使用 Javascript 获取 offsetHeight 或任何 DOM 元素时，高度永远不会确定并且始终等于 0。当我执行相同的 JS在任何浏览器中的代码都可以正常工作并产生特定的元素高度。

google了半天，发现可能和wkhtmltopdf有关，wkhtmltopdf中document的宽高和window都为0，我试着覆盖了body的大小用 CSS 标记并用 wkhtmltopdf 配置参数覆盖视口大小，但 offsetHeight 仍然为 0.

在使用 wkhtmltopdf 打印时，是否有任何已知的变通方法来接收 DOM 元素的高度？

我用的是最新稳定版打印库(0.12.6)

Answer 1

我以前用过 wkHtml2Pdf。
我的建议是立即停止，因为 wkhtmltopdf 使用非常旧的浏览器版本，而且您可能运行无论如何都会遇到问题。另外，wkHtmlToPdf 不能正常工作（而且性能很差）。

相反，您可以使用更好的选择。
该选项是将 Chrome DevTools 与 remote-debugging-protocol:
一起使用 https://chromedevtools.github.io/devtools-protocol/

基本上运行s Chrome 像这样

chrome.exe --remote-debugging-port=9222

可选

$"--user-data-dir=\"{directoryInfo.FullName}\"";

和

"--headless --disable-gpu";

以下是我在服务器上启动 Chrome 进程的方式（C# 代码）

public IChromeProcess Create(int port, bool headless)
{
    string path = System.IO.Path.GetRandomFileName();
    System.IO.DirectoryInfo directoryInfo = System.IO.Directory.CreateDirectory(
        System.IO.Path.Combine(
            System.IO.Path.GetTempPath(), path)
    );

    string remoteDebuggingArg = $"--remote-debugging-port={port}";
    string userDirectoryArg = $"--user-data-dir=\"{directoryInfo.FullName}\"";
    const string headlessArg = "--headless --disable-gpu";

    // https://peter.sh/experiments/chromium-command-line-switches/
    System.Collections.Generic.List<string> chromeProcessArgs = 
        new System.Collections.Generic.List<string>
    {
        remoteDebuggingArg,
        userDirectoryArg,
        // Indicates that the browser is in "browse without sign-in" (Guest session) mode. 
        // Should completely disable extensions, sync and bookmarks.
        "--bwsi", 
        "--no-first-run"
    };


    if (false)
    {
        string proxyProtocol = "socks5";
        proxyProtocol = "http";
        proxyProtocol = "https";
        string proxyIP = "68.183.233.181";
        string proxyPort = "3128";
        string proxyArg = "--proxy-server=\"" + proxyProtocol + "://" + proxyIP + ":" + proxyPort + "\"";
        chromeProcessArgs.Add(proxyArg);
    }


    if (headless)
        chromeProcessArgs.Add(headlessArg);

    if(IsRoot)
        chromeProcessArgs.Add("--no-sandbox");

    string args = string.Join(" ", chromeProcessArgs);
    System.Diagnostics.ProcessStartInfo processStartInfo = new System.Diagnostics.ProcessStartInfo(ChromePath, args);
    System.Diagnostics.Process chromeProcess = System.Diagnostics.Process.Start(processStartInfo);

    string remoteDebuggingUrl = "http://localhost:" + port;
    return new LocalChromeProcess(new System.Uri(remoteDebuggingUrl), () => DirectoryCleaner.Delete(directoryInfo), chromeProcess);
}

我在这里使用这个 C# 库来与 DevTools 交互（通过 WebSockets）：
https://github.com/MasterDevs/ChromeDevTools

如果你在服务器上使用 NodeJS，你可以使用这个：
https://github.com/cyrus-and/chrome-remote-interface
或者对于 TypeScript：
https://github.com/TracerBench/chrome-debugging-client

为了生成 PDF，您需要发出 PrintToPDF-Command:

Dim cm2inch As UnitConversion_t = Function(ByVal centimeters As Double) centimeters * 0.393701
Dim mm2inch As UnitConversion_t = Function(ByVal milimeters As Double) milimeters * 0.0393701

