HTTP default port simplification

[nnposter]

There are 3 or 4 separate places in http.lua where a scheme is translated into default ports, typically with a code like this:

local port = someport
if not port then
  if scheme == "http" then
    port = 80
  elseif scheme == "https" then
    port = 443
  end
end

The following patch moves this code into a separate function, resulting in substantial code clarity.
(The patch assumes that #766 has been already merged in.)

* Provides a common function for obtaining the default port number for
  a given scheme
--- a/nselib/http.lua
+++ b/nselib/http.lua
@@ -157,16 +157,21 @@
   end
 end
 
+--- Provide the default port for a given scheme.
+local function get_default_port (scheme)
+  local ports = {http=80, https=443}
+  return ports[scheme]
+end
+
 --- Get a value suitable for the Host header field.
 -- See RFC 2616 sections 14.23 and 5.2.
 local function get_host_field(host, port)
   if not host then return nil end
-  local ssl = shortport.ssl(host, port)
-  local pn = port.number
-  if not ssl and pn == 80 or ssl and pn == 443 then
+  local scheme = shortport.ssl(host, port) and "https" or "http"
+  if port.number == get_default_port(scheme) then
     return stdnse.get_hostname(host)
   else
-    return stdnse.get_hostname(host) .. ":" .. pn
+    return stdnse.get_hostname(host) .. ":" .. port.number
   end
 end
 
@@ -1485,14 +1490,7 @@
   function (url, host, port)
     -- port fixup, adds default ports 80 and 443 in case no url.port was
     -- defined, we do this based on the url scheme
-    local url_port = url.port
-    if ( not(url_port) ) then
-      if ( url.scheme == "http" ) then
-        url_port = 80
-      elseif( url.scheme == "https" ) then
-        url_port = 443
-      end
-    end
+    local url_port = url.port or get_default_port(url.scheme)
     if (not url_port) or tonumber(url_port) == port.number then
       return true
     end
@@ -1570,11 +1568,7 @@
     u.path = ((u.path:sub(1,1) == "/" and "" ) or "/" ) .. u.path -- ensuring leading slash
   end
   -- do port fixup
-  if ( not(u.port) ) then
-    if ( u.scheme == "http" ) then u.port = 80
-    elseif ( u.scheme == "https") then u.port = 443
-    else u.port = port.number end
-  end
+  u.port = u.port or get_default_port(u.scheme) or port.number
   if ( not(u.path) ) then
     u.path = "/"
   end
@@ -1668,15 +1662,7 @@
   local port = {}
 
   port.service = parsed.scheme
-  port.number = parsed.port
-
-  if not port.number then
-    if parsed.scheme == 'https' then
-      port.number = 443
-    else
-      port.number = 80
-    end
-  end
+  port.number = parsed.port or get_default_port(parsed.scheme)
 
   local path = parsed.path or "/"
   if parsed.query then

Please let me know if you have any questions or concerns; otherwise I will commit the patch in a few weeks.

[nnposter]

I have identified a number of scripts that could benefit from the same code abstraction.

@dmiller-nmap Do you have any concerns over moving get_default_port() to url.lua to make it consumable outside of http.lua?

[nnposter]

Here is the subsequent patch that moves the function to url.lua. Seems like a nice reduction in code clutter:

--- a/nselib/data/http-default-accounts-fingerprints.lua
+++ b/nselib/data/http-default-accounts-fingerprints.lua
@@ -155,10 +155,8 @@
   local parts = tcopy(parsed or {})
   parts.host = parts.host or stdnse.get_hostname(host, port)
   parts.scheme = parts.scheme or shortport.ssl(host, port) and "https" or "http"
-  local pn = parts.port or tostring(port.number)
-  if not (parts.scheme == "http" and pn == "80"
-       or parts.scheme == "https" and pn == "443") then
-    parts.port = pn
+  if not parts.port and port.number ~= url.get_default_port(parts.scheme) then
+    parts.port = tostring(port.number)
   end
   return parts
 end
--- a/nselib/http.lua
+++ b/nselib/http.lua
@@ -158,10 +158,9 @@
 end
 
 --- Provide the default port for a given scheme.
-local function get_default_port (scheme)
-  local ports = {http=80, https=443}
-  return ports[scheme]
-end
+-- The localization is necessary because functions in http.lua like to use
+-- "url" as a local parameter
+local get_default_port = url.get_default_port
 
 --- Get a value suitable for the Host header field.
 -- See RFC 2616 sections 14.23 and 5.2.
--- a/nselib/url.lua
+++ b/nselib/url.lua
@@ -373,4 +373,16 @@
   return table.concat(qstr, '&')
 end
 
+---
+-- Provides the default port for a given URI scheme.
+--
+-- @param scheme for determining the port, such as "http" or "https".
+-- @return A port number as an integer, such as 443 for scheme "https",
+--         or nil in case of an undefined scheme
+-----------------------------------------------------------------------------
+function get_default_port (scheme)
+  local ports = {http=80, https=443}
+  return ports[(scheme or ""):lower()]
+end
+
 return _ENV;
--- a/nselib/httpspider.lua
+++ b/nselib/httpspider.lua
@@ -233,9 +233,7 @@
       base_href = base_href .. '/'
     end
 
