[notmuch] / lib / message.cc

/* message.cc - Results of message-based searches from a notmuch database
 *
 * Copyright © 2009 Carl Worth
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see http://www.gnu.org/licenses/ .
 *
 * Author: Carl Worth <cworth@cworth.org>
 */

#include "notmuch-private.h"
#include "database-private.h"

#include <stdint.h>

#include <gmime/gmime.h>

struct visible _notmuch_message {
    notmuch_database_t *notmuch;
    Xapian::docid doc_id;
    int frozen;
    char *message_id;
    char *thread_id;
    char *in_reply_to;
    notmuch_string_list_t *tag_list;
    notmuch_string_list_t *filename_term_list;
    notmuch_string_list_t *filename_list;
    char *author;
    notmuch_message_file_t *message_file;
    notmuch_message_list_t *replies;
    unsigned long flags;

    Xapian::Document doc;
    Xapian::termcount termpos;
};

#define ARRAY_SIZE(arr) (sizeof (arr) / sizeof (arr[0]))

struct maildir_flag_tag {
    char flag;
    const char *tag;
    notmuch_bool_t inverse;
};

/* ASCII ordered table of Maildir flags and associated tags */
static struct maildir_flag_tag flag2tag[] = {
    { 'D', "draft",   FALSE},
    { 'F', "flagged", FALSE},
    { 'P', "passed",  FALSE},
    { 'R', "replied", FALSE},
    { 'S', "unread",  TRUE }
};

/* We end up having to call the destructor explicitly because we had
 * to use "placement new" in order to initialize C++ objects within a
 * block that we allocated with talloc. So C++ is making talloc
 * slightly less simple to use, (we wouldn't need
 * talloc_set_destructor at all otherwise).
 */
static int
_notmuch_message_destructor (notmuch_message_t *message)
{
    message->doc.~Document ();

    return 0;
}

static notmuch_message_t *
_notmuch_message_create_for_document (const void *talloc_owner,
                                      notmuch_database_t *notmuch,
                                      unsigned int doc_id,
                                      Xapian::Document doc,
                                      notmuch_private_status_t *status)
{
    notmuch_message_t *message;

    if (status)
        *status = NOTMUCH_PRIVATE_STATUS_SUCCESS;

    message = talloc (talloc_owner, notmuch_message_t);
    if (unlikely (message == NULL)) {
        if (status)
            *status = NOTMUCH_PRIVATE_STATUS_OUT_OF_MEMORY;
        return NULL;
    }

    message->notmuch = notmuch;
    message->doc_id = doc_id;

    message->frozen = 0;
    message->flags = 0;

    /* Each of these will be lazily created as needed. */
    message->message_id = NULL;
    message->thread_id = NULL;
    message->in_reply_to = NULL;
    message->tag_list = NULL;
    message->filename_term_list = NULL;
    message->filename_list = NULL;
    message->message_file = NULL;
    message->author = NULL;

    message->replies = _notmuch_message_list_create (message);
    if (unlikely (message->replies == NULL)) {
        if (status)
            *status = NOTMUCH_PRIVATE_STATUS_OUT_OF_MEMORY;
        return NULL;
    }

    /* This is C++'s creepy "placement new", which is really just an
     * ugly way to call a constructor for a pre-allocated object. So
     * it's really not an error to not be checking for OUT_OF_MEMORY
     * here, since this "new" isn't actually allocating memory. This
     * is language-design comedy of the wrong kind. */

    new (&message->doc) Xapian::Document;

    talloc_set_destructor (message, _notmuch_message_destructor);

    message->doc = doc;
    message->termpos = 0;

    return message;
}

/* Create a new notmuch_message_t object for an existing document in
 * the database.
 *
 * Here, 'talloc owner' is an optional talloc context to which the new
 * message will belong. This allows for the caller to not bother
 * calling notmuch_message_destroy on the message, and know that all
 * memory will be reclaimed when 'talloc_owner' is freed. The caller
 * still can call notmuch_message_destroy when finished with the
 * message if desired.
 *
 * The 'talloc_owner' argument can also be NULL, in which case the
 * caller *is* responsible for calling notmuch_message_destroy.
 *
 * If no document exists in the database with document ID of 'doc_id'
 * then this function returns NULL and optionally sets *status to
 * NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND.
 *
 * This function can also fail to due lack of available memory,
 * returning NULL and optionally setting *status to
 * NOTMUCH_PRIVATE_STATUS_OUT_OF_MEMORY.
 *
 * The caller can pass NULL for status if uninterested in
 * distinguishing these two cases.
 */
notmuch_message_t *
_notmuch_message_create (const void *talloc_owner,
                         notmuch_database_t *notmuch,
                         unsigned int doc_id,
                         notmuch_private_status_t *status)
{
    Xapian::Document doc;

    try {
        doc = notmuch->xapian_db->get_document (doc_id);
    } catch (const Xapian::DocNotFoundError &error) {
        if (status)
            *status = NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND;
        return NULL;
    }

    return _notmuch_message_create_for_document (talloc_owner, notmuch,
                                                 doc_id, doc, status);
}

