Network.Wai.Log

A simple logging middleware for WAI applications that supports the 'log-*' family of packages: https://hackage.haskell.org/package/log-base

When logging to stdout using defaultOptions, the output looks like this:

2020-10-27 12:30:23 INFO eid-server: Request received {
  "url": "/api/v1/transaction/new",
  "body_length": "KnownLength 136",
  "method": "POST",
  "user_agent": "curl/7.68.0",
  "request_id": "f2c89425-9ec4-4cd2-ae56-4bab23681fce",
  "remote_host": "127.0.0.1:34694"
}
2020-10-27 12:30:23 INFO eid-server: Sending response {
  "request_id": "f2c89425-9ec4-4cd2-ae56-4bab23681fce"
}
2020-10-27 12:30:23 INFO eid-server: Request complete {
  "response_body": null,
  "url": "/api/v1/transaction/new",
  "method": "POST",
  "status": {
    "code": 400,
    "message": "Bad Request"
  },
  "time": {
    "process": 2.97493e-3,
    "full": 3.159565e-3
  },
  "request_id": "f2c89425-9ec4-4cd2-ae56-4bab23681fce"
}

Create a Middleware

mkLogMiddleware :: MonadLog m => m (LogMiddleware UUID)

Create a LogMiddleware using defaultOptions

Use mkLogMiddlewareWith for custom Options

mkLogMiddlewareWith :: (MonadLog m, ToJSON id) => Options id -> m (LogMiddleware id)

Create a LogMiddleware using the supplied Options

Type

type LogMiddleware id = (id -> Application) -> Application

The classic wai Middleware type is Application -> Application, but that does not work when you want to pass logging context down to the Application.

Instead we pass an id to the Application, containing the request_id, so it can be logged in the application's context.

Options

data Options id

Logging options

Logging response body involves extracting it from Response via IO operations, therefore the logBody option takes Request, Status and ResponseHeaders as arguments to decide whether the IO operations of body extraction have to be performed. The resulting Maybe function is the constructor of a loggable Value from the body bytestring builder.

Constructors

Options

Fields

• logLevel :: LogLevel
• logRequest :: id -> Request -> [Pair]
• logResponse :: id -> Request -> Response -> Value -> ResponseTime -> [Pair]
• logBody :: Maybe (Request -> Status -> ResponseHeaders -> Maybe (Builder -> Value))

  An optional constructor of the response body log value.

• logGetRequestId :: Request -> IO id

  A function for getting the request id

data ResponseTime

Timing data

Constructors

ResponseTime

Fields

• processing :: NominalDiffTime

  Time between request received and application finished processing request

• full :: NominalDiffTime

  Time between request received and response sent

defaultOptions :: Options UUID

Default Options

{ logLevel = LogInfo
, logRequest = defaultLogRequest
, logResponse = defaultLogResponse
, logGetRequestId = 'const nextRandom'
}

defaultLogRequest :: ToJSON id => id -> Request -> [Pair]

Logs the following request values:

• request_uuid
• method
• url path
• remote host
• user agent
• body-length

defaultLogResponse :: ToJSON id => id -> Request -> Response -> Value -> ResponseTime -> [Pair]

Logs the following values:

• request_id
• request method
• request url path
• response_body details provided as Value
• status code
• status message
• time full
• time processing

Time is in seconds as that is how NominalDiffTime is treated by default

mkOpaqueDefaultOptions :: ToJSON id => (Request -> IO id) -> Options id

Build a default Options record for an opaque id given a function for retrieving an id.

Helpers

logRequestId :: (MonadLog m, ToJSON id) => id -> m a -> m a

Helper to consistently log the request id in your application by adding request_id field to log's localData