mprc -- Arbitrary MongoDB Wire Protocol RPC Framework

Overview

MRPC is a set of tools to support writing RPC-like services using the MongoDB wire protocol as a transport layer. The idea is, if you have a MongoDB driver (or are a MongoDB driver,) you should be able to communicate with other services without needing a second client driver, or to fall back to shell scripting for interacting with tools and utility.

Furthermore, it should be trivially easy to use this kind of interface to wrap up functionality for arbitrary tools.

History

The "mongowire" and "bson" packages are heavily adapted from github.com/erh/mongonet. Indeed this repository retains that history.

Use

Create a new service instance with the NewService function:

service := NewService("127.0.0.1", 3000)

For each operation, you must define an mongowire.OpScope and a handler function, as in:

op := &mogowire.OpScope{
     Type:      mongowire.OP_COMMAND,
     Context:   "admin",
     Command:   "listCommand",
}

handler := func(ctx context.Context, w io.Writer, m mongowire.Message) {
     // operation implementation
}

Then register the operation:

err := service.RegisterOperation(op, handler)

The RegisterOperation method returns an error if the operation scope is not unique, or the handler is nil. You can validate an operation scope using its Validate method.

When you have defined all methods, you can start the service using the Run method:

err := service.Run(ctx)

The Run method returns an error if there are any issues starting the service or if the context is canceled.

Quirks

• "Legacy" commands, which are issued as queries against a special collection are "up" converted to OP_COMMAND messages internally (though, mrpc does track that it has performed the conversion so you can see that.) Thus, you must register an OP_COMMAND, even if your clients are sending OP_QUERY messages.
• Handler functions are responsible for determining the "appropriate" response, and the framework cannot ensure that OP_COMMAND requests get OP_COMMAND_REPLY messages.

Dependencies

Currently, mrpc does not vendor its dependencies, and uses:

• github.com/mongodb/grip (for logging)
• github.com/pkg/errors (for error annotation.)
• github.com/evergreen-ci/birch (for bson parsing)