What causes "Invalid path '{path}': leading '//' is not allowed." in iOfficeAI/OfficeCLI?

Ensure exactly one leading slash: if both segments have one, drop one before joining.

iOfficeAI/OfficeCLI · warning · ArgumentException

Invalid path '{path}': leading '//' is not allowed.

Error message

Invalid path '{path}': leading '//' is not allowed.

What it means

Thrown by NormalizeExcelPath when the path starts with '//'. A leading double slash implies an empty first segment; DOCX already rejected this and XLSX was brought to parity so malformed separators do not expose raw OOXML local names.

Source

Thrown at src/officecli/Handlers/Excel/ExcelHandler.Helpers.Sheet.cs:109

    /// </summary>
    // Excel-quoted sheet name: 'My Data (2024)'!A1 — strip one pair of single
    // quotes and un-double embedded quotes ('It''s'!A1 → It's). Excel REQUIRES
    // the quoted form for names with spaces/punctuation, so refs pasted from
    // formulas arrive quoted. Unquoted names pass through unchanged.
    internal static string UnquoteSheetName(string s)
        => s.Length >= 2 && s[0] == '\'' && s[^1] == '\''
            ? s[1..^1].Replace("''", "'")
            : s;

    internal string NormalizeExcelPath(string path)
    {
        // Reject malformed segment separators that previously slipped past
        // the regex matchers and exposed raw OOXML local names. DOCX already
        // rejects these; bring XLSX up to parity.
        if (path.Length > 1 && path != "/" && path.EndsWith("/"))
            throw new ArgumentException($"Invalid path '{path}': trailing '/' is not allowed.");
        if (path.StartsWith("//"))
            throw new ArgumentException($"Invalid path '{path}': leading '//' is not allowed.");
        if (path.Contains("//"))
            throw new ArgumentException($"Invalid path '{path}': empty path segment ('//') is not allowed.");
        // Handle "/Sheet1!A1" — strip leading '/' when '!' is present so native
        // notation is parsed correctly. EXCEPT when the first slash segment
        // names an existing sheet: '!' is legal inside a sheet NAME (Excel
        // forbids only : \ / ? * [ ]), and reinterpreting "/Q1!Results" as
        // bang notation made such a sheet permanently unaddressable.
        if (path.StartsWith('/') && path.Contains('!'))
        {
            var seg0 = path[1..];
            var seg0Slash = seg0.IndexOf('/');
            var first = seg0Slash < 0 ? seg0 : seg0[..seg0Slash];
            if (!GetWorksheets().Any(w => w.Name.Equals(first, StringComparison.OrdinalIgnoreCase)))
                path = path[1..];
        }
        if (path.Equals("/workbook", StringComparison.OrdinalIgnoreCase)) return "/";
        if (path.StartsWith('/')) return path;
        // Excel-quoted sheet ref: 'My Data'!A1 — the '!' separator is the one

View on GitHub (pinned to 1ced45e900)

Solutions

Ensure exactly one leading slash: if both segments have one, drop one before joining.
Use string.TrimStart('/') once then prepend a single '/'.
Validate the joined path with the NormalizePath helper shown for error 704.

Example fix

// before
string path = baseDir.EndsWith('/') ? baseDir + child : baseDir + "/" + child;
// when baseDir='/' and child='/Sheet1' → '//Sheet1'
// after
string joined = string.Join('/', new[] { baseDir.TrimEnd('/'), child.TrimStart('/') });
if (!joined.StartsWith('/')) joined = "/" + joined;

Defensive patterns

Strategy: validation

Validate before calling

static string EnsureSingleLeadingSlash(string p)
    => p.StartsWith("//") ? "/" + p.TrimStart('/') : p;

Type guard

null

Try / catch

try { NormalizeExcelPath(path); }
catch (ArgumentException ex) when (ex.Message.Contains("leading '//'"))
{ path = "/" + path.TrimStart('/'); }

Prevention

Never join two segments that both carry a leading or trailing '/'.
Sanitize at the boundary before passing to path APIs.
Reject paths with empty first segments at parse time.

When it happens

Trigger: Calling a path-based Excel API with '//Sheet1/A1', '///root', or any path beginning with two or more slashes. Common when concatenating '/' + path where path already starts with '/'.

Common situations: Joining a base path that ends in '/' with a child that begins with '/'; copying URL-handling code into path handling; treating '/' like an empty host prefix.

Related errors

AI-assisted analysis of iOfficeAI/OfficeCLI@1ced45e900 (2026-08-13). Data as JSON: /api/errors/e5980f5d9c82f0d2. Report an issue: GitHub.