Separated the LRU cache implementation.

lru-cache.js

@@ -0,0 +1,45 @@
+// Cache any data with a timestamp,
+// remove only the oldest data.
+
+function Cache(size) {
+  if (!this instanceof Cache) { return new Cache(size); }
+  this.size = size;
+  this.cache = Object.create(null);
+  this.cacheTime = Object.create(null);
+  this.cacheSize = 0;
+}
+
+Cache.prototype.set =
+function addToCache(cacheIndex, cached) {
+  this.cache[cacheIndex] = cached;
+  var mostAncient = +(new Date());
+  this.cacheTime[cacheIndex] = mostAncient;
+  if (this.cacheSize >= this.size) {
+    // Find the most ancient image.
+    var ancientCacheIndex = cacheIndex;
+    for (var currentCacheIndex in this.cacheTime) {
+      if (mostAncient > this.cacheTime[currentCacheIndex]) {
+        mostAncient = this.cacheTime[currentCacheIndex];
+        ancientCacheIndex = currentCacheIndex;
+      }
+    }
+    // Delete that image.
+    delete this.cache[ancientCacheIndex];
+    delete this.cacheTime[ancientCacheIndex];
+  } else {
+    this.cacheSize++;
+  }
+}
+
+Cache.prototype.get =
+function getFromCache(cacheIndex) {
+  this.cacheTime[cacheIndex] = +(new Date());
+  return this.cache[cacheIndex];
+}
+
+Cache.prototype.has =
+function hasInCache(cacheIndex) {
+  return this.cache[cacheIndex] !== undefined;
+}
+
+module.exports = Cache;

svg-to-img.js

@@ -2,21 +2,18 @@ var fs = require('fs');
 var os = require('os');
 var path = require('path');
 var phantom = require('phantomjs');
+var LruCache = require('./lru-cache.js');
 var childProcess = require('child_process');
 var phantomScript = path.join(__dirname, 'phantomjs-svg2png.js');
 
-var imgCache = Object.create(null);
-var imgCacheTime = Object.create(null);
-var imgCacheSize = 0;
 // The following is an arbitrary limit (~1.5MB, 1.5kB/image).
-var imgCacheMaxSize = 1000;
+var imgCache = new LruCache(1000);
 
 module.exports = function (svg, format, out, cb) {
   var cacheIndex = format + svg;
-  if (imgCache[cacheIndex] !== undefined) {
+  if (imgCache.has(cacheIndex)) {
     // We own a cache for this svg conversion.
-    (new DataStream(imgCache[cacheIndex])).pipe(out);
-    imgCacheTime[cacheIndex] = +(new Date());
+    (new DataStream(imgCache.get(cacheIndex))).pipe(out);
     return;
   }
   var tmpFile = path.join(os.tmpdir(),
@@ -36,33 +33,12 @@ module.exports = function (svg, format, out, cb) {
     // Remove the temporary file after use.
     inStream.on('end', function() {
       try { out.end(); } catch(e) {}
-      addToCache(cacheIndex, cached);
+      imgCache.set(cacheIndex, cached);
       fs.unlink(tmpFile, cb);
     });
   });
 };
 
-function addToCache(cacheIndex, cached) {
-  imgCache[cacheIndex] = cached;
-  var mostAncient = +(new Date());
-  imgCacheTime[cacheIndex] = mostAncient;
-  if (imgCacheSize >= imgCacheMaxSize) {
-    // Find the most ancient image.
-    var ancientCacheIndex = cacheIndex;
-    for (var currentCacheIndex in imgCacheTime) {
-      if (mostAncient > imgCacheTime[currentCacheIndex]) {
-        mostAncient = imgCacheTime[currentCacheIndex];
-        ancientCacheIndex = currentCacheIndex;
-      }
-    }
-    // Delete that image.
-    delete imgCache[ancientCacheIndex];
-    delete imgCacheTime[ancientCacheIndex];
-  } else {
-    imgCacheSize++;
-  }
-}
-
 // Fake stream from the cache.
 var Readable = require('stream').Readable;
 var util = require('util');