Go | ilManzo's blog

a simple HTTP rewriting proxy

This is an example of using goproxy, a fast and robust multithread proxy engine to develop an HTTP proxy that rewrites content on the fly, with multiple search and substitutions. It can be useful for debugging and other less noble (but useful) purposes … // rewriting_proxy project main.go package main import ( "bytes" "flag" "io/ioutil" "log" "net/http" "github.com/elazarl/goproxy" ) var replacements = []struct { from []byte to []byte }{ {[]byte("#e8ecec"), []byte("Red")}, // ugly colors!! {[]byte("Comic Sans MS"), []byte("Lucida Sans Unicode")}, // for eyes sanity {[]byte("Java "), []byte("Golang ")}, // just joking } func myHandler(resp *http.Response, ctx *goproxy.ProxyCtx) *http.Response { readBody, err := ioutil.ReadAll(resp.Body) if err != nil { //TODO handle read error gracefully return resp } resp.Body.Close() for _, elem := range replacements { readBody = bytes.Replace(readBody, elem.from, elem.to, -1) } resp.Body = ioutil.NopCloser(bytes.NewReader(readBody)) return resp } func main() { verbose := flag.Bool("v", true, "should every proxy request be logged to stdout") proxy := goproxy.NewProxyHttpServer() proxy.Verbose = *verbose proxy.OnResponse().DoFunc(myHandler) log.Fatal(http.ListenAndServe(":8081", proxy)) }

monit helper for quota monitoring in go

I want to keep under control a system where each user has an amount of filesystem quota reserved; in particular I would like to get notified if and when a user exceeds some treshold. Since I already have Monit in place in the server, I took the chance to write a small Go utility in order to retrieve the quota percentage. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 // quotachecker.go package main import ( "os" "os/exec" "regexp" "strconv" "strings" ) func main() { //a fake implementation, just for testing purpose //cmd := exec.Command("/bin/sh", "-c", "cat fakequota.txt") cmd := exec.Command("/usr/bin/repquota", "-a") stdout, err := cmd.Output() if err != nil { panic(err.Error()) } re, err := regexp.Compile("^[[:alnum:]]+\\s+--\\s+\\d+\\s+\\d+") if err != nil { panic(err.Error()) } percent_max := 0 result := strings.Split(string(stdout), "\n") for _, line := range result { match := re.MatchString(line) if !match { continue } fields := strings.Fields(line) spaceused, err := strconv.ParseInt(fields[2], 10, 64) if err != nil { panic(err.Error()) } spacetotal, err := strconv.ParseInt(fields[4], 10, 64) if err != nil { panic(err.Error()) } if spacetotal == 0 { continue } //calculate max percent used percent := int(100 * spaceused / spacetotal) if percent > percent_max { percent_max = int(percent) } } os.Exit(percent_max) } This is also an example on how to run external programs in Go and filter the output using regular expressions. ...

CGI with the Go Programming Language

Following with the GO standard library exploration, I’ve written a toy example for using the CGI features. Native GoLang CGI web applications are very fast and can be useful for example in embedded systems, or in cheap web hosting where is not possible to run custom HTTP servers. The solution has some weak points, starting from lock management, but is only presented as a proof of concept and not for real use cases. ...

sample template usage in the Go Programming Language

The GO programming language has a nice and useful standard library, which includes a powerful templating engine out of the box. Here I wrote an example, generating HTML output from a simple data structure. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 package main import ( "html/template" "log" "os" ) func main() { page := ` <!DOCTYPE html> <html><head><title>my todo list</title></head> <body><h1>my TODO list</h1> <ul> {{ range $item := . }} <li> {{ $item.Priority }} {{ $item.Topic }} </li> {{ end }} </ul> </body></html> ` type Todo struct { Priority int Topic string } var todos = []Todo{ {1, "Take out the dog"}, {2, "Feed the cat"}, {3, "Learn GO programming"}, } t := template.Must(template.New("page").Parse(page)) err := t.Execute(os.Stdout, todos) if err != nil { log.Println("executing template:", err) } } This program generates the following HTML output: ...