Failed to open file for scanning

This article describes an issue which may occur when stressing (high load) MetaDefender ICAP Server on Windows OS.

Symptom

A lot of requests are blocked with reason "MetaDefender Core is overloaded" or "Failed to open file".

From MetaDefender ICAP Server log:

[WARNING] 2022.05.10 15:55:39.284: (icap.scanner) Failed to open file for scanning, errorDetail='Could not open file C:/Program Files/OPSWAT/Metadefender ICAP Server/data/temp/5bea0e35-6ed1-4c3d-b4e7-e12bcee17783/66fc337d-08bf-4846-89eb-732f1fe66d71 for scanning', connectionId='6a0c7f167f0c4d85ac410cf8f414734e', requestId='364b7516ddc74e31a798c2c3afaf1643' [msgid: 3727]

Cause

On Windows OS, the maximum number of files can be opened simultaneously is 512 by default. Anything exceeded will be blocked by Windows OS.

Reference: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/setmaxstdio?view=msvc-170

Solution

Use new setting supported on MetaDefender ICAP Server called maxstdio to increase the limit (applicable to Windows only). Details: Configuration file

Since MD ICAP Server v5.2.0, the default value for maxstdio is set to 4096


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