Golang CGO with large char pointer - SEGSERV - c++

Question

I have a large amount of data being read from TagLib library and passed to GoLang (mpeg image data).
Here is where data is fetched:
void audiotags_mpeg_artwork(TagLib::MPEG::File *mpegFile, int id) {
TagLib::ID3v2::Tag *id3v2 = mpegFile->ID3v2Tag(false);
if (id3v2!=nullptr) {
const TagLib::ID3v2::FrameList frameList = id3v2->frameListMap()["APIC"];
for(auto it = frameList.begin(); it != frameList.end(); it++) {
TagLib::ID3v2::AttachedPictureFrame * frame = (TagLib::ID3v2::AttachedPictureFrame *)(*it);
if (frame!=nullptr && frame->size() > 0) {
const auto &apicBase64 = frame->picture().toBase64();
auto len = apicBase64.size();
if (len > 0) {
// Generate memory for key
char* key = new char[5];
memcpy(key, "APIC", 4);
key[4]='\0';
// Generate memory for picture data
char* val = new char[len];
memcpy (val, apicBase64.data(), len);
// Send to GoLang
go_map_audiotags(id, key, val);
// Free memory
delete[] key;
delete[] val;
}
}
}
}
}
At this point, go_map_autotags works (I use a similar method for other data). This also works for other picture data, however depending on the size this will crash with:
unexpected fault address 0x766a000
fatal error: fault
[signal SIGSEGV: segmentation violation code=0x1 addr=0x766a000 pc=0x404530b]
Within GoLang, I have the following export:
//export go_map_audiotags
func go_map_audiotags(id C.int, key *C.char, val *C.char) {
m := maps[int(id)]
k := strings.ToLower(C.GoString(key))
log.Println("go_map_audiotags k:", k) // <--- works
v := C.GoString(val) // <--- crashes
log.Println("go_map_audiotags v:", v) // <--- Does not reach
m[k] = v
}
Is there a bette way I should be transporting this data? I assume what's happening is:
1) The C.char limit be being reached
2) C++ is, for some reason, recycling the memory before setting v in GoLang

Answer 1

The data stored in val is not null-terminated. In your C code, when you make a copy using memcpy, the null terminator is not included. In the C code, change the code to:
// Generate memory for picture data
char* val = new char[len+1];
memcpy (val, apicBase64.data(), len);
val[len] = '\0';