nginx: support static package metadata

By putting a multi-version file at /tmp/npm/store/<pkgname>/package.json
you can effectively lock a package to a given selection of versions for
the lifetime of the npm registry.

This file should be analogous to what would normally be served up at
https://registry.npmjs.org/<pkgname>

Author: rmg

nginx.conf

@@ -31,6 +31,7 @@ http {
         local ephemeralNPM = require "ephemeral-npm"
         ephemeralNPM.init()
     }
+
     server {
         listen       4873;
         set $npm_config_registry '';
@@ -58,10 +59,19 @@ http {
         # we need to be able to make sub-requests using ngx.location.capture()
         location /-@- {
             internal;
-            rewrite                /-@-/(.+) /$1 break;
-            resolver               127.0.0.1 ipv6=off;
-            proxy_pass             $npm_config_registry;
-            proxy_buffers          32 1m;
+            rewrite            /-@-/(.+) /$1 break;
+            root               /tmp/npm/store;
+            set                $ephemeralCacheStatus "HIT";
+            try_files          /$1/package.json @fetch-meta;
+        }
+        location @fetch-meta {
+            internal;
+            set                $ephemeralCacheStatus "MISS";
+            resolver           127.0.0.1 ipv6=off;
+            proxy_pass         $npm_config_registry;
+            proxy_buffers      512 512k;
+            proxy_temp_path    /tmp/npm/temp;
+            proxy_buffering    on;
             # need to disable encoding in order to be able to process it locally
             proxy_set_header       Accept-Encoding "";
         }