/* Create a new notmuch_message_t object for a specific message ID,
 * (which may or may not already exist in the database).
 *
 * The 'notmuch' database will be the talloc owner of the returned
 * message.
 *
 * This function returns a valid notmuch_message_t whether or not
 * there is already a document in the database with the given message
 * ID. These two cases can be distinguished by the value of *status:
 *
 *
 *   NOTMUCH_PRIVATE_STATUS_SUCCESS:
 *
 *     There is already a document with message ID 'message_id' in the
 *     database. The returned message can be used to query/modify the
 *     document.
 *   NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND:
 *
 *     No document with 'message_id' exists in the database. The
 *     returned message contains a newly created document (not yet
 *     added to the database) and a document ID that is known not to
 *     exist in the database. The caller can modify the message, and a
 *     call to _notmuch_message_sync will add * the document to the
 *     database.
 *
 * If an error occurs, this function will return NULL and *status
 * will be set as appropriate. (The status pointer argument must
 * not be NULL.)
 */
notmuch_message_t *
_notmuch_message_create_for_message_id (notmuch_database_t *notmuch,
                                        const char *message_id,
                                        notmuch_private_status_t *status_ret)
{
    notmuch_message_t *message;
    Xapian::Document doc;
    unsigned int doc_id;
    char *term;

    *status_ret = (notmuch_private_status_t) notmuch_database_find_message (notmuch,
                                                                            message_id,
                                                                            &message);
    if (message)
        return talloc_steal (notmuch, message);
    else if (*status_ret)
        return NULL;

    term = talloc_asprintf (NULL, "%s%s",
                            _find_prefix ("id"), message_id);
    if (term == NULL) {
        *status_ret = NOTMUCH_PRIVATE_STATUS_OUT_OF_MEMORY;
        return NULL;
    }

    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY)
        INTERNAL_ERROR ("Failure to ensure database is writable.");

    try {
        doc.add_term (term, 0);
        talloc_free (term);

        doc.add_value (NOTMUCH_VALUE_MESSAGE_ID, message_id);

        doc_id = _notmuch_database_generate_doc_id (notmuch);
    } catch (const Xapian::Error &error) {
        fprintf (stderr, "A Xapian exception occurred creating message: %s\n",
                 error.get_msg().c_str());
        notmuch->exception_reported = TRUE;
        *status_ret = NOTMUCH_PRIVATE_STATUS_XAPIAN_EXCEPTION;
        return NULL;
    }

    message = _notmuch_message_create_for_document (notmuch, notmuch,
                                                    doc_id, doc, status_ret);

    /* We want to inform the caller that we had to create a new
     * document. */
    if (*status_ret == NOTMUCH_PRIVATE_STATUS_SUCCESS)
        *status_ret = NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND;

    return message;
}

static char *
_notmuch_message_get_term (notmuch_message_t *message,
                           Xapian::TermIterator &i, Xapian::TermIterator &end,
                           const char *prefix)
{
    int prefix_len = strlen (prefix);
    char *value;

    i.skip_to (prefix);

    if (i == end)
        return NULL;

    std::string term = *i;
    if (strncmp (term.c_str(), prefix, prefix_len))
        return NULL;

    value = talloc_strdup (message, term.c_str() + prefix_len);

#if DEBUG_DATABASE_SANITY
    i++;

    if (i != end && strncmp ((*i).c_str (), prefix, prefix_len) == 0) {
        INTERNAL_ERROR ("Mail (doc_id: %d) has duplicate %s terms: %s and %s\n",
                        message->doc_id, prefix, value,
                        (*i).c_str () + prefix_len);
    }
#endif

    return value;
}

void
_notmuch_message_ensure_metadata (notmuch_message_t *message)
{
    Xapian::TermIterator i, end;
    const char *thread_prefix = _find_prefix ("thread"),
        *tag_prefix = _find_prefix ("tag"),
        *id_prefix = _find_prefix ("id"),
        *filename_prefix = _find_prefix ("file-direntry"),
        *replyto_prefix = _find_prefix ("replyto");

    /* We do this all in a single pass because Xapian decompresses the
     * term list every time you iterate over it.  Thus, while this is
     * slightly more costly than looking up individual fields if only
     * one field of the message object is actually used, it's a huge
     * win as more fields are used. */

    i = message->doc.termlist_begin ();
    end = message->doc.termlist_end ();

    /* Get thread */
    if (!message->thread_id)
        message->thread_id =
            _notmuch_message_get_term (message, i, end, thread_prefix);

    /* Get tags */
    assert (strcmp (thread_prefix, tag_prefix) < 0);
    if (!message->tag_list) {
        message->tag_list =
            _notmuch_database_get_terms_with_prefix (message, i, end,
                                                     tag_prefix);
        _notmuch_string_list_sort (message->tag_list);
    }

    /* Get id */
    assert (strcmp (tag_prefix, id_prefix) < 0);
    if (!message->message_id)
        message->message_id =
            _notmuch_message_get_term (message, i, end, id_prefix);

    /* Get filename list.  Here we get only the terms.  We lazily
     * expand them to full file names when needed in
     * _notmuch_message_ensure_filename_list. */
    assert (strcmp (id_prefix, filename_prefix) < 0);
    if (!message->filename_term_list && !message->filename_list)
        message->filename_term_list =
            _notmuch_database_get_terms_with_prefix (message, i, end,
                                                     filename_prefix);

