Lighttpd

-- content-negotiation.lua

--

-- Summary: perform custom content negotiation via lighttpd mod_magnet

--

-- Notes: various filesystem naming conventions might be used to place

-- lang and/or encoding extensions prior to original file extension,

-- or afterwards.  This implementation places lang before and encoding after,

-- demonstrationg how to implement either.

--

--

-- Copyright (c) 2017, Glenn Strauss (gstrauss () gluelogic.com), incremental

-- All rights reserved.

--

-- License: 3-clause BSD

--

-- Redistribution and use in source and binary forms, with or without

-- modification, are permitted provided that the following conditions are met:

-- 

-- - Redistributions of source code must retain the above copyright notice, this

--   list of conditions and the following disclaimer.

-- 

-- - Redistributions in binary form must reproduce the above copyright notice,

--   this list of conditions and the following disclaimer in the documentation

--   and/or other materials provided with the distribution.

-- 

-- - Neither the name of the 'incremental' nor the names of its contributors may

--   be used to endorse or promote products derived from this software without

--   specific prior written permission.

-- 

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

-- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

-- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE

-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF

-- THE POSSIBILITY OF SUCH DAMAGE.

function parse_HTTP_list (header)

    -- parse HTTP list from given request header

    -- There are *many* ways to parse strings in Lua, some more efficient than

    -- others, but none are a one-size-fits-all scenarios.  This is but one

    -- solution and has not been optimized.  Better solutions are welcomed.

    -- For HTTP list parsing with qvalues, the following assumes *no*

    -- quoted-strings containing the ',' or ';' delimiters, which is not fully

    -- RFC-compliant, but is also a reasonable simplification for headers

    -- including Accept-Language and Accept-Encoding, which generally have

    -- well-known sets of values.  Given that the following does not handle

    -- quoted-string, simplify string by removing all whitespace.  Then split

    -- on ',', and for each result, split on ';' and parse for qvalue.  Assume

    -- ';' is followed by "q=..." and nothing else, or ignore.  Ignore items

    -- with q=0 (or equivalent) since default content file will be provided if

    -- there is no better match.

    local tokens = {}, token

    if (not header) then return tokens end

    header = string.gsub(header, "%s+", "")

    for token in string.gmatch(header, "[^,]+") do

        local b, e = string.find(token, ";q=", 1, 1)

        local n = 1

        if b then

            n = tonumber(token:sub(e+1))

            token = (n ~= nil and n > 0) and token:sub(1, b-1) or ""

        else

            b = string.find(token, ";", 1, 1)

            if b then token = token:sub(1, b-1) end

        end

        if (token ~= "") then

            table.insert(tokens, { n, token })

        else

            -- ignore (skip) if invalid (e.g. empty token or invalid qvalue)

        end

    end

    -- sort on qvalue and return simple ordered, indexed list

    table.sort(tokens, function (v1,v2) return v1[1] > v2[1] end)

    local v

    local list = {}

    for _, v in ipairs(tokens) do

        table.insert(list, v[2])

    end

    return list

end

function negotiate_language (path)

    local langs = parse_HTTP_list(lighty.request["Accept-Language"])

    if not langs[1] then return 0 end

    -- split path into basepath and ext

    -- basepath ends in '.' for use below, and if present, ext begins with '.'

    local ext = string.match(path, "(%.[^/]+)$")

    local basepath

    if (ext) then

        basepath = path:sub(1, -#ext)

    else

        basepath = path .. "."

        ext = ""

    end

    -- check if basepath .. lang .. ext exists

    local lang

    for _, lang in ipairs(langs) do

        local attr = nil

        if (string.find(lang, "/", 1, 1)) then

            -- skip lang containing '/'

            -- security: avoid path traversal

            -- since lang is used in filenames, lang must not contain '/'

        else

        if (lang == "en-US" or lang == "en") then

            -- (optional optimization; remove condition if should not apply)

            -- skip if default file is for "en-US" and "en"

            -- (assumes Accept-Language contains only en-US and/or en,

            --  or they are last, i.e. other languages are preferred)

        else

            path = basepath .. lang .. ext

            attr = lighty.stat(path)

        end

        end

        if (attr and attr["is_file"]) then

            lighty.env["physical.path"] = path

            lighty.env["physical.rel-path"] = (#ext)

              and lighty.env["physical.rel-path"]:sub(1, -#ext) .. lang .. ext

              or lighty.env["physical.rel-path"] .. "." .. lang

            return 0

        end

    end

    return 0

end

local encoding_exts =

  {

    ["br"]    = ".br"                          -- brotli

   ,["gzip"]  = ".gz",  ["x-gzip"]  = ".gz"    -- gzip

-- ,["bzip2"] = ".bz2", ["x-bzip2"] = ".bz2"   -- bzip2

  }

function negotiate_encoding (path, content_type)

    local encs = parse_HTTP_list(lighty.request["Accept-Encoding"])

    if not encs[1] then return 0 end

    -- check if pre-encoded file exists with mapped extension

    local enc

    local basepath = path

    for _, enc in ipairs(encs) do

        local ext = encoding_exts[enc:gsub(".*", string.lower)]

        if (ext) then

            path = basepath .. ext

            local attr = lighty.stat(path)

            if (attr and attr["is_file"]) then

                lighty.env["physical.path"] = path

                lighty.env["physical.rel-path"] =

                  lighty.env["physical.rel-path"] .. ext

                lighty.header["Content-Encoding"] = enc

                if (content_type) then

                    lighty.header["Content-Type"] = content_type

                else

                    lighty.header["Content-Type"] = "application/octet-stream"

                end

                return 0

            end

        end

    end

    return 0

end

--

-- content negotiation

--

-- check that default content file exists (or index-file)

local attr = lighty.stat(lighty.env["physical.path"])

if (not attr) then return 0 end

if (not attr["is_file"]) then

    if (attr["is_dir"]) then

        -- check for index file (code below checks only for index.html)

        local path = lighty.env["physical.path"]

        local indexfile =

          string.sub(path, -1) == "/" and "index.html" or "/index.html"

        path = path .. indexfile

        attr = lighty.stat(path)

        if (not attr or not attr["is_file"]) then return 0 end

        -- (below assignments not required; merely shortcut mod_indexfile)

        lighty.env["physical.path"] = path

        lighty.env["physical.rel-path"] =

          lighty.env["physical.rel-path"] .. indexfile

    else

        return 0

    end

end

negotiate_language(lighty.env["physical.path"])

negotiate_encoding(lighty.env["physical.path"], attr["content-type"])

return 0