Im trying to write to a TCP socket in Go but only receive "invalid argument" with this code:
_, err := conn.Write([]byte("test"))
if err != nil {
fmt.Println(err.Error())
}
Here is a simple sample of what you want to do(maybe?), be aware that you should make a tcp server listen to the port 8999 first before run it
nc -l 8999 #or maybe nc -l -p 8999
code:
package main
import (
"net"
)
func main() {
conn, _ := net.Dial("tcp", "localhost:8999")
conn.Write([]byte("test"))
}
If it's not your question, you should provide more information.
Related
I have probably spent way to much time on this, so I decided to try here.
I'm having trouble figuring out why my Register is being called twice?
Best I can figure, it seems to be calling once at sql.Register() and again at sqlx.Connect(). But if I remove the sql.Register(), then theres no drivers.
Honestly, I am pretty new to GoLang, I'm hoping for any sort of direction here.
Code - w/o sql.Register
package main
import (
"fmt"
"database/sql"
"github.com/jmoiron/sqlx"
)
const (
host = "localhost"
port = 5432
user = "postgres"
password = "password"
dbname = "sampledb"
)
/*-------------------------------------------*\
|| Functions ||
\*-------------------------------------------*/
// Error Checking Fn
func CheckError(err error, str string) {
if err != nil {
fmt.Printf("Error # : %s\n", str)
panic(err)
}
}
/*-------------------------------------------*\
|| Main() ||
\*-------------------------------------------*/
func main() {
// Open DB Conn
psqlconn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable", host, port, user, password, dbname)
// sql.Register("postgres", &pq.Driver{})
fmt.Printf(":: Drivers ::\n%s\n", sql.Drivers())
db, err := sqlx.Connect("postgres", psqlconn)
CheckError(err, "Main: sqlx.connect")
defer db.Close()
}
Error - w/o sql.Register
$ go run name-generator.go
:: Drivers ::
[]
Error # : Main: sqlx.connect
panic: sql: unknown driver "postgres" (forgotten import?)
goroutine 1 [running]:
main.CheckError({0xc84320, 0xc000056680}, {0xc6073f, 0x5})
C:/path/to/program.go:26 +0xa7 <--- Func CheckError(): panic(err)
main.main()
C:/path/to/program.go:40 +0x125 <--- Func Main(): CheckError()
exit status 2
Code - w/ sql.Register
package main
import (
"fmt"
"database/sql"
"github.com/jmoiron/sqlx"
"github.com/lib/pq"
)
const (
host = "localhost"
port = 5432
user = "postgres"
password = "password"
dbname = "sampledb"
)
/*-------------------------------------------*\
|| Functions ||
\*-------------------------------------------*/
// Error Checking Fn
func CheckError(err error, str string) {
if err != nil {
fmt.Printf("Error # : %s\n", str)
panic(err)
}
}
/*-------------------------------------------*\
|| Main() ||
\*-------------------------------------------*/
func main() {
// Open DB Conn
psqlconn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable", host, port, user, password, dbname)
sql.Register("postgres", &pq.Driver{})
fmt.Printf(":: Drivers ::\n%s\n", sql.Drivers())
db, err := sqlx.Connect("postgres", psqlconn)
CheckError(err, "Main: sqlx.connect")
defer db.Close()
}
Error - w/ sql.Register
$ go run name-generator.go
panic: sql: Register called twice for driver postgres
goroutine 1 [running]:
database/sql.Register({0xa98bc9, 0x8}, {0xae6680, 0xc8a950})
C:/Program Files/Go/src/database/sql/sql.go:51 +0x13d
main.main()
C:/path/to/program.go:38 +0x11b
exit status 2
Additional Resources
Similar issue, but doesn't solve my problem Link
SQLX Documentation Link
SQL Documentation Link
The package github.com/lib/pq registers it's driver in an init function.
Remove the direct call to register the driver from the application:
sql.Register("postgres", &pq.Driver{}) <-- delete this line
Import github.com/lib/pq for the side effect of executing the init() function:
package main
import (
"fmt"
"database/sql"
"github.com/jmoiron/sqlx"
_ "github.com/lib/pq" // <-- add this line
)
I'm trying to connect a Go application with postgresql.