    /* Get reply to */
    assert (strcmp (filename_prefix, replyto_prefix) < 0);
    if (!message->in_reply_to)
        message->in_reply_to =
            _notmuch_message_get_term (message, i, end, replyto_prefix);
    /* It's perfectly valid for a message to have no In-Reply-To
     * header. For these cases, we return an empty string. */
    if (!message->in_reply_to)
        message->in_reply_to = talloc_strdup (message, "");
}

static void
_notmuch_message_invalidate_metadata (notmuch_message_t *message,
                                      const char *prefix_name)
{
    if (strcmp ("thread", prefix_name) == 0) {
        talloc_free (message->thread_id);
        message->thread_id = NULL;
    }

    if (strcmp ("tag", prefix_name) == 0) {
        talloc_unlink (message, message->tag_list);
        message->tag_list = NULL;
    }

    if (strcmp ("file-direntry", prefix_name) == 0) {
        talloc_free (message->filename_term_list);
        talloc_free (message->filename_list);
        message->filename_term_list = message->filename_list = NULL;
    }

    if (strcmp ("replyto", prefix_name) == 0) {
        talloc_free (message->in_reply_to);
        message->in_reply_to = NULL;
    }
}

unsigned int
_notmuch_message_get_doc_id (notmuch_message_t *message)
{
    return message->doc_id;
}

const char *
notmuch_message_get_message_id (notmuch_message_t *message)
{
    if (!message->message_id)
        _notmuch_message_ensure_metadata (message);
    if (!message->message_id)
        INTERNAL_ERROR ("Message with document ID of %u has no message ID.\n",
                        message->doc_id);
    return message->message_id;
}

static void
_notmuch_message_ensure_message_file (notmuch_message_t *message)
{
    const char *filename;

    if (message->message_file)
        return;

    filename = notmuch_message_get_filename (message);
    if (unlikely (filename == NULL))
        return;

    message->message_file = _notmuch_message_file_open_ctx (message, filename);
}

const char *
notmuch_message_get_header (notmuch_message_t *message, const char *header)
{
    try {
            std::string value;

            /* Fetch header from the appropriate xapian value field if
             * available */
            if (strcasecmp (header, "from") == 0)
                value = message->doc.get_value (NOTMUCH_VALUE_FROM);
            else if (strcasecmp (header, "subject") == 0)
                value = message->doc.get_value (NOTMUCH_VALUE_SUBJECT);
            else if (strcasecmp (header, "message-id") == 0)
                value = message->doc.get_value (NOTMUCH_VALUE_MESSAGE_ID);

            if (!value.empty())
                return talloc_strdup (message, value.c_str ());

    } catch (Xapian::Error &error) {
        fprintf (stderr, "A Xapian exception occurred when reading header: %s\n",
                 error.get_msg().c_str());
        message->notmuch->exception_reported = TRUE;
        return NULL;
    }

    /* Otherwise fall back to parsing the file */
    _notmuch_message_ensure_message_file (message);
    if (message->message_file == NULL)
        return NULL;

    return notmuch_message_file_get_header (message->message_file, header);
}

/* Return the message ID from the In-Reply-To header of 'message'.
 *
 * Returns an empty string ("") if 'message' has no In-Reply-To
 * header.
 *
 * Returns NULL if any error occurs.
 */
const char *
_notmuch_message_get_in_reply_to (notmuch_message_t *message)
{
    if (!message->in_reply_to)
        _notmuch_message_ensure_metadata (message);
    return message->in_reply_to;
}

const char *
notmuch_message_get_thread_id (notmuch_message_t *message)
{
    if (!message->thread_id)
        _notmuch_message_ensure_metadata (message);
    if (!message->thread_id)
        INTERNAL_ERROR ("Message with document ID of %u has no thread ID.\n",
                        message->doc_id);
    return message->thread_id;
}

void
_notmuch_message_add_reply (notmuch_message_t *message,
                            notmuch_message_t *reply)
{
    _notmuch_message_list_add_message (message->replies, reply);
}

notmuch_messages_t *
notmuch_message_get_replies (notmuch_message_t *message)
{
    return _notmuch_messages_create (message->replies);
}

static void
_notmuch_message_remove_terms (notmuch_message_t *message, const char *prefix)
{
    Xapian::TermIterator i;
    size_t prefix_len = strlen (prefix);

    while (1) {
        i = message->doc.termlist_begin ();
        i.skip_to (prefix);

        /* Terminate loop when no terms remain with desired prefix. */
        if (i == message->doc.termlist_end () ||
            strncmp ((*i).c_str (), prefix, prefix_len))
            break;

        try {
            message->doc.remove_term ((*i));
        } catch (const Xapian::InvalidArgumentError) {
            /* Ignore failure to remove non-existent term. */
        }
    }
}

#define RECURSIVE_SUFFIX "/**"

/* Add "path:" terms for directory. */
static notmuch_status_t
_notmuch_message_add_path_terms (notmuch_message_t *message,
                                 const char *directory)
{
    /* Add exact "path:" term. */
    _notmuch_message_add_term (message, "path", directory);

    if (strlen (directory)) {
        char *path, *p;

        path = talloc_asprintf (NULL, "%s%s", directory, RECURSIVE_SUFFIX);
        if (! path)
            return NOTMUCH_STATUS_OUT_OF_MEMORY;

