Import notmuch_0.27.orig.tar.gz

[dgit import orig notmuch_0.27.orig.tar.gz]

1 files changed, 2043 insertions, 0 deletions

diff --git a/lib/database.cc b/lib/database.cc
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+/* database.cc - The database interfaces of the notmuch mail library
+ *
+ * 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 https://www.gnu.org/licenses/ .
+ *
+ * Author: Carl Worth <cworth@cworth.org>
+ */
+
+#include "database-private.h"
+#include "parse-time-vrp.h"
+#include "query-fp.h"
+#include "thread-fp.h"
+#include "regexp-fields.h"
+#include "string-util.h"
+
+#include <iostream>
+
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <signal.h>
+#include <ftw.h>
+
+#include <glib.h> /* g_free, GPtrArray, GHashTable */
+#include <glib-object.h> /* g_type_init */
+
+#include <gmime/gmime.h> /* g_mime_init */
+
+using namespace std;
+
+#define ARRAY_SIZE(arr) (sizeof (arr) / sizeof (arr[0]))
+
+typedef struct {
+    const char *name;
+    const char *prefix;
+    notmuch_field_flag_t flags;
+} prefix_t;
+
+#define NOTMUCH_DATABASE_VERSION 3
+
+#define STRINGIFY(s) _SUB_STRINGIFY(s)
+#define _SUB_STRINGIFY(s) #s
+
+#if HAVE_XAPIAN_DB_RETRY_LOCK
+#define DB_ACTION (Xapian::DB_CREATE_OR_OPEN | Xapian::DB_RETRY_LOCK)
+#else
+#define DB_ACTION Xapian::DB_CREATE_OR_OPEN
+#endif
+
+/* Here's the current schema for our database (for NOTMUCH_DATABASE_VERSION):
+ *
+ * We currently have three different types of documents (mail, ghost,
+ * and directory) and also some metadata.
+ *
+ * Mail document
+ * -------------
+ * A mail document is associated with a particular email message. It
+ * is stored in one or more files on disk (though only one has its
+ * content indexed) and is uniquely identified  by its "id" field
+ * (which is generally the message ID). It is indexed with the
+ * following prefixed terms which the database uses to construct
+ * threads, etc.:
+ *
+ *    Single terms of given prefix:
+ *
+ *	type:	mail
+ *
+ *	id:	Unique ID of mail. This is from the Message-ID header
+ *		if present and not too long (see NOTMUCH_MESSAGE_ID_MAX).
+ *		If it's present and too long, then we use
+ *		"notmuch-sha1-<sha1_sum_of_message_id>".
+ *              If this header is not present, we use
+ *		"notmuch-sha1-<sha1_sum_of_entire_file>".
+ *
+ *	thread:	The ID of the thread to which the mail belongs
+ *
+ *	replyto: The ID from the In-Reply-To header of the mail (if any).
+ *
+ *    Multiple terms of given prefix:
+ *
+ *	reference: All message IDs from In-Reply-To and References
+ *		   headers in the message.
+ *
+ *	tag:	   Any tags associated with this message by the user.
+ *
+ *	file-direntry:  A colon-separated pair of values
+ *		        (INTEGER:STRING), where INTEGER is the
+ *		        document ID of a directory document, and
+ *		        STRING is the name of a file within that
+ *		        directory for this mail message.
+ *
+ *      property:       Has a property with key=value
+ *                 FIXME: if no = is present, should match on any value
+ *
+ *    A mail document also has four values:
+ *
+ *	TIMESTAMP:	The time_t value corresponding to the message's
+ *			Date header.
+ *
+ *	MESSAGE_ID:	The unique ID of the mail mess (see "id" above)
+ *
+ *	FROM:		The value of the "From" header
+ *
+ *	SUBJECT:	The value of the "Subject" header
+ *
+ *	LAST_MOD:	The revision number as of the last tag or
+ *			filename change.
+ *
+ * In addition, terms from the content of the message are added with
+ * "from", "to", "attachment", and "subject" prefixes for use by the
+ * user in searching. Similarly, terms from the path of the mail
+ * message are added with "folder" and "path" prefixes. But the
+ * database doesn't really care itself about any of these.
+ *
+ * The data portion of a mail document is empty.
+ *
+ * Ghost mail document [if NOTMUCH_FEATURE_GHOSTS]
+ * -----------------------------------------------
+ * A ghost mail document is like a mail document, but where we don't
+ * have the message content.  These are used to track thread reference
+ * information for messages we haven't received.
+ *
+ * A ghost mail document has type: ghost; id and thread fields that
+ * are identical to the mail document fields; and a MESSAGE_ID value.
+ *
+ * Directory document
+ * ------------------
+ * A directory document is used by a client of the notmuch library to
+ * maintain data necessary to allow for efficient polling of mail
+ * directories.
+ *
+ * All directory documents contain one term:
+ *
+ *	directory:	The directory path (relative to the database path)
+ *			Or the SHA1 sum of the directory path (if the
+ *			path itself is too long to fit in a Xapian
+ *			term).
+ *
+ * And all directory documents for directories other than top-level
+ * directories also contain the following term:
+ *
+ *	directory-direntry: A colon-separated pair of values
+ *		            (INTEGER:STRING), where INTEGER is the
+ *		            document ID of the parent directory
+ *		            document, and STRING is the name of this
+ *		            directory within that parent.
+ *
+ * All directory documents have a single value:
+ *
+ *	TIMESTAMP:	The mtime of the directory (at last scan)
+ *
+ * The data portion of a directory document contains the path of the
+ * directory (relative to the database path).
+ *
+ * Database metadata
+ * -----------------
+ * Xapian allows us to store arbitrary name-value pairs as
+ * "metadata". We currently use the following metadata names with the
+ * given meanings:
+ *
+ *	version		The database schema version, (which is distinct
+ *			from both the notmuch package version (see
+ *			notmuch --version) and the libnotmuch library
+ *			version. The version is stored as an base-10
+ *			ASCII integer. The initial database version
+ *			was 1, (though a schema existed before that
+ *			were no "version" database value existed at
+ *			all). Successive versions are allocated as
+ *			changes are made to the database (such as by
+ *			indexing new fields).
+ *
+ *	features	The set of features supported by this
+ *			database. This consists of a set of
+ *			'\n'-separated lines, where each is a feature
+ *			name, a '\t', and compatibility flags.  If the
+ *			compatibility flags contain 'w', then the
+ *			opener must support this feature to safely
+ *			write this database.  If the compatibility
+ *			flags contain 'r', then the opener must
+ *			support this feature to read this database.
+ *			Introduced in database version 3.
+ *
+ *	last_thread_id	The last thread ID generated. This is stored
+ *			as a 16-byte hexadecimal ASCII representation
+ *			of a 64-bit unsigned integer. The first ID
+ *			generated is 1 and the value will be
+ *			incremented for each thread ID.
+ *
+ *	C*		metadata keys starting with C indicate
+ *			configuration data. It can be managed with the
+ *			n_database_*config* API.  There is a convention
+ *			of hierarchical keys separated by '.' (e.g.
+ *			query.notmuch stores the value for the named
+ *			query 'notmuch'), but it is not enforced by the
+ *			API.
+ *
+ * Obsolete metadata
+ * -----------------
+ *
+ * If ! NOTMUCH_FEATURE_GHOSTS, there are no ghost mail documents.
+ * Instead, the database has the following additional database
+ * metadata:
+ *
+ *	thread_id_*	A pre-allocated thread ID for a particular
+ *			message. This is actually an arbitrarily large
+ *			family of metadata name. Any particular name is
+ *			formed by concatenating "thread_id_" with a message
+ *			ID (or the SHA1 sum of a message ID if it is very
+ *			long---see description of 'id' in the mail
+ *			document). The value stored is a thread ID.
+ *
+ *			These thread ID metadata values are stored
+ *			whenever a message references a parent message
+ *			that does not yet exist in the database. A
+ *			thread ID will be allocated and stored, and if
+ *			the message is later added, the stored thread
+ *			ID will be used (and the metadata value will
+ *			be cleared).
+ *
+ *			Even before a message is added, it's
+ *			pre-allocated thread ID is useful so that all
+ *			descendant messages that reference this common
+ *			parent can be recognized as belonging to the
+ *			same thread.
+ */
+
+/* With these prefix values we follow the conventions published here:
+ *
+ * https://xapian.org/docs/omega/termprefixes.html
+ *
+ * as much as makes sense. Note that I took some liberty in matching
+ * the reserved prefix values to notmuch concepts, (for example, 'G'
+ * is documented as "newsGroup (or similar entity - e.g. a web forum
+ * name)", for which I think the thread is the closest analogue in
+ * notmuch. This in spite of the fact that we will eventually be
+ * storing mailing-list messages where 'G' for "mailing list name"
+ * might be even a closer analogue. I'm treating the single-character
+ * prefixes preferentially for core notmuch concepts (which will be
+ * nearly universal to all mail messages).
