lib/repo-finder: Add Avahi based OstreeRepoFinder implementation

This is a more complex implementation of OstreeRepoFinder which resolves
ref names to remote URIs by looking for refs advertised by peers on the
local network using DNS-SD records and mDNS (Avahi). The idea is to
allow OS and app updates to be propagated over local networks, without
the internet.

It requires an OSTree server and code to generate the DNS-SD adverts in
order to be fully functional — support for this will be added
separately.

Unit tests are included.

Includes fixes by Krzesimir Nowak <krzesimir@kinvolk.io>.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #924
Approved by: cgwalters

1 files changed, 137 insertions, 0 deletions

diff --git a/src/libostree/ostree-repo-finder-avahi-parser.c b/src/libostree/ostree-repo-finder-avahi-parser.c
new file mode 100644
index 00000000..805f5dff
--- /dev/null
+++ b/src/libostree/ostree-repo-finder-avahi-parser.c
@@ -0,0 +1,137 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright © 2016 Kinvolk GmbH
+ * Copyright © 2017 Endless Mobile, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Authors:
+ *  - Krzesimir Nowak <krzesimir@kinvolk.io>
+ *  - Philip Withnall <withnall@endlessm.com>
+ */
+
+#include "config.h"
+
+#include <avahi-common/strlst.h>
+#include <glib.h>
+#include <glib-object.h>
+#include <string.h>
+
+#include "ostree-autocleanups.h"
+#include "ostree-repo-finder-avahi.h"
+#include "ostree-repo-finder-avahi-private.h"
+
+/* Reference: RFC 6763, §6. */
+static gboolean
+parse_txt_record (const guint8  *txt,
+                  gsize          txt_len,
+                  const gchar  **key,
+                  gsize         *key_len,
+                  const guint8 **value,
+                  gsize         *value_len)
+{
+  gsize i;
+
+  g_return_val_if_fail (key != NULL, FALSE);
+  g_return_val_if_fail (key_len != NULL, FALSE);
+  g_return_val_if_fail (value != NULL, FALSE);
+  g_return_val_if_fail (value_len != NULL, FALSE);
+
+  /* RFC 6763, §6.1. */
+  if (txt_len > 8900)
+    return FALSE;
+
+  *key = (const gchar *) txt;
+  *key_len = 0;
+  *value = NULL;
+  *value_len = 0;
+
+  for (i = 0; i < txt_len; i++)
+    {
+      if (txt[i] >= 0x20 && txt[i] <= 0x7e && txt[i] != '=')
+        {
+          /* Key character. */
+          *key_len = *key_len + 1;
+          continue;
+        }
+      else if (*key_len > 0 && txt[i] == '=')
+        {
+          /* Separator. */
+          *value = txt + (i + 1);
+          *value_len = txt_len - (i + 1);
+          return TRUE;
+        }
+      else
+        {
+          return FALSE;
+        }
+    }
+
+  /* The entire TXT record is the key; there is no ‘=’ or value. */
+  *value = NULL;
+  *value_len = 0;
+
+  return (*key_len > 0);
+}
+
+/* TODO: Docs. Return value is only valid as long as @txt is. Reference: RFC 6763, §6. */
+GHashTable *
+_ostree_txt_records_parse (AvahiStringList *txt)
+{
+  AvahiStringList *l;
+  g_autoptr(GHashTable) out = NULL;
+
+  out = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, (GDestroyNotify) g_bytes_unref);
+
+  for (l = txt; l != NULL; l = avahi_string_list_get_next (l))
+    {
+      const guint8 *txt;
+      gsize txt_len;
+      const gchar *key;
+      const guint8 *value;
+      gsize key_len, value_len;
+      g_autofree gchar *key_allocated = NULL;
+      g_autoptr(GBytes) value_allocated = NULL;
+
+      txt = avahi_string_list_get_text (l);
+      txt_len = avahi_string_list_get_size (l);
+
+      if (!parse_txt_record (txt, txt_len, &key, &key_len, &value, &value_len))
+        {
+          g_debug ("Ignoring invalid TXT record of length %" G_GSIZE_FORMAT,
+                   txt_len);
+          continue;
+        }
+
+      key_allocated = g_ascii_strdown (key, key_len);
+
+      if (g_hash_table_lookup_extended (out, key_allocated, NULL, NULL))
+        {
+          g_debug ("Ignoring duplicate TXT record ‘%s’", key_allocated);
+          continue;
+        }
+
+      /* Distinguish between the case where the entire record is the key
+       * (value == NULL) and the case where the record is the key + ‘=’ and the
+       * value is empty (value != NULL && value_len == 0). */
+      if (value != NULL)
+        value_allocated = g_bytes_new_static (value, value_len);
+
+      g_hash_table_insert (out, g_steal_pointer (&key_allocated), g_steal_pointer (&value_allocated));
+    }
+
+  return g_steal_pointer (&out);
+}