-    if ( ( base_url:getProto() == 'https' and base_url:getPort() == 443 ) or
-        ( base_url:getProto() == 'http' and base_url:getPort() == 80 ) ) then
-
+    if base_url:getPort() == url.get_default_port(base_url:getProto()) then
       if ( leading_slash ) then
         return ("%s://%s/%s"):format(base_url:getProto(), base_url:getHost(), rel_url)
       else
@@ -427,14 +425,7 @@
     self.proto, self.host, self.port, self.file = self.raw:match("^(http[s]?)://([^:/]*)[:]?(%d*)")
     if ( self.proto and self.host ) then
       self.file = self.raw:match("^http[s]?://[^:/]*[:]?%d*(/[^#]*)") or '/'
-      self.port = tonumber(self.port)
-      if ( not(self.port) ) then
-        if ( self.proto:match("https") ) then
-          self.port = 443
-        elseif ( self.proto:match("http")) then
-          self.port = 80
-        end
-      end
+      self.port = tonumber(self.port) or url.get_default_port(self.proto)
 
       self.path  = self.file:match("^([^?]*)[%?]?")
       self.dir   = self.path:match("^(.+%/)") or "/"
--- a/scripts/http-backup-finder.nse
+++ b/scripts/http-backup-finder.nse
@@ -122,13 +122,8 @@
     if ( parsed.path:match(".*%.*.$") ) then
       -- iterate over possible backup files
       for link in backupNames(parsed.path) do
-        local host, port = parsed.host, parsed.port
-
-        -- if no port was found, try to deduce it from the scheme
-        if ( not(port) ) then
-          port = (parsed.scheme == 'https') and 443
-          port = port or ((parsed.scheme == 'http') and 80)
-        end
+        local host = parsed.host
+        local port = parsed.port or url.get_default_port(parsed.scheme)
 
         -- the url.escape doesn't work here as it encodes / to %2F
         -- which results in 400 bad request, so we simple do a space
--- a/scripts/http-favicon.nse
+++ b/scripts/http-favicon.nse
@@ -128,21 +128,17 @@
 -- host, port, and path if the URL is relative. Return nil if the scheme is not
 -- "http" or "https".
 function parse_url_relative(u, host, port, path)
-  local defaultport, scheme, abspath
+  local scheme, abspath
   u = url.parse(u)
   scheme = u.scheme or "http"
-  if scheme == "http" then
-    defaultport = 80
-  elseif scheme == "https" then
-    defaultport = 443
-  else
+  if not (scheme == "http" or scheme == "https") then
     return nil
   end
   abspath = u.path or ""
   if not string.find(abspath, "^/") then
     abspath = dirname(path) .. "/" .. abspath
   end
-  return u.host or host, u.port or defaultport, abspath
+  return u.host or host, u.port or url.get_default_port(scheme), abspath
 end
 
 function parseIcon( body )
--- a/scripts/http-open-redirect.nse
+++ b/scripts/http-open-redirect.nse
@@ -54,13 +54,7 @@
 end
 
 local function getHostPort(parsed)
-  local host, port = parsed.host, parsed.port
-  -- if no port was found, try to deduce it from the scheme
-  if ( not(port) ) then
-    port = (parsed.scheme == 'https') and 443
-    port = port or ((parsed.scheme == 'http') and 80)
-  end
-  return host, port
+  return parsed.host, parsed.port or url.get_default_port(parsed.scheme)
 end
 
 local function isRedirect(status)
--- a/scripts/http-phpself-xss.nse
+++ b/scripts/http-phpself-xss.nse
@@ -143,12 +143,8 @@
 
     --Only work with .php files
     if ( parsed.path and parsed.path:match(".*.php") ) then
-        --The following port/scheme code was seen in http-backup-finder and its neat =)
-        local host, port = parsed.host, parsed.port
-        if ( not(port) ) then
-          port = (parsed.scheme == 'https') and 443
-          port = port or ((parsed.scheme == 'http') and 80)
-        end
+        local host = parsed.host
+        local port = parsed.port or url.get_default_port(parsed.scheme)
         local escaped_link = parsed.path:gsub(" ", "%%20")
         if launch_probe(host,port,escaped_link) then
           table.insert(vulnpages, parsed.scheme..'://'..host..escaped_link..PHP_SELF_PROBE)
--- a/scripts/http-unsafe-output-escaping.nse
+++ b/scripts/http-unsafe-output-escaping.nse
@@ -49,14 +49,9 @@
 local dbg = stdnse.debug2
 
 local function getHostPort(parsed)
-  local host, port = parsed.host, parsed.port
-  -- if no port was found, try to deduce it from the scheme
-  if ( not(port) ) then
-    port = (parsed.scheme == 'https') and 443
-    port = port or ((parsed.scheme == 'http') and 80)
-  end
-  return host, port
+  return parsed.host, parsed.port or url.get_default_port(parsed.scheme)
 end
+
 local function getReflected(parsed, r)
   local reflected_values,not_reflected_values = {},{}
   local count = 0