Initial checkin

README.md

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+## path values
+
+The three examples to go with the blog post at https://hawkins.id.au/posts/go-mux/path-values
+
+These should all work identically, each just shows a different way of achieving
+the same thing - extracing a user id from the path and making the user struct
+(instantiated from some sort of database, faked in common/db/db.go for this
+example) available to the route handler.
+
+    go run go-mux/pathvalues/1-basic
+
+    go run go-mux/pathvalues/2-slightly-less-basic
+
+    go run go-mux/pathvalues/3-middleware

common/db/db.go

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+package db
+
+import "fmt"
+
+type User struct {
+	ID int
+}
+
+func LoadUser(id int) (User, error) {
+	if id < 0 {
+		return User{}, fmt.Errorf("invalid negative user id '%d'", id)
+	}
+	if id > 100 {
+		return User{}, fmt.Errorf("invalid user id '%d'", id)
+	}
+
+	return User{ID: id}, nil
+}
+
+func (u User) String() string {
+	return fmt.Sprintf("this user is id: %d", u.ID)
+}

go.mod

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+module go-mux
+
+go 1.24.1

pathvalues/1-basic/main.go

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+package main
+
+import (
+	"fmt"
+	"go-mux/common/db"
+	"log/slog"
+	"net/http"
+	"strconv"
+)
+
+func main() {
+	http.HandleFunc("/user/{userId}/view", viewUser)
+
+	slog.Info("starting web service on :8080")
+	panic(http.ListenAndServe(":8080", nil))
+}
+
+func viewUser(w http.ResponseWriter, r *http.Request) {
+	userID := r.PathValue("userId")
+	userIDint, err := strconv.Atoi(userID)
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte("bad user id"))
+		return
+	}
+	user, err := db.LoadUser(userIDint)
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte(fmt.Sprintf("could not load user: %s", err.Error())))
+		return
+	}
+
+	slog.Info("loaded user")
+	// show the user id
+	w.Write([]byte(fmt.Sprintf("loaded user %s", user)))
+}

pathvalues/2-slightly-less-basic/main.go

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+package main
+
+import (
+	"fmt"
+	"go-mux/common/db"
+	"log/slog"
+	"net/http"
+	"strconv"
+)
+
+func main() {
+	http.HandleFunc("/user/{userId}/view", viewUser)
+
+	slog.Info("starting web service on :8080")
+	panic(http.ListenAndServe(":8080", nil))
+}
+
+func viewUser(w http.ResponseWriter, r *http.Request) {
+	user, err := loadUserFromRequest(r)
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte(fmt.Sprintf("could not load user: %s", err.Error())))
+		return
+	}
+
+	slog.Info("loaded user")
+	// show the user id
+	w.Write([]byte(fmt.Sprintf("loaded user %s", user)))
+}
+
+func loadUserFromRequest(r *http.Request) (db.User, error) {
+	userID := r.PathValue("userId")
+	userIDint, err := strconv.Atoi(userID)
+	if err != nil {
+		return db.User{}, err
+	}
+	user, err := db.LoadUser(userIDint)
+	if err != nil {
+		return db.User{}, err
+	}
+	return user, nil
+}

pathvalues/3-middleware/main.go

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+package main
+
+import (
+	"context"
+	"fmt"
+	"go-mux/common/db"
+	"log/slog"
+	"net/http"
+	"strconv"
+)
+
+var userContextKey = "user"
+
+func main() {
+	http.Handle("/user/{userId}/view", getUserFromPath(http.HandlerFunc(viewUser)))
+
+	slog.Info("starting web service on :8080")
+	panic(http.ListenAndServe(":8080", nil))
+}
+
+func viewUser(w http.ResponseWriter, r *http.Request) {
+	user := r.Context().Value(userContextKey).(db.User)
+
+	slog.Info("loaded user")
+	// show the user id
+	w.Write([]byte(fmt.Sprintf("loaded user %s", user.String())))
+}
+
+func getUserFromPath(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		userID := r.PathValue("userId")
+		userIDint, err := strconv.Atoi(userID)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte("bad user id"))
+			return
+		}
+		user, err := db.LoadUser(userIDint)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte(fmt.Sprintf("could not load user: %s", err.Error())))
+			return
+		}
+		newContext := context.WithValue(r.Context(), userContextKey, user)
+		r = r.Clone(newContext)
+		next.ServeHTTP(w, r)
+	})
+}