Dim printCommand2 As PrintToPDFCommand = New PrintToPDFCommand() With {
    .Scale = 1,
    .MarginTop = 0,
    .MarginLeft = 0,
    .MarginRight = 0,
    .MarginBottom = 0,
    .PrintBackground = True,
    .Landscape = False,
    .PaperWidth = mm2inch(conversionData.PageWidth),
    .PaperHeight = mm2inch(conversionData.PageHeight) ' 
}

要创建光栅图形，您需要发出 CaptureScreenshot-Command :

Dim screenshot As MasterDevs.ChromeDevTools.CommandResponse(Of CaptureScreenshotCommandResponse) = Await chromeSession.SendAsync(New CaptureScreenshotCommand With {
    .Format = "png"
})
System.Diagnostics.Debug.WriteLine("Screenshot taken.")
conversionData.PngData = System.Convert.FromBase64String(screenshot.Result.Data)

请注意，要使屏幕截图正常工作，您需要通过 SetDeviceMetricsOverride-Command:

设置宽度和高度

Await chromeSession.SendAsync(New SetDeviceMetricsOverrideCommand With {
    .Width = conversionData.ViewPortWidth,
    .Height = conversionData.ViewPortHeight,
    .Scale = 1
})

您可能需要将 overflow:hidden 放在 HTML 上，或者一些 sub-elements，这样您就不会截取滚动条 ;)

顺便说一句，如果您需要 Chrome 的特定版本用于 Windows（Chromium，因为旧的 Chrome 版本出于安全原因不可用），您可以获取它们来自 Chocolatey-Repository： https://chocolatey.org/packages/chromium/#versionhistory

这是我的完整 test-code 供参考（减去一些类）

Imports MasterDevs.ChromeDevTools
Imports MasterDevs.ChromeDevTools.Protocol.Chrome.Browser
Imports MasterDevs.ChromeDevTools.Protocol.Chrome.Page
Imports MasterDevs.ChromeDevTools.Protocol.Chrome.Target

Namespace Portal_Convert.CdpConverter


    Public Class ChromiumBasedConverter


        Private Delegate Function UnitConversion_t(ByVal value As Double) As Double




        Public Shared Sub KillHeadlessChromes(ByVal writer As System.IO.TextWriter)
            Dim allProcesses As System.Diagnostics.Process() = System.Diagnostics.Process.GetProcesses()
            Dim exeName As String = "\chrome.exe"

            If System.Environment.OSVersion.Platform = System.PlatformID.Unix Then
                exeName = "/chrome"
            End If

            For i As Integer = 0 To allProcesses.Length - 1
                Dim proc As System.Diagnostics.Process = allProcesses(i)
                Dim commandLine As String = ProcessUtils.GetCommandLine(proc)
                If String.IsNullOrEmpty(commandLine) Then Continue For
                commandLine = commandLine.ToLowerInvariant()
                If commandLine.IndexOf(exeName, System.StringComparison.InvariantCultureIgnoreCase) = -1 Then Continue For

                If commandLine.IndexOf("--headless", System.StringComparison.InvariantCultureIgnoreCase) <> -1 Then
                    writer.WriteLine($"Killing process {proc.Id} with command line ""{commandLine}""")
                    ProcessUtils.KillProcessAndChildren(proc.Id)
                End If
            Next

            writer.WriteLine($"Finished killing headless chromes")
        End Sub


        Public Shared Sub KillHeadlessChromes()
            KillHeadlessChromes(System.Console.Out)
        End Sub


        Private Shared Function __Assign(Of T)(ByRef target As T, value As T) As T
            target = value
            Return value
        End Function


        Public Shared Function KillHeadlessChromesWeb() As System.Collections.Generic.List(Of String)
            Dim ls As System.Collections.Generic.List(Of String) = New System.Collections.Generic.List(Of String)()
            Dim sb As System.Text.StringBuilder = New System.Text.StringBuilder()

            Using sw As System.IO.StringWriter = New System.IO.StringWriter(sb)
                KillHeadlessChromes(sw)
            End Using

            Using tr As System.IO.TextReader = New System.IO.StringReader(sb.ToString())
                Dim thisLine As String = Nothing

