caddy-log-converter/source/CaddyLog-To-AccessLog.ps1

param (
    [Parameter(Mandatory = $false)][string] $inFile,
    [Parameter(Mandatory = $false)][string] $outFile,
    [Parameter(Mandatory = $false)][int] $lines = 0
)

if ([string]::IsNullOrWhiteSpace($inFile)) {
    $inFile = [System.Environment]::GetEnvironmentVariable("INFILE")
}

if ([string]::IsNullOrWhiteSpace($outFile)) {
    $outFile = [System.Environment]::GetEnvironmentVariable("OUTFILE")
}

$baseDate = (New-Object System.DateTime -ArgumentList @(1970, 1, 1, 0, 0, 0, [DateTimeKind]::Utc)).ToLocalTime()
$builder = New-Object System.Text.StringBuilder

$outputStream = [IO.File]::Open($outFile, [IO.FileMode]::Append, [IO.FileAccess]::Write, [IO.FileShare]::Read)
$outputWriter = New-Object -TypeName System.IO.StreamWriter -ArgumentList @($outputStream, [Text.Encoding]::UTF8)

Get-Content -Tail $lines -Wait -Path $inFile | ForEach-Object {
    $l = ConvertFrom-Json -InputObject $_
    $r = $l.request;

    $userAgent = $r.headers.'User-Agent' | Select-Object -First 1
    $referer = $r.headers.Referer | Select-Object -First 1

    $commonLog = $builder
        .Clear()
        .Append($r.remote_ip)
        .Append(" - [")
        .Append($baseDate.AddSeconds($l.ts).ToString("yyyy-MM-dd HH:mm:ss.fff"))
        .Append("] """)
        .Append($r.host)
        .Append(""" ")
        .Append($r.method)
        .Append(" ")
        .Append($r.uri)
        .Append(" ")
        .Append($r.proto)
        .Append(" ")
        .Append($l.status)
        .Append(" ")
        .Append($l.size)
        .Append(" """)
        .Append($referer)
        .Append(""" """)
        .Append($userAgent)
        .Append("""")
        .ToString()

    Write-Output $commonLog
    $outputWriter.WriteLine($commonLog)
    $outputWriter.Flush()
}