DOCKER-5: Add downloading of images to filesystem

examples/registry-image-download.js

@@ -0,0 +1,110 @@
+#!/usr/bin/env node
+
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+var fs = require('fs');
+var path = require('path');
+var clients = require('../lib/clients');
+
+var idx = clients.index.create({});
+var g_repo = 'library/mongo';
+var g_tag = 'latest';
+var g_dir = path.resolve(__dirname, '..', 'images');
+
+// Create the images directory if it doesn't exist yet.
+if (!fs.existsSync(g_dir)) {
+    try {
+        fs.mkdirSync(g_dir);
+    } catch (ex) {
+        console.error('Unable to create images directory: ' + ex);
+        return;
+    }
+}
+
+console.log("Images dir: " + g_dir);
+
+/**
+ * Returns an array of dependencies (ancestors) for the given repo:tag.
+ */
+function getImageAncestry(client, repo, tag, callback) {
+    client.getRepoTags(function (err2, tags) {
+        if (err2) {
+            return console.error('Error getting repo tags: ' + err2.message);
+        }
+
+        if (!tags.hasOwnProperty(tag)) {
+            console.error('repo "%s" does not have tag "%s"', repo, tags);
+            console.error('available tags: ' + Object.keys(tags).join(', '));
+            return;
+        }
+
+        client.getImageAncestry(tags[tag], callback);
+    });
+}
+
+/**
+ * Downloads the given registry repo:tag (and it's dependencies) into the given
+ * directory.
+ */
+function downloadRegistryImage(client, repo, tag, dirpath) {
+    getImageAncestry(client, repo, tag, function(err, images) {
+        if (err) {
+            console.error('Error getting image ancestry: ' + err.message);
+            return;
+        }
+
+        // Download all images in the ancestry.
+        // TODO: Perhaps queuing, to avoid downloading all at once?
+        images.forEach(function(image) {
+            // Check if the image already exists.
+            var filepath = path.join(dirpath, image);
+            if (fs.existsSync(filepath)) {
+                // TODO: Verify if image is up-to-date (or will docker use a
+                //       different hash if it's modified)?
+                console.log("Already downloaded image: " + image);
+                return;
+            }
+
+            //console.log("Getting meta data for image " + image);
+
+            client.getImageMetadata(image, function(err2, imgData) {
+                if (err2) {
+                    console.error('Error getting image metadata: ' + err2.message);
+                    return;
+                }
+
+                //console.log(imgData);
+                console.log("Downloading image: " + image);
+
+                // Download to a temporary file, then atomic rename on success.
+                // This ensures that if the image file exists, then it's been
+                // fully downloaded.
+                var tmp_filepath = path.join(dirpath, image + ".partial");
+
+                // TODO: If a tmp_filepath exists, could perform HTTP reget.
+                client.downloadImageLayer(image, tmp_filepath,
+                                          function(err3, resp, body) {
+                    if (err3) {
+                        console.error('Error downloading image: ' + err3.message);
+                        return;
+                    }
+
+                    // TODO: Verify download - is there a checksum somewhere?
+
+                    // Download was successful - rename the tmp file.
+                    fs.rename(tmp_filepath, filepath);
+                    console.log("Successfully downloaded image: " + image);
+                });
+            });
+        });
+    });
+}
+
+clients.registry.createWithToken({ repo: g_repo }, function (err, client) {
+    // TODO: g_dir may not exist yet.
+    downloadRegistryImage(client, g_repo, g_tag, g_dir);
+});

lib/clients/registry.js

@@ -13,6 +13,8 @@ var bunyan = require('bunyan');
 var fmt = require('util').format;
 var idxClient = require('./idx');
 var restify = require('restify');
+var request = require('request');
+var fs = require('fs');
 var VError = require('verror').VError;
 
 
@@ -101,6 +103,25 @@ Registry.prototype.getImageMetadata =
 };
 
 
+/**
+ * Downloads the remote image layer.
+ */
+Registry.prototype.downloadImageLayer =
+    function downloadImageLayer(img, filepath, callback) {
+    // Uses the request library for following reasons:
+    //  - automatically following http redirects (e.g. status code 302)
+    //  - to easily redirect (pipe) the response to a file
+    //
+    // TODO: Add retry capability?
+    request({
+        url: fmt('%s/v1/images/%s/layer', REGISTRY_URL, img),
+        headers: {
+            Authorization: this.authHeader
+        }
+    }, callback).pipe(fs.createWriteStream(filepath));
+};
+
+
 /**
  * Gets the remote image's JSON
  */

package.json

@@ -7,6 +7,7 @@
     "assert-plus": "0.1.5",
     "bunyan": "1.2.0",
     "restify": "2.8.3",
+    "request": "2.47.0",
     "vasync": "1.6.1",
     "verror": "1.4.0"
   }