                While (__Assign(thisLine, tr.ReadLine())) IsNot Nothing
                    ls.Add(thisLine)
                End While
            End Using

            sb.Length = 0
            sb = Nothing
            Return ls
        End Function


        Private Shared Async Function InternalConnect(ByVal ci As ConnectionInfo, ByVal remoteDebuggingUri As String) As System.Threading.Tasks.Task
            ci.ChromeProcess = New RemoteChromeProcess(remoteDebuggingUri)
            ci.SessionInfo = Await ci.ChromeProcess.StartNewSession()
        End Function


        Private Shared Async Function ConnectToChrome(ByVal chromePath As String, ByVal remoteDebuggingUri As String) As System.Threading.Tasks.Task(Of ConnectionInfo)
            Dim ci As ConnectionInfo = New ConnectionInfo()

            Try
                Await InternalConnect(ci, remoteDebuggingUri)
            Catch ex As System.Exception

                If ex.InnerException IsNot Nothing AndAlso Object.ReferenceEquals(ex.InnerException.[GetType](), GetType(System.Net.WebException)) Then

                    If (CType(ex.InnerException, System.Net.WebException)).Status = System.Net.WebExceptionStatus.ConnectFailure Then
                        Dim chromeProcessFactory As MasterDevs.ChromeDevTools.IChromeProcessFactory = New MasterDevs.ChromeDevTools.ChromeProcessFactory(New FastStubbornDirectoryCleaner(), chromePath)
                        Dim persistentChromeProcess As MasterDevs.ChromeDevTools.IChromeProcess = chromeProcessFactory.Create(9222, True)

                        ' await cannot be used inside catch ...
                        ' Await InternalConnect(ci, remoteDebuggingUri)
                        InternalConnect(ci, remoteDebuggingUri).Wait()
                        Return ci
                    End If
                End If

                System.Console.WriteLine(chromePath)
                System.Console.WriteLine(ex.Message)
                System.Console.WriteLine(ex.StackTrace)

                If ex.InnerException IsNot Nothing Then
                    System.Console.WriteLine(ex.InnerException.Message)
                    System.Console.WriteLine(ex.InnerException.StackTrace)
                End If

                System.Console.WriteLine(ex.[GetType]().FullName)
                Throw
            End Try

            Return ci
        End Function


        Private Shared Async Function ClosePage(ByVal chromeSession As MasterDevs.ChromeDevTools.IChromeSession, ByVal frameId As String, ByVal headLess As Boolean) As System.Threading.Tasks.Task
            Dim closeTargetTask As System.Threading.Tasks.Task(Of MasterDevs.ChromeDevTools.CommandResponse(Of CloseTargetCommandResponse)) = chromeSession.SendAsync(New CloseTargetCommand() With {
                .TargetId = frameId
            })

            ' await will block forever if headless    
            If Not headLess Then
                Dim closeTargetResponse As MasterDevs.ChromeDevTools.CommandResponse(Of CloseTargetCommandResponse) = Await closeTargetTask
                System.Console.WriteLine(closeTargetResponse)
            Else
                System.Console.WriteLine(closeTargetTask)
            End If
        End Function


        Public Shared Async Function ConvertDataAsync(ByVal conversionData As ConversionData) As System.Threading.Tasks.Task
            Dim chromeSessionFactory As MasterDevs.ChromeDevTools.IChromeSessionFactory = New MasterDevs.ChromeDevTools.ChromeSessionFactory()


            Using connectionInfo As ConnectionInfo = Await ConnectToChrome(conversionData.ChromePath, conversionData.RemoteDebuggingUri)
                Dim chromeSession As MasterDevs.ChromeDevTools.IChromeSession = chromeSessionFactory.Create(connectionInfo.SessionInfo.WebSocketDebuggerUrl)

                Await chromeSession.SendAsync(New SetDeviceMetricsOverrideCommand With {
                    .Width = conversionData.ViewPortWidth,
                    .Height = conversionData.ViewPortHeight,
                    .Scale = 1
                })

                Dim navigateResponse As MasterDevs.ChromeDevTools.CommandResponse(Of NavigateCommandResponse) = Await chromeSession.SendAsync(New NavigateCommand With {
                    .Url = "about:blank"
                })

