I'm writing some web service which supposed to receive an xml file from user, read it and save data to database
This file is gzipped and encoded in UTF-16. So i have to ungzip it, save xml to a file (for future purposes). Next i have to read file into a string, decode it to UTF-8 and kind of xml.Unmarshal([]byte(xmlString), &report)
Currently without saving it into a database
On my local machine i've realized that processing of one request takes about 30% of my CPU and about 300ms of time. For one request looks like okay. But i made script which simultaneously fires 100 requests (via curl ) and i saw that CPU usage is up to 100% and time for one request increased to 2sec
What i wanted to ask is: should i worry about it or maybe on a real web server things are going to be ok? Or maybe i'm doing smth wrong
Here is the code:
func Parse(filename string) Report {
xmlString := getXml(filename)
report := Report{}
xml.Unmarshal([]byte(xmlString), &report)
return report
}
func getXml(filename string) string {
b, err := ioutil.ReadFile(filename)
if err != nil {
fmt.Println("Error opening file:", err)
}
s, err := decodeUTF16(b)
if err != nil {
panic(err)
}
pattern := `<?xml version="1.0" encoding="UTF-16"?>`
res := strings.Replace(s, pattern, "", 1)
return res
}
func decodeUTF16(b []byte) (string, error) {
if len(b)%2 != 0 {
return "", fmt.Errorf("Must have even length byte slice")
}
u16s := make([]uint16, 1)
ret := &bytes.Buffer{}
b8buf := make([]byte, 4)
lb := len(b)
for i := 0; i < lb; i += 2 {
u16s[0] = uint16(b[i]) + (uint16(b[i+1]) << 8)
r := utf16.Decode(u16s)
n := utf8.EncodeRune(b8buf, r[0])
ret.Write(b8buf[:n])
}
return ret.String(), nil
}
Please ask if i forgot something important
Related
I need to hash very large files (>10TB files). So I decided to hash 128KB per MB.
My idea is to divide the file into 1MB blocks and hash only the first 128KB of each block.
The following code works, but it uses insane amounts of memory and I can't tell why...
func partialMD5Hash(filePath string) string {
var blockSize int64 = 1024 * 1024
var sampleSize int64 = 1024 * 128
file, err := os.Open(filePath)
if err != nil {
return "ERROR"
}
defer file.Close()
fileInfo, _ := file.Stat()
fileSize := fileInfo.Size()
hash := md5.New()
var i int64
for i = 0; i < fileSize / blockSize; i++ {
sample := make([]byte, sampleSize)
_, err = file.Read(sample)
if err != nil {
return "ERROR"
}
hash.Write(sample)
_, err := file.Seek(blockSize-sampleSize, 1)
if err != nil {
return "ERROR"
}
}
return hex.EncodeToString(hash.Sum(nil))
}
Any help will be appreciated!
There are several problems with the approach, and with the program.
If you want to hash a large file, you have to hash all of it. Sampling parts of the file will not detect modifications to the parts you didn't sample.
You are allocating a new buffer for every iteration. Instead, allocate one buffer outside the for-loop, and reuse it.
Also, you seem to be ignoring how many bytes actually read. So:
block := make([]byte, blockSize)
for {
n, err = file.Read(block)
if n>0 {
hash.Write(sample[:n])
}
if err==io.EOF {
break
}
if err != nil {
return "ERROR"
}
}
However, the following would be much more concise:
io.Copy(hash,file)
I completed the suggested go-tour, watched some tutorials and gopher-conferences on YouTube. And that's pretty much it.
I have a project which requires me to send get requests and store the results in files. But amount of URL's is around 80 million.
I'm testing with 1000 URLs only.
Problem: I think I couldn't managed to make it concurrent, although I've followed some guidelines. I don't know what's wrong. But maybe I'm wrong and it's concurrent, just did not seem fast to me, the speed felt like sequential requests.
