Golang CGO with large char pointer - SEGSERV

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]='
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;
}
}
}
}
}
';

                    // 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

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] = '
// Generate memory for picture data
char* val = new char[len+1];
memcpy (val, apicBase64.data(), len);
val[len] = '\0';
';