                System.Console.WriteLine("NavigateResponse: " & navigateResponse.Id)
                Dim setContentResponse As MasterDevs.ChromeDevTools.CommandResponse(Of SetDocumentContentCommandResponse) = Await chromeSession.SendAsync(New SetDocumentContentCommand() With {
                    .FrameId = navigateResponse.Result.FrameId,
                    .Html = conversionData.Html
                })

                Dim cm2inch As UnitConversion_t = Function(ByVal centimeters As Double) centimeters * 0.393701
                Dim mm2inch As UnitConversion_t = Function(ByVal milimeters As Double) milimeters * 0.0393701

                Dim printCommand2 As PrintToPDFCommand = New PrintToPDFCommand() With {
                    .Scale = 1,
                    .MarginTop = 0,
                    .MarginLeft = 0,
                    .MarginRight = 0,
                    .MarginBottom = 0,
                    .PrintBackground = True,
                    .Landscape = False,
                    .PaperWidth = mm2inch(conversionData.PageWidth),
                    .PaperHeight = mm2inch(conversionData.PageHeight) ' 
                }

                '.PaperWidth = cm2inch(conversionData.PageWidth),
                '.PaperHeight = cm2inch(conversionData.PageHeight)


                If conversionData.ChromiumActions.HasFlag(ChromiumActions_t.GetVersion) Then

                    Try
                        System.Diagnostics.Debug.WriteLine("Getting browser-version")
                        Dim version As MasterDevs.ChromeDevTools.CommandResponse(Of GetVersionCommandResponse) = Await chromeSession.SendAsync(New GetVersionCommand())
                        System.Diagnostics.Debug.WriteLine("Got browser-version")
                        conversionData.Version = version.Result
                    Catch ex As System.Exception
                        conversionData.Exception = ex
                        System.Diagnostics.Debug.WriteLine(ex.Message)
                    End Try
                End If

                If conversionData.ChromiumActions.HasFlag(ChromiumActions_t.ConvertToImage) Then

                    Try
                        System.Diagnostics.Debug.WriteLine("Taking screenshot")
                        Dim screenshot As MasterDevs.ChromeDevTools.CommandResponse(Of CaptureScreenshotCommandResponse) = Await chromeSession.SendAsync(New CaptureScreenshotCommand With {
                            .Format = "png"
                        })
                        System.Diagnostics.Debug.WriteLine("Screenshot taken.")
                        conversionData.PngData = System.Convert.FromBase64String(screenshot.Result.Data)
                    Catch ex As System.Exception
                        conversionData.Exception = ex
                        System.Diagnostics.Debug.WriteLine(ex.Message)
                    End Try
                End If

                If conversionData.ChromiumActions.HasFlag(ChromiumActions_t.ConvertToPdf) Then

                    Try
                        System.Diagnostics.Debug.WriteLine("Printing PDF")
                        Dim pdf As MasterDevs.ChromeDevTools.CommandResponse(Of PrintToPDFCommandResponse) = Await chromeSession.SendAsync(printCommand2)
                        System.Diagnostics.Debug.WriteLine("PDF printed.")
                        conversionData.PdfData = System.Convert.FromBase64String(pdf.Result.Data)
                    Catch ex As System.Exception
                        conversionData.Exception = ex
                        System.Diagnostics.Debug.WriteLine(ex.Message)
                    End Try
                End If


                System.Console.WriteLine("Closing page")
                Await ClosePage(chromeSession, navigateResponse.Result.FrameId, True)
                System.Console.WriteLine("Page closed")

            End Using ' connectionInfo

        End Function ' ConvertDataAsync


        Public Shared Sub ConvertData(ByVal conversionData As ConversionData)
            ConvertDataAsync(conversionData).Wait()
        End Sub


    End Class


End Namespace

请注意，如果有人使用 C#，最好使用此库：
https://github.com/BaristaLabs/chrome-dev-tools-runtime
它使用较少的外部依赖，并且是 NetCore。我使用另一个只是因为我必须将它移植到旧的框架版本...

使用 wkhtmltopdf 库打印时如何接收 DOM 元素的高度？

How to receive the height of DOM element when printing with wkhtmltopdf library?

javascript

wkhtmltopdf