dotnet/wpf · error · ArgumentException

throw new…

Error message

throw new ArgumentException(SR.ContentTypeCannotHaveLeadingTrailingLWS);

What it means

The ContentType constructor parses an RFC-style media type string (e.g. for System.IO.Packaging). It rejects content types that begin or end with linear white space (spaces, tabs, CR/LF), throwing ArgumentException because leading/trailing LWS makes the value structurally invalid.

Solutions

1. Trim the string before constructing: contentType.Trim().
2. Validate the input starts with the type token and ends with a parameter value or subtype.
3. Check the source (config, XML attribute) for accidental whitespace or line wrapping.

Example fix

// before
var ct = new ContentType(userValue);
// after
var ct = new ContentType(userValue.Trim());

public static bool IsValidContentTypeRaw(string s) =>
    !string.IsNullOrEmpty(s) &&
    !char.IsWhiteSpace(s[0]) && !char.IsWhiteSpace(s[s.Length - 1]);

try { var ct = new ContentType(value); }
catch (ArgumentException ex) when (ex.Message.Contains("white space"))
{ value = value.Trim(); /* retry */ }

When it happens

Trigger: new ContentType(" text/plain"), new ContentType("text/plain "), or strings read from config/files with stray whitespace; also any string whose first or last char is \r, \n, \t, or space.

Common situations: Hand-written content types in PackagePart.CreatePart calls, values parsed from .rels or [Content_Types].xml with formatting, trimming forgotten on user/config input.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Cannot have leading path delimiter.
• CompoundFile path must be non-empty.
• FileMode value is not valid.
• SR.CompoundFilePathNullEmpty
• SR.DataSpaceLabelInvalidEmpty

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ba397432dbac956b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/ContentType.cs:82

        /// we used more as an indication of an absent/unknown ContentType. 
        /// </summary>
        /// <param name="contentType">content-type</param>
        /// <exception cref="ArgumentNullException">If the contentType parameter is null</exception>
        /// <exception cref="ArgumentException">If the contentType string has leading or 
        /// trailing Linear White Spaces(LWS) characters</exception>
        /// <exception cref="ArgumentException">If the contentType string invalid CR-LF characters</exception>
        internal ContentType(string contentType)
        {
            ArgumentNullException.ThrowIfNull(contentType);

            if (contentType.Length == 0)
            {
                _contentType = String.Empty;
            }
            else
            {
                if (IsLinearWhiteSpaceChar(contentType[0]) || IsLinearWhiteSpaceChar(contentType[contentType.Length - 1]))
                    throw new ArgumentException(SR.ContentTypeCannotHaveLeadingTrailingLWS);

                //Carriage return can be expressed as '\r\n' or '\n\r'
                //We need to make sure that a \r is accompanied by \n
                ValidateCarriageReturns(contentType);

                //Begin Parsing                
                int semiColonIndex = contentType.IndexOf(_semicolonSeparator);

                if (semiColonIndex == -1)
                {
                    // Parse content type similar to - type/subtype
                    ParseTypeAndSubType(contentType);
                }
                else
                {
                    // Parse content type similar to - type/subtype ; param1=value1 ; param2=value2 ; param3="value3"
                    ParseTypeAndSubType(contentType.AsSpan(0, semiColonIndex));
                    ParseParameterAndValue(contentType.AsSpan(semiColonIndex));

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