Using pointer to slice from vec when calling C code from Rust

I'm converting code from C to Rust

C code:

uint16_t W25Q64_read(uint32_t addr,uint8_t *buf,uint16_t n){     unsigned char *data;    int rc;      data = (unsigned char*)malloc(n+4);    data[0] = CMD_READ_DATA;    data[1] = (addr>>16) & 0xFF;     // A23-A16    data[2] = (addr>>8) & 0xFF;      // A15-A08    data[3] = addr & 0xFF;           // A07-A00    rc = wiringPiSPIDataRW (_spich,data,n+4);    memcpy(buf,&data[4],n);    free(data);    return rc-4;  }  

Rust code:

pub fn read(&self, address: u32, number_of_bytes: u16) ->  Result<Vec<u8>, u16> {      let s: usize = number_of_bytes as usize + 4;      let mut data = vec![0u8;s];      data[0] = CMD_READ_UNIQUE_ID;      data[1] = (address>>16 & 0xFF) as u8;     // A23-A16      data[2] = (address>>8 & 0xFF) as u8;      // A15-A08      data[3] = (address & 0xFF) as u8;         // A07-A00      let mut _r: i32 = 0;      _r = unsafe{wiringPiSPIDataRW(self.spi_channel,data.as_mut_slice().as_mut_ptr(), data.len() as i32)};      let v = (&(data.as_slice())[4..]).to_vec();      Ok(v)  }  

On the C code, I get 256 255 results when I try to read 256 bytes. On the Rust code, for the same address and same number of bytes, I get

0,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37,46,210,104,44,22,219,93,37  

I always get this, I don't know why.

My assumption is that something is wrong with using a pointer to a slice owned by a vector. Somehow when C code tries to write to this slice, things go wrong. Could this possibly be the problem?

I cannot see anything wrong except for this.

https://stackoverflow.com/questions/66728200/using-pointer-to-slice-from-vec-when-calling-c-code-from-rust March 21, 2021 at 10:06AM