elsa-workflows/elsa-core · warning · HttpBadRequestException

Failed to parse If-Match header value

Error message

Failed to parse If-Match header value

What it means

WriteFileHttpResponse validates conditional requests via the If-Match header for optimistic concurrency. GetIfMatchHeaderValue parses the header into an EntityTagHeaderValue; malformed ETags (missing quotes, stray characters) cause the parse to fail and the activity throws HttpBadRequestException with message 'Failed to parse If-Match header value', rejecting the request as a client error.

Solutions

1. Send the ETag exactly as received, including quotes and any W/ weak validator prefix, e.g. 'If-Match: "33a64df551425fcc55e4d42a148795d9f25f89d4"'.
2. Omit the If-Match header if conditional validation is not required.
3. Handle the HttpBadRequestException to return a 400 with guidance on ETag format to API consumers.

Example fix

// before (client request header)
If-Match: 33a64df551425fcc55e4d42a148795d9f25f89d4
// after
If-Match: "33a64df551425fcc55e4d42a148795d9f25f89d4"

// Client side: ensure the ETag is quoted before sending If-Match
string FormatIfMatch(string etag) => etag.StartsWith('"') ? etag : $"\"{etag.Trim('W', '/')}\"";

try
{
    await workflowRunner.RunAsync(workflow, request);
}
catch (HttpBadRequestException ex) when (ex.Message.Contains("If-Match"))
{
    httpContext.Response.StatusCode = 400;
    await httpContext.Response.WriteAsJsonAsync(new { error = "If-Match must be a quoted ETag" });
}

When it happens

Trigger: A client supplies an If-Match header that is not a valid ETag — e.g., 'If-Match: abc123' (unquoted), 'If-Match: W/weak-without-quotes', or containing commas/invalid characters — while WriteFileHttpResponse evaluates preconditions.

Common situations: Clients storing the ETag and re-sending it without the surrounding quotes, manually built curl requests omitting quotes around the tag, or intermediary systems corrupting the header value.

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.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to parse Range header value
• The workflow definition has been written since the ETag in…
• RequestBodyTooLargeException
• The identity provider metadata could not be resolved.
• The identity provider token exchange failed.

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/ba307ab76a59c675. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Http/Activities/WriteFileHttpResponse.cs:294

            return headers.TryGetValue(HeaderNames.Range, out var header) ? RangeHeaderValue.Parse(header.ToString()) : null;
            
        }
        catch (Exception e)
        {
            throw new HttpBadRequestException("Failed to parse Range header value", e);
        }
    }
    
    private static EntityTagHeaderValue? GetIfMatchHeaderValue(IHeaderDictionary headers)
    {
        try
        {
            return headers.TryGetValue(HeaderNames.IfMatch, out var header) ? new EntityTagHeaderValue(header.ToString()) : null;
            
        }
        catch (Exception e)
        {
            throw new HttpBadRequestException("Failed to parse If-Match header value", e);
        }
    }
}

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