Add Bookkeeping

[kcajmagic]

• Added Bookkeeper to handle logging for different routes.

Closes #34

[schmidtw]

This looks good to me.

[njharter]

why are you removing this block of code?

[schmidtw]

@njharter can this be merged?

[johnabass]

We don't want to be doing bookkeeping this way, in any of our servers:

• Bookkeeping should not be present in application layer code. This makes it hard to refactor later.
• Bookkeeping is a cross-cutting concern, and should be done with an Alice-style decorator. There is already code to facilitate this in the logging and xcontext packages.
• Logging decorations should transfer to every log message in an HTTP code path, not just the bookkeeping message.

[johnabass]

There are (3) basic steps to a better solution. The first (2) need only be done once, for all servers.

(1) Use xcontext.Populate to create an Alice-style decorator:

c := xcontext.Populate(0, logginghttp.SetLogger(
        logginghttp.Header("X-Webpa-Device-Name", "deviceName"),
        // any other go-kit request functions that you want go here, e.g. to pull data from a SAT
    ),
)

(2) Create a bookkeeping decorator, preferably in one place such as the logginghttp package:

b := func(next http.Handler) http.Handler {
    return http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
        logging.GetLogger(request.Context()).Log(level.Key(), level.InfoValue(), logging.MessageKey(), "Bookkeeping")
    })
}

(3) Use both of the above decorators for any handlers in application code:

r := mux.NewRouter()

// decorate one handler
r.Handle("/foobar", alice.New(c, b).Then(myHandler))

// decorate the whole thing
alice.New(c, b).Then(r)

[johnabass]

We don't want this here. This is in application-layer code. We want the bookkeeping done as part of an Alice-style decorator. This decorator can go into the logginghttp package as a standard thing applications can add to their handler mappings.

[johnabass]

This function should not exist in application code. What you want is decoration:

package logginghttp

import (
    "github.com/Comcast/webpa-common/logging"
    "net/http"
)

func Bookkeeper(next http.Handler) http.Handler {
    return http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
        // rely on another decorator, e.g. xcontext.Populate, to supply the fields
        logging.GetLogger(request.Context()).Log(logging.MessageKey(), "Bookkeeping")
        next.ServeHTTP(response, request)
    })
}

[johnabass]

Client code, such as in scytale, will then supply a contextual logger, again via decoration:

// imports omitted
c := xcontext.Populate(0,
    logginghttp.SetLogger(loggerFromViper, logginghttp.Header("X-Example", "example")),
)

// use 'c' to decorate handlers:
alice.New(c, /* other constructors).Then(myHandler)

[johnabass]

Decoding the message is not a very efficient way of accomplishing this. Also, we don't want to require bookkeeping to have a dependence on wrp. We should find a way to do this that doesn't require decoding, perhaps by inserting the wrp message from the fanout into the context.