使用 wkhtmltopdf 库打印时如何接收 DOM 元素的高度？答案

【问题标题】：How to receive the height of DOM element when printing with wkhtmltopdf library?使用 wkhtmltopdf 库打印时如何接收 DOM 元素的高度？
【发布时间】：2020-10-15 06:53:41
【问题描述】：

当我在使用 wkhtmltopdf 库打印时尝试使用 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。当我在任何浏览器中执行相同的 JS 代码时，它可以正常工作并导致元素的特定高度。

google了半天，发现可能和wkhtmltopdf有关，其中document和window的宽高都等于0。我尝试用CSS覆盖body标签的大小，覆盖视口大小与 wkhtmltopdf 配置参数，但 offsetHeight 仍为 0。

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

我使用的是最新稳定版的打印库（0.12.6）

【问题讨论】：

标签： javascript wkhtmltopdf

【解决方案1】：

我过去使用过 wkHtml2Pdf。
我的建议是立即停止，因为 wkhtmltopdf 使用的是非常旧的浏览器版本，无论如何您都可能会遇到问题。此外，wkHtmlToPdf 不能正常工作（而且性能很糟糕）。

相反，您可以使用更好的选择。
该选项是将 Chrome DevTools 与远程调试协议一起使用：
https://chromedevtools.github.io/devtools-protocol/

基本上像这样运行 Chrome

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

可选

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

和

"--headless --disable-gpu";

这是我在服务器上启动 Chrome 进程的方法（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);
}

我在这里使用了这个 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
})

您可能必须在 HTML 或某些子元素上放置 overflow:hidden，这样您就不会截屏滚动条；)

顺便说一句，如果您需要特定版本的 Windows 版 Chrome（Chromium，因为出于安全原因，旧版 Chrome 不可用），您可以从 Chocolatey-Repository 获取它们： https://chocolatey.org/packages/chromium/#versionhistory

这是我的完整测试代码供参考（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#，最好使用这个库：
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反向移植到旧的框架版本......

【讨论】：

Stefan Steiger，谢谢您的回答。我决定改用github.com/Sicos1977/ChromeHtmlToPdf 库，因为最近似乎没有开发 BaristaLabs 的工具。它也基于 .NET Core。