Improve the detection of missing required fields.

Now the limit of tracked fields is configurable at compile-time using
PB_MAX_REQUIRED_FIELDS. Added related test and updated documentation.

Fixes issue #18.

6 files changed, 229 insertions, 24 deletions

diff --git a/docs/reference.rst b/docs/reference.rst
index f4957804..81251fe6 100644
--- a/docs/reference.rst
+++ b/docs/reference.rst
@@ -10,11 +10,12 @@ Compilation options
 ===================
 The following options can be specified using -D switch given to the C compiler:
 
-==================  ==============================================================================================
-__BIG_ENDIAN__       Set this if your platform stores integers and floats in big-endian format.
-                     Mixed-endian systems (different layout for ints and floats) are currently not supported.
-NANOPB_INTERNALS     Set this to expose the field encoder functions that are hidden since nanopb-0.1.3.
-==================  ==============================================================================================
+============================  ==============================================================================================
+__BIG_ENDIAN__                 Set this if your platform stores integers and floats in big-endian format.
+                               Mixed-endian systems (different layout for ints and floats) are currently not supported.
+NANOPB_INTERNALS               Set this to expose the field encoder functions that are hidden since nanopb-0.1.3.
+PB_MAX_REQUIRED_FIELDS         Maximum number of required fields to check for presence. Default value is 64.
+============================  ==============================================================================================
 
 pb.h
 ====
@@ -310,8 +311,6 @@ In addition to EOF, the pb_decode implementation supports terminating a message
 
 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
 
-Because of memory concerns, the detection of missing required fields is not perfect if the structure contains more than 32 fields.
-
 pb_decode_varint
 ----------------
 Read and decode a varint_ encoded integer. ::
diff --git a/pb.h b/pb.h
index 502958be..fc74dbd4 100644
--- a/pb.h
+++ b/pb.h
@@ -22,6 +22,12 @@
 #define UNUSED(x) (void)(x)
 #endif
 
+/* Number of required fields to keep track of
+ * (change here or on compiler command line). */
+#ifndef PB_MAX_REQUIRED_FIELDS
+#define PB_MAX_REQUIRED_FIELDS 64
+#endif
+
 /* List of possible field types. These are used in the autogenerated code.
  * Least-significant 4 bits tell the scalar type
  * Most-significant 4 bits specify repeated/required/packed etc.
diff --git a/pb_decode.c b/pb_decode.c
index 50a11c40..458d5f1e 100644
--- a/pb_decode.c
+++ b/pb_decode.c
@@ -206,18 +206,20 @@ static bool checkreturn make_string_substream(pb_istream_t *stream, pb_istream_t
 
 /* Iterator for pb_field_t list */
 typedef struct {
-    const pb_field_t *start;
-    const pb_field_t *current;
-    int field_index;
-    void *dest_struct;
-    void *pData;
-    void *pSize;
+    const pb_field_t *start; /* Start of the pb_field_t array */
+    const pb_field_t *current; /* Current position of the iterator */
+    int field_index; /* Zero-based index of the field. */
+    int required_field_index; /* Zero-based index that counts only the required fields */
+    void *dest_struct; /* Pointer to the destination structure to decode to */
+    void *pData; /* Pointer where to store current field value */
+    void *pSize; /* Pointer where to store the size of current array field */
 } pb_field_iterator_t;
 
 static void pb_field_init(pb_field_iterator_t *iter, const pb_field_t *fields, void *dest_struct)
 {
     iter->start = iter->current = fields;
     iter->field_index = 0;
+    iter->required_field_index = 0;
     iter->pData = (char*)dest_struct + iter->current->data_offset;
     iter->pSize = (char*)iter->pData + iter->current->size_offset;
     iter->dest_struct = dest_struct;
@@ -231,12 +233,16 @@ static bool pb_field_next(pb_field_iterator_t *iter)
     if (PB_HTYPE(iter->current->type) == PB_HTYPE_ARRAY)
         prev_size *= iter->current->array_size;
     
+    if (PB_HTYPE(iter->current->type) == PB_HTYPE_REQUIRED)
+        iter->required_field_index++;
+    
     iter->current++;
     iter->field_index++;
     if (iter->current->tag == 0)
     {
         iter->current = iter->start;
         iter->field_index = 0;
+        iter->required_field_index = 0;
         iter->pData = iter->dest_struct;
         prev_size = 0;
         notwrapped = false;
@@ -403,9 +409,8 @@ static void pb_message_set_to_defaults(const pb_field_t fields[], void *dest_str
 
 bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
 {
-    uint32_t fields_seen = 0; /* Used to check for required fields */
+    uint8_t fields_seen[(PB_MAX_REQUIRED_FIELDS + 7) / 8] = {}; /* Used to check for required fields */
     pb_field_iterator_t iter;
-    int i;
     
     pb_message_set_to_defaults(fields, dest_struct);
     
@@ -433,21 +438,26 @@ bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void
             continue;
         }
         
