Public/Test-HDTComputerName.ps1
|
function Test-HDTComputerName { <# .SYNOPSIS Judges a computer name against the limit Windows enforces silently. .DESCRIPTION DESIGN 4.5's rule, and the length half of it exists because of a real deployment. rules.yaml built HDTComputerName from a Hyper-V serial number, the result was 35 characters, and WINDOWS SETUP DISCARDED IT WITHOUT COMPLAINT - every step reported Completed, the run reported Succeeded, and the machine came up called WIN-N91191NN153 (SPIKES S9.11). That is the worst shape a defect can take: nothing anywhere said a word. SO THE RULE IS ENFORCED WHERE THE VALUE IS ENTERED AND WHERE IT IS APPLIED. Invoke-HDTApplyUnattendStep refuses it as the name is about to become a machine's identity; the wizard refuses it as a technician types it. Two callers, ONE COPY OF THE RULE - it was inline in the step until the wizard needed it, and a rule with two copies is a rule that drifts. TWO RULES, AND THE DIFFERENCE BETWEEN THEM IS THE POINT. NetBIOS FORBIDS TEN CHARACTERS AND ONLY TEN: . \ / : * ? " < > | Those are refused. A space is refused with them - it is not on Microsoft's list because a computer name cannot contain one at all, and a trailing space is invisible in every place a technician would look for it. DNS IS STRICTER THAN NetBIOS, and a name can be a perfectly legal NetBIOS name that DNS cannot carry. An underscore is the everyday case: HDT_01 is legal, and misbehaves on domain join and DNS registration. So anything outside letters, digits and hyphens is ACCEPTED AND FLAGGED - IsDnsSafe false, Severity 'Warning'. A warning states a real consequence; a refusal would state a rule that does not exist, in front of a technician who has read Microsoft's list. THIS REPLACED A STRICTER RULE, and DESIGN 4.5 was updated to match rather than being quietly diverged from. The old one refused anything but letters, digits and hyphens, which conflated the two rules above and refused legal names. IT DOES NOT TRUNCATE, AND MUST NEVER LEARN TO. A silently shortened name is the same failure this rule exists to stop, with a different spelling. The name comes back exactly as it was handed over. ONE MESSAGE AT A TIME, WORST FIRST: empty, then too long, then an illegal character, then the DNS warning. A technician can act on one; a list of everything wrong with a half-typed name is noise. .PARAMETER Name The proposed computer name. .INPUTS None. This command does not accept pipeline input. .OUTPUTS System.Management.Automation.PSCustomObject with: IsValid the name may be used. False only for a real refusal. IsDnsSafe letters, digits and hyphens only. Severity 'None', 'Warning' or 'Error'. Reason what to tell the technician. Empty when Severity is 'None'. Name exactly what was handed in. Never repaired. .EXAMPLE Test-HDTComputerName -Name 'HDT-01' IsValid true, IsDnsSafe true, Severity None. .EXAMPLE Test-HDTComputerName -Name 'HDT_01' IsValid TRUE, IsDnsSafe false, Severity Warning - a legal NetBIOS name that DNS cannot carry. .EXAMPLE $judgement = Test-HDTComputerName -Name $typed $message.Text = $judgement.Reason $next.IsEnabled = $judgement.IsValid What the wizard does on every keystroke. #> [CmdletBinding()] [OutputType([pscustomobject])] param( [Parameter(Mandatory = $true, Position = 0)] [AllowEmptyString()] [AllowNull()] [string] $Name ) Set-StrictMode -Version Latest $ErrorActionPreference = 'Stop' # MICROSOFT'S LIST, AND A SPACE. The ten are the documented NetBIOS # refusals; the space is here because a computer name cannot contain one and # a trailing space is invisible everywhere a technician would look for it. $forbidden = @('.', '\', '/', ':', '*', '?', '"', '<', '>', '|', ' ') $answer = [ordered] @{ IsValid = $false IsDnsSafe = $false Severity = 'Error' Name = [string] $Name Reason = '' } if ([string]::IsNullOrWhiteSpace($Name)) { $answer['Reason'] = 'a computer name is required.' return [pscustomobject] $answer } # 15 IS THE NETBIOS LIMIT, and it is a limit rather than the first refusal - # a name of exactly 15 is fine. if ($Name.Length -gt 15) { $answer['Reason'] = ('the computer name ''{0}'' is {1} characters. Windows Setup silently ignores a ComputerName over 15 and names the machine itself, so the deployment would appear to succeed and produce a machine nobody named.' -f $Name, $Name.Length) return [pscustomobject] $answer } # NAMED, NOT JUST DETECTED. "contains an illegal character" leaves the # technician hunting through their own typing for it. foreach ($character in $forbidden) { if ($Name.Contains($character)) { $shown = $character if ($character -eq ' ') { $shown = 'a space' } else { $shown = ('''{0}''' -f $character) } $answer['Reason'] = ('a computer name cannot contain {0}. These are not allowed: . \ / : * ? " < > | or spaces.' -f $shown) return [pscustomobject] $answer } } # LEGAL. What is left is whether DNS can carry it, which is a warning and # never a refusal - see the header. $answer['IsValid'] = $true if ($Name -notmatch '^[A-Za-z0-9\-]+$') { $answer['Severity'] = 'Warning' $answer['Reason'] = ('''{0}'' is a legal computer name, but it is not a valid DNS name - only letters, digits and hyphens are. Domain join and DNS registration may misbehave.' -f $Name) return [pscustomobject] $answer } $answer['IsDnsSafe'] = $true $answer['Severity'] = 'None' return [pscustomobject] $answer } |