+ */
+
+static const
+prefix_t prefix_table[] = {
+    /* name			term prefix	flags */
+    { "type",			"T",		NOTMUCH_FIELD_NO_FLAGS },
+    { "reference",		"XREFERENCE",	NOTMUCH_FIELD_NO_FLAGS },
+    { "replyto",		"XREPLYTO",	NOTMUCH_FIELD_NO_FLAGS },
+    { "directory",		"XDIRECTORY",	NOTMUCH_FIELD_NO_FLAGS },
+    { "file-direntry",		"XFDIRENTRY",	NOTMUCH_FIELD_NO_FLAGS },
+    { "directory-direntry",	"XDDIRENTRY",	NOTMUCH_FIELD_NO_FLAGS },
+    { "thread",			"G",		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+    { "tag",			"K",		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+    { "is",			"K",		NOTMUCH_FIELD_EXTERNAL |
+					        NOTMUCH_FIELD_PROCESSOR },
+    { "id",			"Q",		NOTMUCH_FIELD_EXTERNAL },
+    { "mid",			"Q",		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+    { "path",			"P",		NOTMUCH_FIELD_EXTERNAL|
+						NOTMUCH_FIELD_PROCESSOR },
+    { "property",		"XPROPERTY",	NOTMUCH_FIELD_EXTERNAL },
+    /*
+     * Unconditionally add ':' to reduce potential ambiguity with
+     * overlapping prefixes and/or terms that start with capital
+     * letters. See Xapian document termprefixes.html for related
+     * discussion.
+     */
+    { "folder",			"XFOLDER:",	NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+#if HAVE_XAPIAN_FIELD_PROCESSOR
+    { "date",			NULL,		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+    { "query",			NULL,		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROCESSOR },
+#endif
+    { "from",			"XFROM",	NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROBABILISTIC |
+						NOTMUCH_FIELD_PROCESSOR },
+    { "to",			"XTO",		NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROBABILISTIC },
+    { "attachment",		"XATTACHMENT",	NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROBABILISTIC },
+    { "mimetype",		"XMIMETYPE",	NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROBABILISTIC },
+    { "subject",		"XSUBJECT",	NOTMUCH_FIELD_EXTERNAL |
+						NOTMUCH_FIELD_PROBABILISTIC |
+						NOTMUCH_FIELD_PROCESSOR},
+};
+
+static void
+_setup_query_field_default (const prefix_t *prefix, notmuch_database_t *notmuch)
+{
+    if (prefix->flags & NOTMUCH_FIELD_PROBABILISTIC)
+	notmuch->query_parser->add_prefix (prefix->name, prefix->prefix);
+    else
+	notmuch->query_parser->add_boolean_prefix (prefix->name, prefix->prefix);
+}
+
+#if HAVE_XAPIAN_FIELD_PROCESSOR
+static void
+_setup_query_field (const prefix_t *prefix, notmuch_database_t *notmuch)
+{
+    if (prefix->flags & NOTMUCH_FIELD_PROCESSOR) {
+	Xapian::FieldProcessor *fp;
+
+	if (STRNCMP_LITERAL (prefix->name, "date") == 0)
+	    fp = (new DateFieldProcessor())->release ();
+	else if (STRNCMP_LITERAL(prefix->name, "query") == 0)
+	    fp = (new QueryFieldProcessor (*notmuch->query_parser, notmuch))->release ();
+	else if (STRNCMP_LITERAL(prefix->name, "thread") == 0)
+	    fp = (new ThreadFieldProcessor (*notmuch->query_parser, notmuch))->release ();
+	else
+	    fp = (new RegexpFieldProcessor (prefix->name, prefix->flags,
+					    *notmuch->query_parser, notmuch))->release ();
+
+	/* we treat all field-processor fields as boolean in order to get the raw input */
+	notmuch->query_parser->add_boolean_prefix (prefix->name, fp);
+    } else {
+	_setup_query_field_default (prefix, notmuch);
+    }
+}
+#else
+static inline void
+_setup_query_field (const prefix_t *prefix, notmuch_database_t *notmuch)
+{
+    _setup_query_field_default (prefix, notmuch);
+}
+#endif
+
+const char *
+_find_prefix (const char *name)
+{
+    unsigned int i;
+
+    for (i = 0; i < ARRAY_SIZE (prefix_table); i++) {
+	if (strcmp (name, prefix_table[i].name) == 0)
+	    return prefix_table[i].prefix;
+    }
+
+    INTERNAL_ERROR ("No prefix exists for '%s'\n", name);
+
+    return "";
+}
+
+static const struct {
+    /* NOTMUCH_FEATURE_* value. */
+    _notmuch_features value;
+    /* Feature name as it appears in the database.  This name should
+     * be appropriate for displaying to the user if an older version
+     * of notmuch doesn't support this feature. */
+    const char *name;
+    /* Compatibility flags when this feature is declared. */
+    const char *flags;
+} feature_names[] = {
+    { NOTMUCH_FEATURE_FILE_TERMS,
+      "multiple paths per message", "rw" },
+    { NOTMUCH_FEATURE_DIRECTORY_DOCS,
+      "relative directory paths", "rw" },
+    /* Header values are not required for reading a database because a
+     * reader can just refer to the message file. */
+    { NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES,
+      "from/subject/message-ID in database", "w" },
+    { NOTMUCH_FEATURE_BOOL_FOLDER,
+      "exact folder:/path: search", "rw" },
+    { NOTMUCH_FEATURE_GHOSTS,
+      "mail documents for missing messages", "w"},
+    /* Knowledge of the index mime-types are not required for reading
+     * a database because a reader will just be unable to query
+     * them. */
+    { NOTMUCH_FEATURE_INDEXED_MIMETYPES,
+      "indexed MIME types", "w"},
+    { NOTMUCH_FEATURE_LAST_MOD,
+      "modification tracking", "w"},
+};
+
+const char *
+notmuch_status_to_string (notmuch_status_t status)
+{
+    switch (status) {
+    case NOTMUCH_STATUS_SUCCESS:
+	return "No error occurred";
+    case NOTMUCH_STATUS_OUT_OF_MEMORY:
+	return "Out of memory";
+    case NOTMUCH_STATUS_READ_ONLY_DATABASE:
+	return "Attempt to write to a read-only database";
+    case NOTMUCH_STATUS_XAPIAN_EXCEPTION:
+	return "A Xapian exception occurred";
+    case NOTMUCH_STATUS_FILE_ERROR:
+	return "Something went wrong trying to read or write a file";
+    case NOTMUCH_STATUS_FILE_NOT_EMAIL:
+	return "File is not an email";
+    case NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID:
+	return "Message ID is identical to a message in database";
+    case NOTMUCH_STATUS_NULL_POINTER:
+	return "Erroneous NULL pointer";
+    case NOTMUCH_STATUS_TAG_TOO_LONG:
+	return "Tag value is too long (exceeds NOTMUCH_TAG_MAX)";
+    case NOTMUCH_STATUS_UNBALANCED_FREEZE_THAW:
+	return "Unbalanced number of calls to notmuch_message_freeze/thaw";
+    case NOTMUCH_STATUS_UNBALANCED_ATOMIC:
+	return "Unbalanced number of calls to notmuch_database_begin_atomic/end_atomic";
+    case NOTMUCH_STATUS_UNSUPPORTED_OPERATION:
+	return "Unsupported operation";
+    case NOTMUCH_STATUS_UPGRADE_REQUIRED:
+	return "Operation requires a database upgrade";
+    case NOTMUCH_STATUS_PATH_ERROR:
+	return "Path supplied is illegal for this function";
+    case NOTMUCH_STATUS_MALFORMED_CRYPTO_PROTOCOL:
+	return "Crypto protocol missing, malformed, or unintelligible";
+    case NOTMUCH_STATUS_FAILED_CRYPTO_CONTEXT_CREATION:
+	return "Crypto engine initialization failure";
+    case NOTMUCH_STATUS_UNKNOWN_CRYPTO_PROTOCOL:
+	return "Unknown crypto protocol";
+    default:
+    case NOTMUCH_STATUS_LAST_STATUS:
+	return "Unknown error status value";
+    }
+}
+
+void
+_notmuch_database_log (notmuch_database_t *notmuch,
+		      const char *format,
+		      ...)
