Retry request ends with "Content length mismatch"

Question

My problem goes this way:

I have an Azure APIM, I have created an API and addeded the backend retry policy as below.

<backend>
    <retry condition="@("{{Transient-ErrorCode}}".Contains(Convert.ToString(context.Response.StatusCode)))" count="3" interval="5" first-fast-retry="false">
        <forward-request />
    </retry>
</backend>

The server return success(statuscode: 200) for the first time, When it initiate the retry it encountered the following(I am retrying at its success also, for testing the retry is working fine.).

forward-request (1.326 ms)
{
"messages": [
    "Content length mismatch",
    "Content length mismatch"
    ]
}

Please help with your thoughts/experience on the same.

score 5 · Accepted Answer · answered Feb 12 '19 at 17:58

5

This is because request sent by client is not cached in memory by default in APIM, instead it's streamed right from client to backend. So when needs come to retry the request request payload is not there. I assume that you have problems only with requests that have body.

To resolve the issue you first need to cache request body:

<inbound>
    <set-variable name="body" value="@(context.Request.Body.As<string>(preserveContent: true))" />
</inbound>
<backend>
    <retry condition="@("{{Transient-ErrorCode}}".Contains(Convert.ToString(context.Response.StatusCode)))" count="3" interval="5" first-fast-retry="false">
        <set-body>@((string)context.Variables["body"])</set-body>
        <forward-request />
    </retry>
</backend>

answered Feb 12 '19 at 17:58

Vitaliy Kurokhtin

7,205
1
19
18

What would be the best way to check that the request has a body? The use case would be for a global policy. – Jarfish Mar 20 '19 at 05:05
I have put in a check to see if the body is null, then set the variable to an empty string...but i am uncertain of side effects. – Jarfish Mar 20 '19 at 05:37
1

context.Request.HasBody – Vitaliy Kurokhtin Mar 20 '19 at 17:44

camios · Answer 2 · 2020-08-05T04:54:53.227

1

There appears to be an alternative simplification for including the body by using the attribute buffer-request-body on the forward-request policy:

<!-- no need to put body into variable in the inbound policy -->
<backend>
    <retry condition="@("{{Transient-ErrorCode}}".Contains(Convert.ToString(context.Response.StatusCode)))" count="3" interval="5" first-fast-retry="false">
        <!-- no need for the set-body policy -->
        <forward-request buffer-request-body="true" />
    </retry>
</backend>

See doco for forward-request's attributes

edited Aug 05 '20 at 04:54

answered Aug 05 '20 at 04:26

camios

182
13

This is the way – cuasiJoe Dec 18 '20 at 14:26

Retry request ends with "Content length mismatch"

2 Answers2