Allow constructing RadioTapParser from an empty buffer

include/tins/utils/radiotap_parser.h

@@ -60,22 +60,6 @@ public:
 
     typedef PDUOption<uint8_t, RadioTap> option;
 
-    /**
-     * The RadioTap header
-     */
-    TINS_BEGIN_PACK
-    struct RadiotapHeader {
-    #if TINS_IS_LITTLE_ENDIAN
-        uint8_t version; 
-        uint8_t padding;
-    #else
-        uint8_t padding;
-        uint8_t version;
-    #endif // TINS_IS_LITTLE_ENDIAN 
-        uint16_t length;
-        uint32_t flags;
-    } TINS_END_PACK;
-
     /**
      * \brief Constructs a RadioTap parser around a payload
      *
@@ -118,6 +102,11 @@ public:
      * the end of the header)
      */
     bool advance_field();
+
+    /**
+     * Indicates whether this RadioTap options buffer contains any fields set
+     */
+    bool has_fields() const;
 private:
     const uint8_t* find_options_start() const;
     bool advance_to_next_field(bool start_from_zero);

src/utils/radiotap_parser.cpp

@@ -63,7 +63,7 @@ static const FieldMetadata RADIOTAP_METADATA[] = {
     { 3, 1 }, // MCS
 };
 
-static const uint64_t BIT_LIMIT = sizeof(RADIOTAP_METADATA) / sizeof(FieldMetadata) + 1;
+static const uint32_t BIT_LIMIT = sizeof(RADIOTAP_METADATA) / sizeof(FieldMetadata) + 1;
 
 #if TINS_IS_LITTLE_ENDIAN
 TINS_BEGIN_PACK
@@ -141,7 +141,7 @@ void align_buffer(const uint8_t* buffer_start, const uint8_t*& buffer, uint32_t
 }
 
 RadioTapParser::RadioTapParser(const vector<uint8_t>& buffer)
-: current_namespace_(RADIOTAP_NS), current_bit_(0), namespace_index_(0) {
+: current_namespace_(RADIOTAP_NS), current_bit_(BIT_LIMIT), namespace_index_(0) {
     if (buffer.empty()) {
         start_ = 0;
         end_ = 0;
@@ -177,19 +177,28 @@ const uint8_t* RadioTapParser::current_option_ptr() const {
 }
 
 bool RadioTapParser::advance_field() {
+    // If we have no buffer to parse, then we can't advance
+    if (start_ == 0 || current_bit_ == BIT_LIMIT) {
+        return false;
+    }
     // If we manage to advance the field, return true
     if (advance_to_next_field(false /* keep going from current */)) {
         return true;
     }
+    // We finished iterating the current namespace (if any). Reset our bit
+    current_bit_ = BIT_LIMIT;
     // Otherwise, let's try advancing the namespace. If we fail, then we failed
     if (!advance_to_next_namespace()) {
         return false;
     }
-    // Otherwise restart bit and try to find the first field in this namespace
-    current_bit_ = 0;
+    // Try to find the first field in this new namespace
     return advance_to_next_field(true /* start from 0*/);
 }
 
+bool RadioTapParser::has_fields() const {
+    return current_bit_ != BIT_LIMIT;
+}
+
 const uint8_t* RadioTapParser::find_options_start() const {
     uint32_t total_sz = end_ - start_;
     if (TINS_UNLIKELY(total_sz < sizeof(RadioTapFlags))) {
@@ -209,7 +218,7 @@ const uint8_t* RadioTapParser::find_options_start() const {
 
 bool RadioTapParser::advance_to_next_field(bool start_from_zero) {
     const RadioTapFlags* flags = get_flags_ptr();
-    uint64_t bit;
+    uint32_t bit;
     if (start_from_zero) {
         bit = 0;
     }

tests/src/radiotap_test.cpp

@@ -446,6 +446,7 @@ TEST_F(RadioTapTest, RadioTapParsingMultipleNamespaces) {
     }
     // MCS is the last option in this namespace. After this, we should jump to the next one
     EXPECT_TRUE(parser.advance_field());
+    EXPECT_TRUE(parser.has_fields());
 
     // These are on the second namespace
     EXPECT_EQ(RadioTap::DBM_SIGNAL, parser.current_field());
@@ -460,6 +461,15 @@ TEST_F(RadioTapTest, RadioTapParsingMultipleNamespaces) {
     EXPECT_FALSE(parser.advance_field());
     EXPECT_FALSE(parser.advance_field());
     EXPECT_EQ(RadioTapParser::RADIOTAP_NS, parser.current_namespace());
+    EXPECT_FALSE(parser.has_fields());
+}
+
+TEST_F(RadioTapTest, RadioTapParsingUsingEmptyBuffer) {
+    vector<uint8_t> buffer;
+    RadioTapParser parser(buffer);
+    EXPECT_FALSE(parser.has_fields());
+    EXPECT_FALSE(parser.advance_field());
+    EXPECT_FALSE(parser.has_fields());
 }
 
 #endif // TINS_HAVE_DOT11