Restore diameter_codec:decode/2, update diameter_codec(3)

The documentation has been out of date since the string_decode option
was added in commit 1590920c. The optionless decode/2 was removed in the
commit that removed the use of the process dictionary in decode.

2 files changed, 30 insertions, 13 deletions

diff --git a/lib/diameter/doc/src/diameter_codec.xml b/lib/diameter/doc/src/diameter_codec.xml
index 91e96058dd..0117c1c88a 100644
--- a/lib/diameter/doc/src/diameter_codec.xml
+++ b/lib/diameter/doc/src/diameter_codec.xml
@@ -13,7 +13,8 @@
 <erlref>
 <header>
 <copyright>
-<year>2012</year><year>2016</year>
+<year>2012</year>
+<year>2017</year>
 <holder>Ericsson AB. All Rights Reserved.</holder>
 </copyright>
 <legalnotice>
@@ -53,17 +54,17 @@ communicated to &man_app; callbacks.
 Similarly, outgoing Diameter messages are encoded into binary() before
 being passed to the appropriate &man_transport; module for
 transmission.
-The functions in this module implement this encode/decode.</p>
+The functions documented here implement the default encode/decode.</p>
 
-<note>
+<warning>
 <p>
-Calls to this module are made by diameter itself as a consequence of
-configuration passed to &mod_start_service;.
-The encode/decode functions may also be useful for other purposes (eg.
-test) but the diameter user does not need to call them explicitly when
+The diameter user does not need to call functions here explicitly when
 sending and receiving messages using &mod_call; and the callback
-interface documented in &man_app;.</p>
-</note>
+interface documented in &man_app;: diameter itself provides encode/decode
+as a consequence of configuration passed to &mod_start_service;, and
+the results may differ from those returned by the functions documented
+here, depending on configuration.</p>
+</warning>
 
 <p>
 The &header; and &packet; records below
diff --git a/lib/diameter/src/base/diameter_codec.erl b/lib/diameter/src/base/diameter_codec.erl
index a4d816db4e..82fa796e69 100644
--- a/lib/diameter/src/base/diameter_codec.erl
+++ b/lib/diameter/src/base/diameter_codec.erl
@@ -20,10 +20,8 @@
 
 -module(diameter_codec).
 
--export([encode/2,
-         encode/3,
-         decode/3,
-         decode/4,
+-export([encode/2, encode/3,
+         decode/2, decode/3, decode/4,
          collect_avps/1,
          decode_header/1,
          sequence_numbers/1,
@@ -68,6 +66,10 @@
 %%% # encode/2
 %%% ---------------------------------------------------------------------------
 
+%% The representative encode documented in diameter_codec(3). As of
+%% the options that affect encode (eg. ordered_encode), it's no longer
+%% *the* encode.
+
 encode(Mod, Msg) ->
     encode(Mod, #{ordered_encode => true}, Msg).
 
@@ -277,6 +279,20 @@ rec2msg(Mod, Rec) ->
     Mod:rec2msg(element(1, Rec)).
 
 %%% ---------------------------------------------------------------------------
+%%% # decode/2
+%%% ---------------------------------------------------------------------------
+
+%% The representative default decode documented in diameter_codec(3).
+%% As of the options that affect decode (eg. string_decode), it's no
+%% longer *the* decode.
+
+decode(Mod, Pkt) ->
+    Opts = #{string_decode => true,
+             strict_mbit => true,
+             rfc => 6733},
+    decode(Mod, Opts, Pkt).
+
+%%% ---------------------------------------------------------------------------
 %%% # decode/3
 %%% ---------------------------------------------------------------------------