From 9a117d3f5c5448a2c688409f451a13ccd94f6893 Mon Sep 17 00:00:00 2001
From: Jian Han <jianhan@mail.com>
Date: Mon, 22 Jan 2018 22:55:07 +1000
Subject: [PATCH] added error handling channel

---
 concurrency/error_handle/main.go | 87 ++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 concurrency/error_handle/main.go

diff --git a/concurrency/error_handle/main.go b/concurrency/error_handle/main.go
new file mode 100644
index 0000000..fb02ff7
--- /dev/null
+++ b/concurrency/error_handle/main.go
@@ -0,0 +1,87 @@
+package main
+
+// n general, your concurrent processes should send their
+// errors to another part of your program that has complete information
+// about the state of your program, and can make a more informed decision about what to do.
+import (
+	"fmt"
+	"net/http"
+)
+
+func main() {
+	// noErrorHandling()
+	errorHandling()
+}
+
+// Here we create a type that encompasses both the *http.Response and the error
+// possible from an iteration of the loop within our goroutine.
+type Result struct {
+	Error    error
+	Response *http.Response
+}
+
+func errorHandling() {
+	// This line returns a channel that can be read from to retrieve results of an iteration of our loop
+	checkStatus := func(done <-chan interface{}, urls ...string) <-chan Result {
+		results := make(chan Result)
+		go func() {
+			defer close(results)
+			for _, url := range urls {
+				var result Result
+				resp, err := http.Get(url)
+				// Here we create a Result instance with the Error and Response fields set.
+				result = Result{Error: err, Response: resp}
+				select {
+				case <-done:
+					return
+				// This is where we write the Result to our channel
+				case results <- result:
+				}
+			}
+		}()
+		return results
+	}
+	done := make(chan interface{})
+	defer close(done)
+	urls := []string{"https://www.google.com", "https://badhost"}
+	for result := range checkStatus(done, urls...) {
+		// Here, in our main goroutine, we are able to deal with errors coming out of the
+		// goroutine started by checkStatus intelligently, and with the full context of the larger program.
+		if result.Error != nil {
+			fmt.Printf("error: %v", result.Error)
+			continue
+		}
+		fmt.Printf("Response: %v\n", result.Response.Status)
+	}
+}
+
+func noErrorHandling() {
+	checkStatus := func(
+		done <-chan interface{},
+		urls ...string,
+	) <-chan *http.Response {
+		responses := make(chan *http.Response)
+		go func() {
+			defer close(responses)
+			for _, url := range urls {
+				resp, err := http.Get(url)
+				if err != nil {
+					fmt.Println(err)
+					continue
+				}
+				select {
+				case <-done:
+					return
+				case responses <- resp:
+				}
+			}
+		}()
+		return responses
+	}
+	done := make(chan interface{})
+	defer close(done)
+	urls := []string{"https://www.google.com", "https://badhost"}
+	for response := range checkStatus(done, urls...) {
+		fmt.Printf("Response: %v\n", response.Status)
+	}
+}