Curl will try IPv4 as a backup if IPv6 fails, and we don't want that.

Tell it not to.

Also detect if IPv6 is even available.

apt-panopticommon.lua

@@ -23,6 +23,7 @@ APT.verbosity = -1
 APT.origin = false
 APT.redir = false
 APT.keep = false
+APT.IPv46 = ''
 
 APT.options =
 {
@@ -119,6 +120,10 @@ APT.parseArgs = function(args)
     APT.args = args
     local arg = {}
     local sendArgs = ""
+    -- A special test to disable IPv6 tests if IPv6 isn't available.
+    if 1 == APT.exe('ip -6 addr | grep inet6 | grep " global"'):Do().status then
+	table.insert(args, '--tests=-IPv6')
+    end
     if 0 ~= #(args) then
 	local option = ""
 	for i, a in pairs(args) do
@@ -132,6 +137,9 @@ APT.parseArgs = function(args)
 	    elseif "-q" == a then
 		APT.verbosity = -1
 		sendArgs = sendArgs .. a .. " "
+	    elseif ("-4" == a) or ("-6" == a) then
+		APT.IPv46 = a
+		sendArgs = sendArgs .. a .. " "
 	    elseif "-k" == a then
 		APT.keep = true
 		sendArgs = sendArgs .. a .. " "

apt-panopticon.lua

@@ -265,6 +265,7 @@ checkHEAD = function (host, URL, r, retry, sanity)
 	-header "" - add extra headers.
 	-L - DO follow redirects.
 	--max-redirs n - set maximum redirects, default is 50, -1 = unlimited.
+	-4 or -6 - Only use IPv4 or IPv6
 	--retry n - maximum retries, default is 0, no retries.
 	-o file - write to file instead of stdout.
 	--path-as-is - https://curl.haxx.se/libcurl/c/CURLOPT_PATH_AS_IS.html might be useful for URLSanity.
@@ -274,7 +275,7 @@ checkHEAD = function (host, URL, r, retry, sanity)
 	-D file - write the received headers to a file.  This includes the status code and string.
     ]]
     local status = APT.exe(
-	'curl -I --retry 0 -s --path-as-is --connect-timeout ' .. APT.options.timeout.value .. ' --max-redirs 0 ' ..
+	'curl -I --retry 0 -s --path-as-is --connect-timeout ' .. APT.options.timeout.value .. ' --max-redirs 0 ' .. APT.IPv46 .. ' ' ..
 	IP .. ' ' .. '-o /dev/null -D results/"HEADERS_' .. fname .. '" ' ..
 	hdr .. ' -w "#%{http_code} %{ssl_verify_result} %{url_effective}\\n" ' .. PU.scheme .. '://' .. host .. PU.path .. ' >>results/"STATUS_' .. fname .. '"'
     ):Nice():log():Do().status
@@ -519,6 +520,7 @@ local download = "curl" ..
 		 " --create-dirs -f -L" ..
 		 " --fail-early" ..
 		 " --max-time " .. APT.options.maxtime.value ..
+		 APT.IPv46 .. ' ' ..
 		 " --retry " .. APT.options.retries.value ..
 		 " -R -v -z 'results/stamp.old'  --stderr results/"
 local downloads = function(host, URL, meta, release, list)
@@ -1025,9 +1027,9 @@ if 0 < #arg then
 	    APT.allpairs(ips,
 		function(k, v)
 		    if v == "A" then
-			if APT.testing("IPv4") then APT.exe("./apt-panopticon.lua " .. sendArgs .. " " .. pu.host .. path .. " " .. k .. " " .. file):Nice():log():fork() end
+			if APT.testing("IPv4") then APT.exe('./apt-panopticon.lua ' .. sendArgs .. ' -4 ' .. pu.host .. path .. ' ' .. k .. ' ' .. file):Nice():log():fork() end
 		    elseif v == "AAAA" then
-			if APT.testing("IPv6") then APT.exe("./apt-panopticon.lua " .. sendArgs .. " " .. pu.host .. path .. " " .. k .. " " .. file):Nice():log():fork() end
+			if APT.testing("IPv6") then APT.exe('./apt-panopticon.lua ' .. sendArgs .. ' -6 ' .. APT.IPv46 .. ' ' .. pu.host .. path .. ' ' .. k .. ' ' .. file):Nice():log():fork() end
 		    end
 		    D('logging to ' .. APT.logName(pu.host, k, file)[2])
 		end