[stdlib] Introduce new functions epp:read_encoding_from_binary/1,2

3 files changed, 57 insertions, 8 deletions

diff --git a/lib/stdlib/doc/src/epp.xml b/lib/stdlib/doc/src/epp.xml
index 3e8aba2e5f..df7bf883fc 100644
--- a/lib/stdlib/doc/src/epp.xml
+++ b/lib/stdlib/doc/src/epp.xml
@@ -4,7 +4,7 @@
 <erlref>
   <header>
     <copyright>
-      <year>1996</year><year>2012</year>
+      <year>1996</year><year>2013</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -109,7 +109,8 @@
       <fsummary>Return a string representation of an encoding</fsummary>
       <desc>
         <p>Returns a string representation of an encoding. The string
-        is recognized by <c>read_encoding/1,2</c> and
+        is recognized by <c>read_encoding/1,2</c>,
+        <c>read_encoding_from_binary/1,2</c>, and
         <c>set_encoding/1</c> as a valid encoding.</p>
       </desc>
     </func>
@@ -128,6 +129,20 @@
       </desc>
     </func>
     <func>
+      <name name="read_encoding_from_binary" arity="1"/>
+      <name name="read_encoding_from_binary" arity="2"/>
+      <fsummary>Read the encoding from a binary</fsummary>
+      <desc>
+        <p>Read the <seealso marker="#encoding">encoding</seealso> from
+          a binary. Returns the read encoding, or <c>none</c> if no
+          valid encoding was found.</p>
+        <p>The option <c>in_comment_only</c> is <c>true</c> by
+          default, which is correct for Erlang source files. If set to
+          <c>false</c> the encoding string does not necessarily have to
+          occur in a comment.</p>
+      </desc>
+    </func>
+    <func>
       <name name="set_encoding" arity="1"/>
       <fsummary>Read and set the encoding of an IO device</fsummary>
       <desc>
diff --git a/lib/stdlib/src/epp.erl b/lib/stdlib/src/epp.erl
index 475b1bf933..afa39c3fb9 100644
--- a/lib/stdlib/src/epp.erl
+++ b/lib/stdlib/src/epp.erl
@@ -24,7 +24,8 @@
 -export([scan_erl_form/1,parse_erl_form/1,macro_defs/1]).
 -export([parse_file/1, parse_file/3]).
 -export([default_encoding/0, encoding_to_string/1,
-         read_encoding/1, read_encoding/2, set_encoding/1]).
+         read_encoding_from_binary/1, read_encoding_from_binary/2,
+         set_encoding/1, read_encoding/1, read_encoding/2]).
 -export([interpret_file_attribute/1]).
 -export([normalize_typed_record_fields/1,restore_typed_record_fields/1]).
 
@@ -265,13 +266,41 @@ set_encoding(File) ->
     ok = io:setopts(File, [{encoding, Enc}]),
     Encoding.
 
--spec read_encoding_from_file(File, InComment) -> source_encoding() | none when
-      File :: io:device(),
-      InComment :: boolean().
+-spec read_encoding_from_binary(Binary) -> source_encoding() | none when
+      Binary :: binary().
 
 -define(ENC_CHUNK, 32).
 -define(N_ENC_CHUNK, 16). % a total of 512 bytes
 
+read_encoding_from_binary(Binary) ->
+    read_encoding_from_binary(Binary, []).
+
+-spec read_encoding_from_binary(Binary, Options) ->
+                                       source_encoding() | none when
+      Binary :: binary(),
+      Options :: [Option],
+      Option :: {in_comment_only, boolean()}.
+
+read_encoding_from_binary(Binary, Options) ->
+    InComment = proplists:get_value(in_comment_only, Options, true),
+    try
+        com_nl(Binary, fake_reader(0), 0, InComment)
+    catch
+        throw:no ->
+            none
+    end.
+
+fake_reader(N) ->
+    fun() when N =:= ?N_ENC_CHUNK ->
+            throw(no);
+       () ->
+            {<<>>, fake_reader(N+1)}
+    end.
+
+-spec read_encoding_from_file(File, InComment) -> source_encoding() | none when
+      File :: io:device(),
+      InComment :: boolean().
+
 read_encoding_from_file(File, InComment) ->
     {ok, Pos0} = file:position(File, cur),
     Opts = io:getopts(File),
diff --git a/lib/stdlib/test/epp_SUITE.erl b/lib/stdlib/test/epp_SUITE.erl
index 606bbbcbb2..041d521514 100644
--- a/lib/stdlib/test/epp_SUITE.erl
+++ b/lib/stdlib/test/epp_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1998-2012. All Rights Reserved.
+%% Copyright Ericsson AB 1998-2013. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -1342,6 +1342,8 @@ encoding(Enc, File) ->
     E = encoding_nocom(Enc, File).
 
 encoding_com(Enc, File) ->
+    B = list_to_binary(Enc),
+    E = epp:read_encoding_from_binary(B),
     ok = file:write_file(File, Enc),
     {ok, Fd} = file:open(File, [read]),
     E = epp:set_encoding(Fd),
@@ -1349,10 +1351,13 @@ encoding_com(Enc, File) ->
     E = epp:read_encoding(File).
 
 encoding_nocom(Enc, File) ->
+    Options = [{in_comment_only, false}],
+    B = list_to_binary(Enc),
+    E = epp:read_encoding_from_binary(B, Options),
     ok = file:write_file(File, Enc),
     {ok, Fd} = file:open(File, [read]),
     ok = file:close(Fd),
-    epp:read_encoding(File, [{in_comment_only, false}]).
+    E = epp:read_encoding(File, Options).
 
 check(Config, Tests) ->
     eval_tests(Config, fun check_test/2, Tests).