logic to download and check latest manifest version

Author: nshaheed

include/fetch.h

@@ -30,6 +30,7 @@ class FetchBase {
                      fs::path temp_dir, FileType file_type,
                      string checksum) = 0;
   virtual bool fetch_manifest(string url, fs::path dir) = 0;
+  virtual optional<int> fetch_newest_manifest_version(string url) = 0;
 };
 
 class Fetch : public FetchBase {
@@ -42,6 +43,14 @@ class Fetch : public FetchBase {
   // download the manifest from a remote host
   bool fetch_manifest(string url, fs::path dir);
 
+  // ping ccrma servers to find out what is the
+  // newest available manifest version is. This
+  // is to allows chump to inform users if there is
+  // a newer version of chump that will be needed
+  // to access a new manifest verison, in case
+  // there is a breaking change to the manifest schema.
+  optional<int> fetch_newest_manifest_version(string url);
+
 public:
   bool isURL(string path);
 

src/fetch.cpp

@@ -273,3 +273,75 @@ bool Fetch::fetch_manifest(std::string url, fs::path dir) {
 
   return true;
 }
+
+struct MemoryStruct {
+  char *memory;
+  size_t size;
+};
+
+static size_t WriteMemoryCallback(void *contents, size_t size, size_t nmemb,
+                                  void *userp) {
+  size_t realsize = size * nmemb;
+  auto &mem = *static_cast<std::string *>(userp);
+  mem.append(static_cast<char *>(contents), realsize);
+  return realsize;
+}
+
+optional<int> Fetch::fetch_newest_manifest_version(string url) {
+  if (!isURL(url)) {
+    std::cerr << "[chump]: not a URL!" << std::endl;
+    return {};
+  }
+
+  CURL *curl_handle;
+  CURLcode res;
+
+  std::string chunk;
+
+  curl_global_init(CURL_GLOBAL_ALL);
+
+  /* init the curl session */
+  curl_handle = curl_easy_init();
+
+  /* specify URL to get */
+  curl_easy_setopt(curl_handle, CURLOPT_URL, url.c_str());
+
+  /* send all data to this function  */
+  curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
+
+  /* we pass our 'chunk' struct to the callback function */
+  curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, &chunk);
+
+  /* some servers do not like requests that are made without a user-agent
+     field, so we provide one */
+  curl_easy_setopt(curl_handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
+
+  /* get it! */
+  res = curl_easy_perform(curl_handle);
+
+  /* check for errors */
+  if (res != CURLE_OK) {
+    fprintf(stderr, "[chump]: failed to fetch latest manifest version: %s\n",
+            curl_easy_strerror(res));
+    return {};
+  }
+
+  /* cleanup curl stuff */
+  curl_easy_cleanup(curl_handle);
+
+  // free(chunk.memory);
+
+  /* we are done with libcurl, so clean it up */
+  curl_global_cleanup();
+
+  try {
+    int ver_no = std::stoi(chunk);
+    return ver_no;
+  } catch (std::invalid_argument const &ex) {
+    std::cerr << "[chump]: failed to fetch latest manifest version: "
+              << ex.what() << std::endl;
+    return {};
+  }
+
+  return {};
+}

src/manager.cpp

@@ -470,6 +470,21 @@ fs::path Manager::install_path(Package pkg) {
 }
 
 bool Manager::update_manifest() {
+  optional<int> newest_manifest_version = fetch->fetch_newest_manifest_version(
+      "https://chuck.stanford.edu/release/chump/manifest/"
+      "latest-manifest.version");
+
+  if (newest_manifest_version &&
+      newest_manifest_version.value() > MANIFEST_VERSION_NO) {
+    std::cerr
+        << "[chump] there are newer packages available that this version of "
+           "chump cannot manage. visit https://chuck.stanford.edu/release/ and "
+           "install the latest version of chuck (which includes an updated "
+           "version of chump). once you have done this, rerun chump for the "
+           "latest, greatest, chumpiest experience available\n";
+    std::cerr << "[chump] ~~ don't be a lump, update chump ~~\n";
+  }
+
   // Create a temporary directory to download our manifest to
   fs::path temp_dir = {fs::temp_directory_path() /= std::tmpnam(nullptr)};
   fs::create_directory(temp_dir);
@@ -478,7 +493,7 @@ bool Manager::update_manifest() {
   bool result = fetch->fetch_manifest(manifest_url, temp_dir);
 
   if (!result) {
-    std::cerr << "[chump]: failed to fetch manifest.json, exiting."
+    std::cerr << "[chump]: failed to fetch manifest.json, continuing..."
               << std::endl;
     return false;
   }