-        fields_seen |= 1 << (iter.field_index & 31);
+        if (PB_HTYPE(iter.current->type) == PB_HTYPE_REQUIRED
+            && iter.required_field_index < PB_MAX_REQUIRED_FIELDS)
+        {
+            fields_seen[iter.required_field_index >> 3] |= 1 << (iter.required_field_index & 7);
+        }
             
         if (!decode_field(stream, wire_type, &iter))
             return false;
     }
     
-    /* Check that all required fields (mod 31) were present. */
-    for (i = 0; fields[i].tag != 0; i++)
-    {
-        if (PB_HTYPE(fields[i].type) == PB_HTYPE_REQUIRED &&
-            !(fields_seen & (1 << (i & 31))))
+    /* Check that all required fields were present. */
+    pb_field_init(&iter, fields, dest_struct);
+    do {
+        if (PB_HTYPE(iter.current->type) == PB_HTYPE_REQUIRED &&
+            iter.required_field_index < PB_MAX_REQUIRED_FIELDS &&
+            !(fields_seen[iter.required_field_index >> 3] & (1 << (iter.required_field_index & 7))))
         {
             return false;
         }
-    }
+    } while (pb_field_next(&iter));
     
     return true;
 }
diff --git a/tests/Makefile b/tests/Makefile
index 8e2df140..24e9ba62 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -1,6 +1,6 @@
 CFLAGS=-ansi -Wall -Werror -I .. -g -O0 --coverage
 LDFLAGS=--coverage
-DEPS=../pb_decode.h ../pb_encode.h ../pb.h person.pb.h callbacks.pb.h unittests.h unittestproto.pb.h alltypes.pb.h
+DEPS=../pb_decode.h ../pb_encode.h ../pb.h person.pb.h callbacks.pb.h unittests.h unittestproto.pb.h alltypes.pb.h missing_fields.pb.h
 TESTS=test_decode1 test_encode1 decode_unittests encode_unittests
 
 all: breakpoints $(TESTS) run_unittests
@@ -25,6 +25,7 @@ test_encode2: test_encode2.o pb_encode.o person.pb.o
 test_encode3: test_encode3.o pb_encode.o alltypes.pb.o
 test_decode_callbacks: test_decode_callbacks.o pb_decode.o callbacks.pb.o
 test_encode_callbacks: test_encode_callbacks.o pb_encode.o callbacks.pb.o
+test_missing_fields: test_missing_fields.o pb_encode.o pb_decode.o missing_fields.pb.o
 decode_unittests: decode_unittests.o pb_decode.o unittestproto.pb.o
 encode_unittests: encode_unittests.o pb_encode.o unittestproto.pb.o
 
@@ -41,7 +42,7 @@ coverage: run_unittests
 	gcov pb_encode.gcda
 	gcov pb_decode.gcda
 
-run_unittests: decode_unittests encode_unittests test_encode1 test_encode2 test_encode3 test_decode1 test_decode2 test_decode3 test_encode_callbacks test_decode_callbacks
+run_unittests: decode_unittests encode_unittests test_encode1 test_encode2 test_encode3 test_decode1 test_decode2 test_decode3 test_encode_callbacks test_decode_callbacks test_missing_fields
 	rm -f *.gcda
 	
 	./decode_unittests > /dev/null
@@ -61,6 +62,8 @@ run_unittests: decode_unittests encode_unittests test_encode1 test_encode2 test_
 
 	./test_encode3 | ./test_decode3
 	./test_encode3 | protoc --decode=AllTypes -I. -I../generator -I/usr/include alltypes.proto >/dev/null
+	
+	./test_missing_fields
 
