add disk usage task

src/system.js

@@ -5,7 +5,8 @@ exports = module.exports = {
     checkDiskSpace,
     getMemory,
     getMemoryAllocation,
-    du
+    getDiskUsage,
+    updateDiskUsage
 };
 
 const apps = require('./apps.js'),
@@ -145,3 +146,39 @@ function getMemoryAllocation(limit) {
 
     return Math.round(Math.round(limit * ratio) / 1048576) * 1048576; // nearest MB
 }
+
+function getDiskUsage() {
+    const output = safe.JSON.parse(safe.fs.readFileSync(paths.DISK_USAGE_FILE, 'utf8'));
+    return output;
+}
+
+async function updateDiskUsage(progressCallback) {
+    assert.strictEqual(progressCallback, 'function');
+
+    const disks = await getDisks();
+    const filesystems = Object.keys(disks);
+    const now = Date.now();
+
+    let percent = 1;
+
+    for (const filesystem of filesystems) {
+        const disk = disks[filesystem];
+
+        percent += (100/filesystems.length);
+        progressCallback({ percent, message: `Checking contents of ${filesystem}`});
+
+        for (const content of disk.contents) {
+            progressCallback({ message: `Checking du of ${JSON.stringify(content)}`});
+            if (content.type === 'docker') {
+                content.usage = (await docker.du()).LayersSize;
+            } else {
+                content.usage = await du(content.path, { exclude: content.exclude });
+            }
+            progressCallback({ message: `du of ${JSON.stringify(content)}: ${content.usage}`});
+        }
+    }
+
+    if (!safe.fs.writeFileSync(paths.DISK_USAGE_FILE, JSON.stringify({ ts: now, disks }), 'utf8')) throw new BoxError(BoxError.FS_ERROR, `Could not write du cache file: ${safe.error.message}`);
+
+    return disks;
+}