The app import postgresql driver:
"crypto/tls"
"database/sql"
"fmt"
"log"
"os"
"os/signal"
...
_ "github.com/go-sql-driver/mysql"
_ "github.com/lib/pq"
_ "github.com/mattn/go-sqlite3"
and uses like it to connect to the database:
driver, cnxn := dbFromURI(dbURI)
db, err := sql.Open(driver, cnxn)
if err != nil {
panic(err)
}
and the dbFromUri method just split the info
func dbFromURI(uri string) (string, string) {
parts := strings.Split(uri, "://")
return parts[0], parts[1]
}
My URI works locally when i run the command : psql postgresql://user:user#172.20.0.1:5432/lcp
But in go i Go, I got
./lcpserver
2021/03/07 02:00:42 Reading config /root/lcp-server-install/lcp-home/config/config.yaml
panic: pq: SSL is not enabled on the server
I tried this URI for Go without success : psql postgresql://user:user#172.20.0.1:5432/lcp?sslmode=disable
Do you have any idea why i can't connect ?
I tried with my aws rds postgres database, and got same result. Thnaks for the help.
complete code of the server
https://github.com/readium/readium-lcp-server/blob/master/lcpserver/lcpserver.go
I change the typo and the demo provided i succeed the connexion. But in the lcp server i style got the same issue.
postgres://user:user#172.20.0.1:5432/lcp?sslmode=disable
EDIT 2:
The error is due to the fact that the script tries prepare command. I update the minimal example and it fails too.
package main
import (
"database/sql"
"fmt"
"strings"
_ "github.com/lib/pq"
)
func dbFromURI(uri string) (string, string) {
parts := strings.Split(uri, "://")
return parts[0], parts[1]
}
func main() {
driver, cnxn := dbFromURI("postgres://user:user#172.20.0.1:5432/lcp?sslmode=disable")
fmt.Println("The driver " + driver)
fmt.Println("The cnxn " + cnxn)
db, err := sql.Open(driver, cnxn)
_, err = db.Prepare("SELECT id,encryption_key,location,length,sha256,type FROM content WHERE id = ? LIMIT 1")
if err != nil {
fmt.Println("Prepare failed")
fmt.Println(err)
}
if err == nil {
fmt.Println("Successfully connected")
} else {
panic(err)
}
}
I got :
prepare failed
pq: SSL is not enabled on the server
2021/03/07 17:20:13 This panic 3
panic: pq: SSL is not enabled on the server
The first problem is a typo in the connection string: postgresql://user:user#172.20.0.1:5432/lcp?sslmode=disable. In Go code it should be postgres://user:user#172.20.0.1:5432/lcp?sslmode=disable.
We also need to pass the full connection string as the second argument to sql.Open. For now, the dbFromURI function returns user:user#172.20.0.1:5432/lcp?sslmode=disable, but we need postgres://user:user#172.20.0.1:5432/lcp?sslmode=disable, because pq is waiting for this prefix to parse it.
After fixing this, I was able to establish a connection using a minimal postgres client based on your code.
To try this yourself, start the server with the following command:
docker run --rm -p 5432:5432 -e POSTGRES_PASSWORD=some_password postgres
And try to connect using the following client code:
package main
import (
"database/sql"
"fmt"
_ "github.com/lib/pq"
)
func main() {
cnxn := "postgres://postgres:some_password#127.0.0.1:5432/lcp?sslmode=disable"
_, err := sql.Open("postgres", cnxn)
if err != nil {
panic(err)
}
_, err = db.Prepare("SELECT id,encryption_key,location,length,sha256,type FROM content WHERE id = ? LIMIT 1")
if err != nil {
fmt.Println("Prepare failed")
panic(err)
}
}
There are two go apps, one is stapi listening on port 8050 and providing RESTful APIs, another is client to consume those APIs.
Both are running on different servers, client is often getting error when calling APIs with HTTP POST method. Below are few lines from client log (real IP replaced with imaginary one)
2018/02/17 11:42:58 ERROR: [DoLogin] API Error: [Post https://123.123.123.123:8050/v1/st/verifyuser: dial tcp 123.123.123.123:8050: getsockopt: connection refused]
2018/02/17 11:47:14 ERROR: [CreateAttempt] Error: [Post https://123.123.123.123:8050/v1/userattempts/createattempt: dial tcp 123.123.123.123:8050: getsockopt: connection refused]
It is intermittent and making the app unreliable, out of approx 1k request i got such error for approx 50+ request.
