Adaptation of @shore's proposal from #95
Peter Bourgon
8 years ago
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// ContextCanceled indicates the request context was canceled.
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var ErrContextCanceled = errors.New("context canceled")
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// Chain is a helper function for composing middlewares. Requests will
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// traverse them in the order they're declared. That is, the first middleware
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// is treated as the outermost middleware.
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func Chain(outer Middleware, others ...Middleware) Middleware {
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return func(next Endpoint) Endpoint {
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for i := len(others) - 1; i >= 0; i-- { // reverse
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next = others[i](next)
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}
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return outer(next)
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}
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}
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package endpoint_test
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import (
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"fmt"
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"golang.org/x/net/context"
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"github.com/go-kit/kit/endpoint"
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)
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func ExampleChain() {
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e := endpoint.Chain(
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annotate("first"),
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annotate("second"),
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annotate("third"),
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)(myEndpoint)
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if _, err := e(ctx, req); err != nil {
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panic(err)
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}
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// Output:
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// first pre
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// second pre
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// third pre
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// my endpoint!
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// third post
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// second post
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// first post
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}
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var (
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ctx = context.Background()
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req = struct{}{}
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)
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func annotate(s string) endpoint.Middleware {
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return func(next endpoint.Endpoint) endpoint.Endpoint {
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return func(ctx context.Context, request interface{}) (interface{}, error) {
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fmt.Println(s, "pre")
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defer fmt.Println(s, "post")
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return next(ctx, request)
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}
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}
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}
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func myEndpoint(context.Context, interface{}) (interface{}, error) {
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fmt.Println("my endpoint!")
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return struct{}{}, nil
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}
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