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bytes: document null termination #4

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22 changes: 20 additions & 2 deletions lib/std/core/bytes.kk
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,25 @@
found in the LICENSE file at the root of this distribution.
---------------------------------------------------------------------------*/

// Byte arrays
/*
Byte arrays

**Null Termination**:

The functions in this module maintain the following invariant for `bytes` values,
in order to efficiently convert between `string` and `bytes`:

- The physical buffer is at least one byte larger than the logical length
- The memory address directly after the end of the logical length is set to the null byte.

Code using the functions in this module does not need to worry about this invariant,
however low-level C code performing direct memory access may need to be careful to
maintain it.

Violating this invariant could lead to memory-safty issues, for example the `string`
function could potentially read past the end of a buffer with no terminating null byte.
*/

module std/core/bytes
import std/core/types
import std/core/exn
Expand All @@ -26,7 +44,7 @@ pub extern alloc( n : ssize_t ) : bytes
c inline "kk_bytes_alloc_buf(#1, NULL, kk_context())"
js inline "new Uint8Array(#1).fill(0)"

// Converts an array of bytes to a string. (Unsafe, ensure that the bytes have a zero terminated string)
// Converts an array of bytes to a string.
pub extern string( bytes : bytes ) : string
c "kk_string_convert_from_qutf8"
js inline "String.fromCharCode.apply(null, #1)"
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