pw_protobuf: Replace contents of strings and bytes when decoding

An incorrect reading of the protobuf spec had the table decoder appending subsequent strings and bytes fields to each other, not replacing the contents. Correct that. Change-Id: I826aeff12dd6038c7b0fdc596203d4c195bd5b19 Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/93501 Pigweed-Auto-Submit: Scott James Remnant <[email protected]> Reviewed-by: Keir Mierle <[email protected]> Commit-Queue: Auto-Submit <[email protected]>
google · May 3, 2022 · be0fe60 · be0fe60
1 parent 8731e91
commit be0fe60
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Showing 2 changed files with 31 additions and 5 deletions.
diff --git a/pw_protobuf/codegen_message_test.cc b/pw_protobuf/codegen_message_test.cc
@@ -658,6 +658,33 @@ TEST(CodegenMessage, ReadStringCallback) {
   ASSERT_EQ(status, OkStatus());
 }
 
+TEST(CodegenMessage, ReadMultipleString) {
+  // clang-format off
+  constexpr uint8_t proto_data[] = {
+    // pigweed.error_message
+    0x2a, 0x10, 'n', 'o', 't', ' ', 'a', ' ',
+    't', 'y', 'p', 'e', 'w', 'r', 'i', 't', 'e', 'r',
+    // pigweed.error_message
+    0x02a, 0x07, 'o', 'n', ' ', 'f', 'i', 'r', 'e'
+  };
+  // clang-format on
+
+  stream::MemoryReader reader(std::as_bytes(std::span(proto_data)));
+  Pigweed::StreamDecoder pigweed(reader);
+
+  Pigweed::Message message{};
+  const auto status = pigweed.Read(message);
+  ASSERT_EQ(status, OkStatus());
+
+  constexpr std::string_view kExpectedErrorMessage{"on fire"};
+
+  EXPECT_EQ(message.error_message.size(), kExpectedErrorMessage.size());
+  EXPECT_EQ(std::memcmp(message.error_message.data(),
+                        kExpectedErrorMessage.data(),
+                        kExpectedErrorMessage.size()),
+            0);
+}
+
 TEST(CodegenMessage, ReadRepeatedStrings) {
   // clang-format off
   constexpr uint8_t proto_data[] = {

diff --git a/pw_protobuf/stream_decoder.cc b/pw_protobuf/stream_decoder.cc
@@ -636,14 +636,13 @@ Status StreamDecoder::Read(std::span<std::byte> message,
           PW_CHECK(field->elem_size() == sizeof(std::byte),
                    "Mismatched message field type and size");
           auto* vector = reinterpret_cast<pw::Vector<std::byte>*>(out.data());
-          if (vector->full()) {
+          if (vector->capacity() < delimited_field_size_) {
             return Status::ResourceExhausted();
           }
-          const size_t old_size = vector->size();
           vector->resize(vector->capacity());
-          const auto sws = ReadDelimitedField(
-              std::span(vector->data(), vector->size()).subspan(old_size));
-          vector->resize(old_size + sws.size());
+          const auto sws =
+              ReadDelimitedField(std::span(vector->data(), vector->size()));
+          vector->resize(sws.size());
           PW_TRY(sws);
         }
         break;