Here is the code I've written:
package main
import (
"bufio"
"io/ioutil"
"log"
"net/http"
"os"
"sync"
"time"
)
var wg sync.WaitGroup // synchronization to wait for all the goroutines
func crawler(urlChannel <-chan string) {
defer wg.Done()
client := &http.Client{Timeout: 10 * time.Second} // single client is sufficient for multiple requests
for urlItem := range urlChannel {
req1, _ := http.NewRequest("GET", "http://"+urlItem, nil) // generating the request
req1.Header.Add("User-agent", "Mozilla/5.0 (X11; Linux i586; rv:31.0) Gecko/20100101 Firefox/74.0") // changing user-agent
resp1, respErr1 := client.Do(req1) // sending the prepared request and getting the response
if respErr1 != nil {
continue
}
defer resp1.Body.Close()
if resp1.StatusCode/100 == 2 { // means server responded with 2xx code
text1, readErr1 := ioutil.ReadAll(resp1.Body) // try to read the sourcecode of the website
if readErr1 != nil {
log.Fatal(readErr1)
}
f1, fileErr1 := os.Create("200/" + urlItem + ".txt") // creating the relative file
if fileErr1 != nil {
log.Fatal(fileErr1)
}
defer f1.Close()
_, writeErr1 := f1.Write(text1) // writing the sourcecode into our file
if writeErr1 != nil {
log.Fatal(writeErr1)
}
}
}
}
func main() {
file, err := os.Open("urls.txt") // the file containing the url's
if err != nil {
log.Fatal(err)
}
defer file.Close() // don't forget to close the file
urlChannel := make(chan string, 1000) // create a channel to store all the url's
scanner := bufio.NewScanner(file) // each line has another url
for scanner.Scan() {
urlChannel <- scanner.Text()
}
close(urlChannel)
_ = os.Mkdir("200", 0755) // if it's there, it will create an error, and we will simply ignore it
for i := 0; i < 10; i++ {
wg.Add(1)
go crawler(urlChannel)
}
wg.Wait()
}
My question is: why is this code not working concurrently? How can I solve the problem I've mentioned above. Is there something that I'm doing wrong for making concurrent GET requests?
Here's some code to get you thinking. I put the URLs in the code so it is self-sufficient, but you'd probably be piping them to stdin in practice. There's a few things I'm doing here that I think are improvements, or at least worth thinking about.
Before we get started, I'll point out that I put the complete url in the input stream. For one thing, this lets me support http and https both. I don't really see the logic behind hard coding the scheme in the code rather than leaving it in the data.
First, it can handle arbitrarily sized response bodies (your version reads the body into memory, so it is limited by some number of concurrent large requests filling memory). I do this with io.Copy().
[edited]
text1, readErr1 := ioutil.ReadAll(resp1.Body) reads the entire http body. If the body is large, it will take up lots of memory. io.Copy(f1,resp1.Body) would instead copy the data from the http response body directly to the file, without having to hold the whole thing in memory. It may be done in one Read/Write or many.
http.Response.Body is an io.ReadCloser because the HTTP protocol expects the body to be read progressively. http.Response does not yet have the entire body, until it is read. That's why it's not just a []byte. Writing it to the filesystem progressively while the data "streams" in from the tcp socket means that a finite amount of system resources can download an unlimited amount of data.
But there's even more benefit. io.Copy will call ReadFrom() on the file. If you look at the linux implementation (for example): https://golang.org/src/os/readfrom_linux.go , and dig a bit, you'll see it actually uses copy_file_range That system call is cool because
The copy_file_range() system call performs an in-kernel copy between two file descriptors without the additional cost of transferring data from the kernel to user space and then back into the kernel.
*os.File knows how to ask the kernel to deliver data directly from the tcp socket to the file without your program even having to touch it.
See https://golang.org/pkg/io/#Copy.
Second, I make sure to use all the url components in the filename. URLs with different query strings go to different files. The fragment probably doesn't differentiate response bodies, so including that in the path may be ill considered. There's no awesome heuristic for turning URLs into valid file paths - if this were a serious task, I'd probably store the data in files based on a shasum of the url or something - and create an index of results stored in a metadata file.
Third, I handle all errors. req1, _ := http.NewRequest(... might seem like a convenient shortcut, but what it really means is that you won't know the real cause of any errors - at best. I usually add some descriptive text to the errors when percolating up, to make sure I can easily tell which error I'm returning.
