option to ignore some atoms to make json smaller

Author: kuenishi

c_src/encoder.c

@@ -266,6 +266,21 @@ match_json(ErlNifEnv* env, ERL_NIF_TERM term, State *st){
   return 0;
 }
 
+static inline int
+enc_should_be_ignored(ErlNifEnv* env, ERL_NIF_TERM atom, const EncEntry* entry){
+  if(!enif_is_atom(env, atom)){
+    return 0;
+  }
+  unsigned i;
+  for(i=0; i<entry->ignored_len; ++i){
+    if(enif_is_identical(atom, entry->ignored[i])){
+      return 1;
+    }
+  }
+  return 0;
+}
+
+
 static inline int
 match_record(ErlNifEnv* env, int arity, const ERL_NIF_TERM *tuple, State *st){
 
@@ -279,7 +294,7 @@ match_record(ErlNifEnv* env, int arity, const ERL_NIF_TERM *tuple, State *st){
       b_putc('{', st);
       for(k = 0; k < records[i].arity; k++){
 
-        if(tuple[k+1] != st->priv->am_null){
+        if(!enc_should_be_ignored(env, tuple[k+1], st->records)){
           EncField field = fields[fds_offset + k];
           bin_size += field.size;
 	//FIXME {

c_src/jsonx.c

@@ -8,6 +8,10 @@ enc_rt_dtor(ErlNifEnv* env, void* obj){
   EncEntry *entry = (EncEntry*)obj;
   enif_release_binary(&entry->bin);
   entry->bin.data = NULL;
+  if(entry->ignored){
+    enif_free(entry->ignored);
+    entry->ignored = NULL;
+  }
   entry = NULL;
 }
 
@@ -73,7 +77,7 @@ make_encoder_resource_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]){
   enif_get_uint(env, argv[4], &bin_sz);
   PrivData* priv = (PrivData*)enif_priv_data(env);
   unsigned resource_sz = enc_resource_size(rs_len, fs_len);
-  EncEntry *enc_entry = (EncEntry*)enif_alloc_resource(priv->encoder_RSTYPE, resource_sz); 
+  EncEntry *enc_entry = (EncEntry*)enif_alloc_resource(priv->encoder_RSTYPE, resource_sz);
   //memset(enc_entry, 0, resource_sz);
   enc_entry->records_cnt = rs_len;
   enc_entry->fields_cnt = fs_len;
@@ -101,6 +105,7 @@ make_encoder_resource_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]){
     i++;
     list = tail;
   }
+
   list = argv[3];
   i = 0;
   while(enif_get_list_cell(env, list, &head, &tail)){
@@ -116,6 +121,23 @@ make_encoder_resource_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]){
     i++;
     list = tail;
   }
+
+  list = argv[6];
+  if(!enif_get_list_length(env, list, &(enc_entry->ignored_len)))
+    goto error;
+  enc_entry->ignored = (ERL_NIF_TERM*)enif_alloc(enc_entry->ignored_len*sizeof(ERL_NIF_TERM));
+  i = 0;
+  while(enif_get_list_cell(env, list, &head, &tail)){
+    // ignored term should be atoms
+    if(enif_is_atom(env, head)){
+      enc_entry->ignored[i] = head;
+    }else{
+      enif_free(enc_entry->ignored);
+      goto error;
+    }
+    i++;
+    list = tail;
+  }
   ERL_NIF_TERM ret = enif_make_resource(env, (void *)enc_entry);
   enif_release_resource(enc_entry);
   return ret;
@@ -201,7 +223,7 @@ nif_funcs[] = {
   {"encode_res", 2, encode_nif}, // with resource
   {"decode_opt", 2, decode_nif}, // with options
   {"decode_res", 4, decode_nif}, // with options, resource and strict flag
-  {"make_encoder_resource", 6, make_encoder_resource_nif},
+  {"make_encoder_resource", 7, make_encoder_resource_nif},
   {"make_decoder_resource", 6, make_decoder_resource_nif}
 };
 

