Introduction to bract.ring

This module provides Ring support for the Bract framework.

Starting a web server

The inducer bract.ring.inducer/start-server can start a web server using a supplied Ring handler. Include it in your inducer chain and populate the following keys in the context:

  :bract.ring/ring-handler   (fn [request])  ; a valid Ring handler
  :bract.ring/server-starter bract.ring.server/start-http-kit-server
  :bract.ring/server-options {:port 3000}

You may choose any supported server starter from the bract.ring.server namespace. You may also put the server options in the config (referred to by context key :bract.core/config) under the key "bract.ring.server.options".

Applying middleware to Ring handler

You may apply middleware to a Ring handler (required to be available under the context key :bract.ring/ring-handler) using the inducer bract.ring.inducer/apply-middlewares:

  :bract.ring/ring-handler (fn [request])  ; a valid Ring handler
  :app/inducers            [(bract.ring.inducer/apply-middlewares
                              [ring.middleware.content-type/wrap-content-type
                               ring.middleware.params/wrap-params])]

The above example applies two middlewares to the Ring handler. In practice, you would add the Ring handler to the context via an application inducer.

Applying wrapper to Ring handler

A wrapper is like a middleware (see above section) function, but with arity (fn [handler context]). There are several useful wrappers available in the bract.ring.wrapper namespace. Below is an example how you could apply wrappers to a Ring handler:

  :bract.ring/ring-handler (fn [request])  ; a valid Ring handler
  :app/inducers            [(bract.ring.inducer/apply-wrappers
                              [bract.ring.wrapper/info-endpoint-wrapper
                               bract.ring.wrapper/ping-endpoint-wrapper])]

In practice, you would add the Ring handler to the context via an application inducer.

Context keys

Context key	Value type	Description
:bract.ring/ring-handler	arity-1 or arity-3 ring handler function	Ring handler (sync or async)
:bract.ring/server-starter	(fn [handler options]) -> (fn stopper [])	See section Starting a web server
:bract.ring/server-stopper	(fn [context (fn stopper [])]) -> context	Server stopper function
:bract.ring/server-options	map	Server options

Provided default context

The file resources/bract/ring/context.edn (which may be referred as bract/ring/context.edn from an application) provides all wrappers from the namespace bract.ring.wrapper under the key :bract.ring/wrappers.

Config keys

Legend:

- FQFN: Fully qualified function name (string or symbol)
- FNable: Function or FQFN
- FNable-0: Zero arity function or FQFN
- FNable-1: Arity-1 function or FQFN

Config key	Value type	Description
"bract.ring.server.options"

Wrapper enabled check

The following config flags are looked up by respective Ring wrappers to determine whether to apply the wrapper:

Config key	Value type	Description
"bract.ring.health.check.enabled"	boolean	Enable health check wrapper?
"bract.ring.info.endpoint.enabled"	boolean	Enable /info endpoint wrapper?
"bract.ring.ping.endpoint.enabled"	boolean	Enable /ping endpoint wrapper?
"bract.ring.uri.trailing.slash.enabled"	boolean	Enable URI trailing slash wrapper?
"bract.ring.uri.prefix.match.enabled"	boolean	Enable URI prefix match wrapper?
"bract.ring.params.normalize.enabled"	boolean	Enable Ring params normalize wrapper?
"bract.ring.unexpected.500.enabled"	boolean	Enable unexpected response 500 wrapper?
"bract.ring.traffic.drain.enabled"	boolean	Enable traffic drain wrapper?
"bract.ring.distributed.trace.enabled"	boolean	Enable distributed trace wrapper?

Wrapper config

The configs related to various wrappers are listed below:

Health check wrapper

Config key	Value type	Description
"bract.ring.health.check.uris"	vector of string	URIs for health check endpoint, e.g. ["/health" "/health/"]
"bract.ring.health.body.encoder"	FNable-1	(fn [data]) -> Ring response body, e.g. clojure.core/pr-str
"bract.ring.health.content.type"	string	Ring response Content-type header, e.g. "application/edn"
"bract.ring.health.http.codes"	map keyword:string	HTTP codes, e.g. {:critical 503 :degraded 500 :healthy 200}

/info endpoint wrapper

Config key	Value type	Description
"bract.ring.info.endpoint.uris"	vector of string	URIs for /info endpoint, e.g. ["/info" "/info/"]
"bract.ring.info.body.encoder"	FNable-1	(fn [data]) -> Ring response body, e.g. clojure.core/pr-str
"bract.ring.info.content.type"	string	Ring response Content-type header, e.g. "application/edn"

/ping endpoint wrapper

Config key	Value type	Description
"bract.ring.ping.endpoint.uris"	vector of string	URIs for /info endpoint, e.g. ["/info" "/info/"]
"bract.ring.ping.endpoint.body"	Ring response body	A valid Ring response body, e.g. "pong"
"bract.ring.ping.content.type"	string	Ring response Content-type header, e.g. "text/plain"

Trailing slash wrapper

Config key	Value type	Description
"bract.ring.uri.trailing.slash.action"	Keyword	Operative keyword - :add or :remove

Prefix match wrapper

Config key	Value type	Description
"bract.ring.uri.prefix.match.token"	string	The prefix string to match
"bract.ring.uri.prefix.strip.flag"	boolean	Whether strip the prefix from the URI, e.g. true
"bract.ring.uri.prefix.backup.flag"	boolean	Whether backup the original URI in the request, e.g. true
"bract.ring.uri.prefix.backup.key"	keyword	Key to store original URI at in request, e.g. :original-uri

Params normalize wrapper

Config key	Value type	Description
"bract.ring.params.normalize.function"	arity-1 FQFN	Function to normalize param value, e.g. clojure.core/first

Unexpected->500 wrapper

Config key	Value type	Description
"bract.ring.unexpected.response.fn"	arity-3 FQFN	Unexpected response handler e.g. b.r.util/bad-response->500
"bract.ring.unexpected.exception.fn"	arity-2 FQFN	Exception handler, e.g. b.r.util/exception->500

Traffic drain wrapper

Config key	Value type	Description
"bract.ring.traffic.conn.close.flag"	boolean	Whether send Connection: close response header, e.g. true

Distributed trace wrapper

Config key	Value type	Description
"bract.ring.trace.trace.id.header"	string	Trace ID header, e.g. "x-trace-id"
"bract.ring.trace.parent.id.header"	string	Parent ID header, e.g. "x-trace-parent-id"
"bract.ring.trace.trace.id.req.flag"	boolean	Whether Trace ID is required, e.g. false
"bract.ring.trace.trace.id.valid.fn"	arity-1 FQFN	Function to return error on invalid Trace ID, nil otherwise
"bract.ring.trace.trace.id.req.key"	keyword	Request key to put trace ID under, e.g. :trace-id
"bract.ring.trace.span.id.req.key"	keyword	Request key to put request ID under, e.g. :span-id
"bract.ring.trace.parent.id.req.key"	keyword	Request key to put parent ID under, e.g. :parent-id

Provided default config

The files resources/bract/ring/config.edn (which may be referred as bract/ring/context.edn from an application)

File	Available in application as	Contents
config.edn	bract/ring/config.edn	Useful defaults for prod
config.dev.edn	bract/ring/config.dev.edn	Useful defaults DEV mode