From 6bd4fc6943112db14c0b71fac707cf3def22aa83 Mon Sep 17 00:00:00 2001
From: Hans Nilsson <hans@erlang.org>
Date: Wed, 8 Aug 2018 19:31:27 +0200
Subject: ssh: Circular trace buffer primitives

---
 lib/ssh/src/ssh.hrl     |  25 +++++++++++
 lib/ssh/src/ssh_dbg.erl | 108 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 132 insertions(+), 1 deletion(-)

(limited to 'lib/ssh')

diff --git a/lib/ssh/src/ssh.hrl b/lib/ssh/src/ssh.hrl
index 9631427749..01c44cb371 100644
--- a/lib/ssh/src/ssh.hrl
+++ b/lib/ssh/src/ssh.hrl
@@ -492,4 +492,29 @@
 -define(wr_record(N), ?wr_record(N, [])).
 
 
+%% Circular trace buffer macros
+
+-record(circ_buf_entry,
+        {
+          module,
+          line,
+          function,
+          pid = self(),
+          value
+        }).
+
+-define(CIRC_BUF_IN(VALUE),
+        ssh_dbg:cbuf_in(
+          #circ_buf_entry{module = ?MODULE,
+                          line = ?LINE,
+                          function = {?FUNCTION_NAME,?FUNCTION_ARITY},
+                          pid = self(),
+                          value = (VALUE)
+                         })
+       ).
+
+-define(CIRC_BUF_IN_ONCE(VALUE),
+        ((fun(V) -> ?CIRC_BUF_IN(V), V end)(VALUE))
+       ).
+                 
 -endif. % SSH_HRL defined
diff --git a/lib/ssh/src/ssh_dbg.erl b/lib/ssh/src/ssh_dbg.erl
index b53c09b17d..3681e03cc2 100644
--- a/lib/ssh/src/ssh_dbg.erl
+++ b/lib/ssh/src/ssh_dbg.erl
@@ -54,7 +54,13 @@
          start_tracer/0, start_tracer/1,
          on/1,  on/0,
          off/1, off/0,
-         go_on/0
+         go_on/0,
+         %% Circular buffer
+         cbuf_start/0, cbuf_start/1,
+         cbuf_stop_clear/0,
+         cbuf_in/1,
+         cbuf_list/0,
+         fmt_cbuf_items/0, fmt_cbuf_item/1
 	]).
 
 -export([shrink_bin/1,
@@ -331,3 +337,103 @@ ts({_,_,Usec}=Now) when is_integer(Usec) ->
     io_lib:format("~.2.0w:~.2.0w:~.2.0w.~.6.0w",[HH,MM,SS,Usec]);
 ts(_) ->
     "-".
+
+%%%================================================================
+-define(CIRC_BUF, circ_buf).
+
+cbuf_start() ->
+    cbuf_start(20).
+
+cbuf_start(CbufMaxLen) ->
+    put(?CIRC_BUF, {CbufMaxLen,queue:new()}),
+    ok.
+
+
+cbuf_stop_clear() ->
+    case erase(?CIRC_BUF) of
+        undefined ->
+            [];
+        {_CbufMaxLen,Queue} ->
+            queue:to_list(Queue)
+    end.
+
+
+cbuf_in(Value) ->
+    case get(?CIRC_BUF) of
+        undefined ->
+            disabled;
+        {CbufMaxLen,Queue} ->
+            UpdatedQueue =
+                try queue:head(Queue) of
+                    {Value, TS0, Cnt0} ->
+                        %% Same Value as last saved in the queue
+                        queue:in_r({Value, TS0, Cnt0+1},
+                                 queue:drop(Queue)
+                                );
+                    _ ->
+                        queue:in_r({Value, erlang:timestamp(), 1},
+                                   truncate_cbuf(Queue, CbufMaxLen)
+                                )
+                catch
+                    error:empty ->
+                        queue:in_r({Value, erlang:timestamp(), 1}, Queue)
+                end,
+            put(?CIRC_BUF, {CbufMaxLen,UpdatedQueue}),
+            ok
+    end.
+
+
+cbuf_list() ->
+    case get(?CIRC_BUF) of
+        undefined ->
+            [];
+        {_CbufMaxLen,Queue} ->
+            queue:to_list(Queue)
+    end.
+
+
+truncate_cbuf(Q, CbufMaxLen) ->
+    case queue:len(Q) of
+        N when N>=CbufMaxLen ->
+            truncate_cbuf(element(2,queue:out_r(Q)), CbufMaxLen);
+        _ ->
+            Q
+    end.
+
+fmt_cbuf_items() ->
+    lists:flatten(
+      io_lib:format("Circular trace buffer. Latest item first.~n~s~n",
+                    [case get(?CIRC_BUF) of
+                         {Max,_} ->
+                             L = cbuf_list(),
+                             [io_lib:format("==== ~.*w: ~s~n",[num_digits(Max),N,fmt_cbuf_item(X)]) ||
+                                 {N,X} <- lists:zip(lists:seq(1,length(L)), L)
+                             ];
+                         _ ->
+                             io_lib:format("Not started.~n",[])
+                     end])).
+                   
+
+num_digits(0) -> 1;
+num_digits(N) when N>0 -> 1+trunc(math:log10(N)).
+    
+
+fmt_cbuf_item({Value, TimeStamp, N}) ->
+    io_lib:format("~s~s~n~s~n",
+                  [fmt_ts(TimeStamp),
+                   [io_lib:format(" (Repeated ~p times)",[N]) || N>1],
+                   fmt_value(Value)]).
+
+
+fmt_ts(TS = {_,_,Us}) ->
+    {{YY,MM,DD},{H,M,S}} = calendar:now_to_universal_time(TS),
+    io_lib:format("~w-~.2.0w-~.2.0w ~.2.0w:~.2.0w:~.2.0w.~.6.0w UTC",[YY,MM,DD,H,M,S,Us]).
+    
+fmt_value(#circ_buf_entry{module = M,
+                          line = L,
+                          function = {F,A},
+                          pid = Pid,
+                          value = V}) ->
+    io_lib:format("~p:~p  ~p/~p ~p~n~s",[M,L,F,A,Pid,fmt_value(V)]);
+fmt_value(Value) ->
+    io_lib:format("~p",[Value]).
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