binary protocol notes from the facebook hackathon

[Dustin Sallings]

On Jul 10, 2007, at 9:23, Brad Fitzpatrick wrote:

> REQUEST STRUCTURE:
>
>   * Magic byte / version
>   * Cmd byte
>   * Key len byte  (if no key, 0)
>   * Reserved byte (should be 0)
>
>   * 4 byte opaque id.  (will be copied back in response; means  
> nothing to server)
>
>   * 4 byte body length (network order; not including 12 byte header)
>
>   [ cmd-specific fixed-width fields ]
>
>   * key, if key length above is non-zero.
>
>   [ cmd-specific variable-width field ]

	I found a problem when implementing this.  Given the above  
structure, we always know the length of a key, but we can't know the  
location of a key unless we know how to process the given command.

	I don't know that this is a huge problem, but it thwarted some of my  
generic lower-level packet handling code in my test server.

	Perhaps we could resurrect the reserved byte and use it as a fixed- 
field word (or byte) count?  I remember this coming up in the  
discussion, but I think we decided it was redundant as the command  
should know what its headers are.

	Any opinions?

-- 
Dustin Sallings