+{
+    va_list va_args;
+
+    va_start (va_args, format);
+
+    if (notmuch->status_string)
+	talloc_free (notmuch->status_string);
+
+    notmuch->status_string = talloc_vasprintf (notmuch, format, va_args);
+    va_end (va_args);
+}
+
+void
+_notmuch_database_log_append (notmuch_database_t *notmuch,
+		      const char *format,
+		      ...)
+{
+    va_list va_args;
+
+    va_start (va_args, format);
+
+    if (notmuch->status_string)
+	notmuch->status_string = talloc_vasprintf_append (notmuch->status_string, format, va_args);
+    else
+	notmuch->status_string = talloc_vasprintf (notmuch, format, va_args);
+
+    va_end (va_args);
+}
+
+static void
+find_doc_ids_for_term (notmuch_database_t *notmuch,
+		       const char *term,
+		       Xapian::PostingIterator *begin,
+		       Xapian::PostingIterator *end)
+{
+    *begin = notmuch->xapian_db->postlist_begin (term);
+
+    *end = notmuch->xapian_db->postlist_end (term);
+}
+
+void
+_notmuch_database_find_doc_ids (notmuch_database_t *notmuch,
+				const char *prefix_name,
+				const char *value,
+				Xapian::PostingIterator *begin,
+				Xapian::PostingIterator *end)
+{
+    char *term;
+
+    term = talloc_asprintf (notmuch, "%s%s",
+			    _find_prefix (prefix_name), value);
+
+    find_doc_ids_for_term (notmuch, term, begin, end);
+
+    talloc_free (term);
+}
+
+notmuch_private_status_t
+_notmuch_database_find_unique_doc_id (notmuch_database_t *notmuch,
+				      const char *prefix_name,
+				      const char *value,
+				      unsigned int *doc_id)
+{
+    Xapian::PostingIterator i, end;
+
+    _notmuch_database_find_doc_ids (notmuch, prefix_name, value, &i, &end);
+
+    if (i == end) {
+	*doc_id = 0;
+	return NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND;
+    }
+
+    *doc_id = *i;
+
+#if DEBUG_DATABASE_SANITY
+    i++;
+
+    if (i != end)
+	INTERNAL_ERROR ("Term %s:%s is not unique as expected.\n",
+			prefix_name, value);
+#endif
+
+    return NOTMUCH_PRIVATE_STATUS_SUCCESS;
+}
+
+static Xapian::Document
+find_document_for_doc_id (notmuch_database_t *notmuch, unsigned doc_id)
+{
+    return notmuch->xapian_db->get_document (doc_id);
+}
+
+/* Generate a compressed version of 'message_id' of the form:
+ *
+ *	notmuch-sha1-<sha1_sum_of_message_id>
+ */
+char *
+_notmuch_message_id_compressed (void *ctx, const char *message_id)
+{
+    char *sha1, *compressed;
+
+    sha1 = _notmuch_sha1_of_string (message_id);
+
+    compressed = talloc_asprintf (ctx, "notmuch-sha1-%s", sha1);
+    free (sha1);
+
+    return compressed;
+}
+
+notmuch_status_t
+notmuch_database_find_message (notmuch_database_t *notmuch,
+			       const char *message_id,
+			       notmuch_message_t **message_ret)
+{
+    notmuch_private_status_t status;
+    unsigned int doc_id;
+
+    if (message_ret == NULL)
+	return NOTMUCH_STATUS_NULL_POINTER;
+
+    if (strlen (message_id) > NOTMUCH_MESSAGE_ID_MAX)
+	message_id = _notmuch_message_id_compressed (notmuch, message_id);
+
+    try {
+	status = _notmuch_database_find_unique_doc_id (notmuch, "id",
+						       message_id, &doc_id);
+
+	if (status == NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND)
+	    *message_ret = NULL;
+	else {
+	    *message_ret = _notmuch_message_create (notmuch, notmuch, doc_id,
+						    NULL);
+	    if (*message_ret == NULL)
+		return NOTMUCH_STATUS_OUT_OF_MEMORY;
+	}
+
+	return NOTMUCH_STATUS_SUCCESS;
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "A Xapian exception occurred finding message: %s.\n",
+		 error.get_msg().c_str());
+	notmuch->exception_reported = true;
+	*message_ret = NULL;
+	return NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+}
+
+notmuch_status_t
+notmuch_database_create (const char *path, notmuch_database_t **database)
+{
+    char *status_string = NULL;
+    notmuch_status_t status;
+
+    status = notmuch_database_create_verbose (path, database,
+					      &status_string);
+
+    if (status_string) {
+	fputs (status_string, stderr);
+	free (status_string);
+    }
+
+    return status;
+}
+
+notmuch_status_t
+notmuch_database_create_verbose (const char *path,
+				 notmuch_database_t **database,
+				 char **status_string)
+{
+    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;
+    notmuch_database_t *notmuch = NULL;
+    char *notmuch_path = NULL;
+    char *message = NULL;
+    struct stat st;
+    int err;
+
+    if (path == NULL) {
+	message = strdup ("Error: Cannot create a database for a NULL path.\n");
+	status = NOTMUCH_STATUS_NULL_POINTER;
+	goto DONE;
+    }
+
+    if (path[0] != '/') {
+	message = strdup ("Error: Database path must be absolute.\n");
+	status = NOTMUCH_STATUS_PATH_ERROR;
+	goto DONE;
+    }
+
+    err = stat (path, &st);
+    if (err) {
+	IGNORE_RESULT (asprintf (&message, "Error: Cannot create database at %s: %s.\n",
+				path, strerror (errno)));
+	status = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    if (! S_ISDIR (st.st_mode)) {
+	IGNORE_RESULT (asprintf (&message, "Error: Cannot create database at %s: "
+				 "Not a directory.\n",
+				 path));
+	status = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    notmuch_path = talloc_asprintf (NULL, "%s/%s", path, ".notmuch");
+
+    err = mkdir (notmuch_path, 0755);
+
+    if (err) {
+	IGNORE_RESULT (asprintf (&message, "Error: Cannot create directory %s: %s.\n",
+				 notmuch_path, strerror (errno)));
+	status = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    status = notmuch_database_open_verbose (path,
+					    NOTMUCH_DATABASE_MODE_READ_WRITE,
+					    &notmuch, &message);
+    if (status)
+	goto DONE;
+
+    /* Upgrade doesn't add these feature to existing databases, but
+     * new databases have them. */
+    notmuch->features |= NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES;
+    notmuch->features |= NOTMUCH_FEATURE_INDEXED_MIMETYPES;
+
+    status = notmuch_database_upgrade (notmuch, NULL, NULL);
+    if (status) {
+	notmuch_database_close(notmuch);
+	notmuch = NULL;
+    }
+
+  DONE:
+    if (notmuch_path)
+	talloc_free (notmuch_path);
+
+    if (message) {
+	if (status_string)
+	    *status_string = message;
+	else
+	    free (message);
+    }
+    if (database)
+	*database = notmuch;
+    else
+	talloc_free (notmuch);
+    return status;
+}
+
+notmuch_status_t
+_notmuch_database_ensure_writable (notmuch_database_t *notmuch)
+{
+    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY) {
+	_notmuch_database_log (notmuch, "Cannot write to a read-only database.\n");
+	return NOTMUCH_STATUS_READ_ONLY_DATABASE;
+    }
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+/* Allocate a revision number for the next change. */
+unsigned long
+_notmuch_database_new_revision (notmuch_database_t *notmuch)
+{
+    unsigned long new_revision = notmuch->revision + 1;
+
+    /* If we're in an atomic section, hold off on updating the
+     * committed revision number until we commit the atomic section.
+     */
+    if (notmuch->atomic_nesting)
+	notmuch->atomic_dirty = true;
+    else
+	notmuch->revision = new_revision;
+
+    return new_revision;
+}
+
+/* Parse a database features string from the given database version.
+ * Returns the feature bit set.
+ *
+ * For version < 3, this ignores the features string and returns a
+ * hard-coded set of features.
+ *
+ * If there are unrecognized features that are required to open the
+ * database in mode (which should be 'r' or 'w'), return a
+ * comma-separated list of unrecognized but required features in
+ * *incompat_out suitable for presenting to the user.  *incompat_out
+ * will be allocated from ctx.
