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feat: Helpers for working with middlewares
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‎README.md‎

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@@ -33,3 +33,50 @@ func addProduct(w http.ResponseWriter, r *http.Request) error {
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return errhandler.SendJSON(w, p)
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}
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```
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### Middleware
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errhandler contains helper objects for building middleware
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* A `errhandler.Middleware` type, which is simply a function that takes a Wrap function and returns a Wrap function:
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```go
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mux := http.NewServeMux()
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mux.Handle("GET /products/{id}", errhandler.Wrap(midLog(getProduct)))
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...
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func midLog(n errhandler.Wrap) errhandler.Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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log.Printf("1 %s %s", r.Method, r.URL.Path)
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return n(w, r)
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}
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}
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func addProduct(w http.ResponseWriter, r *http.Request) error {
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...
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}
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```
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* A `errhandler.Chain` function, which allows `Middleware` functions easy to chain:
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```go
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chain := errhandler.Chain(midLog1, midLog2)
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mux := http.NewServeMux()
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mux.Handle("GET /products", errhandler.Wrap(chain(getProducts)))
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func midLog1(n errhandler.Wrap) errhandler.Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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log.Printf("1 %s %s", r.Method, r.URL.Path)
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return n(w, r)
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}
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}
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func midLog2(n errhandler.Wrap) errhandler.Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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log.Printf("2 %s %s", r.Method, r.URL.Path)
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return n(w, r)
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}
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}
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```

‎examples/basic/README.md‎

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Start server
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```sh
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go run examples/basic/main.go
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```
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Test server
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```sh
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curl -s http://localhost:3000/products/a32fb2bd-b402-4bea-93c2-4a0a567b2261 | jq
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curl -s http://localhost:3000/products | jq
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```

‎examples/basic/main.go‎

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package main
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import (
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"fmt"
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"log"
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"net/http"
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"github.com/codingconcepts/errhandler"
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)
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var products = map[string]product{
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"a32fb2bd-b402-4bea-93c2-4a0a567b2261": {
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ID: "a32fb2bd-b402-4bea-93c2-4a0a567b2261",
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Name: "a",
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Price: 10.99,
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},
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"b68ed795-0604-4696-8eb2-5b4b927330a0": {
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ID: "b68ed795-0604-4696-8eb2-5b4b927330a0",
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Name: "b",
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Price: 20.99,
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},
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}
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func main() {
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mux := http.NewServeMux()
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mux.Handle("GET /products", errhandler.Wrap(getProducts))
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mux.Handle("GET /products/{id}", errhandler.Wrap(getProduct))
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server := &http.Server{Addr: "localhost:3000", Handler: mux}
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log.Fatal(server.ListenAndServe())
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}
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func getProducts(w http.ResponseWriter, r *http.Request) error {
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return errhandler.SendJSON(w, products)
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}
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func getProduct(w http.ResponseWriter, r *http.Request) error {
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id := r.PathValue("id")
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p, ok := products[id]
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if !ok {
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return fmt.Errorf("no product with id: %s", id)
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}
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return errhandler.SendJSON(w, p)
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}
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type product struct {
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ID string `json:"id"`
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Name string `json:"name"`
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Price float64 `json:"price"`
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}

‎examples/middleware/README.md‎

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Start server
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```sh
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go run examples/middleware/main.go
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```
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Test server
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```sh
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curl -s http://localhost:3000/products/a32fb2bd-b402-4bea-93c2-4a0a567b2261 | jq
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curl -s http://localhost:3000/products | jq
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```

‎examples/middleware/main.go‎

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package main
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import (
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"fmt"
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"log"
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"net/http"
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"github.com/codingconcepts/errhandler"
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)
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var products = map[string]product{
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"a32fb2bd-b402-4bea-93c2-4a0a567b2261": {
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ID: "a32fb2bd-b402-4bea-93c2-4a0a567b2261",
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Name: "a",
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Price: 10.99,
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},
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"b68ed795-0604-4696-8eb2-5b4b927330a0": {
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ID: "b68ed795-0604-4696-8eb2-5b4b927330a0",
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Name: "b",
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Price: 20.99,
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},
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}
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func main() {
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chain := errhandler.Chain(midLog1, midLog2)
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mux := http.NewServeMux()
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mux.Handle("GET /products", errhandler.Wrap(chain(getProducts)))
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mux.Handle("GET /products/{id}", errhandler.Wrap(midLog1(getProduct)))
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server := &http.Server{Addr: "localhost:3000", Handler: mux}
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log.Fatal(server.ListenAndServe())
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}
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func midLog1(n errhandler.Wrap) errhandler.Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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log.Printf("1 %s %s", r.Method, r.URL.Path)
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return n(w, r)
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}
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}
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func midLog2(n errhandler.Wrap) errhandler.Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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log.Printf("2 %s %s", r.Method, r.URL.Path)
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return n(w, r)
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}
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}
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func getProducts(w http.ResponseWriter, r *http.Request) error {
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return errhandler.SendJSON(w, products)
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}
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func getProduct(w http.ResponseWriter, r *http.Request) error {
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id := r.PathValue("id")
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p, ok := products[id]
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if !ok {
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return fmt.Errorf("no product with id: %s", id)
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}
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return errhandler.SendJSON(w, p)
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}
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type product struct {
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ID string `json:"id"`
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Name string `json:"name"`
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Price float64 `json:"price"`
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}