Finally, I return successfully processed URLs so that I can see the final results. When scanning millions of URLS, you'd probably also want a list of which failed, but a count of successful is a good start at sending final data back for summary.
package main
import (
"bufio"
"bytes"
"fmt"
"io"
"log"
"net/http"
"net/url"
"os"
"path/filepath"
"time"
)
const urls_text = `http://danf.us/
https://farrellit.net/?3=2
`
func crawler(urls <-chan *url.URL, done chan<- int) {
var processed int = 0
defer func() { done <- processed }()
client := http.Client{Timeout: 10 * time.Second}
for u := range urls {
if req, err := http.NewRequest("GET", u.String(), nil); err != nil {
log.Printf("Couldn't create new request for %s: %s", u.String(), err.Error())
} else {
req.Header.Add("User-agent", "Mozilla/5.0 (X11; Linux i586; rv:31.0) Gecko/20100101 Firefox/74.0") // changing user-agent
if res, err := client.Do(req); err != nil {
log.Printf("Failed to get %s: %s", u.String(), err.Error())
} else {
filename := filepath.Base(u.EscapedPath())
if filename == "/" || filename == "" {
filename = "response"
} else {
log.Printf("URL Filename is '%s'", filename)
}
destpath := filepath.Join(
res.Status, u.Scheme, u.Hostname(), u.EscapedPath(),
fmt.Sprintf("?%s",u.RawQuery), fmt.Sprintf("#%s",u.Fragment), filename,
)
if err := os.MkdirAll(filepath.Dir(destpath), 0755); err != nil {
log.Printf("Couldn't create directory %s: %s", filepath.Dir(destpath), err.Error())
} else if f, err := os.OpenFile(destpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644); err != nil {
log.Printf("Couldn't open destination file %s: %s", destpath, err.Error())
} else {
if b, err := io.Copy(f, res.Body); err != nil {
log.Printf("Could not copy %s body to %s: %s", u.String(), destpath, err.Error())
} else {
log.Printf("Copied %d bytes from body of %s to %s", b, u.String(), destpath)
processed++
}
f.Close()
}
res.Body.Close()
}
}
}
}
const workers = 3
func main() {
urls := make(chan *url.URL)
done := make(chan int)
var submitted int = 0
var inputted int = 0
var successful int = 0
for i := 0; i < workers; i++ {
go crawler(urls, done)
}
sc := bufio.NewScanner(bytes.NewBufferString(urls_text))
for sc.Scan() {
inputted++
if u, err := url.Parse(sc.Text()); err != nil {
log.Printf("Could not parse %s as url: %w", sc.Text(), err)
} else {
submitted++
urls <- u
}
}
close(urls)
for i := 0; i < workers; i++ {
successful += <-done
}
log.Printf("%d urls input, %d could not be parsed. %d/%d valid URLs successful (%.0f%%)",
inputted, inputted-submitted,
successful, submitted,
float64(successful)/float64(submitted)*100.0,
)
}
When setting up a concurrent pipeline, a good guideline to follow is to always first set up and instantiate the listeners that will execute concurrently (in your case, crawlers), and then start feeding them data through the pipeline (in your case, the urlChannel).
In your example, the only thing preventing a deadlock is the fact that you've instantiated a buffered channel with the same number of rows that your test file has (1000 rows). What the code does is it puts URLs inside the urlChannel. Since there are 1000 rows inside your file, the urlChannel can take all of them without blocking. If you put more URLs inside the file, the execution will block after filling up the urlChannel.
