dotfiles: stop the ssh.exe check from deleting the ssh.exe it verifies

[dotfiles] / setup-windows-with-uac.ps1

diff --git a/setup-windows-with-uac.ps1 b/setup-windows-with-uac.ps1
index a11e1752ddba9ad4995d8797966e0ef8fdb018a8..4b7ea948dccce4a7c6b51b0b256499c10fd77716 100644 (file)
--- a/setup-windows-with-uac.ps1
+++ b/setup-windows-with-uac.ps1
@@ -436,13 +436,26 @@ try {
     # $global:LASTEXITCODE is cleared first because an exe that cannot start at\r
     # all throws without setting one, and the stale 0 from the previous native\r
     # command would otherwise read as success.\r
+    #\r
+    # DRAIN THE OUTPUT BEFORE READING $LASTEXITCODE. `... | Select-Object -First 1`\r
+    # was the original spelling here, and it is a trap: Select-Object stops the\r
+    # pipeline the instant it has its one object, and that is when ssh.exe has\r
+    # WRITTEN its banner - not when it has exited. PowerShell then tears the\r
+    # pipeline down, kills the still-running process, and reports -1. Measured on a\r
+    # healthy binary on an x64 box: 24 of 25 runs reported exit -1 through\r
+    # Select-Object, and 25 of 25 reported 0 when the output was collected first.\r
+    #\r
+    # So this check was deleting a perfectly good ssh.exe on almost every run, on\r
+    # every architecture, and the resulting fallback to the in-box client - the\r
+    # ~17MB/s one this whole step exists to avoid - looked like a property of the\r
+    # release rather than a bug in the test. Collect, THEN take the first line.\r
     $SshExe = Join-Path $RsyncDir 'ssh.exe'\r
     if ($WantSsh -and (Test-Path $SshExe)) {\r
         $prevEap = $ErrorActionPreference\r
         $ErrorActionPreference = 'Continue'\r
         $global:LASTEXITCODE = $null\r
         $sshVer = $null\r
-        try { $sshVer = (& $SshExe -V 2>&1 | Select-Object -First 1) } catch { }\r
+        try { $sshOut = (& $SshExe -V 2>&1); $sshVer = $sshOut | Select-Object -First 1 } catch { }\r
         finally { $ErrorActionPreference = $prevEap }\r
         if ($LASTEXITCODE -eq 0) {\r
             Write-Host "    ssh.exe runs: $sshVer"\r