+ */
+static _notmuch_features
+_parse_features (const void *ctx, const char *features, unsigned int version,
+		 char mode, char **incompat_out)
+{
+    _notmuch_features res = static_cast<_notmuch_features>(0);
+    unsigned int namelen, i;
+    size_t llen = 0;
+    const char *flags;
+
+    /* Prior to database version 3, features were implied by the
+     * version number. */
+    if (version == 0)
+	return NOTMUCH_FEATURES_V0;
+    else if (version == 1)
+	return NOTMUCH_FEATURES_V1;
+    else if (version == 2)
+	return NOTMUCH_FEATURES_V2;
+
+    /* Parse the features string */
+    while ((features = strtok_len_c (features + llen, "\n", &llen)) != NULL) {
+	flags = strchr (features, '\t');
+	if (! flags || flags > features + llen)
+	    continue;
+	namelen = flags - features;
+
+	for (i = 0; i < ARRAY_SIZE (feature_names); ++i) {
+	    if (strlen (feature_names[i].name) == namelen &&
+		strncmp (feature_names[i].name, features, namelen) == 0) {
+		res |= feature_names[i].value;
+		break;
+	    }
+	}
+
+	if (i == ARRAY_SIZE (feature_names) && incompat_out) {
+	    /* Unrecognized feature */
+	    const char *have = strchr (flags, mode);
+	    if (have && have < features + llen) {
+		/* This feature is required to access this database in
+		 * 'mode', but we don't understand it. */
+		if (! *incompat_out)
+		    *incompat_out = talloc_strdup (ctx, "");
+		*incompat_out = talloc_asprintf_append_buffer (
+		    *incompat_out, "%s%.*s", **incompat_out ? ", " : "",
+		    namelen, features);
+	    }
+	}
+    }
+
+    return res;
+}
+
+static char *
+_print_features (const void *ctx, unsigned int features)
+{
+    unsigned int i;
+    char *res = talloc_strdup (ctx, "");
+
+    for (i = 0; i < ARRAY_SIZE (feature_names); ++i)
+	if (features & feature_names[i].value)
+	    res = talloc_asprintf_append_buffer (
+		res, "%s\t%s\n", feature_names[i].name, feature_names[i].flags);
+
+    return res;
+}
+
+notmuch_status_t
+notmuch_database_open (const char *path,
+		       notmuch_database_mode_t mode,
+		       notmuch_database_t **database)
+{
+    char *status_string = NULL;
+    notmuch_status_t status;
+
+    status = notmuch_database_open_verbose (path, mode, database,
+					   &status_string);
+
+    if (status_string) {
+	fputs (status_string, stderr);
+	free (status_string);
+    }
+
+    return status;
+}
+
+notmuch_status_t
+notmuch_database_open_verbose (const char *path,
+			       notmuch_database_mode_t mode,
+			       notmuch_database_t **database,
+			       char **status_string)
+{
+    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;
+    void *local = talloc_new (NULL);
+    notmuch_database_t *notmuch = NULL;
+    char *notmuch_path, *xapian_path, *incompat_features;
+    char *message = NULL;
+    struct stat st;
+    int err;
+    unsigned int i, version;
+    static int initialized = 0;
+
+    if (path == NULL) {
+	message = strdup ("Error: Cannot open a database for a NULL path.\n");
+	status = NOTMUCH_STATUS_NULL_POINTER;
+	goto DONE;
+    }
+
+    if (path[0] != '/') {
+	message = strdup ("Error: Database path must be absolute.\n");
+	status = NOTMUCH_STATUS_PATH_ERROR;
+	goto DONE;
+    }
+
+    if (! (notmuch_path = talloc_asprintf (local, "%s/%s", path, ".notmuch"))) {
+	message = strdup ("Out of memory\n");
+	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	goto DONE;
+    }
+
+    err = stat (notmuch_path, &st);
+    if (err) {
+	IGNORE_RESULT (asprintf (&message, "Error opening database at %s: %s\n",
+				 notmuch_path, strerror (errno)));
+	status = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    if (! (xapian_path = talloc_asprintf (local, "%s/%s", notmuch_path, "xapian"))) {
+	message = strdup ("Out of memory\n");
+	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	goto DONE;
+    }
+
+    /* Initialize the GLib type system and threads */
+#if !GLIB_CHECK_VERSION(2, 35, 1)
+    g_type_init ();
+#endif
+
+    /* Initialize gmime */
+    if (! initialized) {
+	g_mime_init (GMIME_ENABLE_RFC2047_WORKAROUNDS);
+	initialized = 1;
+    }
+
+    notmuch = talloc_zero (NULL, notmuch_database_t);
+    notmuch->exception_reported = false;
+    notmuch->status_string = NULL;
+    notmuch->path = talloc_strdup (notmuch, path);
+
+    strip_trailing(notmuch->path, '/');
+
+    notmuch->mode = mode;
+    notmuch->atomic_nesting = 0;
+    notmuch->view = 1;
+    try {
+	string last_thread_id;
+	string last_mod;
+
+	if (mode == NOTMUCH_DATABASE_MODE_READ_WRITE) {
+	    notmuch->xapian_db = new Xapian::WritableDatabase (xapian_path,
+							       DB_ACTION);
+	} else {
+	    notmuch->xapian_db = new Xapian::Database (xapian_path);
+	}
+
+	/* Check version.  As of database version 3, we represent
+	 * changes in terms of features, so assume a version bump
+	 * means a dramatically incompatible change. */
+	version = notmuch_database_get_version (notmuch);
+	if (version > NOTMUCH_DATABASE_VERSION) {
+	    IGNORE_RESULT (asprintf (&message,
+		      "Error: Notmuch database at %s\n"
+		      "       has a newer database format version (%u) than supported by this\n"
+		      "       version of notmuch (%u).\n",
+				     notmuch_path, version, NOTMUCH_DATABASE_VERSION));
+	    notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;
+	    notmuch_database_destroy (notmuch);
+	    notmuch = NULL;
+	    status = NOTMUCH_STATUS_FILE_ERROR;
+	    goto DONE;
+	}
+
+	/* Check features. */
+	incompat_features = NULL;
+	notmuch->features = _parse_features (
+	    local, notmuch->xapian_db->get_metadata ("features").c_str (),
+	    version, mode == NOTMUCH_DATABASE_MODE_READ_WRITE ? 'w' : 'r',
+	    &incompat_features);
+	if (incompat_features) {
+	    IGNORE_RESULT (asprintf (&message,
+		"Error: Notmuch database at %s\n"
+		"       requires features (%s)\n"
+		"       not supported by this version of notmuch.\n",
+				     notmuch_path, incompat_features));
+	    notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;
+	    notmuch_database_destroy (notmuch);
+	    notmuch = NULL;
+	    status = NOTMUCH_STATUS_FILE_ERROR;
+	    goto DONE;
+	}
+
+	notmuch->last_doc_id = notmuch->xapian_db->get_lastdocid ();
+	last_thread_id = notmuch->xapian_db->get_metadata ("last_thread_id");
+	if (last_thread_id.empty ()) {
+	    notmuch->last_thread_id = 0;
+	} else {
+	    const char *str;
+	    char *end;
+
+	    str = last_thread_id.c_str ();
+	    notmuch->last_thread_id = strtoull (str, &end, 16);
+	    if (*end != '\0')
+		INTERNAL_ERROR ("Malformed database last_thread_id: %s", str);
+	}
+
+	/* Get current highest revision number. */
+	last_mod = notmuch->xapian_db->get_value_upper_bound (
+	    NOTMUCH_VALUE_LAST_MOD);
+	if (last_mod.empty ())
+	    notmuch->revision = 0;
+	else
+	    notmuch->revision = Xapian::sortable_unserialise (last_mod);
+	notmuch->uuid = talloc_strdup (
+	    notmuch, notmuch->xapian_db->get_uuid ().c_str ());
+
+	notmuch->query_parser = new Xapian::QueryParser;
+	notmuch->term_gen = new Xapian::TermGenerator;
+	notmuch->term_gen->set_stemmer (Xapian::Stem ("english"));
+	notmuch->value_range_processor = new Xapian::NumberValueRangeProcessor (NOTMUCH_VALUE_TIMESTAMP);
+	notmuch->date_range_processor = new ParseTimeValueRangeProcessor (NOTMUCH_VALUE_TIMESTAMP);
+	notmuch->last_mod_range_processor = new Xapian::NumberValueRangeProcessor (NOTMUCH_VALUE_LAST_MOD, "lastmod:");
