Original title: Generating URL for a row inside render_cell hook

Hey,
I am using Datasette to view a database that contains video metadata. It has BLOB columns that contain video thumbnails in JPG format (around 100-500KB per row).

I've registered an output formatter that extends datasette.blob_renderer.render_blob function and serves the column with image/jpeg content type.

from datasette.blob_renderer import render_blob

async def render_jpg(datasette, database, rows, columns, request, table, view_name):
    response = await render_blob(datasette, database, rows, columns, request, table, view_name)
    response.content_type = "image/jpeg"
    response.headers["Content-Disposition"] = f'inline; filename="image.jpg"'
    return response


@hookimpl
def register_output_renderer():
    return {
        "extension": "jpg",
        "render": render_jpg,
        "can_render": lambda: True,
    }

This works well. I can visit http://localhost:8001/mydb/videos/1.jpg?_blob_column=thumbnail and view the image.

I want to display the image directly with an <img> tag (lazy-loaded of course). So, I need a URL, because embedding base64 would increase the page size too much (each image > 100KB).

Datasette generates a link with .blob extension for blob columns. It does this by calling datasette.urls.row_blob

But I have no way of getting the row inside the render_cell hook.

@hookimpl
def render_cell(value, column, table, database, datasette):
    if isinstance(value, bytes) and imghdr.what(None, value):
        # generate url
        return '$renderedLink'

Any pointers?