pre-cache related packages when caching

This results in the registry pre-warm itself in response to the first
request.

Dockerfile

@@ -1,7 +1,8 @@
 FROM openresty/openresty:alpine
 MAINTAINER Ryan Graham <[email protected]>
 
-RUN apk --no-cache add dnsmasq
+RUN apk --no-cache add dnsmasq perl curl \
+ && opm get pintsized/lua-resty-http
 
 ADD entrypoint.sh nginx.conf ephemeral-npm.lua /
 

ephemeral-npm.lua

@@ -1,4 +1,5 @@
 local cjson = require "cjson.safe"
+local http = require "resty.http"
 
 local _M = {}
 
@@ -11,6 +12,44 @@ function _M.init()
     npmConfig:set('npm_upstream_pattern', pattern)
 end
 
+function _M.prefetchRelatedPackages(premature, selfHost, pkg)
+    local httpc = http.new()
+    httpc:connect('127.0.0.1', 4873)
+    local distTags = pkg['dist-tags'] or {}
+    local versions = pkg.versions or {}
+    local latestVersion = distTags.latest
+    local latest = versions[latestVersion] or {}
+    local deps = latest.dependencies or {}
+    local reqs = {}
+    -- find any deps that we haven't already seen and queue them for fetching
+    for k, v in pairs(deps) do
+        if meta:get('/' .. k) == nil then
+            table.insert(reqs, {
+                path = '/' .. k,
+                method = 'GET',
+                headers = {
+                    ["Host"] = selfHost,
+                },
+            })
+        end
+    end
+    -- extract all the tarball URLs and fetch them to force them to be cached
+    for v,p in pairs(versions) do
+        local scheme, host, port, path, query = unpack(httpc:parse_uri(p.dist.tarball))
+        table.insert(reqs, {
+            path = path,
+            method = 'GET',
+        })
+    end
+    local responses, err = httpc:request_pipeline(reqs)
+    for i,r in ipairs(responses) do
+        if r.status then
+            r:read_body() -- to oblivion!
+        end
+    end
+    httpc:close()
+end
+
 function _M.getPackage()
     local uri = ngx.var.uri
     local meta = ngx.shared.npmMeta
@@ -27,7 +66,8 @@ function _M.getPackage()
             -- next time
             return ngx.redirect(uri, ngx.HTTP_MOVED_TEMPORARILY)
         end
-        meta:set(uri, body)
+        local succ, err, forcible = meta:set(uri, body)
+        ngx.timer.at(0.1, _M.prefetchRelatedPackages, ngx.var.http_host, pkgJSON)
     end
     ngx.header["Content-Length"] = #body
     ngx.print(body)