mongo.gridfile.writer: The mongo.gridfile.writer class
In jonkatz2/rmongodb: R-MongoDB driver

Objects of class "mongo.gridfile.writer" are used to buffer multiple writes to a single GridFS file.

Use mongo.gridfile.writer.create to create an object of this class,
mongo.gridfile.writer.write to write data to it, and
mongo.gridfile.writer.finish when done writing.

mongo.gridfile.writer objects have "mongo.gridfile.writer" as their class and contain an externally managed pointer to the actual data used to manage operations on the GridFS. This pointer is stored in the "mongo.gridfile" attribute of the object. The object also has a "mongo.gridfs" attribute holding a pointer to the mongo.gridfs object used in creation to prevent garbage collection on the mongo.gridfs object while the mongo.gridfile.writer is still active.

mongo.gridfs,
mongo.gridfile.writer.create,
mongo.gridfile.writer.write,
mongo.gridfile.writer.finish.

mongo <- mongo.create()
if (mongo.is.connected(mongo)) {
    gridfs <- mongo.gridfs.create(mongo, "grid")

    gfw <- mongo.gridfile.writer.create(gridfs, "test.dat")

    # store 4 bytes
    mongo.gridfile.writer.write(gfw, charToRaw("test"))

    # store string & LF plus 0-byte terminator
    buf <- writeBin("Test\n", as.raw(1))
    mongo.gridfile.writer.write(gfw, buf)

    # store PI as a float
    buf <- writeBin(3.1415926, as.raw(1), size=4, endian="little")
    mongo.gridfile.writer.write(gfw, buf)

    mongo.gridfile.writer.finish(gfw)
    mongo.gridfs.destroy(gridfs)
}