/
middlewares.go
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/
middlewares.go
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// Copyright (c) 2020 Uber Technologies, Inc.
//
// 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.
package zanzibar
import (
"context"
jsonschema "github.com/mcuadros/go-jsonschema-generator"
)
// MiddlewareStack is a stack of Middleware Handlers that can be invoked as an Handle.
// MiddlewareStack middlewares are evaluated for requests in the order that they are added to the stack
// followed by the underlying HandlerFn. The middleware responses are then executed in reverse.
type MiddlewareStack struct {
middlewares []MiddlewareHandle
handle HandlerFn
}
// NewStack returns a new MiddlewareStack instance with no middleware preconfigured.
func NewStack(middlewares []MiddlewareHandle,
handle HandlerFn) *MiddlewareStack {
return &MiddlewareStack{
handle: handle,
middlewares: middlewares,
}
}
// Middlewares returns a list of all the handlers in the current MiddlewareStack.
func (m *MiddlewareStack) Middlewares() []MiddlewareHandle {
return m.middlewares
}
// MiddlewareHandle used to define middleware
type MiddlewareHandle interface {
// implement HandleRequest for your middleware. Return false
// if the handler writes to the response body.
HandleRequest(
ctx context.Context,
req *ServerHTTPRequest,
res *ServerHTTPResponse,
shared SharedState,
) bool
// implement HandleResponse for your middleware. Return false
// if the handler writes to the response body.
HandleResponse(
ctx context.Context,
res *ServerHTTPResponse,
shared SharedState,
)
// return any shared state for this middleware.
JSONSchema() *jsonschema.Document
Name() string
}
// SharedState used to access other middlewares in the chain.
type SharedState struct {
middlewareDict map[string]interface{}
}
// NewSharedState constructs a ShardState
func NewSharedState(middlewares []MiddlewareHandle) SharedState {
sharedState := SharedState{}
sharedState.middlewareDict = make(map[string]interface{})
for i := 0; i < len(middlewares); i++ {
sharedState.middlewareDict[middlewares[i].Name()] = nil
}
return sharedState
}
// GetState returns the state from a different middleware
func (s SharedState) GetState(name string) interface{} {
return s.middlewareDict[name]
}
// SetState sets value of a middleware shared state
func (s SharedState) SetState(m MiddlewareHandle, state interface{}) {
s.middlewareDict[m.Name()] = state
}
// Handle executes the middlewares in a stack and underlying handler.
func (m *MiddlewareStack) Handle(
ctx context.Context,
req *ServerHTTPRequest,
res *ServerHTTPResponse) {
shared := NewSharedState(m.middlewares)
for i := 0; i < len(m.middlewares); i++ {
ok := m.middlewares[i].HandleRequest(ctx, req, res, shared)
// If a middleware errors and writes to the response header
// then abort the rest of the stack and evaluate the response
// handlers for the middlewares seen so far.
if ok == false {
for j := i; j >= 0; j-- {
m.middlewares[j].HandleResponse(ctx, res, shared)
}
return
}
}
m.handle(ctx, req, res)
for i := len(m.middlewares) - 1; i >= 0; i-- {
m.middlewares[i].HandleResponse(ctx, res, shared)
}
}