 run_fuzztest: test_decode2
 	bash -c 'I=1; while true; do cat /dev/urandom | ./test_decode2 > /dev/null; I=$$(($$I+1)); echo -en "\r$$I"; done'
diff --git a/tests/missing_fields.proto b/tests/missing_fields.proto
new file mode 100644
index 00000000..cbb23ba1
--- /dev/null
+++ b/tests/missing_fields.proto
@@ -0,0 +1,138 @@
+/* Test for one missing field among many */
+
+message AllFields
+{
+    required int32 field1 = 1;
+    required int32 field2 = 2;
+    required int32 field3 = 3;
+    required int32 field4 = 4;
+    required int32 field5 = 5;
+    required int32 field6 = 6;
+    required int32 field7 = 7;
+    required int32 field8 = 8;
+    required int32 field9 = 9;
+    required int32 field10 = 10;
+    required int32 field11 = 11;
+    required int32 field12 = 12;
+    required int32 field13 = 13;
+    required int32 field14 = 14;
+    required int32 field15 = 15;
+    required int32 field16 = 16;
+    required int32 field17 = 17;
+    required int32 field18 = 18;
+    required int32 field19 = 19;
+    required int32 field20 = 20;
+    required int32 field21 = 21;
+    required int32 field22 = 22;
+    required int32 field23 = 23;
+    required int32 field24 = 24;
+    required int32 field25 = 25;
+    required int32 field26 = 26;
+    required int32 field27 = 27;
+    required int32 field28 = 28;
+    required int32 field29 = 29;
+    required int32 field30 = 30;
+    required int32 field31 = 31;
+    required int32 field32 = 32;
+    required int32 field33 = 33;
+    required int32 field34 = 34;
+    required int32 field35 = 35;
+    required int32 field36 = 36;
+    required int32 field37 = 37;
+    required int32 field38 = 38;
+    required int32 field39 = 39;
+    required int32 field40 = 40;
+    required int32 field41 = 41;
+    required int32 field42 = 42;
+    required int32 field43 = 43;
+    required int32 field44 = 44;
+    required int32 field45 = 45;
+    required int32 field46 = 46;
+    required int32 field47 = 47;
+    required int32 field48 = 48;
+    required int32 field49 = 49;
+    required int32 field50 = 50;
+    required int32 field51 = 51;
+    required int32 field52 = 52;
+    required int32 field53 = 53;
+    required int32 field54 = 54;
+    required int32 field55 = 55;
+    required int32 field56 = 56;
+    required int32 field57 = 57;
+    required int32 field58 = 58;
+    required int32 field59 = 59;
+    required int32 field60 = 60;
+    required int32 field61 = 61;
+    required int32 field62 = 62;
+    required int32 field63 = 63;
+    required int32 field64 = 64;
+}
+
+message MissingField
+{
+    required int32 field1 = 1;
+    required int32 field2 = 2;
+    required int32 field3 = 3;
+    required int32 field4 = 4;
+    required int32 field5 = 5;
+    required int32 field6 = 6;
+    required int32 field7 = 7;
+    required int32 field8 = 8;
+    required int32 field9 = 9;
+    required int32 field10 = 10;
+    required int32 field11 = 11;
+    required int32 field12 = 12;
+    required int32 field13 = 13;
+    required int32 field14 = 14;
+    required int32 field15 = 15;
+    required int32 field16 = 16;
+    required int32 field17 = 17;
+    required int32 field18 = 18;
+    required int32 field19 = 19;
+    required int32 field20 = 20;
+    required int32 field21 = 21;
+    required int32 field22 = 22;
+    required int32 field23 = 23;
+    required int32 field24 = 24;
+    required int32 field25 = 25;
+    required int32 field26 = 26;
+    required int32 field27 = 27;
+    required int32 field28 = 28;
+    required int32 field29 = 29;
+    required int32 field30 = 30;
+    required int32 field31 = 31;
+    required int32 field32 = 32;
+    required int32 field33 = 33;
+    required int32 field34 = 34;
+    required int32 field35 = 35;
+    required int32 field36 = 36;
+    required int32 field37 = 37;
+    required int32 field38 = 38;
+    required int32 field39 = 39;
+    required int32 field40 = 40;
+    required int32 field41 = 41;
+    required int32 field42 = 42;
+    required int32 field43 = 43;
+    required int32 field44 = 44;
+    required int32 field45 = 45;
+    required int32 field46 = 46;
+    required int32 field47 = 47;
+    required int32 field48 = 48;
+    required int32 field49 = 49;
+    required int32 field50 = 50;
+    required int32 field51 = 51;
+    required int32 field52 = 52;
+    required int32 field53 = 53;
+    required int32 field54 = 54;
+    required int32 field55 = 55;
+    required int32 field56 = 56;
+    required int32 field57 = 57;
+    required int32 field58 = 58;
+    required int32 field59 = 59;
+    required int32 field60 = 60;
+    required int32 field61 = 61;
+    required int32 field62 = 62;
+/*    required int32 field63 = 63; */
+    required int32 field64 = 64;
+}
+
diff --git a/tests/test_missing_fields.c b/tests/test_missing_fields.c
new file mode 100644
index 00000000..46cd7d96
--- /dev/null
+++ b/tests/test_missing_fields.c
@@ -0,0 +1,49 @@
+/* Checks that missing required fields are detected properly */
+
+#include <stdio.h>
+#include <pb_encode.h>
+#include <pb_decode.h>
+#include "missing_fields.pb.h"
+
+int main()
+{
+    uint8_t buffer[512] = {};
+    
+    /* Create a message with one missing field */
+    {
+        MissingField msg = {};
+        pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
+        if (!pb_encode(&stream, MissingField_fields, &msg))
+        {
+            printf("Encode failed.\n");
+            return 1;
+        }
+    }
+
+    /* Test that it decodes properly if we don't require that field */
+    {
+        MissingField msg = {};
+        pb_istream_t stream = pb_istream_from_buffer(buffer, sizeof(buffer));
+        
+        if (!pb_decode(&stream, MissingField_fields, &msg))
+        {
+            printf("Decode failed.\n");
+            return 2;
+        }
+    }
+    
+    /* Test that it does *not* decode properly if we require the field */
+    {
+        AllFields msg = {};
+        pb_istream_t stream = pb_istream_from_buffer(buffer, sizeof(buffer));
+        
+        if (pb_decode(&stream, AllFields_fields, &msg))
+        {
+            printf("Decode didn't detect missing field.\n");
+            return 3;
+        }
+    }
+    
+    return 0; /* All ok */
+}
+