        /* Add recursive "path:" terms for directory and all parents. */
        for (p = path + strlen (path) - 1; p > path; p--) {
            if (*p == '/') {
                strcpy (p, RECURSIVE_SUFFIX);
                _notmuch_message_add_term (message, "path", path);
            }
        }

        talloc_free (path);
    }

    /* Recursive all-matching path:** for consistency. */
    _notmuch_message_add_term (message, "path", "**");

    return NOTMUCH_STATUS_SUCCESS;
}

/* Add directory based terms for all filenames of the message. */
static notmuch_status_t
_notmuch_message_add_directory_terms (void *ctx, notmuch_message_t *message)
{
    const char *direntry_prefix = _find_prefix ("file-direntry");
    int direntry_prefix_len = strlen (direntry_prefix);
    Xapian::TermIterator i = message->doc.termlist_begin ();
    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;

    for (i.skip_to (direntry_prefix); i != message->doc.termlist_end (); i++) {
        unsigned int directory_id;
        const char *direntry, *directory;
        char *colon;

        /* Terminate loop at first term without desired prefix. */
        if (strncmp ((*i).c_str (), direntry_prefix, direntry_prefix_len))
            break;

        /* Indicate that there are filenames remaining. */
        status = NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID;

        direntry = (*i).c_str ();
        direntry += direntry_prefix_len;

        directory_id = strtol (direntry, &colon, 10);

        if (colon == NULL || *colon != ':')
            INTERNAL_ERROR ("malformed direntry");

        directory = _notmuch_database_get_directory_path (ctx,
                                                          message->notmuch,
                                                          directory_id);
        if (strlen (directory))
            _notmuch_message_gen_terms (message, "folder", directory);

        _notmuch_message_add_path_terms (message, directory);
    }

    return status;
}

/* Add an additional 'filename' for 'message'.
 *
 * This change will not be reflected in the database until the next
 * call to _notmuch_message_sync. */
notmuch_status_t
_notmuch_message_add_filename (notmuch_message_t *message,
                               const char *filename)
{
    const char *relative, *directory;
    notmuch_status_t status;
    void *local = talloc_new (message);
    char *direntry;

    if (filename == NULL)
        INTERNAL_ERROR ("Message filename cannot be NULL.");

    relative = _notmuch_database_relative_path (message->notmuch, filename);

    status = _notmuch_database_split_path (local, relative, &directory, NULL);
    if (status)
        return status;

    status = _notmuch_database_filename_to_direntry (
        local, message->notmuch, filename, NOTMUCH_FIND_CREATE, &direntry);
    if (status)
        return status;

    /* New file-direntry allows navigating to this message with
     * notmuch_directory_get_child_files() . */
    _notmuch_message_add_term (message, "file-direntry", direntry);

    /* New terms allow user to search with folder: specification. */
    _notmuch_message_gen_terms (message, "folder", directory);

    _notmuch_message_add_path_terms (message, directory);

    talloc_free (local);

    return NOTMUCH_STATUS_SUCCESS;
}

/* Remove a particular 'filename' from 'message'.
 *
 * This change will not be reflected in the database until the next
 * call to _notmuch_message_sync.
 *
 * If this message still has other filenames, returns
 * NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID.
 *
 * Note: This function does not remove a document from the database,
 * even if the specified filename is the only filename for this
 * message. For that functionality, see
 * _notmuch_database_remove_message. */
notmuch_status_t
_notmuch_message_remove_filename (notmuch_message_t *message,
                                  const char *filename)
{
    void *local = talloc_new (message);
    const char *folder_prefix = _find_prefix ("folder");
    char *zfolder_prefix = talloc_asprintf(local, "Z%s", folder_prefix);
    char *direntry;
    notmuch_private_status_t private_status;
    notmuch_status_t status;

    status = _notmuch_database_filename_to_direntry (
        local, message->notmuch, filename, NOTMUCH_FIND_LOOKUP, &direntry);
    if (status || !direntry)
        return status;

    /* Unlink this file from its parent directory. */
    private_status = _notmuch_message_remove_term (message,
                                                   "file-direntry", direntry);
    status = COERCE_STATUS (private_status,
                            "Unexpected error from _notmuch_message_remove_term");
    if (status)
        return status;

    /* Re-synchronize "folder:" and "path:" terms for this message. */

    /* Remove all "folder:" terms. */
    _notmuch_message_remove_terms (message, folder_prefix);

    /* Remove all "folder:" stemmed terms. */
    _notmuch_message_remove_terms (message, zfolder_prefix);

    /* Remove all "path:" terms. */
    _notmuch_message_remove_terms (message, _find_prefix ("path"));

    /* Add back terms for all remaining filenames of the message. */
    status = _notmuch_message_add_directory_terms (local, message);

    talloc_free (local);

    return status;
}

char *
_notmuch_message_talloc_copy_data (notmuch_message_t *message)
{
    return talloc_strdup (message, message->doc.get_data ().c_str ());
}

void
_notmuch_message_clear_data (notmuch_message_t *message)
{
    message->doc.set_data ("");
}

static void
_notmuch_message_ensure_filename_list (notmuch_message_t *message)
{
    notmuch_string_node_t *node;

    if (message->filename_list)
        return;

    if (!message->filename_term_list)
        _notmuch_message_ensure_metadata (message);

    message->filename_list = _notmuch_string_list_create (message);
    node = message->filename_term_list->head;

    if (!node) {
        /* A message document created by an old version of notmuch
         * (prior to rename support) will have the filename in the
         * data of the document rather than as a file-direntry term.
         *
         * It would be nice to do the upgrade of the document directly
         * here, but the database is likely open in read-only mode. */
        const char *data;

        data = message->doc.get_data ().c_str ();

        if (data == NULL)
            INTERNAL_ERROR ("message with no filename");

