From: Timo Sirainen <timo.sirainen@dovecot.fi>
Date: Thu, 26 Oct 2017 12:17:04 +0000 (+0300)
Subject: lib: Add istream.snapshot() method for referencing the current memarea
X-Git-Tag: 2.3.0.rc1~647
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=82ea464c113f43aaa2b2e23de334cf3081c332be;p=thirdparty%2Fdovecot%2Fcore.git

lib: Add istream.snapshot() method for referencing the current memarea

It will be used by following commits.
---

diff --git a/src/lib/istream-private.h b/src/lib/istream-private.h
index f41370c880..14b57df9ce 100644
--- a/src/lib/istream-private.h
+++ b/src/lib/istream-private.h
@@ -20,6 +20,9 @@ struct istream_private {
 	int (*stat)(struct istream_private *stream, bool exact);
 	int (*get_size)(struct istream_private *stream, bool exact, uoff_t *size_r);
 	void (*switch_ioloop)(struct istream_private *stream);
+	struct istream_snapshot *
+		(*snapshot)(struct istream_private *stream,
+			    struct istream_snapshot *prev_snapshot);
 
 /* data: */
 	struct istream istream;
@@ -44,6 +47,7 @@ struct istream_private {
 	uoff_t parent_expected_offset;
 
 	struct memarea *memarea;
+	struct istream_snapshot *prev_snapshot;
 	/* increased every time the stream is changed (e.g. seek, read).
 	   this way streams can check if their parent streams have been
 	   accessed behind them. */
@@ -56,6 +60,11 @@ struct istream_private {
 	bool nonpersistent_buffers:1;
 };
 
+struct istream_snapshot {
+	struct istream_snapshot *prev_snapshot;
+	struct memarea *old_memarea;
+};
+
 struct istream * ATTR_NOWARN_UNUSED_RESULT
 i_stream_create(struct istream_private *stream, struct istream *parent, int fd)
 	ATTR_NULL(2);
@@ -75,6 +84,13 @@ ssize_t i_stream_read_copy_from_parent(struct istream *istream);
 void i_stream_default_seek_nonseekable(struct istream_private *stream,
 				       uoff_t v_offset, bool mark);
 
+/* Default snapshot handling: use memarea if it exists, otherwise snapshot
+   parent stream. */
+struct istream_snapshot *
+i_stream_default_snapshot(struct istream_private *stream,
+			  struct istream_snapshot *prev_snapshot);
+void i_stream_snapshot_free(struct istream_snapshot **snapshot);
+
 void i_stream_set_io(struct istream *stream, struct io *io);
 void i_stream_unset_io(struct istream *stream, struct io *io);
 
diff --git a/src/lib/istream.c b/src/lib/istream.c
index b13c687d0a..56711082ce 100644
--- a/src/lib/istream.c
+++ b/src/lib/istream.c
@@ -60,6 +60,7 @@ void i_stream_unref(struct istream **stream)
 	if (_stream->iostream.refcount == 1) {
 		if (_stream->line_str != NULL)
 			str_free(&_stream->line_str);
+		i_stream_snapshot_free(&_stream->prev_snapshot);
 	}
 	if (!io_stream_unref(&(*stream)->real_stream->iostream)) {
 		i_stream_unref(&(*stream)->real_stream->parent);
@@ -180,6 +181,58 @@ static void i_stream_update(struct istream_private *stream)
 	}
 }
 
+static bool snapshot_has_memarea(struct istream_snapshot *snapshot,
+				 struct memarea *memarea)
+{
+	if (snapshot->old_memarea == memarea)
+		return TRUE;
+	if (snapshot->prev_snapshot != NULL)
+		return snapshot_has_memarea(snapshot->prev_snapshot, memarea);
+	return FALSE;
+}
+
+struct istream_snapshot *
+i_stream_default_snapshot(struct istream_private *stream,
+			  struct istream_snapshot *prev_snapshot)
+{
+	struct istream_snapshot *snapshot;
+
+	if (stream->memarea != NULL) {
+		if (prev_snapshot != NULL) {
+			if (snapshot_has_memarea(prev_snapshot, stream->memarea))
+				return prev_snapshot;
+		}
+		/* This stream has a memarea. Reference it, so we can later on
+		   rollback if needed. */
+		snapshot = i_new(struct istream_snapshot, 1);
+		snapshot->old_memarea = stream->memarea;
+		snapshot->prev_snapshot = prev_snapshot;
+		memarea_ref(snapshot->old_memarea);
+		return snapshot;
+	}
+	if (stream->parent == NULL) {
+		i_panic("%s is missing istream.snapshot() implementation",
+			i_stream_get_name(&stream->istream));
+	}
+	struct istream_private *_parent_stream =
+		stream->parent->real_stream;
+	return _parent_stream->snapshot(_parent_stream, prev_snapshot);
+}
+
+void i_stream_snapshot_free(struct istream_snapshot **_snapshot)
+{
+	struct istream_snapshot *snapshot = *_snapshot;
+
+	if (*_snapshot == NULL)
+		return;
+	*_snapshot = NULL;
+
+	i_stream_snapshot_free(&snapshot->prev_snapshot);
+	if (snapshot->old_memarea != NULL)
+		memarea_unref(&snapshot->old_memarea);
+	i_free(snapshot);
+}
+
 ssize_t i_stream_read(struct istream *stream)
 {
 	struct istream_private *_stream = stream->real_stream;
@@ -929,6 +982,11 @@ i_stream_create(struct istream_private *_stream, struct istream *parent, int fd)
 	_stream->fd = fd;
 	if (parent != NULL)
 		i_stream_init_parent(_stream, parent);
+	else if (_stream->memarea == NULL) {
+		/* The stream has no parent and no memarea yet. We'll assume
+		   that it wants to be using memareas for the reads. */
+		_stream->memarea = memarea_init_empty();
+	}
 	_stream->istream.real_stream = _stream;
 
 	if (_stream->iostream.close == NULL)
@@ -944,6 +1002,8 @@ i_stream_create(struct istream_private *_stream, struct istream *parent, int fd)
 		_stream->stat = i_stream_default_stat;
 	if (_stream->get_size == NULL)
 		_stream->get_size = i_stream_default_get_size;
+	if (_stream->snapshot == NULL)
+		_stream->snapshot = i_stream_default_snapshot;
 	if (_stream->iostream.set_max_buffer_size == NULL) {
 		_stream->iostream.set_max_buffer_size =
 			i_stream_default_set_max_buffer_size;