Consider a header file defining this method:

ErrorCode_t GetBlob(Handle_const_t hHandle, uint8_t* const pValue, size_t* const pnSize);

This method writes n bytes into the array starting at the pointer of pValue. The size n will be set at the pointer of pnSize.

The header can be converted into Java source code using jextract, which gives:

public static long GetBlob(MemorySegment hHandle, MemorySegment pValue, MemorySegment pnSize) {
    // ..
}

After reading /questions/76978598 and /questions/71250218 I allocated a C_POINTER with unbounded address layout and called the method:

    MemorySegment handle = ..;
    MemorySegment arrayPointer = Arena.global().allocate(C_POINTER);
    MemorySegment sizePointer = Arena.global().allocate(JAVA_LONG);
    Accessor_h.GetBlob(handle, arrayPointer, sizePointer);

The call is successful. The sizePointer contains the size of the array.

But reading the array data fails. I tried the following:

    arrayPointer.get(C_POINTER, 0L)
        .toArray(JAVA_BYTE); // fails with "Segment is too large to wrap as byte[]. Size: 9223372036854775807"

Or:

    arrayPointer.get(C_POINTER, 0L)
            .asSlice(0L, sizePointer.get(JAVA_LONG, 0L))
            .toArray(JAVA_BYTE); // SIGSEGV (0xb)

Or:

    arrayPointer
            .toArray(JAVA_BYTE); // seems to contain the correct data, but only the first eight bytes

Or:

    arrayPointer
            .asSlice(0L, sizePointer.get(JAVA_LONG, 0L))
            .toArray(JAVA_BYTE); // fails with "java.lang.IndexOutOfBoundsException: Out of bound access on segment MemorySegment"

What can I do, to safely read the byte array in Java?