I want to download just part of a text-like file from the internet using go. It appears that curl --max-filesize and --range aren't respected by the websites I want to download from. Additionally, I read that the http MaxBytesReader still downloads the entire file, but only stores part of it.
Is there a way to just get the first kb of a file and then close the connection? The equivalent of pressing "x" when a large page is loading, on chrome.
I'm thinking that I can run a thread that reads a website to a file, and then kill the thread after a ms or two. Is this possible?
One simple way to do it without much error handling (which would have to added could be):
import (
"fmt"
"io"
"io/ioutil"
"net/http"
)
const readLimit = 1024 // bytes
func main() {
resp, err := http.Get("http://example.com/")
if err != nil {
// handle error
}
fixedReader := io.LimitedReader{R: resp.Body, N: readLimit}
data, _ := ioutil.ReadAll(fixedReader)
resp.Body.Close()
fmt.Println(string(data))
}
Related
I wrote a simple video server as follow:
package main
import (
"log"
"net/http"
"os"
"time"
)
func ServeHTTP(w http.ResponseWriter, r *http.Request) {
video, err := os.Open("/Users/icheer/Downloads/jsc/jsc.mp4")
if err != nil {
log.Fatal(err)
}
defer video.Close()
http.ServeContent(w, r, "jsc.mp4", time.Now(), video)
}
func main() {
http.HandleFunc("/", ServeHTTP)
_ = http.ListenAndServe(":8080", nil)
}
It works well, but I am curious about what chrome do when I open http://localhost:8080 in chrome.
Why the first request status code is 200, but the 'Time' is 'Pending', what 'Pending' exactly mean? How did chrome know the request show 'Pending'? And what confused me most is, i do not know which line of my golang code result in that. As the source code net/http/fs.go shows,
the sendSize is the total length of the video 5357093240, so I think the first request should return all bytes data of the video , but in fact, the response Size is 177B as the first picture shows, I do not know which line of the golang code result in that.
I am trying to write a simple web app that will listen for UDP packets.
But I can either only listen for UDP packets, or run the web app...
I am not familiar with GoLang, but here's the code I'm using to...
listen for UDP:
ServerConn, _ := net.ListenUDP("udp", &net.UDPAddr{IP:[]byte{#,#,#,#},Port:####,Zone:""})
defer ServerConn.Close()
buf := make([]byte, 1024)
for {
n, addr, _ := ServerConn.ReadFromUDP(buf)
fmt.Println("Received ", string(buf[0:n]), " from ", addr)
}
Server logic:
package main
We import 4 important libraries
1. “net/http” to access the core go http functionality
2. “fmt” for formatting our text
3. “html/template” a library that allows us to interact with our html file.
4. "time" - a library for working with date and time.
import (
"net/http"
"fmt"
"time"
"html/template"
)
//Create a struct that holds information to be displayed in our HTML file
type Welcome struct {
Name string
Time string
}
//Go application entrypoint
func main() {
//Instantiate a Welcome struct object and pass in some random information.
//We shall get the name of the user as a query parameter from the URL
welcome := Welcome{"Anonymous", time.Now().Format(time.Stamp)}
//We tell Go exactly where we can find our html file. We ask Go to parse the html file (Notice
// the relative path). We wrap it in a call to template.Must() which handles any errors and halts if there are fatal errors
templates := template.Must(template.ParseFiles("templates/welcome-template.html"))
//Our HTML comes with CSS that go needs to provide when we run the app. Here we tell go to create
// a handle that looks in the static directory, go then uses the "/static/" as a url that our
//html can refer to when looking for our css and other files.
http.Handle("/static/", //final url can be anything
http.StripPrefix("/static/",
http.FileServer(http.Dir("static")))) //Go looks in the relative "static" directory first using http.FileServer(), then matches it to a
//url of our choice as shown in http.Handle("/static/"). This url is what we need when referencing our css files
//once the server begins. Our html code would therefore be <link rel="stylesheet" href="/static/stylesheet/...">
//It is important to note the url in http.Handle can be whatever we like, so long as we are consistent.
//This method takes in the URL path "/" and a function that takes in a response writer, and a http request.
http.HandleFunc("/" , func(w http.ResponseWriter, r *http.Request) {
//Takes the name from the URL query e.g ?name=Martin, will set welcome.Name = Martin.
if name := r.FormValue("name"); name != "" {
welcome.Name = name;
}
//If errors show an internal server error message
//I also pass the welcome struct to the welcome-template.html file.
if err := templates.ExecuteTemplate(w, "welcome-template.html", welcome); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
})
//Start the web server, set the port to listen to 8080. Without a path it assumes localhost
//Print any errors from starting the webserver using fmt
fmt.Println("Listening");
fmt.Println(http.ListenAndServe(":8080", nil));
}
taken from(https://medium.com/google-cloud/building-a-go-web-app-from-scratch-to-deploying-on-google-cloud-part-1-building-a-simple-go-aee452a2e654)
I tried putting both of these extracts in 1 file, as well as running 2 files at the same time using
go run *.go
Any help would be appreciated!
