dlfile: Detect and handle I/O errors during finalization

Correctly handling, and more importantly, recovering from any possible
I/O errors is a huge pain and fairly complex. The current fixes should
allow full recovery when the move to the final destination fails, even
across ncdc restarts. But there's probably still some error sequences
that can't be recovered from. That's hard/impossible to really fix,
because the ftruncate() and file move can't be done as a single atomic
operation.

Also, recovery across restarts assumes that the changes to the
db.sqlite3 file do get flushed.

Author: Yorhel

src/dlfile.c

@@ -121,11 +121,11 @@ static gboolean dlfile_save_bitmap_timeout(gpointer dat) {
   dl_t *dl = dat;
   g_static_mutex_lock(&dl->lock);
   dl->bitmap_src = 0;
-  if(dl->incfd >= 0 && !dlfile_save_bitmap(dl, dl->incfd)) {
+  if(dl->incfd > 0 && !dlfile_save_bitmap(dl, dl->incfd)) {
     g_warning("Error writing bitmap for `%s': %s.", dl->dest, g_strerror(errno));
     dl_queue_seterr(dl, DLE_IO_INC, g_strerror(errno));
   }
-  if(dl->incfd >= 0 && !dl->active_threads) {
+  if(dl->incfd > 0 && !dl->active_threads) {
     close(dl->incfd);
     dl->incfd = 0;
   }
@@ -290,6 +290,18 @@ static gboolean dlfile_load_threads(dl_t *dl, int fd) {
 
 
 void dlfile_load(dl_t *dl) {
+  /* If moving to the destination failed in a previous run, assume that the
+   * incoming file is complete and all that's left to do is resume the
+   * finalization (which the user has to initiate by clearing the error). This
+   * needs to be handled as a special case because the incoming file will not
+   * contain the bitmap anymore at this point, and the loading process below
+   * will fail. */
+  if(dl->prio == DLP_ERR && dl->error == DLE_IO_DEST) {
+    g_message("Download for `%s' in IO_DEST error state, assuming `%s' contains the finished download.", dl->dest, dl->inc);
+    dl->have = dl->size;
+    return;
+  }
+
   dl->have = 0;
   int fd = open(dl->inc, O_RDWR);
   if(fd < 0) {
@@ -352,8 +364,8 @@ static gboolean dlfile_open(dl_t *dl) {
     return FALSE;
   }
 
-  /* Everything else has already been initialized if we have a thread */
-  if(dl->threads)
+  /* Everything else has already been initialized if we have a thread or bitmap */
+  if(dl->threads || dl->bitmap)
     return TRUE;
 
   if(!dl->islist) {
@@ -387,20 +399,33 @@ void dlfile_finished(dl_t *dl) {
   /* Regular files: Remove bitmap from the file
    * File lists: Ensure that the file size is correct after we've downloaded a
    *   longer file list before that got interrupted. */
-  /* TODO: Error handling */
-  ftruncate(dl->incfd, dl->size);
-  close(dl->incfd);
+  if(ftruncate(dl->incfd, dl->size) < 0) {
+    g_warning("Error truncating the incoming file for `%s': %s.", dl->dest, g_strerror(errno));
+    dl_queue_seterr(dl, DLE_IO_INC, g_strerror(errno));
+    return;
+  }
+  int r = close(dl->incfd);
   dl->incfd = 0;
+  if(r < 0) {
+    g_warning("Error closing the incoming file for `%s': %s.", dl->dest, g_strerror(errno));
+    dl_queue_seterr(dl, DLE_IO_INC, g_strerror(errno));
+    return;
+  }
 
   char *fdest = g_filename_from_utf8(dl->dest, -1, NULL, NULL, NULL);
   if(!fdest)
     fdest = g_strdup(dl->dest);
 
   /* Create destination directory, if it does not exist yet. */
   char *parent = g_path_get_dirname(fdest);
-  g_mkdir_with_parents(parent, 0755);
-  /* TODO: Error handling */
+  r = g_mkdir_with_parents(parent, 0755);
   g_free(parent);
+  if(r < 0) {
+    g_warning("Error creating directory for `%s': %s.", dl->dest, g_strerror(errno));
+    dl_queue_seterr(dl, DLE_IO_DEST, g_strerror(errno));
+    g_free(fdest);
+    return;
+  }
 
   /* Prevent overwiting other files by appending a prefix to the destination if
    * it already exists. It is assumed that fn + any dupe-prevention-extension
@@ -412,17 +437,18 @@ void dlfile_finished(dl_t *dl) {
     g_free(dest);
     dest = g_strdup_printf("%s.%d", fdest, num++);
   }
+  g_free(fdest);
 
   GError *err = NULL;
   file_move(dl->inc, dest, dl->islist, &err);
+  g_free(dest);
   if(err) {
-    /* TODO: Error handling. */
+    g_warning("Error moving file to destination `%s': %s.", dl->dest, err->message);
+    dl_queue_seterr(dl, DLE_IO_DEST, err->message);
     g_error_free(err);
+    return;
   }
 
-  g_free(dest);
-  g_free(fdest);
-
   dl_finished(dl);
 }