Animating a PNG example: Semantics unclear?

[josephg]

In section 5.1 it has this example:

     Request:
       GET /animated-braid.png
       Subscribe

     Response:
       HTTP/1.1 209 Subscribe
       Subscribe
       Content-Type: image/png         | Version
       Patches: 2                      |
                                       |
       Content-Length: 1239            | | Patch
       Content-Range: bytes=100-200    | |
                                       | |
       <binary data>                   | |
                                       |
       Content-Length: 62638           | | Patch
       Content-Range: bytes=348-887    | |
                                       | | 
       <binary data>                   | |

This is a weird use case:

• Its almost impossible to figure out a binary patch to a PNG because the content is internally gzipped iirc. (if you do, you'll probably end up with a patch that just replaces the entire contents of the file)
• Its unclear whether this overwrites the specified bytes or truncates? Like, what happens if the new content is smaller than the old content? (And I might be revealing my ignorance of the content-range: bytes= header by asking this, but how does this format indicate the size of the file should be truncated?

The example might be better either:

• Using a bitmap instead of a PNG - because then the byte ranges at least make a bit of sense, and the file size will stay constant
• Or don't use patches in this example, and simply re-send the content with each change
  • And we can write a second example which uses patches

[canadaduane]

A better example might also be modifying HTML from the server in an "animated" sort of way.

[toomim]

Closing as duplicate of #77