Dynamic Configuration Refactoring

vendor/github.com/containous/alice/LICENSE

@@ -0,0 +1,20 @@
+The MIT License (MIT)
+
+Copyright (c) 2014 Justinas Stankevicius
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/containous/alice/chain.go

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+// Package alice provides a convenient way to chain http handlers.
+package alice
+
+import "net/http"
+
+// Constructor A constructor for a piece of middleware.
+// Some middleware use this constructor out of the box,
+// so in most cases you can just pass somepackage.New
+type Constructor func(http.Handler) (http.Handler, error)
+
+// Chain acts as a list of http.Handler constructors.
+// Chain is effectively immutable:
+// once created, it will always hold
+// the same set of constructors in the same order.
+type Chain struct {
+	constructors []Constructor
+}
+
+// New creates a new chain,
+// memorizing the given list of middleware constructors.
+// New serves no other function,
+// constructors are only called upon a call to Then().
+func New(constructors ...Constructor) Chain {
+	return Chain{constructors: constructors}
+}
+
+// Then chains the middleware and returns the final http.Handler.
+//     New(m1, m2, m3).Then(h)
+// is equivalent to:
+//     m1(m2(m3(h)))
+// When the request comes in, it will be passed to m1, then m2, then m3
+// and finally, the given handler
+// (assuming every middleware calls the following one).
+//
+// A chain can be safely reused by calling Then() several times.
+//     stdStack := alice.New(ratelimitHandler, csrfHandler)
+//     indexPipe = stdStack.Then(indexHandler)
+//     authPipe = stdStack.Then(authHandler)
+// Note that constructors are called on every call to Then()
+// and thus several instances of the same middleware will be created
+// when a chain is reused in this way.
+// For proper middleware, this should cause no problems.
+//
+// Then() treats nil as http.DefaultServeMux.
+func (c Chain) Then(h http.Handler) (http.Handler, error) {
+	if h == nil {
+		h = http.DefaultServeMux
+	}
+
+	for i := range c.constructors {
+		handler, err := c.constructors[len(c.constructors)-1-i](h)
+		if err != nil {
+			return nil, err
+		}
+		h = handler
+	}
+
+	return h, nil
+}
+
+// ThenFunc works identically to Then, but takes
+// a HandlerFunc instead of a Handler.
+//
+// The following two statements are equivalent:
+//     c.Then(http.HandlerFunc(fn))
+//     c.ThenFunc(fn)
+//
+// ThenFunc provides all the guarantees of Then.
+func (c Chain) ThenFunc(fn http.HandlerFunc) (http.Handler, error) {
+	if fn == nil {
+		return c.Then(nil)
+	}
+	return c.Then(fn)
+}
+
+// Append extends a chain, adding the specified constructors
+// as the last ones in the request flow.
+//
+// Append returns a new chain, leaving the original one untouched.
+//
+//     stdChain := alice.New(m1, m2)
+//     extChain := stdChain.Append(m3, m4)
+//     // requests in stdChain go m1 -> m2
+//     // requests in extChain go m1 -> m2 -> m3 -> m4
+func (c Chain) Append(constructors ...Constructor) Chain {
+	newCons := make([]Constructor, 0, len(c.constructors)+len(constructors))
+	newCons = append(newCons, c.constructors...)
+	newCons = append(newCons, constructors...)
+
+	return Chain{newCons}
+}
+
+// Extend extends a chain by adding the specified chain
+// as the last one in the request flow.
+//
+// Extend returns a new chain, leaving the original one untouched.
+//
+//     stdChain := alice.New(m1, m2)
+//     ext1Chain := alice.New(m3, m4)
+//     ext2Chain := stdChain.Extend(ext1Chain)
+//     // requests in stdChain go  m1 -> m2
+//     // requests in ext1Chain go m3 -> m4
+//     // requests in ext2Chain go m1 -> m2 -> m3 -> m4
+//
+// Another example:
+//  aHtmlAfterNosurf := alice.New(m2)
+// 	aHtml := alice.New(m1, func(h http.Handler) http.Handler {
+// 		csrf := nosurf.New(h)
+// 		csrf.SetFailureHandler(aHtmlAfterNosurf.ThenFunc(csrfFail))
+// 		return csrf
+// 	}).Extend(aHtmlAfterNosurf)
+//		// requests to aHtml hitting nosurfs success handler go m1 -> nosurf -> m2 -> target-handler
+//		// requests to aHtml hitting nosurfs failure handler go m1 -> nosurf -> m2 -> csrfFail
+func (c Chain) Extend(chain Chain) Chain {
+	return c.Append(chain.constructors...)
+}