Here is the version of the code that should work:
package main
import (
"bufio"
"io/ioutil"
"log"
"net/http"
"os"
"sync"
"time"
)
func crawler(wg *sync.WaitGroup, urlChannel <-chan string) {
defer wg.Done()
client := &http.Client{Timeout: 10 * time.Second} // single client is sufficient for multiple requests
for urlItem := range urlChannel {
req1, _ := http.NewRequest("GET", "http://"+urlItem, nil) // generating the request
req1.Header.Add("User-agent", "Mozilla/5.0 (X11; Linux i586; rv:31.0) Gecko/20100101 Firefox/74.0") // changing user-agent
resp1, respErr1 := client.Do(req1) // sending the prepared request and getting the response
if respErr1 != nil {
continue
}
if resp1.StatusCode/100 == 2 { // means server responded with 2xx code
text1, readErr1 := ioutil.ReadAll(resp1.Body) // try to read the sourcecode of the website
if readErr1 != nil {
log.Fatal(readErr1)
}
resp1.Body.Close()
f1, fileErr1 := os.Create("200/" + urlItem + ".txt") // creating the relative file
if fileErr1 != nil {
log.Fatal(fileErr1)
}
_, writeErr1 := f1.Write(text1) // writing the sourcecode into our file
if writeErr1 != nil {
log.Fatal(writeErr1)
}
f1.Close()
}
}
}
func main() {
var wg sync.WaitGroup
file, err := os.Open("urls.txt") // the file containing the url's
if err != nil {
log.Fatal(err)
}
defer file.Close() // don't forget to close the file
urlChannel := make(chan string)
_ = os.Mkdir("200", 0755) // if it's there, it will create an error, and we will simply ignore it
// first, initialize crawlers
wg.Add(10)
for i := 0; i < 10; i++ {
go crawler(&wg, urlChannel)
}
//after crawlers are initialized, start feeding them data through the channel
scanner := bufio.NewScanner(file) // each line has another url
for scanner.Scan() {
urlChannel <- scanner.Text()
}
close(urlChannel)
wg.Wait()
}
I'm trying to improve the performance of an app.
One part of its code uploads a file to a server in chunks.
The original version simply does this in a sequential loop. However, it's slow and during the sequence it also needs to talk to another server before uploading each chunk.
The upload of chunks could simply be placed in a goroutine. It works, but is not a good solution because if the source file is extremely large it ends up using a large amount of memory.
So, I try to limit the number of active goroutines by using a buffered channel. Here is some code that shows my attempt. I've stripped it down to show the concept and you can run it to test for yourself.
package main
import (
"fmt"
"io"
"os"
"time"
)
const defaultChunkSize = 1 * 1024 * 1024
// Lets have 4 workers
var c = make(chan int, 4)
func UploadFile(f *os.File) error {
fi, err := f.Stat()
if err != nil {
return fmt.Errorf("err: %s", err)
}
size := fi.Size()
total := (int)(size/defaultChunkSize + 1)
// Upload parts
buf := make([]byte, defaultChunkSize)
for partno := 1; partno <= total; partno++ {
readChunk := func(offset int, buf []byte) (int, error) {
fmt.Println("readChunk", partno, offset)
n, err := f.ReadAt(buf, int64(offset))
if err != nil {
return n, err
}
return n, nil
}
// This will block if there are not enough worker slots available
c <- partno
// The actual worker.
go func() {
offset := (partno - 1) * defaultChunkSize
n, err := readChunk(offset, buf)
if err != nil && err != io.EOF {
return
}
err = uploadPart(partno, buf[:n])
if err != nil {
fmt.Println("Uploadpart failed:", err)
}
<-c
}()
}
return nil
}
func uploadPart(partno int, buf []byte) error {
fmt.Printf("Uploading partno: %d, buflen=%d\n", partno, len(buf))
// Actually upload the part. Lets test it by instead writing each
// buffer to another file. We can then use diff to compare the
// source and dest files.
// Open file. Seek to (partno - 1) * defaultChunkSize, write buffer
f, err := os.OpenFile("/home/matthewh/Downloads/out.tar.gz", os.O_CREATE|os.O_WRONLY, 0755)
if err != nil {
fmt.Printf("err: %s\n", err)
}
n, err := f.WriteAt(buf, int64((partno-1)*defaultChunkSize))
if err != nil {
fmt.Printf("err=%s\n", err)
}
fmt.Printf("%d bytes written\n", n)
defer f.Close()
return nil
}
func main() {
filename := "/home/matthewh/Downloads/largefile.tar.gz"
fmt.Printf("Opening file: %s\n", filename)
f, err := os.Open(filename)
if err != nil {
panic(err)
}
UploadFile(f)
}
It almost works. But there are several problems.
1) The final partno 22 is occuring 3 times. The correct length is actually 612545 as the file length isn't a multiple of 1MB.
// Sample output
...
readChunk 21 20971520
readChunk 22 22020096
Uploading partno: 22, buflen=1048576
Uploading partno: 22, buflen=612545
Uploading partno: 22, buflen=1048576
Another problem, the upload could fail and I am not familiar enough with go and how best to solve failure of the goroutine.
