Add return_truncated decode flag

README.md

@@ -48,6 +48,9 @@ The options for decode are:
   JSON term is decoded the return value of decode/2 becomes
   `{has_trailer, FirstTerm, RestData::iodata()}`. This is useful to
   decode multiple terms in a single binary.
+* `return_truncated`  - If the JSON passed to the decoder is incomplete
+  return `{truncated, Pos}`, where `Pos`, is the length of JSON read
+  before hitting the end of the interpretable term.
 * `dedupe_keys` - If a key is repeated in a JSON object this flag
   will ensure that the parsed object only contains a single entry
   containing the last value seen. This mirrors the parsing beahvior

c_src/decoder.c

@@ -52,6 +52,7 @@ typedef struct {
     size_t          bytes_per_red;
     int             is_partial;
     int             return_maps;
+    int             return_truncated;
     int             return_trailer;
     int             dedupe_keys;
     int             copy_strings;
@@ -84,6 +85,7 @@ dec_new(ErlNifEnv* env)
     d->is_partial = 0;
     d->return_maps = 0;
     d->return_trailer = 0;
+    d->return_truncated = 0;
     d->dedupe_keys = 0;
     d->copy_strings = 0;
     d->null_term = d->atoms->atom_null;
@@ -689,6 +691,8 @@ decode_init(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 #endif
         } else if(enif_compare(val, d->atoms->atom_return_trailer) == 0) {
             d->return_trailer = 1;
+        } else if(enif_compare(val, d->atoms->atom_return_truncated) == 0) {
+            d->return_truncated = 1;
         } else if(enif_compare(val, d->atoms->atom_dedupe_keys) == 0) {
             d->dedupe_keys = 1;
         } else if(enif_compare(val, d->atoms->atom_copy_strings) == 0) {
@@ -1035,7 +1039,12 @@ decode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
     }
 
     if(dec_curr(d) != st_done) {
-        ret = dec_error(d, "truncated_json");
+        if (d->return_truncated) {
+            ret = enif_make_tuple2(env, d->atoms->atom_truncated,
+                                   enif_make_int(d->env, d->i+1));
+        } else {
+            ret = dec_error(d, "truncated_json");
+        }
     } else if(d->is_partial) {
         ret = enif_make_tuple2(env, d->atoms->atom_partial, val);
     } else {

c_src/jiffy.c

@@ -24,9 +24,11 @@ load(ErlNifEnv* env, void** priv, ERL_NIF_TERM info)
     st->atom_pretty = make_atom(env, "pretty");
     st->atom_force_utf8 = make_atom(env, "force_utf8");
     st->atom_iter = make_atom(env, "iter");
+    st->atom_truncated = make_atom(env, "truncated");
     st->atom_bytes_per_iter = make_atom(env, "bytes_per_iter");
     st->atom_return_maps = make_atom(env, "return_maps");
     st->atom_return_trailer = make_atom(env, "return_trailer");
+    st->atom_return_truncated = make_atom(env, "return_truncated");
     st->atom_has_trailer = make_atom(env, "has_trailer");
     st->atom_nil = make_atom(env, "nil");
     st->atom_use_nil = make_atom(env, "use_nil");

c_src/jiffy.h

@@ -27,9 +27,11 @@ typedef struct {
     ERL_NIF_TERM    atom_pretty;
     ERL_NIF_TERM    atom_force_utf8;
     ERL_NIF_TERM    atom_iter;
+    ERL_NIF_TERM    atom_truncated;
     ERL_NIF_TERM    atom_bytes_per_iter;
     ERL_NIF_TERM    atom_return_maps;
     ERL_NIF_TERM    atom_return_trailer;
+    ERL_NIF_TERM    atom_return_truncated;
     ERL_NIF_TERM    atom_has_trailer;
     ERL_NIF_TERM    atom_nil;
     ERL_NIF_TERM    atom_use_nil;

src/jiffy.erl

@@ -34,11 +34,13 @@
 -endif.
 
 -type jiffy_decode_result() :: json_value()
-                        | {has_trailer, json_value(), binary()}.
+                        | {has_trailer, json_value(), binary()}
+                        | {truncated, non_neg_integer()}.
 
 -type decode_option() :: return_maps
                         | use_nil
                         | return_trailer
+                        | return_truncated
                         | dedupe_keys
                         | {null_term, any()}
                         | {bytes_per_iter, non_neg_integer()}

test/jiffy_18_return_truncated_tests.erl

@@ -0,0 +1,25 @@
+% This file is part of Jiffy released under the MIT license.
+% See the LICENSE file for more information.
+
+-module(jiffy_18_return_truncated_tests).
+
+-include_lib("eunit/include/eunit.hrl").
+
+cases() ->
+    [
+        {<<"">>, 1},
+        {<<"{">>, 2}
+    ].
+
+return_truncated_test_() ->
+    Opts = [return_truncated],
+    {"Test return_truncated", lists:map(fun({Data, Pos}) ->
+        ?_assertEqual({truncated, Pos}, jiffy:decode(Data, Opts))
+                                      end, cases())}.
+
+error_truncated_test_() ->
+    Opts = [],
+    {"Test truncated error case", lists:map(fun({Data, Pos}) ->
+        Error = {error, {Pos, truncated_json}},
+        ?_assertException(throw, Error, jiffy:decode(Data, Opts))
+                                        end, cases())}.