‎middleware.go‎

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package errhandler
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// Middleware is a helper for adding middleware to wrapped handelers.
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type Middleware func(Wrap) Wrap
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// Chain multiple middleware functions together into a single middleware.
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func Chain(m ...Middleware) Middleware {
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return func(n Wrap) Wrap {
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for i := len(m) - 1; i >= 0; i-- {
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n = m[i](n)
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}
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return n
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}
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}

‎middleware_test.go‎

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package errhandler
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import (
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"context"
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"net/http"
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"net/http/httptest"
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"testing"
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)
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type contextKey string
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func TestMiddleware(t *testing.T) {
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tests := []struct {
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name string
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handler Wrap
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middleware Middleware
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expectedStatus int
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expectedBody string
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}{
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{
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name: "single middleware",
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middleware: func(n Wrap) Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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ctx := context.WithValue(r.Context(), contextKey("value"), 1)
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r = r.WithContext(ctx)
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return n(w, r)
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}
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},
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handler: Wrap(func(w http.ResponseWriter, r *http.Request) error {
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m := map[string]any{
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"value": r.Context().Value(contextKey("value")),
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}
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return SendJSON(w, m)
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}),
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expectedStatus: http.StatusOK,
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expectedBody: "{\"value\":1}\n",
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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req := httptest.NewRequest(http.MethodGet, "http://example.com/foo", nil)
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w := httptest.NewRecorder()
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tt.middleware(tt.handler).ServeHTTP(w, req)
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res := w.Result()
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defer res.Body.Close()
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if res.StatusCode != tt.expectedStatus {
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t.Errorf("expected status %d, got %d", tt.expectedStatus, res.StatusCode)
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}
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actualBody := w.Body.String()
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if actualBody != tt.expectedBody {
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t.Errorf("expected body %q, got %q", tt.expectedBody, actualBody)
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}
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})
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}
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}
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func TestChain(t *testing.T) {
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tests := []struct {
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name string
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handler Wrap
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middlewares []Middleware
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expectedStatus int
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expectedBody string
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}{
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{
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name: "multiple middlewares",
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middlewares: []Middleware{
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func(n Wrap) Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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ctx := context.WithValue(r.Context(), contextKey("value"), 1)
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r = r.WithContext(ctx)
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return n(w, r)
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}
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},
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func(n Wrap) Wrap {
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return func(w http.ResponseWriter, r *http.Request) error {
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value, ok := r.Context().Value(contextKey("value")).(int)
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if !ok {
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t.Fatalf("expected integer but didn't get one")
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}
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ctx := context.WithValue(r.Context(), contextKey("value"), value+2)
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r = r.WithContext(ctx)
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return n(w, r)
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}
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},
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},
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handler: Wrap(func(w http.ResponseWriter, r *http.Request) error {
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m := map[string]any{
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"value": r.Context().Value(contextKey("value")),
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}
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return SendJSON(w, m)
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}),
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expectedStatus: http.StatusOK,
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expectedBody: "{\"value\":3}\n",
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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req := httptest.NewRequest(http.MethodGet, "http://example.com/foo", nil)
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w := httptest.NewRecorder()
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chain := Chain(tt.middlewares...)
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chain(tt.handler).ServeHTTP(w, req)
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res := w.Result()
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defer res.Body.Close()
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if res.StatusCode != tt.expectedStatus {
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t.Errorf("expected status %d, got %d", tt.expectedStatus, res.StatusCode)
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}
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actualBody := w.Body.String()
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if actualBody != tt.expectedBody {
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t.Errorf("expected body %q, got %q", tt.expectedBody, actualBody)
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}
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})
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}
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}

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