        _notmuch_string_list_append (message->filename_list, data);

        return;
    }

    for (; node; node = node->next) {
        void *local = talloc_new (message);
        const char *db_path, *directory, *basename, *filename;
        char *colon, *direntry = NULL;
        unsigned int directory_id;

        direntry = node->string;

        directory_id = strtol (direntry, &colon, 10);

        if (colon == NULL || *colon != ':')
            INTERNAL_ERROR ("malformed direntry");

        basename = colon + 1;

        *colon = '\0';

        db_path = notmuch_database_get_path (message->notmuch);

        directory = _notmuch_database_get_directory_path (local,
                                                          message->notmuch,
                                                          directory_id);

        if (strlen (directory))
            filename = talloc_asprintf (message, "%s/%s/%s",
                                        db_path, directory, basename);
        else
            filename = talloc_asprintf (message, "%s/%s",
                                        db_path, basename);

        _notmuch_string_list_append (message->filename_list, filename);

        talloc_free (local);
    }

    talloc_free (message->filename_term_list);
    message->filename_term_list = NULL;
}

const char *
notmuch_message_get_filename (notmuch_message_t *message)
{
    _notmuch_message_ensure_filename_list (message);

    if (message->filename_list == NULL)
        return NULL;

    if (message->filename_list->head == NULL ||
        message->filename_list->head->string == NULL)
    {
        INTERNAL_ERROR ("message with no filename");
    }

    return message->filename_list->head->string;
}

notmuch_filenames_t *
notmuch_message_get_filenames (notmuch_message_t *message)
{
    _notmuch_message_ensure_filename_list (message);

    return _notmuch_filenames_create (message, message->filename_list);
}

notmuch_bool_t
notmuch_message_get_flag (notmuch_message_t *message,
                          notmuch_message_flag_t flag)
{
    return message->flags & (1 << flag);
}

void
notmuch_message_set_flag (notmuch_message_t *message,
                          notmuch_message_flag_t flag, notmuch_bool_t enable)
{
    if (enable)
        message->flags |= (1 << flag);
    else
        message->flags &= ~(1 << flag);
}

time_t
notmuch_message_get_date (notmuch_message_t *message)
{
    std::string value;

    try {
        value = message->doc.get_value (NOTMUCH_VALUE_TIMESTAMP);
    } catch (Xapian::Error &error) {
        fprintf (stderr, "A Xapian exception occurred when reading date: %s\n",
                 error.get_msg().c_str());
        message->notmuch->exception_reported = TRUE;
        return 0;
    }

    return Xapian::sortable_unserialise (value);
}

notmuch_tags_t *
notmuch_message_get_tags (notmuch_message_t *message)
{
    notmuch_tags_t *tags;

    if (!message->tag_list)
        _notmuch_message_ensure_metadata (message);

    tags = _notmuch_tags_create (message, message->tag_list);
    /* _notmuch_tags_create steals the reference to the tag_list, but
     * in this case it's still used by the message, so we add an
     * *additional* talloc reference to the list.  As a result, it's
     * possible to modify the message tags (which talloc_unlink's the
     * current list from the message) while still iterating because
     * the iterator will keep the current list alive. */
    if (!talloc_reference (message, message->tag_list))
        return NULL;

    return tags;
}

const char *
notmuch_message_get_author (notmuch_message_t *message)
{
    return message->author;
}

void
notmuch_message_set_author (notmuch_message_t *message,
                            const char *author)
{
    if (message->author)
        talloc_free(message->author);
    message->author = talloc_strdup(message, author);
    return;
}

void
_notmuch_message_set_header_values (notmuch_message_t *message,
                                    const char *date,
                                    const char *from,
                                    const char *subject)
{
    time_t time_value;

    /* GMime really doesn't want to see a NULL date, so protect its
     * sensibilities. */
    if (date == NULL || *date == '\0')
        time_value = 0;
    else
        time_value = g_mime_utils_header_decode_date (date, NULL);

    message->doc.add_value (NOTMUCH_VALUE_TIMESTAMP,
                            Xapian::sortable_serialise (time_value));
    message->doc.add_value (NOTMUCH_VALUE_FROM, from);
    message->doc.add_value (NOTMUCH_VALUE_SUBJECT, subject);
}

/* Synchronize changes made to message->doc out into the database. */
void
_notmuch_message_sync (notmuch_message_t *message)
{
    Xapian::WritableDatabase *db;

    if (message->notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY)
        return;

    db = static_cast <Xapian::WritableDatabase *> (message->notmuch->xapian_db);
    db->replace_document (message->doc_id, message->doc);
}

/* Delete a message document from the database. */
notmuch_status_t
_notmuch_message_delete (notmuch_message_t *message)
{
    notmuch_status_t status;
    Xapian::WritableDatabase *db;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    db = static_cast <Xapian::WritableDatabase *> (message->notmuch->xapian_db);
    db->delete_document (message->doc_id);
    return NOTMUCH_STATUS_SUCCESS;
}

/* Ensure that 'message' is not holding any file object open. Future
 * calls to various functions will still automatically open the
 * message file as needed.
 */
void
_notmuch_message_close (notmuch_message_t *message)
{
    if (message->message_file) {
        notmuch_message_file_close (message->message_file);
        message->message_file = NULL;
    }
}

