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Technical Tip: Logging HTTP request and response headers locally using FortiADC scripting

Forum|Forum|1 month ago
June 5, 2026
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Description

This article describes how to use FortiADC HTTP scripting to read the client-to-server HTTP communication passing through a virtual server, extract the HTTP request headers sent by the client and the HTTP response headers returned by the real server, and write them to the local script log.

This is useful in troubleshooting and auditing scenarios where the exact headers exchanged need to be inspected. The script generates two separate log entries per transaction, one for the request and one for the response and each containing only its own headers together with the relevant source and destination IP address and port.

Scope

FortiADC.

Solution

Step 1: Create the LUA Script from the FortiADC GUI.

Paste the following script:

-- ============================================================

-- FortiADC HTTP Transaction Logger

-- VS Scripting | FortiADC 7.x / 8.x

-- One log entry for the request, one for the response.

-- Each carries only its own headers + its own connection tuple.

-- ============================================================

when HTTP_REQUEST {

    -- Client-side tuple (front end is unaffected by backend NAT)

    sip = IP:client_addr()      -- source: real client IP

    sp  = IP:client_port()      -- source: real client port

    dip = IP:local_addr()       -- dest:   virtual server IP

    dp  = IP:local_port()       -- dest:   virtual server port

    method = HTTP:method_get()

    host   = HTTP:header_get_value("Host")

    if (host == nil) then host = "-" end

    uri    = HTTP:uri_get()

    log("[REQ] src=%s:%s dst=%s:%s %s %s%s
", sip, sp, dip, dp, method, host, uri)

    h = HTTP:header_get_names()

    if (h ~= nil) then

        for k, v in pairs(h) do

            log("[REQ] %s: %s
", k, v)

        end

    end

}

when HTTP_RESPONSE {

    -- Server-side tuple (backend connection: FortiADC <-> real server)

    sip = IP:server_addr()      -- source: real server IP

    sp  = IP:server_port()      -- source: real server port

    dip = IP:local_addr()       -- dest:   FortiADC backend interface IP

    dp  = IP:local_port()       -- dest:   FortiADC backend port

    status = HTTP:status_code_get()

    log("[RESP] src=%s:%s dst=%s:%s status=%d
", sip, sp, dip, dp, status)

    h = HTTP:header_get_names()

    if (h ~= nil) then

        for k, v in pairs(h) do

            log("[RESP] %s: %s
", k, v)

        end

    end

}

Assign the script to a Virtual Server: