degesch: optimize buffer memory usage

We have approximately 5 formatter_items per buffer_line.  Let's assume
we're on a 64-bit machine.  Then there were (5 * 2) + 3 useless pointers
(104 bytes) as well as 5 * (4 + 4) = 40 bytes of wasted space because
of needless padding.  That's 144 bytes already.  Compared to that, this
change adds 16 bytes of overhead for an array sentinel, i.e. 128B less.

With a limit of 1000 lines per buffer, we've saved ~128kB per buffer
on completely useless data, and code complexity stays roughly the same.

All in all, memory usage for buffers should be about 50% lower.

2 files changed, 41 insertions, 35 deletions

diff --git a/NEWS b/NEWS
index f19388c..60e07d3 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,8 @@
 
  * degesch: backlog limit was made configurable
 
+ * degesch: optimize buffer memory usage
+
  * kike: add support for IRCv3.2 server-time
 
  * Remote addresses are now resolved asynchronously
diff --git a/degesch.c b/degesch.c
index 26f0065..93d9316 100644
--- a/degesch.c
+++ b/degesch.c
@@ -968,6 +968,7 @@ REF_COUNTABLE_METHODS (channel)
 
 enum formatter_item_type
 {
+	FORMATTER_ITEM_END,                 ///< Sentinel value for arrays
 	FORMATTER_ITEM_TEXT,                ///< Text
 	FORMATTER_ITEM_ATTR,                ///< Formatting attributes
 	FORMATTER_ITEM_FG_COLOR,            ///< Foreground color
@@ -978,26 +979,16 @@ enum formatter_item_type
 
 struct formatter_item
 {
-	LIST_HEADER (struct formatter_item)
-
-	enum formatter_item_type type;      ///< Type of this item
+	enum formatter_item_type type : 16; ///< Type of this item
+	int attribute                 : 16; ///< Attribute ID
 	int color;                          ///< Color
-	int attribute;                      ///< Attribute ID
-	char *text;                         ///< Either text or an attribute string
+	char *text;                         ///< String
 };
 
-static struct formatter_item *
-formatter_item_new (void)
-{
-	struct formatter_item *self = xcalloc (1, sizeof *self);
-	return self;
-}
-
 static void
-formatter_item_destroy (struct formatter_item *self)
+formatter_item_free (struct formatter_item *self)
 {
 	free (self->text);
-	free (self);
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -1008,7 +999,8 @@ struct formatter
 	struct server *s;                   ///< Server
 
 	struct formatter_item *items;       ///< Items
-	struct formatter_item *items_tail;  ///< Tail of items
+	size_t items_len;                   ///< Items used
+	size_t items_alloc;                 ///< Items allocated
 };
 
 static void
@@ -1018,13 +1010,16 @@ formatter_init (struct formatter *self,
 	memset (self, 0, sizeof *self);
 	self->ctx = ctx;
 	self->s = s;
+	self->items = xcalloc (sizeof *self->items, (self->items_alloc = 16));
+	self->items_len = 0;
 }
 
 static void
 formatter_free (struct formatter *self)
 {
-	LIST_FOR_EACH (struct formatter_item, iter, self->items)
-		formatter_item_destroy (iter);
+	for (size_t i = 0; i < self->items_len; i++)
+		formatter_item_free (&self->items[i]);
+	free (self->items);
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -1045,21 +1040,31 @@ struct buffer_line
 
 	int flags;                          ///< Flags
 	time_t when;                        ///< Time of the event
-	struct formatter formatter;         ///< Line data
+	struct formatter_item items[];      ///< Line data
 };
 
+/// Create a new buffer line stealing all data from the provided formatter
 struct buffer_line *
 buffer_line_new (struct formatter *f)
 {
-	struct buffer_line *self = xcalloc (1, sizeof *self);
-	self->formatter = *f;
+	// We make space for one more item that gets initialized to all zeros,
+	// meaning FORMATTER_ITEM_END (because it's the first value in the enum)
+	size_t items_size = f->items_len * sizeof *f->items;
+	struct buffer_line *self =
+		xcalloc (1, sizeof *self + items_size + sizeof *self->items);
+	memcpy (self->items, f->items, items_size);
+
+	// We've stolen pointers from the formatter, let's destroy it altogether
+	free (f->items);
+	memset (f, 0, sizeof *f);
 	return self;
 }
 
 static void
 buffer_line_destroy (struct buffer_line *self)
 {
-	formatter_free (&self->formatter);
+	for (struct formatter_item *iter = self->items; iter->type; iter++)
+		formatter_item_free (iter);
 	free (self);
 }
 
@@ -2619,9 +2624,10 @@ formatter_add_item (struct formatter *self, struct formatter_item template_)
 	if (template_.text)
 		template_.text = xstrdup (template_.text);
 
-	struct formatter_item *item = formatter_item_new ();
-	*item = template_;
-	LIST_APPEND_WITH_TAIL (self->items, self->items_tail, item);
+	if (self->items_len == self->items_alloc)
+		self->items = xreallocarray
+			(self->items, sizeof *self->items, (self->items_alloc <<= 1));
+	self->items[self->items_len++] = template_;
 }
 
 #define FORMATTER_ADD_ITEM(self, type_, ...) formatter_add_item ((self), \
@@ -2911,13 +2917,6 @@ formatter_add (struct formatter *self, const char *format, ...)
 	va_end (ap);
 }
 
-static void
-formatter_add_from (struct formatter *self, struct formatter *other)
-{
-	for (struct formatter_item *iter = other->items; iter; iter = iter->next)
-		formatter_add_item (self, *iter);
-}
-
 static bool
 formatter_flush_attr
 	(struct attribute_printer *state, struct formatter_item *item)
@@ -2969,9 +2968,12 @@ formatter_flush (struct formatter *self, FILE *stream, bool raw_attributes)
 {
 	if (!raw_attributes && !get_attribute_printer (stream))
 	{
-		LIST_FOR_EACH (struct formatter_item, iter, self->items)
+		for (size_t i = 0; i < self->items_len; i++)
+		{
+			struct formatter_item *iter = &self->items[i];
 			if (iter->type == FORMATTER_ITEM_TEXT)
 				fputs (iter->text, stream);
+		}
 		return;
 	}
 
@@ -2980,8 +2982,9 @@ formatter_flush (struct formatter *self, FILE *stream, bool raw_attributes)
 	attribute_printer_reset (&state);
 
 	int attribute_ignore = 0;
-	LIST_FOR_EACH (struct formatter_item, iter, self->items)
+	for (size_t i = 0; i < self->items_len; i++)
 	{
+		struct formatter_item *iter = &self->items[i];
 		if      (iter->type == FORMATTER_ITEM_TEXT)
 			formatter_flush_text (self->ctx, iter->text, stream);
 		else if (iter->type == FORMATTER_ITEM_IGNORE_ATTR)
@@ -3051,7 +3054,9 @@ buffer_line_flush (struct buffer_line *line, struct formatter *f, FILE *output,
 	if (flags & BUFFER_LINE_STATUS)  formatter_add (f, " -  ");
 	if (flags & BUFFER_LINE_ERROR)   formatter_add (f, "#a=!=#r ", ATTR_ERROR);
 
-	formatter_add_from (f, &line->formatter);
+	for (struct formatter_item *iter = line->items; iter->type; iter++)
+		formatter_add_item (f, *iter);
+
 	formatter_add (f, "\n");
 	formatter_flush (f, output, raw_attributes);
 	formatter_free (f);
@@ -3141,7 +3146,6 @@ log_formatter (struct app_context *ctx,
 	if (!buffer)
 		buffer = ctx->global_buffer;
 
-	// Move the formatter inside
 	struct buffer_line *line = buffer_line_new (f);
 	line->flags = flags;
 	// TODO: allow providing custom time (IRCv3.2 server-time)