/* Add a name:value term to 'message', (the actual term will be
 * encoded by prefixing the value with a short prefix). See
 * NORMAL_PREFIX and BOOLEAN_PREFIX arrays for the mapping of term
 * names to prefix values.
 *
 * This change will not be reflected in the database until the next
 * call to _notmuch_message_sync. */
notmuch_private_status_t
_notmuch_message_add_term (notmuch_message_t *message,
                           const char *prefix_name,
                           const char *value)
{

    char *term;

    if (value == NULL)
        return NOTMUCH_PRIVATE_STATUS_NULL_POINTER;

    term = talloc_asprintf (message, "%s%s",
                            _find_prefix (prefix_name), value);

    if (strlen (term) > NOTMUCH_TERM_MAX)
        return NOTMUCH_PRIVATE_STATUS_TERM_TOO_LONG;

    message->doc.add_term (term, 0);

    talloc_free (term);

    _notmuch_message_invalidate_metadata (message, prefix_name);

    return NOTMUCH_PRIVATE_STATUS_SUCCESS;
}

/* Parse 'text' and add a term to 'message' for each parsed word. Each
 * term will be added both prefixed (if prefix_name is not NULL) and
 * also non-prefixed). */
notmuch_private_status_t
_notmuch_message_gen_terms (notmuch_message_t *message,
                            const char *prefix_name,
                            const char *text)
{
    Xapian::TermGenerator *term_gen = message->notmuch->term_gen;

    if (text == NULL)
        return NOTMUCH_PRIVATE_STATUS_NULL_POINTER;

    term_gen->set_document (message->doc);
    term_gen->set_termpos (message->termpos);

    if (prefix_name) {
        const char *prefix = _find_prefix (prefix_name);

        term_gen->index_text (text, 1, prefix);
        message->termpos = term_gen->get_termpos ();
    }

    term_gen->index_text (text);

    return NOTMUCH_PRIVATE_STATUS_SUCCESS;
}

/* Remove a name:value term from 'message', (the actual term will be
 * encoded by prefixing the value with a short prefix). See
 * NORMAL_PREFIX and BOOLEAN_PREFIX arrays for the mapping of term
 * names to prefix values.
 *
 * This change will not be reflected in the database until the next
 * call to _notmuch_message_sync. */
notmuch_private_status_t
_notmuch_message_remove_term (notmuch_message_t *message,
                              const char *prefix_name,
                              const char *value)
{
    char *term;

    if (value == NULL)
        return NOTMUCH_PRIVATE_STATUS_NULL_POINTER;

    term = talloc_asprintf (message, "%s%s",
                            _find_prefix (prefix_name), value);

    if (strlen (term) > NOTMUCH_TERM_MAX)
        return NOTMUCH_PRIVATE_STATUS_TERM_TOO_LONG;

    try {
        message->doc.remove_term (term);
    } catch (const Xapian::InvalidArgumentError) {
        /* We'll let the philosopher's try to wrestle with the
         * question of whether failing to remove that which was not
         * there in the first place is failure. For us, we'll silently
         * consider it all good. */
    }

    talloc_free (term);

    _notmuch_message_invalidate_metadata (message, prefix_name);

    return NOTMUCH_PRIVATE_STATUS_SUCCESS;
}

notmuch_status_t
notmuch_message_add_tag (notmuch_message_t *message, const char *tag)
{
    notmuch_private_status_t private_status;
    notmuch_status_t status;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    if (tag == NULL)
        return NOTMUCH_STATUS_NULL_POINTER;

    if (strlen (tag) > NOTMUCH_TAG_MAX)
        return NOTMUCH_STATUS_TAG_TOO_LONG;

    private_status = _notmuch_message_add_term (message, "tag", tag);
    if (private_status) {
        INTERNAL_ERROR ("_notmuch_message_add_term return unexpected value: %d\n",
                        private_status);
    }

    if (! message->frozen)
        _notmuch_message_sync (message);

    return NOTMUCH_STATUS_SUCCESS;
}

notmuch_status_t
notmuch_message_remove_tag (notmuch_message_t *message, const char *tag)
{
    notmuch_private_status_t private_status;
    notmuch_status_t status;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    if (tag == NULL)
        return NOTMUCH_STATUS_NULL_POINTER;

    if (strlen (tag) > NOTMUCH_TAG_MAX)
        return NOTMUCH_STATUS_TAG_TOO_LONG;

    private_status = _notmuch_message_remove_term (message, "tag", tag);
    if (private_status) {
        INTERNAL_ERROR ("_notmuch_message_remove_term return unexpected value: %d\n",
                        private_status);
    }

    if (! message->frozen)
        _notmuch_message_sync (message);

    return NOTMUCH_STATUS_SUCCESS;
}

/* Is the given filename within a maildir directory?
 *
 * Specifically, is the final directory component of 'filename' either
 * "cur" or "new". If so, return a pointer to that final directory
 * component within 'filename'. If not, return NULL.
 *
 * A non-NULL return value is guaranteed to be a valid string pointer
 * pointing to the characters "new/" or "cur/", (but not
 * NUL-terminated).
 */
static const char *
_filename_is_in_maildir (const char *filename)
{
    const char *slash, *dir = NULL;

    /* Find the last '/' separating directory from filename. */
    slash = strrchr (filename, '/');
    if (slash == NULL)
        return NULL;