+
+	notmuch->query_parser->set_default_op (Xapian::Query::OP_AND);
+	notmuch->query_parser->set_database (*notmuch->xapian_db);
+	notmuch->query_parser->set_stemmer (Xapian::Stem ("english"));
+	notmuch->query_parser->set_stemming_strategy (Xapian::QueryParser::STEM_SOME);
+	notmuch->query_parser->add_valuerangeprocessor (notmuch->value_range_processor);
+	notmuch->query_parser->add_valuerangeprocessor (notmuch->date_range_processor);
+	notmuch->query_parser->add_valuerangeprocessor (notmuch->last_mod_range_processor);
+
+	for (i = 0; i < ARRAY_SIZE (prefix_table); i++) {
+	    const prefix_t *prefix = &prefix_table[i];
+	    if (prefix->flags & NOTMUCH_FIELD_EXTERNAL) {
+		_setup_query_field (prefix, notmuch);
+	    }
+	}
+    } catch (const Xapian::Error &error) {
+	IGNORE_RESULT (asprintf (&message, "A Xapian exception occurred opening database: %s\n",
+				 error.get_msg().c_str()));
+	notmuch_database_destroy (notmuch);
+	notmuch = NULL;
+	status = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+  DONE:
+    talloc_free (local);
+
+    if (message) {
+	if (status_string)
+	    *status_string = message;
+	else
+	    free (message);
+    }
+
+    if (database)
+	*database = notmuch;
+    else
+	talloc_free (notmuch);
+    return status;
+}
+
+notmuch_status_t
+notmuch_database_close (notmuch_database_t *notmuch)
+{
+    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;
+
+    /* Many Xapian objects (and thus notmuch objects) hold references to
+     * the database, so merely deleting the database may not suffice to
+     * close it.  Thus, we explicitly close it here. */
+    if (notmuch->xapian_db != NULL) {
+	try {
+	    /* If there's an outstanding transaction, it's unclear if
+	     * closing the Xapian database commits everything up to
+	     * that transaction, or may discard committed (but
+	     * unflushed) transactions.  To be certain, explicitly
+	     * cancel any outstanding transaction before closing. */
+	    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_WRITE &&
+		notmuch->atomic_nesting)
+		(static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db))
+		    ->cancel_transaction ();
+
+	    /* Close the database.  This implicitly flushes
+	     * outstanding changes. */
+	    notmuch->xapian_db->close();
+	} catch (const Xapian::Error &error) {
+	    status = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+	    if (! notmuch->exception_reported) {
+		_notmuch_database_log (notmuch, "Error: A Xapian exception occurred closing database: %s\n",
+			 error.get_msg().c_str());
+	    }
+	}
+    }
+
+    delete notmuch->term_gen;
+    notmuch->term_gen = NULL;
+    delete notmuch->query_parser;
+    notmuch->query_parser = NULL;
+    delete notmuch->xapian_db;
+    notmuch->xapian_db = NULL;
+    delete notmuch->value_range_processor;
+    notmuch->value_range_processor = NULL;
+    delete notmuch->date_range_processor;
+    notmuch->date_range_processor = NULL;
+    delete notmuch->last_mod_range_processor;
+    notmuch->last_mod_range_processor = NULL;
+
+    return status;
+}
+
+notmuch_status_t
+_notmuch_database_reopen (notmuch_database_t *notmuch)
+{
+    if (notmuch->mode != NOTMUCH_DATABASE_MODE_READ_ONLY)
+	return NOTMUCH_STATUS_UNSUPPORTED_OPERATION;
+
+    try {
+	notmuch->xapian_db->reopen ();
+    } catch (const Xapian::Error &error) {
+	if (! notmuch->exception_reported) {
+	    _notmuch_database_log (notmuch, "Error: A Xapian exception reopening database: %s\n",
+				   error.get_msg ().c_str ());
+	    notmuch->exception_reported = true;
+	}
+	return NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+    notmuch->view++;
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+static int
+unlink_cb (const char *path,
+	   unused (const struct stat *sb),
+	   unused (int type),
+	   unused (struct FTW *ftw))
+{
+    return remove (path);
+}
+
+static int
+rmtree (const char *path)
+{
+    return nftw (path, unlink_cb, 64, FTW_DEPTH | FTW_PHYS);
+}
+
+class NotmuchCompactor : public Xapian::Compactor
+{
+    notmuch_compact_status_cb_t status_cb;
+    void *status_closure;
+
+public:
+    NotmuchCompactor(notmuch_compact_status_cb_t cb, void *closure) :
+	status_cb (cb), status_closure (closure) { }
+
+    virtual void
+    set_status (const std::string &table, const std::string &status)
+    {
+	char *msg;
+
+	if (status_cb == NULL)
+	    return;
+
+	if (status.length () == 0)
+	    msg = talloc_asprintf (NULL, "compacting table %s", table.c_str());
+	else
+	    msg = talloc_asprintf (NULL, "     %s", status.c_str());
+
+	if (msg == NULL) {
+	    return;
+	}
+
+	status_cb (msg, status_closure);
+	talloc_free (msg);
+    }
+};
+
+/* Compacts the given database, optionally saving the original database
+ * in backup_path. Additionally, a callback function can be provided to
+ * give the user feedback on the progress of the (likely long-lived)
+ * compaction process.
+ *
+ * The backup path must point to a directory on the same volume as the
+ * original database. Passing a NULL backup_path will result in the
+ * uncompacted database being deleted after compaction has finished.
+ * Note that the database write lock will be held during the
+ * compaction process to protect data integrity.
+ */
+notmuch_status_t
+notmuch_database_compact (const char *path,
+			  const char *backup_path,
+			  notmuch_compact_status_cb_t status_cb,
+			  void *closure)
+{
+    void *local;
+    char *notmuch_path, *xapian_path, *compact_xapian_path;
+    notmuch_status_t ret = NOTMUCH_STATUS_SUCCESS;
+    notmuch_database_t *notmuch = NULL;
+    struct stat statbuf;
+    bool keep_backup;
+    char *message = NULL;
+
+    local = talloc_new (NULL);
+    if (! local)
+	return NOTMUCH_STATUS_OUT_OF_MEMORY;
+
+    ret = notmuch_database_open_verbose (path,
+					 NOTMUCH_DATABASE_MODE_READ_WRITE,
+					 &notmuch,
+					 &message);
+    if (ret) {
+	if (status_cb) status_cb (message, closure);
+	goto DONE;
+    }
+
+    if (! (notmuch_path = talloc_asprintf (local, "%s/%s", path, ".notmuch"))) {
+	ret = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	goto DONE;
+    }
+
+    if (! (xapian_path = talloc_asprintf (local, "%s/%s", notmuch_path, "xapian"))) {
+	ret = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	goto DONE;
+    }
+
+    if (! (compact_xapian_path = talloc_asprintf (local, "%s.compact", xapian_path))) {
+	ret = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	goto DONE;
+    }
+
+    if (backup_path == NULL) {
+	if (! (backup_path = talloc_asprintf (local, "%s.old", xapian_path))) {
+	    ret = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	    goto DONE;
+	}
+	keep_backup = false;
+    }
+    else {
+	keep_backup = true;
+    }
+
+    if (stat (backup_path, &statbuf) != -1) {
+	_notmuch_database_log (notmuch, "Path already exists: %s\n", backup_path);
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+    if (errno != ENOENT) {
+	_notmuch_database_log (notmuch, "Unknown error while stat()ing path: %s\n",
+		 strerror (errno));
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    /* Unconditionally attempt to remove old work-in-progress database (if
+     * any). This is "protected" by database lock. If this fails due to write
+     * errors (etc), the following code will fail and provide error message.
