'wdcli backup': Rework backup process

This commit reworks the backup process to dynamically find the list of
components.

internal/component/control/self.go

@@ -0,0 +1,134 @@
+package control
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+// self returns the handler for the self overrides
+func (control Control) self(io stream.IOStream) (redirect Redirect, err error) {
+	// open the overrides file
+	overrides, err := os.Open(control.Config.SelfOverridesFile)
+	io.Printf("loading overrides from %q\n", control.Config.SelfOverridesFile)
+	if err != nil {
+		return redirect, err
+	}
+	defer overrides.Close()
+
+	// decode the overrides file
+	if err := json.NewDecoder(overrides).Decode(&redirect.Overrides); err != nil {
+		return redirect, err
+	}
+
+	if redirect.Overrides == nil {
+		redirect.Overrides = make(map[string]string)
+	}
+	redirect.Overrides[""] = control.Config.SelfRedirect.String()
+
+	// create a redirect server
+	redirect.Fallback, err = control.selfFallback()
+	if err != nil {
+		return redirect, err
+	}
+	redirect.Absolute = false
+	redirect.Permanent = false
+
+	// and return!
+	return redirect, nil
+}
+
+func (control *Control) selfFallback() (http.Handler, error) {
+	return http.HandlerFunc(control.serveFallback), nil
+}
+
+var notFoundText = []byte("not found")
+
+func (control *Control) serveFallback(w http.ResponseWriter, r *http.Request) {
+
+	slug := control.Config.SlugFromHost(r.Host)
+	if slug == "" {
+		w.WriteHeader(http.StatusNotFound)
+		w.Write(notFoundText)
+		return
+	}
+
+	if ok, _ := control.Instances.Has(slug); !ok {
+		w.WriteHeader(http.StatusNotFound)
+		fmt.Fprintf(w, "WissKI %q not found\n", slug)
+		return
+	}
+
+	w.WriteHeader(http.StatusBadGateway)
+	fmt.Fprintf(w, "WissKI %q is currently offline\n", slug)
+
+}
+
+// Redirect implements a redirect server that redirects all requests.
+// It implements http.Handler.
+type Redirect struct {
+	// Target is the target URL to redirect to.
+	Target string
+
+	// Fallback is used when target is the empty string.
+	Fallback http.Handler
+
+	// Absolute determines if the request path should be appended to the target URL when redirecting.
+	// By default this path is always appended, set Absolute to true to prevent this.
+	Absolute bool
+
+	// Overrides is a map from paths to URLs that should override the default target.
+	Overrides map[string]string
+
+	// Permanent determines if the redirect responses issued should return
+	// Permanent Redirect (Status Code 308) or Temporary Redirect (Status Code 307).
+	Permanent bool
+}
+
+// Redirect determines the redirect URL for a specific incoming request
+// If it returns the empty string, the fallback is used.
+func (redirect Redirect) Redirect(r *http.Request) string {
+	// if we have an override for this URL, use it immediatly
+	url := strings.TrimSuffix(r.URL.Path, "/")
+	if override, ok := redirect.Overrides[url]; ok {
+		return override
+	}
+
+	if redirect.Target == "" {
+		return ""
+	}
+
+	// if we are in absolute redirect mode, always return the absolute URL
+	if redirect.Absolute {
+		return redirect.Target
+	}
+
+	// return the target + the redirected URL
+	dest := strings.TrimSuffix(redirect.Target, "/") + r.URL.Path
+	if len(r.URL.RawQuery) > 0 {
+		dest += "?" + r.URL.RawQuery
+	}
+	return dest
+}
+
+// ServeHTTP implements the http.Handler interface and redirects a single request to redirect.Target.
+func (redirect Redirect) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	dest := redirect.Redirect(r)
+	if dest == "" {
+		redirect.Fallback.ServeHTTP(w, r)
+		return
+	}
+
+	// determine if we are temporary or permanent redirect
+	status := http.StatusTemporaryRedirect
+	if redirect.Permanent {
+		status = http.StatusPermanentRedirect
+	}
+
+	// and do the redirect
+	http.Redirect(w, r, dest, status)
+}