implement the GET_LOG_MARKERS IPC request/reply

docs/ipc

@@ -1,7 +1,7 @@
 IPC interface (interprocess communication)
 ==========================================
 Michael Stapelberg <michael+i3@stapelberg.de>
-October 2011
+December 2011
 
 This document describes how to interface with i3 from a separate process. This
 is useful for example to remote-control i3 (to write test cases for example) or
@@ -68,6 +68,10 @@ GET_BAR_CONFIG (6)::
 	Gets the configuration (as JSON map) of the workspace bar with the
 	given ID. If no ID is provided, an array with all configured bar IDs is
 	returned instead.
+GET_LOG_MARKERS (7)::
+	Gets the SHM log markers for the current position, the last wrap, the
+	SHM segment name and segment size. This is necessary for tools like
+	i3-dump-log which want to display the SHM log.
 
 So, a typical message could look like this:
 --------------------------------------------------
@@ -111,18 +115,20 @@ The following reply types are implemented:
 
 COMMAND (0)::
 	Confirmation/Error code for the COMMAND message.
-GET_WORKSPACES (1)::
+WORKSPACES (1)::
 	Reply to the GET_WORKSPACES message.
 SUBSCRIBE (2)::
 	Confirmation/Error code for the SUBSCRIBE message.
-GET_OUTPUTS (3)::
+OUTPUTS (3)::
 	Reply to the GET_OUTPUTS message.
-GET_TREE (4)::
+TREE (4)::
 	Reply to the GET_TREE message.
-GET_MARKS (5)::
+MARKS (5)::
 	Reply to the GET_MARKS message.
-GET_BAR_CONFIG (6)::
+BAR_CONFIG (6)::
 	Reply to the GET_BAR_CONFIG message.
+LOG_MARKERS (7)::
+	Reply to the GET_LOG_MARKERS message.
 
 === COMMAND reply
 
@@ -134,7 +140,7 @@ property is +success (bool)+, but this will be expanded in future versions.
 { "success": true }
 -------------------
 
-=== GET_WORKSPACES reply
+=== WORKSPACES reply
 
 The reply consists of a serialized list of workspaces. Each workspace has the
 following properties:
@@ -248,7 +254,7 @@ rect (map)::
 ]
 -------------------
 
-=== GET_TREE reply
+=== TREE reply
 
 The reply consists of a serialized tree. Each node in the tree (representing
 one container) has at least the properties listed below. While the nodes might
@@ -431,7 +437,7 @@ JSON dump:
 }
 ------------------------
 
-=== GET_MARKS reply
+=== MARKS reply
 
 The reply consists of a single array of strings for each container that has a
 mark. The order of that array is undefined. If more than one container has the
@@ -440,7 +446,7 @@ contents are not unique).
 
 If no window has a mark the response will be the empty array [].
 
-=== GET_BAR_CONFIG reply
+=== BAR_CONFIG reply
 
 This can be used by third-party workspace bars (especially i3bar, but others
 are free to implement compatible alternatives) to get the +bar+ block
@@ -524,6 +530,40 @@ urgent_workspace_text/urgent_workspace_bar::
 }
 --------------
 
+=== LOG_MARKERS reply
+
+Gets the SHM log markers for the current position, the last wrap, the
+SHM segment name and segment size. This is necessary for tools like
+i3-dump-log which want to display the SHM log.
+
+The reply is a JSON map with the following entries:
+
+shmname (string)::
+	The name of the SHM segment, will be of the format +/i3-log-<pid>+.
+size (integer)::
+	The size (in bytes) of the SHM segment. If this is 0, SHM logging is
+	disabled.
+offset_next_write (integer)::
+	The offset in the SHM segment at which the next write will happen.
+	Tools should start printing lines from here, since the bytes following
+	this offset are the oldest log lines. However, the first line might be
+	garbled, so it makes sense to skip all bytes until the first \0.
+offset_last_wrap (integer)::
+	The offset in the SHM segment at which the last wrap occured. i3 only
+	stores entire messages in the SHM log, so it might waste a few bytes at
+	the end to be more efficient. Tools should not print content after the
+	offset_last_wrap.
+
+*Example*:
+-----------------------------
+{
+  "offset_next_write":132839,
+  "offset_last_wrap":26214400,
+  "shmname":"/i3-log-3392",
+  "size":26214400
+}
+-----------------------------
+
 == Events
 
 [[events]]

include/i3/ipc.h

@@ -40,6 +40,9 @@
 /** Request the configuration for a specific 'bar' */
 #define I3_IPC_MESSAGE_TYPE_GET_BAR_CONFIG      6
 
+/** Request the SHM debug log start/wrap markers */
+#define I3_IPC_MESSAGE_TYPE_GET_LOG_MARKERS     7
+
 /*
  * Messages from i3 to clients
  *
@@ -66,6 +69,9 @@
 /** Bar config reply type */
 #define I3_IPC_REPLY_TYPE_BAR_CONFIG            6
 
+/** Request the SHM debug log start/wrap markers */
+#define I3_IPC_REPLY_TYPE_LOG_MARKERS           7
+
 /*
  * Events from i3 to clients. Events have the first bit set high.
  *

src/ipc.c

@@ -612,6 +612,48 @@ IPC_HANDLER(get_bar_config) {
     y(free);
 }
 
+/*
+ * Formats the reply message for a GET_LOG_MARKERS request and sends it to the
+ * client.
+ *
+ */
+IPC_HANDLER(get_log_markers) {
+#if YAJL_MAJOR >= 2
+    yajl_gen gen = yajl_gen_alloc(NULL);
+#else
+    yajl_gen gen = yajl_gen_alloc(NULL, NULL);
+#endif
+
+    int offset_next_write, offset_last_wrap, logsize;
+    get_log_markers(&offset_next_write, &offset_last_wrap, &logsize);
+
+    y(map_open);
+    ystr("offset_next_write");
+    y(integer, offset_next_write);
+
+    ystr("offset_last_wrap");
+    y(integer, offset_last_wrap);
+
+    ystr("shmname");
+    ystr(shmlogname);
+
+    ystr("size");
+    y(integer, logsize);
+
+    y(map_close);
+
+    const unsigned char *payload;
+#if YAJL_MAJOR >= 2
+    size_t length;
+#else
+    unsigned int length;
+#endif
+    y(get_buf, &payload, &length);
+
+    ipc_send_message(fd, length, I3_IPC_REPLY_TYPE_LOG_MARKERS, payload);
+    y(free);
+}
+
 /*
  * Callback for the YAJL parser (will be called when a string is parsed).
  *
@@ -697,14 +739,15 @@ IPC_HANDLER(subscribe) {
 
 /* The index of each callback function corresponds to the numeric
  * value of the message type (see include/i3/ipc.h) */
-handler_t handlers[7] = {
+handler_t handlers[8] = {
     handle_command,
     handle_get_workspaces,
     handle_subscribe,
     handle_get_outputs,
     handle_tree,
     handle_get_marks,
-    handle_get_bar_config
+    handle_get_bar_config,
+    handle_get_log_markers
 };
 
 /*