+     */
+    (void) rmtree (compact_xapian_path);
+
+    try {
+	NotmuchCompactor compactor (status_cb, closure);
+
+	compactor.set_renumber (false);
+	compactor.add_source (xapian_path);
+	compactor.set_destdir (compact_xapian_path);
+	compactor.compact ();
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "Error while compacting: %s\n", error.get_msg().c_str());
+	ret = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+	goto DONE;
+    }
+
+    if (rename (xapian_path, backup_path)) {
+	_notmuch_database_log (notmuch, "Error moving %s to %s: %s\n",
+		 xapian_path, backup_path, strerror (errno));
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    if (rename (compact_xapian_path, xapian_path)) {
+	_notmuch_database_log (notmuch, "Error moving %s to %s: %s\n",
+		 compact_xapian_path, xapian_path, strerror (errno));
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+
+    if (! keep_backup) {
+	if (rmtree (backup_path)) {
+	    _notmuch_database_log (notmuch, "Error removing old database %s: %s\n",
+		     backup_path, strerror (errno));
+	    ret = NOTMUCH_STATUS_FILE_ERROR;
+	    goto DONE;
+	}
+    }
+
+  DONE:
+    if (notmuch) {
+	notmuch_status_t ret2;
+
+	const char *str = notmuch_database_status_string (notmuch);
+	if (status_cb && str)
+	    status_cb (str, closure);
+
+	ret2 = notmuch_database_destroy (notmuch);
+
+	/* don't clobber previous error status */
+	if (ret == NOTMUCH_STATUS_SUCCESS && ret2 != NOTMUCH_STATUS_SUCCESS)
+	    ret = ret2;
+    }
+
+    talloc_free (local);
+
+    return ret;
+}
+
+notmuch_status_t
+notmuch_database_destroy (notmuch_database_t *notmuch)
+{
+    notmuch_status_t status;
+
+    status = notmuch_database_close (notmuch);
+    talloc_free (notmuch);
+
+    return status;
+}
+
+const char *
+notmuch_database_get_path (notmuch_database_t *notmuch)
+{
+    return notmuch->path;
+}
+
+unsigned int
+notmuch_database_get_version (notmuch_database_t *notmuch)
+{
+    unsigned int version;
+    string version_string;
+    const char *str;
+    char *end;
+
+    version_string = notmuch->xapian_db->get_metadata ("version");
+    if (version_string.empty ())
+	return 0;
+
+    str = version_string.c_str ();
+    if (str == NULL || *str == '\0')
+	return 0;
+
+    version = strtoul (str, &end, 10);
+    if (*end != '\0')
+	INTERNAL_ERROR ("Malformed database version: %s", str);
+
+    return version;
+}
+
+notmuch_bool_t
+notmuch_database_needs_upgrade (notmuch_database_t *notmuch)
+{
+    return notmuch->mode == NOTMUCH_DATABASE_MODE_READ_WRITE &&
+	((NOTMUCH_FEATURES_CURRENT & ~notmuch->features) ||
+	 (notmuch_database_get_version (notmuch) < NOTMUCH_DATABASE_VERSION));
+}
+
+static volatile sig_atomic_t do_progress_notify = 0;
+
+static void
+handle_sigalrm (unused (int signal))
+{
+    do_progress_notify = 1;
+}
+
+/* Upgrade the current database.
+ *
+ * After opening a database in read-write mode, the client should
+ * check if an upgrade is needed (notmuch_database_needs_upgrade) and
+ * if so, upgrade with this function before making any modifications.
+ *
+ * The optional progress_notify callback can be used by the caller to
+ * provide progress indication to the user. If non-NULL it will be
+ * called periodically with 'count' as the number of messages upgraded
+ * so far and 'total' the overall number of messages that will be
+ * converted.
+ */
+notmuch_status_t
+notmuch_database_upgrade (notmuch_database_t *notmuch,
+			  void (*progress_notify) (void *closure,
+						   double progress),
+			  void *closure)
+{
+    void *local = talloc_new (NULL);
+    Xapian::TermIterator t, t_end;
+    Xapian::WritableDatabase *db;
+    struct sigaction action;
+    struct itimerval timerval;
+    bool timer_is_active = false;
+    enum _notmuch_features target_features, new_features;
+    notmuch_status_t status;
+    notmuch_private_status_t private_status;
+    notmuch_query_t *query = NULL;
+    unsigned int count = 0, total = 0;
+
+    status = _notmuch_database_ensure_writable (notmuch);
+    if (status)
+	return status;
+
+    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+
+    target_features = notmuch->features | NOTMUCH_FEATURES_CURRENT;
+    new_features = NOTMUCH_FEATURES_CURRENT & ~notmuch->features;
+
+    if (! notmuch_database_needs_upgrade (notmuch))
+	return NOTMUCH_STATUS_SUCCESS;
+
+    if (progress_notify) {
+	/* Set up our handler for SIGALRM */
+	memset (&action, 0, sizeof (struct sigaction));
+	action.sa_handler = handle_sigalrm;
+	sigemptyset (&action.sa_mask);
+	action.sa_flags = SA_RESTART;
+	sigaction (SIGALRM, &action, NULL);
+
+	/* Then start a timer to send SIGALRM once per second. */
+	timerval.it_interval.tv_sec = 1;
+	timerval.it_interval.tv_usec = 0;
+	timerval.it_value.tv_sec = 1;
+	timerval.it_value.tv_usec = 0;
+	setitimer (ITIMER_REAL, &timerval, NULL);
+
+	timer_is_active = true;
+    }
+
+    /* Figure out how much total work we need to do. */
+    if (new_features &
+	(NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER |
+	 NOTMUCH_FEATURE_LAST_MOD)) {
+	query = notmuch_query_create (notmuch, "");
+	unsigned msg_count;
+
+	status = notmuch_query_count_messages (query, &msg_count);
+	if (status)
+	    goto DONE;
+
+	total += msg_count;
+	notmuch_query_destroy (query);
+	query = NULL;
+    }
+    if (new_features & NOTMUCH_FEATURE_DIRECTORY_DOCS) {
+	t_end = db->allterms_end ("XTIMESTAMP");
+	for (t = db->allterms_begin ("XTIMESTAMP"); t != t_end; t++)
+	    ++total;
+    }
+    if (new_features & NOTMUCH_FEATURE_GHOSTS) {
+	/* The ghost message upgrade converts all thread_id_*
+	 * metadata values into ghost message documents. */
+	t_end = db->metadata_keys_end ("thread_id_");
+	for (t = db->metadata_keys_begin ("thread_id_"); t != t_end; ++t)
+	    ++total;
+    }
+
+    /* Perform the upgrade in a transaction. */
+    db->begin_transaction (true);
+
+    /* Set the target features so we write out changes in the desired
+     * format. */
+    notmuch->features = target_features;
+
+    /* Perform per-message upgrades. */
+    if (new_features &
+	(NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER |
+	 NOTMUCH_FEATURE_LAST_MOD)) {
+	notmuch_messages_t *messages;
+	notmuch_message_t *message;
+	char *filename;
+
+	query = notmuch_query_create (notmuch, "");
+
+	status = notmuch_query_search_messages (query, &messages);
+	if (status)
+	    goto DONE;
+	for (;
+	     notmuch_messages_valid (messages);
+	     notmuch_messages_move_to_next (messages))
+	{
+	    if (do_progress_notify) {
+		progress_notify (closure, (double) count / total);
+		do_progress_notify = 0;
+	    }
+
+	    message = notmuch_messages_get (messages);
+
+	    /* Before version 1, each message document had its
+	     * filename in the data field. Copy that into the new
+	     * format by calling notmuch_message_add_filename.
+	     */
+	    if (new_features & NOTMUCH_FEATURE_FILE_TERMS) {
+		filename = _notmuch_message_talloc_copy_data (message);
+		if (filename && *filename != '\0') {
+		    _notmuch_message_add_filename (message, filename);
+		    _notmuch_message_clear_data (message);
+		}
+		talloc_free (filename);
+	    }
+
+	    /* Prior to version 2, the "folder:" prefix was
+	     * probabilistic and stemmed. Change it to the current
+	     * boolean prefix. Add "path:" prefixes while at it.
+	     */
+	    if (new_features & NOTMUCH_FEATURE_BOOL_FOLDER)
+		_notmuch_message_upgrade_folder (message);
+
+	    /* Prior to NOTMUCH_FEATURE_LAST_MOD, messages did not
+	     * track modification revisions.  Give all messages the
+	     * next available revision; since we just started tracking
+	     * revisions for this database, that will be 1.
+	     */
+	    if (new_features & NOTMUCH_FEATURE_LAST_MOD)
+		_notmuch_message_upgrade_last_mod (message);
+
+	    _notmuch_message_sync (message);
+
+	    notmuch_message_destroy (message);
+
+	    count++;
+	}
+
+	notmuch_query_destroy (query);
+	query = NULL;
+    }
+
+    /* Perform per-directory upgrades. */
+
+    /* Before version 1 we stored directory timestamps in
+     * XTIMESTAMP documents instead of the current XDIRECTORY
+     * documents. So copy those as well. */
+    if (new_features & NOTMUCH_FEATURE_DIRECTORY_DOCS) {
+	t_end = notmuch->xapian_db->allterms_end ("XTIMESTAMP");
+
+	for (t = notmuch->xapian_db->allterms_begin ("XTIMESTAMP");
+	     t != t_end;
+	     t++)
+	{
+	    Xapian::PostingIterator p, p_end;
+	    std::string term = *t;
+
+	    p_end = notmuch->xapian_db->postlist_end (term);
+
+	    for (p = notmuch->xapian_db->postlist_begin (term);
+		 p != p_end;
+		 p++)
+	    {
+		Xapian::Document document;
+		time_t mtime;
+		notmuch_directory_t *directory;
+
+		if (do_progress_notify) {
+		    progress_notify (closure, (double) count / total);
+		    do_progress_notify = 0;
+		}
+
+		document = find_document_for_doc_id (notmuch, *p);
+		mtime = Xapian::sortable_unserialise (
+		    document.get_value (NOTMUCH_VALUE_TIMESTAMP));
+
+		directory = _notmuch_directory_create (notmuch, term.c_str() + 10,
+						       NOTMUCH_FIND_CREATE, &status);
+		notmuch_directory_set_mtime (directory, mtime);
+		notmuch_directory_destroy (directory);
+
+		db->delete_document (*p);
+	    }
+
+	    ++count;
+	}
+    }
+
+    /* Perform metadata upgrades. */
+
+    /* Prior to NOTMUCH_FEATURE_GHOSTS, thread IDs for missing
+     * messages were stored as database metadata. Change these to
+     * ghost messages.
