include /etc/nginx/conf.d/include/cors;
include /etc/nginx/conf.d/include/proxy-buffer;
include /etc/nginx/conf.d/include/proxy-cache-downloads;
include /etc/nginx/conf.d/include/track-download;

limit_conn downloads_by_ip 100; # ddos protection: max 100 downloads at a time

# ensure that skylink that we pass around is base64 encoded (transform base32 encoded ones)
# this is important because we want only one format in cache keys and logs
set_by_lua_block $skylink { return require("skynet.skylink").parse(ngx.var.skylink) }

# $skylink_v1 and $skylink_v2 variables default to the same value but in case the requested skylink was:
# a) skylink v1 - it would not matter, no additional logic is executed
# b) skylink v2 - in a lua block below we will resolve the skylink v2 into skylink v1 and update 
#      $skylink_v1 variable so then the proxy request to skyd can be cached in nginx (proxy_cache_key 
#      in proxy-cache-downloads includes $skylink_v1 as a part of the cache key)
set $skylink_v1 $skylink;
set $skylink_v2 $skylink;

# variable for Skynet-Proof header that we need to inject 
# into a response if the request was for skylink v2
set $skynet_proof '';

# default download rate to unlimited
set $limit_rate 0;

access_by_lua_block {
    local httpc = require("resty.http").new()

    -- detect whether requested skylink is v2
    local isBase32v2 = string.len(ngx.var.skylink) == 55 and string.sub(ngx.var.skylink, 0, 2) == "04"
    local isBase64v2 = string.len(ngx.var.skylink) == 46 and string.sub(ngx.var.skylink, 0, 2) == "AQ"
    
    if isBase32v2 or isBase64v2 then
        -- 10.10.10.10 points to sia service (alias not available when using resty-http)
        local res, err = httpc:request_uri("http://10.10.10.10:9980/skynet/resolve/" .. ngx.var.skylink_v2, {
            headers = { ["User-Agent"] = "Sia-Agent" }
        })

        -- print error and exit with 500 or exit with response if status is not 200
        if err or (res and res.status ~= ngx.HTTP_OK) then
            ngx.status = (err and ngx.HTTP_INTERNAL_SERVER_ERROR) or res.status
            ngx.header["content-type"] = "text/plain"
            ngx.say(err or res.body)
            return ngx.exit(ngx.status)
        end

        local json = require('cjson')
        local resolve = json.decode(res.body)
        ngx.var.skylink_v1 = resolve.skylink
        ngx.var.skynet_proof = res.headers["Skynet-Proof"]
    end

    -- check if skylink v1 is present on blocklist (compare hashes)
    if require("skynet.blocklist").is_blocked(ngx.var.skylink_v1) then
        return require("skynet.blocklist").exit_illegal()
    end

    -- if skylink is found on nocache list then set internal nocache variable
    -- to tell nginx that it should not try and cache this file (too large)
    if ngx.shared.nocache:get(ngx.var.skylink_v1) then
        ngx.var.nocache = "1"
    end

    if require("skynet.account").accounts_enabled() then
        -- check if portal is in authenticated only mode
        if require("skynet.account").is_access_unauthorized() then
            return require("skynet.account").exit_access_unauthorized()
        end

        -- get account limits of currently authenticated user
        local limits = require("skynet.account").get_account_limits()

        -- apply download speed limit
        ngx.var.limit_rate = limits.download
    end
}

header_filter_by_lua_block {
    ngx.header["Skynet-Portal-Api"] = os.getenv("SKYNET_PORTAL_API")
    ngx.header["Skynet-Server-Api"] = os.getenv("SKYNET_SERVER_API")

    -- not empty skynet_proof means this is a skylink v2 request
    -- so we should replace the Skynet-Proof header with the one
    -- we got from /skynet/resolve/ endpoint, otherwise we would
    -- be serving cached empty v1 skylink Skynet-Proof header
    if ngx.var.skynet_proof and ngx.var.skynet_proof ~= "" then
        ngx.header["Skynet-Proof"] = ngx.var.skynet_proof
    end

    -- add skylink to nocache list if it exceeds 1GB (1e+9 bytes) threshold
    -- (content length can be nil for already cached files - we can ignore them)
    if ngx.header["Content-Length"] and tonumber(ngx.header["Content-Length"]) > 1e+9 then
        ngx.shared.nocache:set(ngx.var.skylink_v1, ngx.header["Content-Length"])
    end
}

limit_rate_after 512k;
limit_rate $limit_rate;

proxy_read_timeout 600;
proxy_set_header User-Agent: Sia-Agent;

# in case the requested skylink was v2 and we already resolved it to skylink v1, we are going to pass resolved 
# skylink v1 to skyd to save that extra skylink v2 lookup in skyd but in turn, in case skyd returns a redirect 
# we need to rewrite the skylink v1 to skylink v2 in the location header with proxy_redirect
proxy_redirect $skylink_v1 $skylink_v2;
proxy_pass http://sia:9980/skynet/skylink/$skylink_v1$path$is_args$args;
