If an archive is corrupted (CRC error) retry the download

Previously the CRC error was quite annoying to recover because
the user needed to manually delete the corrupted file from the
staging folder (without knowing the exact path of the file to
remove).

Now the IDE tries autonomously to resolve the situation by
removing the file and downloading it again.

Fixes #5394 #4303

Author: cmaglie

Diff for: arduino-core/src/cc/arduino/contributions/DownloadableContributionsDownloader.java

@@ -62,20 +62,38 @@ public File download(DownloadableContribution contribution, Progress progress, f
       Files.delete(outputFile);
     }
 
-    // Need to download or resume downloading?
-    if (!Files.isRegularFile(outputFile, LinkOption.NOFOLLOW_LINKS) || (Files.size(outputFile) < contribution.getSize())) {
-      download(url, outputFile.toFile(), progress, statusText, progressListener);
-    }
+    boolean downloaded = false;
+    while (true) {
+      // Need to download or resume downloading?
+      if (!Files.isRegularFile(outputFile, LinkOption.NOFOLLOW_LINKS) || (Files.size(outputFile) < contribution.getSize())) {
+        download(url, outputFile.toFile(), progress, statusText, progressListener);
+        downloaded = true;
+      }
 
-    // Test checksum
-    progress.setStatus(tr("Verifying archive integrity..."));
-    progressListener.onProgress(progress);
-    String checksum = contribution.getChecksum();
-    if (hasChecksum(contribution)) {
-      String algo = checksum.split(":")[0];
-      if (!FileHash.hash(outputFile.toFile(), algo).equalsIgnoreCase(checksum)) {
-        throw new Exception(tr("CRC doesn't match. File is corrupted."));
+      // Test checksum
+      progress.setStatus(tr("Verifying archive integrity..."));
+      progressListener.onProgress(progress);
+      if (hasChecksum(contribution)) {
+        String checksum = contribution.getChecksum();
+        String algo = checksum.split(":")[0];
+        String crc = FileHash.hash(outputFile.toFile(), algo);
+        if (!crc.equalsIgnoreCase(checksum)) {
+          // If the file has not been downloaded it may be a leftover of
+          // a previous download that failed. In this case delete it and
+          // try to download it again.
+          if (!downloaded) {
+            Files.delete(outputFile);
+            downloaded = true; // Redundant to avoid loops in case delete fails
+            continue;
+          }
+
+          // Otherwise throw the error.
+          throw new Exception(tr("CRC doesn't match, file is corrupted. It may be a temporary problem, please retry later."));
+        }
       }
+
+      // Download completed successfully
+      break;
     }
 
     contribution.setDownloaded(true);

Diff for: build/shared/revisions.txt

@@ -5,6 +5,8 @@ ARDUINO 1.6.13
 * Fixed regression on command line upload.
 * Bugifx installing libraries from command line: the IDE tries to update the libraries index but it
   didn't use it straight away (this caused issues mainly on CI environments)
+* Libraries and Boards Managers: if a download error happens (CRC error) the IDE tries to download the file again
+  without the need to remove the corrupted file manually.
 
 [core]
 * avr: set default values for "upload.verify" and "program.verify" (allows compatibility with older IDE). Thanks @per1234