Generate random thread IDs instead of using an arbitrary Message-ID.

Previously, we used as the thread-id the message-id of the first
message in the thread that we happened to find. In fact, this is a
totally arbitrary identifier, so it might as well be random. And an
advantage of actually using a random identifier is that we now have
fixed-length thead identifiers, (and the way is open to even allow
abbreviated identifiers like git does---though we're less likely to
show these identifiers to actual users).

diff --git a/notmuch-index-message.cc b/notmuch-index-message.cc
index 7610aa41f97c455ef0cf650ad3a52ac03886f2d8..3175d2d829b26b9c8db72d9d962bdf141cdb9851 100644 (file)
--- a/notmuch-index-message.cc
+++ b/notmuch-index-message.cc
@@ -128,7 +128,40 @@ find_prefix (const char *name)
     return "";
 }
 
-int TERM_COMBINED = 0;
+/* "128 bits of thread-id ought to be enough for anybody" */
+#define NOTMUCH_THREAD_ID_BITS  128
+#define NOTMUCH_THREAD_ID_DIGITS (NOTMUCH_THREAD_ID_BITS / 4)
+typedef struct _thread_id {
+    char str[NOTMUCH_THREAD_ID_DIGITS + 1];
+} thread_id_t;
+
+static void
+thread_id_generate (thread_id_t *thread_id)
+{
+    FILE *urandom;
+    uint32_t value;
+    char *s;
+    int i;
+
+    urandom = fopen ("/dev/urandom", "r");
+    if (urandom == NULL) {
+       fprintf (stderr, "Error opening /dev/urandom: %s\n",
+                strerror (errno));
+       fprintf (stderr, "Perhaps notmuch needs some portability fixes for your platform?\n");
+       exit (1);
+    }
+
+    s = thread_id->str;
+    for (i = 0; i < NOTMUCH_THREAD_ID_DIGITS; i += 8) {
+       fread ((void *) &value, sizeof (value), 1, urandom);
+       sprintf (s, "%08x", value);
+       s += 8;
+    }
+
+    fclose (urandom);
+
+    printf ("Generated thread id: %s\n", thread_id->str);
+}
 
 static void
 add_term (Xapian::Document doc,
@@ -690,9 +723,13 @@ index_file (Xapian::WritableDatabase db,
 
        g_string_free (thread_id, TRUE);
     } else if (message_id) {
-       /* If not referenced thread, use the message ID */
-       add_term (doc, "thread", message_id);
-       doc.add_value (NOTMUCH_VALUE_THREAD, message_id);
+       /* If not part of any existing thread, generate a new thread_id. */
+       thread_id_t thread_id;
+
+       thread_id_generate (&thread_id);
+
+       add_term (doc, "thread", thread_id.str);
+       doc.add_value (NOTMUCH_VALUE_THREAD, thread_id.str);
     }
 
     doc.add_value (NOTMUCH_VALUE_DATE, Xapian::sortable_serialise (time));