[Here is some streaming code.](https://1drv.ms/u/s!AnhU14JA-AKe9QvmMBdQUDjThm1e?e=nIi6y7) Sorry it's not yet documented. It should be somewhat obvious, as it helps implement shell functions described thusly:
```
.blobextract TABLE COL ROW FILE ?DB? Extract DB blob into named file.
Parameters must specify a blob selected by:
SELECT COL FROM DB.table WHERE rowid = ROW
FILE may be '-' for extraction to stdout.
.blobreplace TABLE COL ROW FILE ?DB? Replace DB blob with file content.
Otherwise like .blobextract except that FILE must
name a readable file. ('-' is not stdin.)
```