c_src/jsonx.h

@@ -72,6 +72,8 @@ typedef struct{
   ErlNifBinary bin;
   unsigned records_cnt;
   unsigned fields_cnt;
+  ERL_NIF_TERM* ignored;
+  unsigned ignored_len;
 }EncEntry;
 
 static inline EncRecord*

examples/records_examples.erl

@@ -8,6 +8,10 @@ encoder1() ->
     jsonx:encoder([{person,   record_info(fields, person)},
                    {person2,  record_info(fields, person2)} ]).
 
+encoder1_ignore() ->
+    jsonx:encoder([{person,   record_info(fields, person)},
+                   {person2,  record_info(fields, person2)} ], [{ignore, [null]}]).
+
 decoder1() ->
     jsonx:decoder([{person,   record_info(fields, person)},
                    {person2,  record_info(fields, person2)}]).

src/jsonx.erl

@@ -30,11 +30,14 @@
 %%      </ul>
 
 -module(jsonx).
--export([encode/1, decode/1, decode/2, encoder/1, decoder/1, decoder/2]).
+-export([encode/1, decode/1, decode/2,
+         encoder/1, encoder/2, decoder/1, decoder/2]).
 -on_load(init/0).
 -define(LIBNAME, jsonx).
 -define(APPNAME, jsonx).
 
+-include_lib("eunit/include/eunit.hrl").
+
 %% =================
 %% API Encoding JSON
 %% =================
@@ -51,8 +54,17 @@ encode(JSON_TERM)->
       RECORDS_DESC :: [{tag, [names]}],
       ENCODER      :: function().
 encoder(Records_desc) ->
+    encoder(Records_desc, []).
+
+%%@doc Build a JSON encoder.
+-spec encoder(RECORDS_DESC, OPTIONS) -> ENCODER when
+      RECORDS_DESC :: [{tag, [names]}],
+      OPTIONS      :: [{ignore, [atom()]}],
+      ENCODER      :: function().
+encoder(Records_desc, Options) ->
     {Rcnt, Fcnt, Binsz, Records, Fields, Bin} = prepare_enc_desc(Records_desc),
-    Resource = make_encoder_resource(Rcnt, Fcnt, Records, Fields, Binsz, Bin),
+    Ignored = proplists:get_value(ignore, Options, []),
+    Resource = make_encoder_resource(Rcnt, Fcnt, Records, Fields, Binsz, Bin, Ignored),
     fun(JSON_TERM) -> encode_res(JSON_TERM, Resource) end.
 
 %% ==================
@@ -116,7 +128,7 @@ decode_opt(_JSON, _FORMAT) ->
 decode_res(_JSON_TERM, _FORMAT, _RESOURCE, _STRICT_FLAG) ->
     not_loaded(?LINE).
 
-make_encoder_resource(_Rcnt, _Fcnt, _Records, _Fields, _Binsz, _Bin) ->
+make_encoder_resource(_Rcnt, _Fcnt, _Records, _Fields, _Binsz, _Bin, _Ignored) ->
     not_loaded(?LINE).
 
 make_decoder_resource(_RecCnt, _UKeyCnt, _KeyCnt, _UKeys, _Keys, _Records3) ->

test/encode_records_test.erl

@@ -25,5 +25,6 @@ encrec2_test() ->
 
 encrec3_test() ->
     %%F = jsonx:encoder([ {spam, [a, b, c]} ], [{ignore,null}]),
-    F = jsonx:encoder([ {spam, [a, b, c]} ]),
-    <<"{}">> = F({spam, null, null, null}). 
+    F = jsonx:encoder([ {spam, [a, b, c]} ], [{ignore, [null, undefined]}]),
+    <<"{}">> = F({spam, null, null, null}),
+    <<"{\"a\": \"nall\"}">> = F({spam, nall, null, undefined}).