Finally, I want to ordinarily return some data from the uploadPart when it succeeds. Specifically, it'll be a string (an HTTP ETag header value). These etag values need to be collected by the main function.
What is a better way to structure this code in this instance? I've not yet found a good golang design pattern that correctly fulfills my needs here.
Skipping for the moment the question of how better to structure this code, I see a bug in your code which may be causing the problem you're seeing. Since the function you're running in the goroutine uses the variable partno, which changes with each iteration of the loop, your goroutine isn't necessarily seeing the value of partno at the time you invoked the goroutine. A common way of fixing this is to create a local copy of that variable inside the loop:
for partno := 1; partno <= total; partno++ {
partno := partno
// ...
}
Data race #1
Multiple goroutines are using the same buffer concurrently. Note that one gorouting may be filling it with a new chunk while another is still reading an old chunk from it. Instead, each goroutine should have it's own buffer.
Data race #2
As Andy Schweig has pointed, the value in partno is updated by the loop before the goroutine created in that iteration has a chance to read it. This is why the final partno 22 occurs multiple times. To fix it, you can pass partno as a argument to the anonymous function. That will ensure each goroutine has it's own part number.
Also, you can use a channel to pass the results from the workers. Maybe a struct type with the part number and error. That way, you will be able to observe the progress and retry failed uploads.
For an example of a good pattern check out this example from the GOPL book.
Suggested changes
As noted by dev.bmax buf moved into go routine, as noted by Andy Schweig partno is param to anon function, also added WaitGroup since UploadFile was exiting before uploads were complete. Also defer f.Close() file, good habit.
package main
import (
"fmt"
"io"
"os"
"sync"
"time"
)
const defaultChunkSize = 1 * 1024 * 1024
// wg for uploads to complete
var wg sync.WaitGroup
// Lets have 4 workers
var c = make(chan int, 4)
func UploadFile(f *os.File) error {
// wait for all the uploads to complete before function exit
defer wg.Wait()
fi, err := f.Stat()
if err != nil {
return fmt.Errorf("err: %s", err)
}
size := fi.Size()
fmt.Printf("file size: %v\n", size)
total := int(size/defaultChunkSize + 1)
// Upload parts
for partno := 1; partno <= total; partno++ {
readChunk := func(offset int, buf []byte, partno int) (int, error) {
fmt.Println("readChunk", partno, offset)
n, err := f.ReadAt(buf, int64(offset))
if err != nil {
return n, err
}
return n, nil
}
// This will block if there are not enough worker slots available
c <- partno
// The actual worker.
go func(partno int) {
// wait for me to be done
wg.Add(1)
defer wg.Done()
buf := make([]byte, defaultChunkSize)
offset := (partno - 1) * defaultChunkSize
n, err := readChunk(offset, buf, partno)
if err != nil && err != io.EOF {
return
}
err = uploadPart(partno, buf[:n])
if err != nil {
fmt.Println("Uploadpart failed:", err)
}
<-c
}(partno)
}
return nil
}
func uploadPart(partno int, buf []byte) error {
fmt.Printf("Uploading partno: %d, buflen=%d\n", partno, len(buf))
// Actually do the upload. Simulate long running task with a sleep
time.Sleep(time.Second)
return nil
}
func main() {
filename := "/home/matthewh/Downloads/largefile.tar.gz"
fmt.Printf("Opening file: %s\n", filename)
f, err := os.Open(filename)
if err != nil {
panic(err)
}
defer f.Close()
UploadFile(f)
}
I'm sure you can deal a little smarter with the buf situation. I'm just letting go deal with the garbage. Since you are limiting your workers to specific number 4 you really need only 4 x defaultChunkSize buffers. Please do share if you come up with something simple and shareworth.
Have fun!
I've written a little server which receives a blob of data in the form of an io.Reader, adds a header and streams the result back to the caller.
My implementation isn't particularly efficient as I'm buffering the blob's data in-memory so that I can calculate the blob's length, which needs to form part of the header.
I've seen some examples of io.Pipe() with io.TeeReader but they're more for splitting an io.Reader into two, and writing them away in parallel.
The blobs I'm dealing with are around 100KB, so not huge but if my server gets busy, memory's going to quickly become an issue...
