add commands for command records

[shikhar]

Acts on a stream, I reckon something like...

.. trim <trim-point>

.. fence <token>

SDK exposes a CommandRecord type, this would utilize that to prepare a record to append

[shikhar]

@vrongmeal also think about how to display command records when reading, maybe stderr-only? a TryFrom<..> for CommandRecord?

[vrongmeal]

@shikhar by .. trim <trim-point> do you mean the .. is an indicator of an internal command? Or am I missing something?

If yes, we can simply have:

.trim <trim-point>
.fence <token>

Similar to sqlite ^

I was also thinking if we have a way to add headers to an append record. Maybe multiple "header" command messages followed by the actual message.

.header KEY1=VAL1
.header KEY2=VAL2
message

The above would evaluate as:

AppendRecord::new("message")
  .with_headers(vec![
    Header::new("KEY1", "VAL1"),
    Header::new("KEY2", "VAL2"),
  ])

[vrongmeal]

also think about how to display command records when reading, maybe stderr-only? a TryFrom<..> for CommandRecord?

Didn't catch this. When do we want to display a command record?

[shikhar]

Ah no, I had meant these would be stream-level commands that result in a unary append() request with the command record. So .. was a plceholder for s2 stream $basin $stream.

I don't want to be further interpreting the newline-delimited plaintext data we currently support. We do need to consider alternate formats that allow encoding headers as well as binary data, but let's do that separately.

[shikhar]

also think about how to display command records when reading, maybe stderr-only? a TryFrom<..> for CommandRecord?

Didn't catch this. When do we want to display a command record?

Command records have binary payloads - so we can't display them with the current interpretation read makes of treating all records as plaintext. I was suggesting we can skip over displaying them on stdout, and only on stderr.