+     */
+    if (new_features & NOTMUCH_FEATURE_GHOSTS) {
+	notmuch_message_t *message;
+	std::string message_id, thread_id;
+
+	t_end = db->metadata_keys_end (NOTMUCH_METADATA_THREAD_ID_PREFIX);
+	for (t = db->metadata_keys_begin (NOTMUCH_METADATA_THREAD_ID_PREFIX);
+	     t != t_end; ++t) {
+	    if (do_progress_notify) {
+		progress_notify (closure, (double) count / total);
+		do_progress_notify = 0;
+	    }
+
+	    message_id = (*t).substr (
+		strlen (NOTMUCH_METADATA_THREAD_ID_PREFIX));
+	    thread_id = db->get_metadata (*t);
+
+	    /* Create ghost message */
+	    message = _notmuch_message_create_for_message_id (
+		notmuch, message_id.c_str (), &private_status);
+	    if (private_status == NOTMUCH_PRIVATE_STATUS_SUCCESS) {
+		/* Document already exists; ignore the stored thread ID */
+	    } else if (private_status ==
+		       NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND) {
+		private_status = _notmuch_message_initialize_ghost (
+		    message, thread_id.c_str ());
+		if (! private_status)
+		    _notmuch_message_sync (message);
+	    }
+
+	    if (private_status) {
+		_notmuch_database_log (notmuch,
+			 "Upgrade failed while creating ghost messages.\n");
+		status = COERCE_STATUS (private_status, "Unexpected status from _notmuch_message_initialize_ghost");
+		goto DONE;
+	    }
+
+	    /* Clear saved metadata thread ID */
+	    db->set_metadata (*t, "");
+
+	    ++count;
+	}
+    }
+
+    status = NOTMUCH_STATUS_SUCCESS;
+    db->set_metadata ("features", _print_features (local, notmuch->features));
+    db->set_metadata ("version", STRINGIFY (NOTMUCH_DATABASE_VERSION));
+
+ DONE:
+    if (status == NOTMUCH_STATUS_SUCCESS)
+	db->commit_transaction ();
+    else
+	db->cancel_transaction ();
+
+    if (timer_is_active) {
+	/* Now stop the timer. */
+	timerval.it_interval.tv_sec = 0;
+	timerval.it_interval.tv_usec = 0;
+	timerval.it_value.tv_sec = 0;
+	timerval.it_value.tv_usec = 0;
+	setitimer (ITIMER_REAL, &timerval, NULL);
+
+	/* And disable the signal handler. */
+	action.sa_handler = SIG_IGN;
+	sigaction (SIGALRM, &action, NULL);
+    }
+
+    if (query)
+	notmuch_query_destroy (query);
+
+    talloc_free (local);
+    return status;
+}
+
+notmuch_status_t
+notmuch_database_begin_atomic (notmuch_database_t *notmuch)
+{
+    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY ||
+	notmuch->atomic_nesting > 0)
+	goto DONE;
+
+    if (notmuch_database_needs_upgrade (notmuch))
+	return NOTMUCH_STATUS_UPGRADE_REQUIRED;
+
+    try {
+	(static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db))->begin_transaction (false);
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "A Xapian exception occurred beginning transaction: %s.\n",
+		 error.get_msg().c_str());
+	notmuch->exception_reported = true;
+	return NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+DONE:
+    notmuch->atomic_nesting++;
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+notmuch_status_t
+notmuch_database_end_atomic (notmuch_database_t *notmuch)
+{
+    Xapian::WritableDatabase *db;
+
+    if (notmuch->atomic_nesting == 0)
+	return NOTMUCH_STATUS_UNBALANCED_ATOMIC;
+
+    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY ||
+	notmuch->atomic_nesting > 1)
+	goto DONE;
+
+    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+    try {
+	db->commit_transaction ();
+
+	/* This is a hack for testing.  Xapian never flushes on a
+	 * non-flushed commit, even if the flush threshold is 1.
+	 * However, we rely on flushing to test atomicity. */
+	const char *thresh = getenv ("XAPIAN_FLUSH_THRESHOLD");
+	if (thresh && atoi (thresh) == 1)
+	    db->commit ();
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "A Xapian exception occurred committing transaction: %s.\n",
+		 error.get_msg().c_str());
+	notmuch->exception_reported = true;
+	return NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+    if (notmuch->atomic_dirty) {
+	++notmuch->revision;
+	notmuch->atomic_dirty = false;
+    }
+
+DONE:
+    notmuch->atomic_nesting--;
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+unsigned long
+notmuch_database_get_revision (notmuch_database_t *notmuch,
+				const char **uuid)
+{
+    if (uuid)
+	*uuid = notmuch->uuid;
+    return notmuch->revision;
+}
+
+/* We allow the user to use arbitrarily long paths for directories. But
+ * we have a term-length limit. So if we exceed that, we'll use the
+ * SHA-1 of the path for the database term.
+ *
+ * Note: This function may return the original value of 'path'. If it
+ * does not, then the caller is responsible to free() the returned
+ * value.
+ */
+const char *
+_notmuch_database_get_directory_db_path (const char *path)
+{
+    int term_len = strlen (_find_prefix ("directory")) + strlen (path);
+
+    if (term_len > NOTMUCH_TERM_MAX)
+	return _notmuch_sha1_of_string (path);
+    else
+	return path;
+}
+
+/* Given a path, split it into two parts: the directory part is all
+ * components except for the last, and the basename is that last
+ * component. Getting the return-value for either part is optional
+ * (the caller can pass NULL).
+ *
+ * The original 'path' can represent either a regular file or a
+ * directory---the splitting will be carried out in the same way in
+ * either case. Trailing slashes on 'path' will be ignored, and any
+ * cases of multiple '/' characters appearing in series will be
+ * treated as a single '/'.
+ *
+ * Allocation (if any) will have 'ctx' as the talloc owner. But
+ * pointers will be returned within the original path string whenever
+ * possible.
+ *
+ * Note: If 'path' is non-empty and contains no non-trailing slash,
+ * (that is, consists of a filename with no parent directory), then
+ * the directory returned will be an empty string. However, if 'path'
+ * is an empty string, then both directory and basename will be
+ * returned as NULL.
+ */
+notmuch_status_t
+_notmuch_database_split_path (void *ctx,
+			      const char *path,
+			      const char **directory,
+			      const char **basename)
+{
+    const char *slash;
+
+    if (path == NULL || *path == '\0') {
+	if (directory)
+	    *directory = NULL;
+	if (basename)
+	    *basename = NULL;
+	return NOTMUCH_STATUS_SUCCESS;
+    }
+
+    /* Find the last slash (not counting a trailing slash), if any. */
+
+    slash = path + strlen (path) - 1;
+
+    /* First, skip trailing slashes. */
+    while (slash != path && *slash == '/')
+	--slash;
+
+    /* Then, find a slash. */
+    while (slash != path && *slash != '/') {
+	if (basename)
+	    *basename = slash;
+
+	--slash;
+    }
+
+    /* Finally, skip multiple slashes. */
+    while (slash != path && *(slash - 1) == '/')
+	--slash;
+
+    if (slash == path) {
+	if (directory)
+	    *directory = talloc_strdup (ctx, "");
+	if (basename)
+	    *basename = path;
+    } else {
+	if (directory)
+	    *directory = talloc_strndup (ctx, path, slash - path);
+    }
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+/* Find the document ID of the specified directory.
+ *
+ * If (flags & NOTMUCH_FIND_CREATE), a new directory document will be
+ * created if one does not exist for 'path'.  Otherwise, if the
+ * directory document does not exist, this sets *directory_id to
+ * ((unsigned int)-1) and returns NOTMUCH_STATUS_SUCCESS.