Any ideas?
func addHeader(in io.Reader) (out io.Reader, err error) {
buf := new(bytes.Buffer)
if _, err = io.Copy(buf, in); err != nil {
return
}
header := bytes.NewReader([]byte(fmt.Sprintf("header:%d", buf.Len())))
return io.MultiReader(header, buf), nil
}
I appreciate it's not a good idea to return interfaces from functions but this code isn't destined to become an API, so I'm not too concerned with that bit.
In general, the only way to determine the length of data in an io.Reader is to read until EOF. There are ways to determine the length of the data for specific types.
func addHeader(in io.Reader) (out io.Reader, err error) {
n := 0
switch v := in.(type) {
case *bytes.Buffer:
n = v.Len()
case *bytes.Reader:
n = v.Len()
case *strings.Reader:
n = v.Len()
case io.Seeker:
cur, err := v.Seek(0, 1)
if err != nil {
return nil, err
}
end, err := v.Seek(0, 2)
if err != nil {
return nil, err
}
_, err = v.Seek(cur, 0)
if err != nil {
return nil, err
}
n = int(end - cur)
default:
var buf bytes.Buffer
if _, err := buf.ReadFrom(in); err != nil {
return nil, err
}
n = buf.Len()
in = &buf
}
header := strings.NewReader(fmt.Sprintf("header:%d", n))
return io.MultiReader(header, in), nil
}
This is similar to how the net/http package determines the content length of the request body.
I’ve written a short program in Go to communicate with a sensor through a serial port:
package main
import (
"fmt"
"github.com/tarm/goserial"
"time"
)
func main() {
c := &serial.Config{Name: "/dev/ttyUSB0", Baud: 9600}
s, err := serial.OpenPort(c)
if err != nil {
fmt.Println(err)
}
_, err = s.Write([]byte("\x16\x02N0C0 G A\x03\x0d\x0a"))
if err != nil {
fmt.Println(err)
}
time.Sleep(time.Second/2)
buf := make([]byte, 40)
n, err := s.Read(buf)
if err != nil {
fmt.Println(err)
}
fmt.Println(string(buf[:n]))
s.Close()
}
It works fine, but after writing to the port I have to wait about half a second before I can start reading from it. I would like to use a while-loop instead of time.Sleep to read all incoming data. My attempt doesn’t work:
buf := make([]byte, 40)
n := 0
for {
n, _ := s.Read(buf)
if n > 0 {
break
}
}
fmt.Println(string(buf[:n]))
I guess buf gets overwritten after every loop pass. Any suggestions?
Your problem is that Read() will return whenever it has some data - it won't wait for all the data. See the io.Reader specification for more info
What you want to do is read until you reach some delimiter. I don't know exactly what format you are trying to use, but it looks like maybe \x0a is the end delimiter.
In which case you would use a bufio.Reader like this
reader := bufio.NewReader(s)
reply, err := reader.ReadBytes('\x0a')
if err != nil {
panic(err)
}
fmt.Println(reply)
Which will read data until the first \x0a.
I guess buf gets overwritten after every loop pass. Any suggestions?
Yes, buf will get overwritten with every call to Read().
A timeout on the file handle would be the approach I would take.
s, _ := os.OpenFile("/dev/ttyS0", syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
t := syscall.Termios{
Iflag: syscall.IGNPAR,
Cflag: syscall.CS8 | syscall.CREAD | syscall.CLOCAL | syscall.B115200,
Cc: [32]uint8{syscall.VMIN: 0, syscall.VTIME: uint8(20)}, //2.0s timeout
Ispeed: syscall.B115200,
Ospeed: syscall.B115200,
}
// syscall
syscall.Syscall6(syscall.SYS_IOCTL, uintptr(s.Fd()),
uintptr(syscall.TCSETS), uintptr(unsafe.Pointer(&t)),
0, 0, 0)
// Send message
n, _ := s.Write([]byte("Test message"))
// Receive reply
for {
buf := make([]byte, 128)
n, err = s.Read(buf)
if err != nil { // err will equal io.EOF
break
}
fmt.Printf("%v\n", string(buf))
}
Also note, if there is no more data read and there is no error, os.File.Read() will return an error of io.EOF,
as you can see here.