    /* Jump back 4 characters to where the previous '/' will be if the
     * directory is named "cur" or "new". */
    if (slash - filename < 4)
        return NULL;

    slash -= 4;

    if (*slash != '/')
        return NULL;

    dir = slash + 1;

    if (STRNCMP_LITERAL (dir, "cur/") == 0 ||
        STRNCMP_LITERAL (dir, "new/") == 0)
    {
        return dir;
    }

    return NULL;
}

notmuch_status_t
notmuch_message_maildir_flags_to_tags (notmuch_message_t *message)
{
    const char *flags;
    notmuch_status_t status;
    notmuch_filenames_t *filenames;
    const char *filename, *dir;
    char *combined_flags = talloc_strdup (message, "");
    unsigned i;
    int seen_maildir_info = 0;

    for (filenames = notmuch_message_get_filenames (message);
         notmuch_filenames_valid (filenames);
         notmuch_filenames_move_to_next (filenames))
    {
        filename = notmuch_filenames_get (filenames);
        dir = _filename_is_in_maildir (filename);

        if (! dir)
            continue;

        flags = strstr (filename, ":2,");
        if (flags) {
            seen_maildir_info = 1;
            flags += 3;
            combined_flags = talloc_strdup_append (combined_flags, flags);
        } else if (STRNCMP_LITERAL (dir, "new/") == 0) {
            /* Messages are delivered to new/ with no "info" part, but
             * they effectively have default maildir flags.  According
             * to the spec, we should ignore the info part for
             * messages in new/, but some MUAs (mutt) can set maildir
             * flags on messages in new/, so we're liberal in what we
             * accept. */
            seen_maildir_info = 1;
        }
    }

    /* If none of the filenames have any maildir info field (not even
     * an empty info with no flags set) then there's no information to
     * go on, so do nothing. */
    if (! seen_maildir_info)
        return NOTMUCH_STATUS_SUCCESS;

    status = notmuch_message_freeze (message);
    if (status)
        return status;

    for (i = 0; i < ARRAY_SIZE(flag2tag); i++) {
        if ((strchr (combined_flags, flag2tag[i].flag) != NULL)
            ^ 
            flag2tag[i].inverse)
        {
            status = notmuch_message_add_tag (message, flag2tag[i].tag);
        } else {
            status = notmuch_message_remove_tag (message, flag2tag[i].tag);
        }
        if (status)
            return status;
    }
    status = notmuch_message_thaw (message);

    talloc_free (combined_flags);

    return status;
}

/* From the set of tags on 'message' and the flag2tag table, compute a
 * set of maildir-flag actions to be taken, (flags that should be
 * either set or cleared).
 *
 * The result is returned as two talloced strings: to_set, and to_clear
 */
static void
_get_maildir_flag_actions (notmuch_message_t *message,
                           char **to_set_ret,
                           char **to_clear_ret)
{
    char *to_set, *to_clear;
    notmuch_tags_t *tags;
    const char *tag;
    unsigned i;

    to_set = talloc_strdup (message, "");
    to_clear = talloc_strdup (message, "");

    /* First, find flags for all set tags. */
    for (tags = notmuch_message_get_tags (message);
         notmuch_tags_valid (tags);
         notmuch_tags_move_to_next (tags))
    {
        tag = notmuch_tags_get (tags);

        for (i = 0; i < ARRAY_SIZE (flag2tag); i++) {
            if (strcmp (tag, flag2tag[i].tag) == 0) {
                if (flag2tag[i].inverse)
                    to_clear = talloc_asprintf_append (to_clear,
                                                       "%c",
                                                       flag2tag[i].flag);
                else
                    to_set = talloc_asprintf_append (to_set,
                                                     "%c",
                                                     flag2tag[i].flag);
            }
        }
    }

    /* Then, find the flags for all tags not present. */
    for (i = 0; i < ARRAY_SIZE (flag2tag); i++) {
        if (flag2tag[i].inverse) {
            if (strchr (to_clear, flag2tag[i].flag) == NULL)
                to_set = talloc_asprintf_append (to_set, "%c", flag2tag[i].flag);
        } else {
            if (strchr (to_set, flag2tag[i].flag) == NULL)
                to_clear = talloc_asprintf_append (to_clear, "%c", flag2tag[i].flag);
        }
    }

    *to_set_ret = to_set;
    *to_clear_ret = to_clear;
}

/* Given 'filename' and a set of maildir flags to set and to clear,
 * compute the new maildir filename.
 *
 * If the existing filename is in the directory "new", the new
 * filename will be in the directory "cur", except for the case when
 * no flags are changed and the existing filename does not contain
 * maildir info (starting with ",2:").
 *
 * After a sequence of ":2," in the filename, any subsequent
 * single-character flags will be added or removed according to the
 * characters in flags_to_set and flags_to_clear. Any existing flags
 * not mentioned in either string will remain. The final list of flags
 * will be in ASCII order.
 *
 * If the original flags seem invalid, (repeated characters or
 * non-ASCII ordering of flags), this function will return NULL
 * (meaning that renaming would not be safe and should not occur).
 */
static char*
_new_maildir_filename (void *ctx,
                       const char *filename,
                       const char *flags_to_set,
                       const char *flags_to_clear)
{
    const char *info, *flags;
    unsigned int flag, last_flag;
    char *filename_new, *dir;
    char flag_map[128];
    int flags_in_map = 0;
    notmuch_bool_t flags_changed = FALSE;
    unsigned int i;
    char *s;

    memset (flag_map, 0, sizeof (flag_map));

    info = strstr (filename, ":2,");

    if (info == NULL) {
        info = filename + strlen(filename);
    } else {
        /* Loop through existing flags in filename. */
        for (flags = info + 3, last_flag = 0;
             *flags;
             last_flag = flag, flags++)
        {
            flag = *flags;

