XmlException UrdfImporter

[rprb93]

• [X] I am at the right place and my issue is directly related to ROS#. General technical questions I would post e.g. at ROS Answers or Stack Overflow. For library-specific questions I would look for help in the corresponding library forums.
• [X] I have thoroughly read the Contributing Guideline and writing this issue is the right thing to do in my case.

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I found a bug!

• [X] I am using the latest ROS# version available here on the master branch.

• [X] I am adding all required information, code and data files, screenshots and log files so that you can reproduce the problem.

• My OS is: MacOS 11.6 and Ubuntu 20.04

• My Unity Version is: 2020.3.16f1

• My ROS Distribution is: noetic

Here is my bug description: I'm trying to import a URDF from ROS to my Unity workspace, but an XMLExecption happen. When I start the plugin, on the ROS side I saw a WebSocket client connecting. After, an error happened in the Unity terminal reporting:

XmlException: Data at the root level is invalid. Line 1, position 1.

System.Xml.XmlTextReaderImpl.Throw (System.Exception e) (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.XmlTextReaderImpl.Throw (System.String res, System.String arg) (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.XmlTextReaderImpl.Throw (System.String res) (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace () (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.XmlTextReaderImpl.ParseDocumentContent () (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.XmlTextReaderImpl.Read () (at <1d98d70bb7d8453b80c25aa561fdecd1>:0) System.Xml.Linq.XDocument.Load (System.Xml.XmlReader reader, System.Xml.Linq.LoadOptions options) (at <a9ef27d60e3144519c0741b6584ba229>:0) System.Xml.Linq.XDocument.Parse (System.String text, System.Xml.Linq.LoadOptions options) (at <a9ef27d60e3144519c0741b6584ba229>:0) System.Xml.Linq.XDocument.Parse (System.String text) (at <a9ef27d60e3144519c0741b6584ba229>:0) RosSharp.RosBridgeClient.UrdfTransfer.UrdfTransferFromRos.ImportResourceFiles (System.String fileContents) (at <0f423d031f3c48f18d807ebe4816015c>:0) RosSharp.RosBridgeClient.UrdfTransfer.UrdfTransferFromRos+<>c__DisplayClass7_0.<ReceiveRobotDescription>b__0 () (at <0f423d031f3c48f18d807ebe4816015c>:0) System.Threading.ThreadHelper.ThreadStart_Context (System.Object state) (at <437ba245d8404784b9fbab9b439ac908>:0) System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx) (at <437ba245d8404784b9fbab9b439ac908>:0) System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx) (at <437ba245d8404784b9fbab9b439ac908>:0) System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state) (at <437ba245d8404784b9fbab9b439ac908>:0) System.Threading.ThreadHelper.ThreadStart () (at <437ba245d8404784b9fbab9b439ac908>:0) UnityEngine.<>c:<RegisterUECatcher>b__0_0(Object, UnhandledExceptionEventArgs) (at /Users/builduser/buildslave/unity/build/Runtime/Export/Scripting/UnhandledExceptionHandler.bindings.cs:46)

I already try downgrading the ROS# version and the Unity version and didn't solve the problem. Some help? The system already worked in times.

[MartinBischoff]

Hi @rprb93 ,

please let me know if this answer resolves your problem: https://stackoverflow.com/a/27743515

I'm thinking about adding the suggested check to the beginning of the XML import:

string _byteOrderMarkUtf8 = Encoding.UTF8.GetString(Encoding.UTF8.GetPreamble());
if (xml.StartsWith(_byteOrderMarkUtf8))
{
    xml = xml.Remove(0, _byteOrderMarkUtf8.Length);
}

[rprb93]

Hi @MartinBischoff ,

I saw this suggestion, but I don't know where I need to put these codes.

[MartinBischoff]

Hi @rprb93 the responsible class UrdfTransferFromRos is already mentioned in your error message above. I' suggest to put the code in FormatTextFileContents(). In this method the received file contents is already treated with various fixes before it is actually saved in WriteTextFile().

[rprb93]

Is it normal Libraries folder are not in Unity Assets? The FormatTextFileContents() are only in Libraries folder.

[MartinBischoff]

Yes. This has been addressed in multiple issues already. Also see README.md As URDF Import is independent of Unity, we put it in the Library VS solution.

[rprb93]

Nothing changed with the modification.

I put the code in FormatTextFileContents(), resulting in:

private static string FormatTextFileContents(string fileContents)
{
    string _byteOrderMarkUtf8 = Encoding.UTF8.GetString(Encoding.UTF8.GetPreamble());
    if (fileContents.StartsWith(_byteOrderMarkUtf8))
    {
        fileContents = fileContents.Remove(0, _byteOrderMarkUtf8.Length);
    }

    // remove enclosing quotations if existent:
    if (fileContents.Substring(0, 1) == "\"" && fileContents.Substring(fileContents.Length - 1, 1) == "\"")
        fileContents = fileContents.Substring(1, fileContents.Length - 2);

    // replace \" quotation sign by actual quotation:
    fileContents = fileContents.Replace("\\\"", "\"");

    // replace \n newline sign by actual new line:
    return fileContents.Replace("\\n", Environment.NewLine);
}

Compiled without errors and copied the RosBridgeClient.dll to ...\Unity3D\Assets\RosSharp\Plugins\.

[rprb93]

I solve the problem. It was my mistake in URDF Parameter. The URDF Parameter name need matches in publish launch (ROS side) and in the URDF Transfer plugin (Unity Side).