Method alloc_for_len

crates/table/src/page.rs:575–594

Allocates a linked-list of granules, in the var-len storage of the page, for a var-len object of `obj_len` bytes. Returns a [`VarLenRef`] pointing to the head of that list, and a boolean `in_blob` for whether the allocation is a `BlobHash` and the object must be inserted into the large-blob store. The length of each granule is set, but no data is written to any granule. Thus, the caller must pro

(&mut self, obj_len: usize)

    /// 2. The caller must initialize each granule with data for the claimed length
    ///    of the granule's data.
    pub fn alloc_for_len(&mut self, obj_len: usize) -> Result<(VarLenRef, bool), Error> {
        // Safety post-requirements of `alloc_for_obj_common`:
        // 1. caller promised they will be satisfied.
        // 2a. already satisfied as the closure below returns all the summands of `obj_len`.
        // 2b. caller promised in 2. that they will satisfy this.
        self.alloc_for_obj_common(obj_len, |req_granules| {
            let rem = obj_len % VarLenGranule::DATA_SIZE;
            (0..req_granules).map(move |rev_idx| {
                let len = if rev_idx == 0 && rem != 0 {
                    // The first allocated granule will be the last in the list.
                    // Thus, `rev_idx == 0` is the last element and might not take up a full granule.
                    rem
                } else {
                    VarLenGranule::DATA_SIZE
                };
                // Caller will initialize the granule's data for `len` bytes.
                (<&[u8]>::default(), len)
            })
        })
    }

    /// Returns an iterator over all offsets of the `VarLenGranule`s of the var-len object
    /// that has its first granule at offset `first_granule`.