Function write_overflow_pages

internal/cbm/sqlite_writer.c:856–895

--- Overflow page writer --- Writes overflow pages for payload bytes that exceed local storage. Returns the first overflow page number (embedded in the leaf cell). Each overflow page: 4-byte next-page pointer + up to (CBM_PAGE_SIZE-4) bytes of data.

// Returns the first overflow page number (embedded in the leaf cell).
// Each overflow page: 4-byte next-page pointer + up to (CBM_PAGE_SIZE-4) bytes of data.
static uint32_t write_overflow_pages(FILE *fp, uint32_t *next_page, const uint8_t *data,
                                     int data_len) {
    int per_page = CBM_PAGE_SIZE - BTREE_PTR_SIZE;
    uint32_t first_page = 0;
    long prev_next_ptr_offset = -SKIP_ONE;

    int offset = 0;
    while (offset < data_len) {
        uint32_t pnum = (*next_page)++;
        if (first_page == 0) {
            first_page = pnum;
        }

        // Backpatch previous overflow page's next-page pointer
        if (prev_next_ptr_offset >= 0) {
            uint8_t ptr[BTREE_PTR_SIZE];
            put_u32(ptr, pnum);
            (void)fseek(fp, prev_next_ptr_offset, SEEK_SET);
            (void)fwrite(ptr, SKIP_ONE, BTREE_PTR_SIZE, fp);
        }

        int chunk = data_len - offset;
        if (chunk > per_page) {
            chunk = per_page;
        }

        uint8_t page[CBM_PAGE_SIZE];
        memset(page, 0, CBM_PAGE_SIZE);
        put_u32(page, 0); // next-page pointer — 0 for now, backpatched on next iteration
        memcpy(page + BTREE_PTR_SIZE, data + offset, chunk);

        long page_offset = (long)(pnum - SKIP_ONE) * CBM_PAGE_SIZE;
        prev_next_ptr_offset = page_offset;
        (void)fseek(fp, page_offset, SEEK_SET);
        (void)fwrite(page, SKIP_ONE, CBM_PAGE_SIZE, fp);

        offset += chunk;
    }
    return first_page;
}

// --- Index record builders ---