You're going to need to start looking into goroutines - since you're asking to do two things concurrently. I suggest doing some reading into channels, goroutines, and concurrency in general :)
I'm new to Golang and trying to get a basic http app running using the httprouter API. I've hit a wall with reading posted form data, despite following the advice given in another StackOverflow question.
Here's my code (minus irrelevancies):
import (
"fmt"
"net/http"
"github.com/julienschmidt/httprouter"
)
func main() {
r := httprouter.New()
r.POST("/sub", func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
r.Header.Set("content-type", "text/html")
err := r.ParseForm()
if err != nil {
fmt.Fprintf(w, "<h1>Error: %s</h1>\n", err)
}
fmt.Fprintf(w, "<h1>Submitted message!</h1>\n<p>-%s-</p>\n", r.PostFormValue("msg"))
})
http.ListenAndServe("localhost:3000", r)
}
In the output, where I should see -hello-, I just see --. When I inspect the http request in Firefox, in the Form Data panel, I see msg:"hello", so why is r.PostFormValue("msg") returning a blank string?
Thanks to Volker for pointing out an error. When I commented out the line r.Header.Set("content-type", "text/html"), the problem was resolved. Perhaps that was the issue, or perhaps there was some issue with the IDE (LiteIDE) caching an old version of the code. In any case, I can now read the posted value.
I've been using the gocraft-web package so far to do some development on an HTTP service. It's really great because you can stick middleware in it to check for stuff like the presence of a Cookie in the header.
At the moment I am wanting to implement request signing. Getting the client to sign the request is easy enough, but I am wanting to check it for all endpoints with a common piece of middleware. Basically the middleware needs to find the key to check against, compute the request HMAC, and check it against the supplied HMAC (presumably in the Authorization Header).
Computing the actual HMAC is really easy in go.
The problem is: reading the message in middleware makes it unavailable to the final endpoint.
The best solution I have come up with (example shown below) is to read everything from the Request in the middleware and stuffing it back into a bytes.Buffer for later reading. Is there a better way to do this? The current implementation seems a bit hackish.
Reading everything into memory sucks, but I can probably just put my service behind a proxy and limit the size of requests anyways. The actual content will always be pretty small(under 5 kilobytes). The extra copy introduced by this approach is likely to be quite slow, but computing the HMAC of a message is not exactly cheap to begin with.
The advantage to this is that it is transparent: it will work with any other go http code that just expects to read from Request.Body without any magic.
I suppose I could be a bit slicker and use a io.TeeReader.
This is my solution so far. If you post to localhost:3300 some JSON it prints the sha512 to the terminal in the server process, but also the response is able to contain a listing of the keys & values in it.
package main
import "fmt"
import "github.com/gocraft/web"
import "net/http"
import "bytes"
import "crypto/sha512"
import "io"
import "encoding/hex"
import "encoding/json"
type Context struct{}
type echoer struct {
*bytes.Buffer
}
func (e echoer) Close() error {
//Just do nothing to make the interface happy
return nil
}
func middlewareThatLooksAtBody(rw web.ResponseWriter, req *web.Request, next web.NextMiddlewareFunc) {
var replacement echoer
replacement.Buffer = &bytes.Buffer{}
hash := sha512.New()
hash.Write([]byte(req.Method))
reader := req.Body
var bytes []byte = make([]byte, 64)
for {
amount, err := reader.Read(bytes)
fmt.Printf("Read %d bytes\n", amount)
if err != nil {
if err == io.EOF {
break
}
panic(err)
}
if amount == 0 {
break
}
hash.Write(bytes)
replacement.Write(bytes)
}
//Is this needed?
reader.Close()
//replacement.Seek(0, 0)
req.Body = replacement
fmt.Printf("%v\n", hex.EncodeToString(hash.Sum(nil)))
next(rw, req)
}
func echoJson(rw web.ResponseWriter, req *web.Request) {
dec := json.NewDecoder(req.Body)
var obj map[string]interface{}
err := dec.Decode(&obj)
if err != nil {
rw.WriteHeader(http.StatusBadRequest)
fmt.Fprintf(rw, "%v\n", err)
return
}
for k, v := range obj {
fmt.Fprintf(rw, "%v = %v\n", k, v)
}
}
func main() {
router := web.New(Context{})
router.Middleware(middlewareThatLooksAtBody)
router.Post("/", echoJson)
http.ListenAndServe("localhost:3300", router)
}
From your description, it looks like you need to read all the bytes from the request body, regardless of what your handlers will do.
If so, then you have at least a couple of options that would avoid the extra copy:
1) Store the read contents inside your gocraft context.
