add_message: Fix to not add multiple documents with the same message ID

Here's the second big fix to message-ID handling, (the first was to
generate message IDs when an email contained none). Now, with no
document missing a message ID, and no two documents having the same
message ID, we have a nice consistent database where the message ID
can be used as a unique key.

1 files changed, 7 insertions, 0 deletions

diff --git a/message.cc b/message.cc
index 281da4f..ce600af 100644
--- a/message.cc
+++ b/message.cc
@@ -41,6 +41,13 @@ struct _notmuch_thread_ids {
     char *next;
 };
 
+/* "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;
+
 #define ARRAY_SIZE(arr) (sizeof (arr) / sizeof (arr[0]))
 
 /* These prefix values are specifically chosen to be compatible