Simple client to view records of tables via Txn

[manhdaovan]

As the issue here: #41
I want to add a simple client to view the records of tables in memdb.

The idea is I added a thing called Explorer, which can explore data of table with given table name, and a http server to display explored data.

• To init an Explorer, you just need passing an instance of Txn struct to memdb.NewExplorer method. Then you can use any http server to display records with your own implement.

• Or you can use explorer_server.NewServer to init built-in explorer server.
  (You need Gin as dependency, and given assets and templates paths to Gin as well)

• Please ref to explorer_example/main.go for more details.

Here are some screenshots:

• List all tables:
  

• List records of a table:

  • In html format:
    

  • In json format:
    

[hashicorp-cla]

All committers have signed the CLA.

[manhdaovan]

TODO: need changing to "github.com/hashicorp/go-memdb" after merged.

[manhdaovan]

TODO: need changing to "github.com/hashicorp/go-memdb" after merged.

[salaxander]

@manhdaovan @armon @dadgar et all - Any chance of revisiting this? It would be a hugely helpful feature for a project I'm working on :)

[dnephin]

Thank you @manhdaovan for all of your work on this! And thank you @salaxander for your interest!

I think this is a really cool idea. Being able to explore the tables and indexes in a memdb would be a really useful.

Unfortunately I don't think this is something we can maintain as part of go-memdb. It significantly expands the scope of this repo, and introduces new dependencies and technologies that we don't already use.

I'd like to propose the following as a path forward:

1. Create a new repo for this UI client and add the code to the new repo
2. Figure out what additional methods we need to export in memdb to make this UI possible from an separate package
3. Add a link to the new repo from the go-memdb readme or docs, so that others can find this tool

I'm happy to help with 2 and 3. I believe currently explorer.go needs to access internals, but I wonder if we could take another approach. Could we pass in the full memdb.DBSchema to the explorer? Would that provide a lot of the data that explorer needs? It is possible to call Txn.Get(table, "id") (with no additional arguments) and get back all the entries in the table. I think would allow the explorer to do the necessary pagination. I only took a quick look, so maybe I have missed anything.

[salaxander]

@dnephin Sounds like a good path forward! I'm happy to help out in whatever capacity is needed :)

[manhdaovan]

Oh, I didnt have a look to this PR for a long time

@dnephin
You are correct. Explorer needs to access to some internal stuff to get the data, so 2 is the best choice I think.

@salaxander
The no 2 is already implemented here, then we can easily to access to schema from outside. So maybe you can get started to build an UI for it.

Btw, as no 2 is already implemented, then this PR is unnecessary anymore.