2) Do all body data processing and validation in the middleware and store the results of the processing in the context.
Granted, this means that your handlers now must know that they should look for the contents in the context instead of the req.Body.
I think it's a decent trade-off though, given your requirements.
I'm playing with Go (first time ever) and I want to build a tool to retrieve images from Internet and cut them (even resize) but I'm stuck on the first step.
package main
import (
"fmt"
"http"
)
var client = http.Client{}
func cutterHandler(res http.ResponseWriter, req *http.Request) {
reqImg, err := client.Get("http://www.google.com/intl/en_com/images/srpr/logo3w.png")
if err != nil {
fmt.Fprintf(res, "Error %d", err)
return
}
buffer := make([]byte, reqImg.ContentLength)
reqImg.Body.Read(buffer)
res.Header().Set("Content-Length", fmt.Sprint(reqImg.ContentLength)) /* value: 7007 */
res.Header().Set("Content-Type", reqImg.Header.Get("Content-Type")) /* value: image/png */
res.Write(buffer)
}
func main() {
http.HandleFunc("/cut", cutterHandler)
http.ListenAndServe(":8080", nil) /* TODO Configurable */
}
I'm able to request an image (let's use Google logo) and to get its kind and size.
Indeed, I'm just re-writing the image (look at this as a toy "proxy"), setting Content-Length and Content-Type and writing the byte slice back but I get it wrong somewhere. See how it looks the final image rendered on Chromium 12.0.742.112 (90304):
Also I checked the downloaded file and it is a 7007 bytes PNG image. It should be working properly if we look at the request:
GET /cut HTTP/1.1
User-Agent: curl/7.22.0 (i486-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.0e zlib/1.2.3.4 libidn/1.23 libssh2/1.2.8 librtmp/2.3
Host: 127.0.0.1:8080
Accept: /
HTTP/1.1 200 OK
Content-Length: 7007
Content-Type: image/png
Date: Tue, 27 Dec 2011 19:51:53 GMT
[PNG data]
What do you think I'm doing wrong here?
Disclaimer: I'm scratching my own itch, so probably I'm using the wrong tool :) Anyway, I can implement it on Ruby but before I would like to give Go a try.
Update: still scratching itches but... I think this is going to be a good side-of-side project so I'm opening it https://github.com/imdario/go-lazor If it is not useful, at least somebody can find usefulness with the references used to develop it. They were for me.
I think you went too fast to the serve things part.
Focus on the first step, downloading the image.
Here you have a little program that downloads that image to memory.
It works on my 2011-12-22 weekly version, for r60.3 you just need to gofix the imports.
package main
import (
"log"
"io/ioutil"
"net/http"
)
const url = "http://www.google.com/intl/en_com/images/srpr/logo3w.png"
func main() {
// Just a simple GET request to the image URL
// We get back a *Response, and an error
res, err := http.Get(url)
if err != nil {
log.Fatalf("http.Get -> %v", err)
}
// We read all the bytes of the image
// Types: data []byte
data, err = ioutil.ReadAll(res.Body)
if err != nil {
log.Fatalf("ioutil.ReadAll -> %v", err)
}
// You have to manually close the body, check docs
// This is required if you want to use things like
// Keep-Alive and other HTTP sorcery.
res.Body.Close()
// You can now save it to disk or whatever...
ioutil.WriteFile("google_logo.png", data, 0666)
log.Println("I saved your image buddy!")
}
Voilá!
This will get the image to memory inside data.
Once you have that, you can decode it, crop it and serve back to the browser.
Hope this helps.
I tried your code and noticed that the image you were serving was the right size, but the contents of the file past a certain point were all 0x00.
Review the io.Reader documentation. The important thing to remember is that Read reads up to the number of bytes you request. It can read fewer with no error returned. (You should be checking the error too, but that's not an issue here.)
If you want to make sure your buffer is completely full, use io.ReadFull. In this case it's simpler to just copy the entire contents of the Reader with io.Copy.
It's also important to remember to close HTTP request bodies.
I would rewrite the code this way:
package main
import (
"fmt"
"http"
"io"
)
var client = http.Client{}
func cutterHandler(res http.ResponseWriter, req *http.Request) {
reqImg, err := client.Get("http://www.google.com/intl/en_com/images/srpr/logo3w.png")
if err != nil {
fmt.Fprintf(res, "Error %d", err)
return
}
res.Header().Set("Content-Length", fmt.Sprint(reqImg.ContentLength))
res.Header().Set("Content-Type", reqImg.Header.Get("Content-Type"))
if _, err = io.Copy(res, reqImg.Body); err != nil {
// handle error
}
reqImg.Body.Close()
}
func main() {
http.HandleFunc("/cut", cutterHandler)
http.ListenAndServe(":8080", nil) /* TODO Configurable */
}