1 files changed, 74 insertions, 0 deletions
diff --git a/doc/progs/error4.go b/doc/progs/error4.go
new file mode 100644
index 000000000..8f35cf74b
--- /dev/null
+++ b/doc/progs/error4.go
@@ -0,0 +1,74 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains the code snippets included in "Error Handling and Go."
+
+package main
+
+import (
+	"net/http"
+	"text/template"
+)
+
+type appError struct {
+	Error   error
+	Message string
+	Code    int
+}
+
+// STOP OMIT
+
+type appHandler func(http.ResponseWriter, *http.Request) *appError
+
+func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if e := fn(w, r); e != nil { // e is *appError, not os.Error.
+		c := appengine.NewContext(r)
+		c.Errorf("%v", e.Error)
+		http.Error(w, e.Message, e.Code)
+	}
+}
+
+// STOP OMIT
+
+func viewRecord(w http.ResponseWriter, r *http.Request) *appError {
+	c := appengine.NewContext(r)
+	key := datastore.NewKey(c, "Record", r.FormValue("id"), 0, nil)
+	record := new(Record)
+	if err := datastore.Get(c, key, record); err != nil {
+		return &appError{err, "Record not found", 404}
+	}
+	if err := viewTemplate.Execute(w, record); err != nil {
+		return &appError{err, "Can't display record", 500}
+	}
+	return nil
+}
+
+// STOP OMIT
+
+func init() {
+	http.Handle("/view", appHandler(viewRecord))
+}
+
+type ap struct{}
+
+func (ap) NewContext(*http.Request) *ctx { return nil }
+
+type ctx struct{}
+
+func (*ctx) Errorf(string, ...interface{}) {}
+
+var appengine ap
+
+type ds struct{}
+
+func (ds) NewKey(*ctx, string, string, int, *int) string { return "" }
+func (ds) Get(*ctx, string, *Record) error               { return nil }
+
+var datastore ds
+
+type Record struct{}
+
+var viewTemplate *template.Template
+
+func main() {}