1package middleware
2
3import (
4 "context"
5)
6
7// BuildInput provides the input parameters for the BuildMiddleware to consume.
8// BuildMiddleware may modify the Request value before forwarding the input
9// along to the next BuildHandler.
10type BuildInput struct {
11 Request interface{}
12}
13
14// BuildOutput provides the result returned by the next BuildHandler.
15type BuildOutput struct {
16 Result interface{}
17}
18
19// BuildHandler provides the interface for the next handler the
20// BuildMiddleware will call in the middleware chain.
21type BuildHandler interface {
22 HandleBuild(ctx context.Context, in BuildInput) (
23 out BuildOutput, metadata Metadata, err error,
24 )
25}
26
27// BuildMiddleware provides the interface for middleware specific to the
28// serialize step. Delegates to the next BuildHandler for further
29// processing.
30type BuildMiddleware interface {
31 // Unique ID for the middleware in theBuildStep. The step does not allow
32 // duplicate IDs.
33 ID() string
34
35 // Invokes the middleware behavior which must delegate to the next handler
36 // for the middleware chain to continue. The method must return a result or
37 // error to its caller.
38 HandleBuild(ctx context.Context, in BuildInput, next BuildHandler) (
39 out BuildOutput, metadata Metadata, err error,
40 )
41}
42
43// BuildMiddlewareFunc returns a BuildMiddleware with the unique ID provided,
44// and the func to be invoked.
45func BuildMiddlewareFunc(id string, fn func(context.Context, BuildInput, BuildHandler) (BuildOutput, Metadata, error)) BuildMiddleware {
46 return buildMiddlewareFunc{
47 id: id,
48 fn: fn,
49 }
50}
51
52type buildMiddlewareFunc struct {
53 // Unique ID for the middleware.
54 id string
55
56 // Middleware function to be called.
57 fn func(context.Context, BuildInput, BuildHandler) (BuildOutput, Metadata, error)
58}
59
60// ID returns the unique ID for the middleware.
61func (s buildMiddlewareFunc) ID() string { return s.id }
62
63// HandleBuild invokes the middleware Fn.
64func (s buildMiddlewareFunc) HandleBuild(ctx context.Context, in BuildInput, next BuildHandler) (
65 out BuildOutput, metadata Metadata, err error,
66) {
67 return s.fn(ctx, in, next)
68}
69
70var _ BuildMiddleware = (buildMiddlewareFunc{})
71
72// BuildStep provides the ordered grouping of BuildMiddleware to be invoked on
73// a handler.
74type BuildStep struct {
75 ids *orderedIDs
76}
77
78// NewBuildStep returns a BuildStep ready to have middleware for
79// initialization added to it.
80func NewBuildStep() *BuildStep {
81 return &BuildStep{
82 ids: newOrderedIDs(),
83 }
84}
85
86var _ Middleware = (*BuildStep)(nil)
87
88// ID returns the unique name of the step as a middleware.
89func (s *BuildStep) ID() string {
90 return "Build stack step"
91}
92
93// HandleMiddleware invokes the middleware by decorating the next handler
94// provided. Returns the result of the middleware and handler being invoked.
95//
96// Implements Middleware interface.
97func (s *BuildStep) HandleMiddleware(ctx context.Context, in interface{}, next Handler) (
98 out interface{}, metadata Metadata, err error,
99) {
100 order := s.ids.GetOrder()
101
102 var h BuildHandler = buildWrapHandler{Next: next}
103 for i := len(order) - 1; i >= 0; i-- {
104 h = decoratedBuildHandler{
105 Next: h,
106 With: order[i].(BuildMiddleware),
107 }
108 }
109
110 sIn := BuildInput{
111 Request: in,
112 }
113
114 res, metadata, err := h.HandleBuild(ctx, sIn)
115 return res.Result, metadata, err
116}
117
118// Get retrieves the middleware identified by id. If the middleware is not present, returns false.
119func (s *BuildStep) Get(id string) (BuildMiddleware, bool) {
120 get, ok := s.ids.Get(id)
121 if !ok {
122 return nil, false
123 }
124 return get.(BuildMiddleware), ok
125}
126
127// Add injects the middleware to the relative position of the middleware group.
128// Returns an error if the middleware already exists.
129func (s *BuildStep) Add(m BuildMiddleware, pos RelativePosition) error {
130 return s.ids.Add(m, pos)
131}
132
133// Insert injects the middleware relative to an existing middleware id.
134// Returns an error if the original middleware does not exist, or the middleware
135// being added already exists.
136func (s *BuildStep) Insert(m BuildMiddleware, relativeTo string, pos RelativePosition) error {
137 return s.ids.Insert(m, relativeTo, pos)
138}
139
140// Swap removes the middleware by id, replacing it with the new middleware.
141// Returns the middleware removed, or an error if the middleware to be removed
142// doesn't exist.
143func (s *BuildStep) Swap(id string, m BuildMiddleware) (BuildMiddleware, error) {
144 removed, err := s.ids.Swap(id, m)
145 if err != nil {
146 return nil, err
147 }
148
149 return removed.(BuildMiddleware), nil
150}
151
152// Remove removes the middleware by id. Returns error if the middleware
153// doesn't exist.
154func (s *BuildStep) Remove(id string) (BuildMiddleware, error) {
155 removed, err := s.ids.Remove(id)
156 if err != nil {
157 return nil, err
158 }
159
160 return removed.(BuildMiddleware), nil
161}
162
163// List returns a list of the middleware in the step.
164func (s *BuildStep) List() []string {
165 return s.ids.List()
166}
167
168// Clear removes all middleware in the step.
169func (s *BuildStep) Clear() {
170 s.ids.Clear()
171}
172
173type buildWrapHandler struct {
174 Next Handler
175}
176
177var _ BuildHandler = (*buildWrapHandler)(nil)
178
179// Implements BuildHandler, converts types and delegates to underlying
180// generic handler.
181func (w buildWrapHandler) HandleBuild(ctx context.Context, in BuildInput) (
182 out BuildOutput, metadata Metadata, err error,
183) {
184 res, metadata, err := w.Next.Handle(ctx, in.Request)
185 return BuildOutput{
186 Result: res,
187 }, metadata, err
188}
189
190type decoratedBuildHandler struct {
191 Next BuildHandler
192 With BuildMiddleware
193}
194
195var _ BuildHandler = (*decoratedBuildHandler)(nil)
196
197func (h decoratedBuildHandler) HandleBuild(ctx context.Context, in BuildInput) (
198 out BuildOutput, metadata Metadata, err error,
199) {
200 return h.With.HandleBuild(ctx, in, h.Next)
201}
202
203// BuildHandlerFunc provides a wrapper around a function to be used as a build middleware handler.
204type BuildHandlerFunc func(context.Context, BuildInput) (BuildOutput, Metadata, error)
205
206// HandleBuild invokes the wrapped function with the provided arguments.
207func (b BuildHandlerFunc) HandleBuild(ctx context.Context, in BuildInput) (BuildOutput, Metadata, error) {
208 return b(ctx, in)
209}
210
211var _ BuildHandler = BuildHandlerFunc(nil)