            /* Original flags not in ASCII order. Abort. */
            if (flag < last_flag)
                return NULL;

            /* Non-ASCII flag. Abort. */
            if (flag > sizeof(flag_map) - 1)
                return NULL;

            /* Repeated flag value. Abort. */
            if (flag_map[flag])
                return NULL;

            flag_map[flag] = 1;
            flags_in_map++;
        }
    }

    /* Then set and clear our flags from tags. */
    for (flags = flags_to_set; *flags; flags++) {
        flag = *flags;
        if (flag_map[flag] == 0) {
            flag_map[flag] = 1;
            flags_in_map++;
            flags_changed = TRUE;
        }
    }

    for (flags = flags_to_clear; *flags; flags++) {
        flag = *flags;
        if (flag_map[flag]) {
            flag_map[flag] = 0;
            flags_in_map--;
            flags_changed = TRUE;
        }
    }

    /* Messages in new/ without maildir info can be kept in new/ if no
     * flags have changed. */
    dir = (char *) _filename_is_in_maildir (filename);
    if (dir && STRNCMP_LITERAL (dir, "new/") == 0 && !*info && !flags_changed)
        return talloc_strdup (ctx, filename);

    filename_new = (char *) talloc_size (ctx,
                                         info - filename +
                                         strlen (":2,") + flags_in_map + 1);
    if (unlikely (filename_new == NULL))
        return NULL;

    strncpy (filename_new, filename, info - filename);
    filename_new[info - filename] = '\0';

    strcat (filename_new, ":2,");

    s = filename_new + strlen (filename_new);
    for (i = 0; i < sizeof (flag_map); i++)
    {
        if (flag_map[i]) {
            *s = i;
            s++;
        }
    }
    *s = '\0';

    /* If message is in new/ move it under cur/. */
    dir = (char *) _filename_is_in_maildir (filename_new);
    if (dir && STRNCMP_LITERAL (dir, "new/") == 0)
        memcpy (dir, "cur/", 4);

    return filename_new;
}

notmuch_status_t
notmuch_message_tags_to_maildir_flags (notmuch_message_t *message)
{
    notmuch_filenames_t *filenames;
    const char *filename;
    char *filename_new;
    char *to_set, *to_clear;
    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;

    _get_maildir_flag_actions (message, &to_set, &to_clear);

    for (filenames = notmuch_message_get_filenames (message);
         notmuch_filenames_valid (filenames);
         notmuch_filenames_move_to_next (filenames))
    {
        filename = notmuch_filenames_get (filenames);

        if (! _filename_is_in_maildir (filename))
            continue;

        filename_new = _new_maildir_filename (message, filename,
                                              to_set, to_clear);
        if (filename_new == NULL)
            continue;

        if (strcmp (filename, filename_new)) {
            int err;
            notmuch_status_t new_status;

            err = rename (filename, filename_new);
            if (err)
                continue;

            new_status = _notmuch_message_remove_filename (message,
                                                           filename);
            /* Hold on to only the first error. */
            if (! status && new_status
                && new_status != NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID) {
                status = new_status;
                continue;
            }

            new_status = _notmuch_message_add_filename (message,
                                                        filename_new);
            /* Hold on to only the first error. */
            if (! status && new_status) {
                status = new_status;
                continue;
            }

            _notmuch_message_sync (message);
        }

        talloc_free (filename_new);
    }

    talloc_free (to_set);
    talloc_free (to_clear);

    return NOTMUCH_STATUS_SUCCESS;
}

notmuch_status_t
notmuch_message_remove_all_tags (notmuch_message_t *message)
{
    notmuch_private_status_t private_status;
    notmuch_status_t status;
    notmuch_tags_t *tags;
    const char *tag;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    for (tags = notmuch_message_get_tags (message);
         notmuch_tags_valid (tags);
         notmuch_tags_move_to_next (tags))
    {
        tag = notmuch_tags_get (tags);

        private_status = _notmuch_message_remove_term (message, "tag", tag);
        if (private_status) {
            INTERNAL_ERROR ("_notmuch_message_remove_term return unexpected value: %d\n",
                            private_status);
        }
    }

    if (! message->frozen)
        _notmuch_message_sync (message);

    talloc_free (tags);
    return NOTMUCH_STATUS_SUCCESS;
}

notmuch_status_t
notmuch_message_freeze (notmuch_message_t *message)
{
    notmuch_status_t status;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    message->frozen++;

    return NOTMUCH_STATUS_SUCCESS;
}

notmuch_status_t
notmuch_message_thaw (notmuch_message_t *message)
{
    notmuch_status_t status;

    status = _notmuch_database_ensure_writable (message->notmuch);
    if (status)
        return status;

    if (message->frozen > 0) {
        message->frozen--;
        if (message->frozen == 0)
            _notmuch_message_sync (message);
        return NOTMUCH_STATUS_SUCCESS;
    } else {
        return NOTMUCH_STATUS_UNBALANCED_FREEZE_THAW;
    }
}

void
notmuch_message_destroy (notmuch_message_t *message)
{
    talloc_free (message);
}