iOfficeAI/OfficeCLI · error · ArgumentException

Invalid data URI: missing comma separator

Error message

Invalid data URI: missing comma separator

What it means

Thrown by FileSource.ResolveDataUri when a data: URI has no comma separating the header from the payload. RFC 2397 data URIs are shaped 'data:[<mediatype>][;base64],<data>'; without the comma the payload cannot be located.

Source

Thrown at src/officecli/Core/FileSource.cs:132

        // Try extension from URL path
        var uri = new Uri(url);
        var ext = Path.GetExtension(uri.AbsolutePath).ToLowerInvariant();

        // Fallback: infer from content-type header
        if (string.IsNullOrEmpty(ext))
        {
            var mime = response.Content.Headers.ContentType?.MediaType;
            ext = MimeToExtension(mime);
        }

        return (new MemoryStream(bytes), ext);
    }

    private static (MemoryStream, string) ResolveDataUri(string dataUri)
    {
        var commaIdx = dataUri.IndexOf(',');
        if (commaIdx < 0)
            throw new ArgumentException("Invalid data URI: missing comma separator");

        var header = dataUri[..commaIdx];
        var data = dataUri[(commaIdx + 1)..];

        if (!header.Contains("base64", StringComparison.OrdinalIgnoreCase))
            throw new ArgumentException("Only base64-encoded data URIs are supported");

        var mimeStart = header.IndexOf(':') + 1;
        var mimeEnd = header.IndexOf(';');
        var mime = mimeEnd > mimeStart ? header[mimeStart..mimeEnd] : header[mimeStart..];

        var ext = MimeToExtension(mime);
        return (new MemoryStream(Convert.FromBase64String(data)), ext);
    }

    private static string MimeToExtension(string? mime)
    {
        if (string.IsNullOrEmpty(mime)) return "";

View on GitHub (pinned to 1ced45e900)

Solutions

1. Ensure the data URI is well-formed: data:<mime>;base64,<payload>.
2. Use a URI/data-URI builder rather than hand-concatenating.
3. If you only have raw base64, add the proper 'data:<mime>;base64,' prefix including the comma.

Example fix

// before
FileSource.Resolve("data:image/png;base64"); // missing ,<payload>
// after
FileSource.Resolve($"data:image/png;base64,{base64Payload}");

static bool IsPlausibleDataUri(string s) =>
    s.StartsWith("data:", StringComparison.OrdinalIgnoreCase) && s.Contains(',');

static bool LooksLikeDataUri(string s) => s.StartsWith("data:", StringComparison.OrdinalIgnoreCase) && s.IndexOf(',') > 4;

try { var r = FileSource.Resolve(dataUri); }
catch (ArgumentException ex) when (ex.Message.Contains("missing comma separator"))
{ /* rebuild the data URI with a proper header+comma */ }

When it happens

Trigger: Calling FileSource.Resolve with a string starting with 'data:' (case-insensitive) that contains no ',' character. IndexOf(',') returns -1 and the guard throws.

Common situations: Truncated/pasted data URI missing the payload; a data: URL built by string concatenation that dropped the comma; a base64 string passed without the data: prefix wrapper correctly.

Related errors

• Only base64-encoded data URIs are supported
• File source cannot be empty
• Invalid data URI: missing comma separator
• Only base64-encoded data URIs are supported
• Invalid data URI: empty base64 payload (would produce a 0-by

AI-assisted analysis of iOfficeAI/OfficeCLI@1ced45e900 (2026-08-13). Data as JSON: /api/errors/54f697bee0df169a. Report an issue: GitHub.