Re: DatabaseModifiedErrors causing troubles

[Gaute Hope <eg@gaute.vetsj.com>]

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On Thu, Aug 21, 2014 at 10:59 AM, Gaute Hope <eg@gaute.vetsj.com> wrote:
> For portability I would suggest starting to move towards the GError
> scheme provided by glib (also used by gmime). This is a somewhat major
> effort though since ensuring that error propagation is done right [0] is
> somewhat tricky. It provides more or less the same functionality as
> exceptions do in C++.
>
> There is also the problem of having to change the API - one way to avoid
> that is to create wrappers that behave like the old API, but don't
> handle errors that good. This requires the addition of addiontal _error
> variations of the current set of functions. It will be a mess.
>
> [0] https://developer.gnome.org/glib/stable/glib-Error-Reporting.html

Here's a quick mockup of how that could look.

Cheers, Gaute

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From eb49e311e312a5c9510ca24dec24ad1c60aedee9 Mon Sep 17 00:00:00 2001
From: Gaute Hope <eg@gaute.vetsj.com>
Date: Thu, 21 Aug 2014 10:56:57 +0200
Subject: [PATCH] mockup: Illustration of GError for error reporting

---
 lib/database.cc | 23 +++++++++++++++++++++--
 lib/notmuch.h   | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/lib/database.cc b/lib/database.cc
index 9c0952a..085152f 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -42,6 +42,8 @@ typedef struct {
     const char *prefix;
 } prefix_t;
 
+GQuark notmuch_error_quark;
+
 #define NOTMUCH_DATABASE_VERSION 2
 
 #define STRINGIFY(s) _SUB_STRINGIFY(s)
@@ -367,16 +369,28 @@ _message_id_compressed (void *ctx, const char *message_id)
     return compressed;
 }
 
+/* deprecated wrapper */
 notmuch_status_t
 notmuch_database_find_message (notmuch_database_t *notmuch,
 			       const char *message_id,
 			       notmuch_message_t **message_ret)
 {
+  return notmuch_database_find_message_err (notmuch, message_id, message_ret, NULL);
+}
+
+notmuch_status_t
+notmuch_database_find_message_err (notmuch_database_t *notmuch,
+			       const char *message_id,
+			       notmuch_message_t **message_ret,
+             GError **err)
+{
     notmuch_private_status_t status;
     unsigned int doc_id;
 
-    if (message_ret == NULL)
-	return NOTMUCH_STATUS_NULL_POINTER;
+    if (message_ret == NULL) {
+      g_set_error (err, NOTMUCH_ERROR, NOTMUCH_STATUS_NULL_POINTER, notmuch_status_to_string (NOTMUCH_STATUS_NULL_POINTER));
+      return NOTMUCH_STATUS_NULL_POINTER;
+    }
 
     if (strlen (message_id) > NOTMUCH_MESSAGE_ID_MAX)
 	message_id = _message_id_compressed (notmuch, message_id);
@@ -633,6 +647,11 @@ notmuch_database_open (const char *path,
     unsigned int i, version;
     static int initialized = 0;
 
+    /* Initialize GError system */
+    if (! initialized) {
+      notmuch_error_quark = g_quark_from_static_string ("notmuch");
+    }
+
     if (path == NULL) {
 	fprintf (stderr, "Error: Cannot open a database for a NULL path.\n");
 	status = NOTMUCH_STATUS_NULL_POINTER;
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 3c5ec98..af28e09 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -42,6 +42,7 @@
 NOTMUCH_BEGIN_DECLS
 
 #include <time.h>
+#include <glib.h>
 
 #ifndef FALSE
 #define FALSE 0
@@ -159,6 +160,12 @@ typedef enum _notmuch_status {
      * The operation is not supported.
      */
     NOTMUCH_STATUS_UNSUPPORTED_OPERATION,
+
+    /* An Xapian::DatabaseModifiedError has occurred, all decendants of
+     * database are invalid and the database must be reopened.
+     */
+    NOTMUCH_STATUS_XAPIAN_DATABASE_MODIFIED_ERROR,
+
     /**
      * Not an actual status value. Just a way to find out how many
      * valid status values there are.
@@ -166,6 +173,18 @@ typedef enum _notmuch_status {
     NOTMUCH_STATUS_LAST_STATUS
 } notmuch_status_t;
 
+
+/* errors */
+extern GQuark notmuch_error_quark;
+
+
+/**
+ * NOTMUCH_ERROR:
+ *
+ * The Notmuch error domain GQuark value.
+ **/
+#define NOTMUCH_ERROR notmuch_error_quark
+
 /**
  * Get a string representation of a notmuch_status_t value.
  *
@@ -554,6 +573,35 @@ notmuch_database_find_message (notmuch_database_t *database,
 			       notmuch_message_t **message);
 
 /**
+ * Find a message with the given message_id.
+ *
+ * If a message with the given message_id is found then, on successful return
+ * (NOTMUCH_STATUS_SUCCESS) '*message' will be initialized to a message
+ * object.  The caller should call notmuch_message_destroy when done with the
+ * message.
+ *
+ * On any failure or when the message is not found, this function initializes
+ * '*message' to NULL. This means, when NOTMUCH_STATUS_SUCCESS is returned, the
+ * caller is supposed to check '*message' for NULL to find out whether the
+ * message with the given message_id was found.
+ *
+ * Return value:
+ *
+ * NOTMUCH_STATUS_SUCCESS: Successful return, check '*message'.
+ *
+ * NOTMUCH_STATUS_NULL_POINTER: The given 'message' argument is NULL
+ *
+ * NOTMUCH_STATUS_OUT_OF_MEMORY: Out of memory, creating message object
+ *
+ * NOTMUCH_STATUS_XAPIAN_EXCEPTION: A Xapian exception occurred
+ */
+notmuch_status_t
+notmuch_database_find_message_err (notmuch_database_t *database,
+			       const char *message_id,
+			       notmuch_message_t **message,
+             GError **err);
+
+/**
  * Find a message with the given filename.
  *
  * If the database contains a message with the given filename then, on
-- 
2.0.4