+ */
+notmuch_status_t
+_notmuch_database_find_directory_id (notmuch_database_t *notmuch,
+				     const char *path,
+				     notmuch_find_flags_t flags,
+				     unsigned int *directory_id)
+{
+    notmuch_directory_t *directory;
+    notmuch_status_t status;
+
+    if (path == NULL) {
+	*directory_id = 0;
+	return NOTMUCH_STATUS_SUCCESS;
+    }
+
+    directory = _notmuch_directory_create (notmuch, path, flags, &status);
+    if (status || !directory) {
+	*directory_id = -1;
+	return status;
+    }
+
+    *directory_id = _notmuch_directory_get_document_id (directory);
+
+    notmuch_directory_destroy (directory);
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+const char *
+_notmuch_database_get_directory_path (void *ctx,
+				      notmuch_database_t *notmuch,
+				      unsigned int doc_id)
+{
+    Xapian::Document document;
+
+    document = find_document_for_doc_id (notmuch, doc_id);
+
+    return talloc_strdup (ctx, document.get_data ().c_str ());
+}
+
+/* Given a legal 'filename' for the database, (either relative to
+ * database path or absolute with initial components identical to
+ * database path), return a new string (with 'ctx' as the talloc
+ * owner) suitable for use as a direntry term value.
+ *
+ * If (flags & NOTMUCH_FIND_CREATE), the necessary directory documents
+ * will be created in the database as needed.  Otherwise, if the
+ * necessary directory documents do not exist, this sets
+ * *direntry to NULL and returns NOTMUCH_STATUS_SUCCESS.
+ */
+notmuch_status_t
+_notmuch_database_filename_to_direntry (void *ctx,
+					notmuch_database_t *notmuch,
+					const char *filename,
+					notmuch_find_flags_t flags,
+					char **direntry)
+{
+    const char *relative, *directory, *basename;
+    Xapian::docid directory_id;
+    notmuch_status_t status;
+
+    relative = _notmuch_database_relative_path (notmuch, filename);
+
+    status = _notmuch_database_split_path (ctx, relative,
+					   &directory, &basename);
+    if (status)
+	return status;
+
+    status = _notmuch_database_find_directory_id (notmuch, directory, flags,
+						  &directory_id);
+    if (status || directory_id == (unsigned int)-1) {
+	*direntry = NULL;
+	return status;
+    }
+
+    *direntry = talloc_asprintf (ctx, "%u:%s", directory_id, basename);
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
+/* Given a legal 'path' for the database, return the relative path.
+ *
+ * The return value will be a pointer to the original path contents,
+ * and will be either the original string (if 'path' was relative) or
+ * a portion of the string (if path was absolute and begins with the
+ * database path).
+ */
+const char *
+_notmuch_database_relative_path (notmuch_database_t *notmuch,
+				 const char *path)
+{
+    const char *db_path, *relative;
+    unsigned int db_path_len;
+
+    db_path = notmuch_database_get_path (notmuch);
+    db_path_len = strlen (db_path);
+
+    relative = path;
+
+    if (*relative == '/') {
+	while (*relative == '/' && *(relative+1) == '/')
+	    relative++;
+
+	if (strncmp (relative, db_path, db_path_len) == 0)
+	{
+	    relative += db_path_len;
+	    while (*relative == '/')
+		relative++;
+	}
+    }
+
+    return relative;
+}
+
+notmuch_status_t
+notmuch_database_get_directory (notmuch_database_t *notmuch,
+				const char *path,
+				notmuch_directory_t **directory)
+{
+    notmuch_status_t status;
+
+    if (directory == NULL)
+	return NOTMUCH_STATUS_NULL_POINTER;
+    *directory = NULL;
+
+    try {
+	*directory = _notmuch_directory_create (notmuch, path,
+						NOTMUCH_FIND_LOOKUP, &status);
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "A Xapian exception occurred getting directory: %s.\n",
+		 error.get_msg().c_str());
+	notmuch->exception_reported = true;
+	status = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+    return status;
+}
+
+/* Allocate a document ID that satisfies the following criteria:
+ *
+ * 1. The ID does not exist for any document in the Xapian database
+ *
+ * 2. The ID was not previously returned from this function
+ *
+ * 3. The ID is the smallest integer satisfying (1) and (2)
+ *
+ * This function will trigger an internal error if these constraints
+ * cannot all be satisfied, (that is, the pool of available document
+ * IDs has been exhausted).
+ */
+unsigned int
+_notmuch_database_generate_doc_id (notmuch_database_t *notmuch)
+{
+    assert (notmuch->last_doc_id >= notmuch->xapian_db->get_lastdocid ());
+
+    notmuch->last_doc_id++;
+
+    if (notmuch->last_doc_id == 0)
+	INTERNAL_ERROR ("Xapian document IDs are exhausted.\n");
+
+    return notmuch->last_doc_id;
+}
+
+notmuch_status_t
+notmuch_database_remove_message (notmuch_database_t *notmuch,
+				 const char *filename)
+{
+    notmuch_status_t status;
+    notmuch_message_t *message;
+
+    status = notmuch_database_find_message_by_filename (notmuch, filename,
+							&message);
+
+    if (status == NOTMUCH_STATUS_SUCCESS && message) {
+	    status = _notmuch_message_remove_filename (message, filename);
+	    if (status == NOTMUCH_STATUS_SUCCESS)
+		_notmuch_message_delete (message);
+	    else if (status == NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID)
+		_notmuch_message_sync (message);
+
+	    notmuch_message_destroy (message);
+    }
+
+    return status;
+}
+
+notmuch_status_t
+notmuch_database_find_message_by_filename (notmuch_database_t *notmuch,
+					   const char *filename,
+					   notmuch_message_t **message_ret)
+{
+    void *local;
+    const char *prefix = _find_prefix ("file-direntry");
+    char *direntry, *term;
+    Xapian::PostingIterator i, end;
+    notmuch_status_t status;
+
+    if (message_ret == NULL)
+	return NOTMUCH_STATUS_NULL_POINTER;
+
+    if (! (notmuch->features & NOTMUCH_FEATURE_FILE_TERMS))
+	return NOTMUCH_STATUS_UPGRADE_REQUIRED;
+
+    /* return NULL on any failure */
+    *message_ret = NULL;
+
+    local = talloc_new (notmuch);
+
+    try {
+	status = _notmuch_database_filename_to_direntry (
+	    local, notmuch, filename, NOTMUCH_FIND_LOOKUP, &direntry);
+	if (status || !direntry)
+	    goto DONE;
+
+	term = talloc_asprintf (local, "%s%s", prefix, direntry);
+
+	find_doc_ids_for_term (notmuch, term, &i, &end);
+
+	if (i != end) {
+	    notmuch_private_status_t private_status;
+
+	    *message_ret = _notmuch_message_create (notmuch, notmuch, *i,
+						    &private_status);
+	    if (*message_ret == NULL)
+		status = NOTMUCH_STATUS_OUT_OF_MEMORY;
+	}
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (notmuch, "Error: A Xapian exception occurred finding message by filename: %s\n",
+		 error.get_msg().c_str());
+	notmuch->exception_reported = true;
+	status = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+  DONE:
+    talloc_free (local);
+
+    if (status && *message_ret) {
+	notmuch_message_destroy (*message_ret);
+	*message_ret = NULL;
+    }
+    return status;
+}
+
+notmuch_string_list_t *
+_notmuch_database_get_terms_with_prefix (void *ctx, Xapian::TermIterator &i,
+					 Xapian::TermIterator &end,
+					 const char *prefix)
+{
+    int prefix_len = strlen (prefix);
+    notmuch_string_list_t *list;
+
+    list = _notmuch_string_list_create (ctx);
+    if (unlikely (list == NULL))
+	return NULL;
+
+    for (i.skip_to (prefix); i != end; i++) {
+	/* Terminate loop at first term without desired prefix. */
+	if (strncmp ((*i).c_str (), prefix, prefix_len))
+	    break;
+
+	_notmuch_string_list_append (list, (*i).c_str () + prefix_len);
+    }
+
+    return list;
+}
+
+notmuch_tags_t *
+notmuch_database_get_all_tags (notmuch_database_t *db)
+{
+    Xapian::TermIterator i, end;
+    notmuch_string_list_t *tags;
+
+    try {
+	i = db->xapian_db->allterms_begin();
+	end = db->xapian_db->allterms_end();
+	tags = _notmuch_database_get_terms_with_prefix (db, i, end,
+							_find_prefix ("tag"));
+	_notmuch_string_list_sort (tags);
+	return _notmuch_tags_create (db, tags);
+    } catch (const Xapian::Error &error) {
+	_notmuch_database_log (db, "A Xapian exception occurred getting tags: %s.\n",
+		 error.get_msg().c_str());
+	db->exception_reported = true;
+	return NULL;
+    }
+}
+
+const char *
+notmuch_database_status_string (const notmuch_database_t *notmuch)
+{
+    return notmuch->status_string;
+}