Initially stapi was listening on all IPs
httpSrv := http.Server{
Addr: ":8050",
Handler: router, // < gin router
...
}
But after reading the workaroung in Golang HTTP Post error: connection refused i modified the stapi app and make it listening on different IPs, as shown below
$ sudo lsof -i -P -n | grep LISTEN
stapi 4775 samtech 10u IPv4 2388179 0t0 TCP 123.123.123.123:8050 (LISTEN)
stapi 4775 samtech 11u IPv6 2388181 0t0 TCP [::1]:8050 (LISTEN)
stapi 4775 samtech 12u IPv4 2388183 0t0 TCP 127.0.0.1:8050 (LISTEN)
But still the issue is same, what else i should check and fix ? Please suggest.
API is protected with JWT, here is how client is making POST requests
func (w *OST) DoLogin(c *gin.Context) {
...
ud := stapimodels.UserLogin{}
err := c.BindJSON(&ud)
...
//call api to save user response
url := config.AppConfig.APIBaseURL + "st/verifyuser"
res, err := api.JwtApi.APIPost(url, &ud)
if err != nil {
g.Logger.Errorm("DoLogin", "Error: %v", err)
t.Error("Error", err.Error())
return
}
...
}
//APIPost - call given apiurl with POST method and pass data
func (j *JwtAPI) APIPost(apiurl string, postdata interface{}) (*APIResult, error) {
if postdata == nil {
return nil, fmt.Errorf("postdata is nil")
}
jsondata, err := toJSON(postdata)
if err != nil {
return nil, err
}
resp, err := j.makeRequest(http.MethodPost, apiurl, jsondata)
if err != nil {
return nil, err
}
defer resp.Body.Close()
res := APIResult{}
json.NewDecoder(resp.Body).Decode(&res)
return &res, nil
}
//makeRequest makes http request for given url with given method
// also inject Authorization Header
func (j *JwtAPI) makeRequest(method, apiurl string, body io.Reader) (*http.Response, error) {
retry := 0
//Create []byte buffer from body - so it can be passed in further retries
var buf []byte
if body != nil {
buf, _ = ioutil.ReadAll(body)
}
r, err := http.NewRequest(method, apiurl, bytes.NewReader(buf))
if err != nil {
return nil, err
}
r.Header.Set("Authorization", "bearer "+j.token.AccessToken)
r.Header.Set("Content-Type", "application/json")
client := j.getClient()
resp, err := client.Do(r)
if err != nil {
return nil, err
}
return resp, nil
}
func (j *JwtAPI) getClient() *http.Client {
// default timeout (if not set by client)
timeoutInSec := 10
if j.Timeout.Seconds() > 0 {
// client sets timeout, so use it
timeoutInSec = int(j.Timeout.Seconds())
}
client := &http.Client{
Timeout: time.Second * time.Duration(timeoutInSec),
}
return client
}
To make your code more resilient you should add some retries with back-offs, so even when the connection was refused it is still working.
Connection refused means that the port is not opened. Is there any firewall or proxies in between? The authentication part shouldn't matter here because it doesn't even get to this point.
Some things that you can check:
Make sure the service is running
Check for firewall configuration
Implement retries for resilience
Is the IP-Address fixed? Is Dynamic DNS used and maybe not updated?
Package for back-off retrying
As for implementing the back-off you might try this package:
https://github.com/cenkalti/backoff
It is listing examples on how to use it and it's pretty much exactly what you need:
// An operation that may fail.
operation := func() error {
// do the request here and check the response code (or check the response body depending on your need) . e.g. above 500 should retry, above 400 and below 500, it should be a client side error and retrying might not help much
return nil // or an error
}
err := Retry(operation, NewExponentialBackOff())
if err != nil {
// Handle error.
return
}
// Operation is successful.
in GO net/http Response Body annotation says:
It is the caller's responsibility to close Body. The default HTTP client's Transport does not attempt to reuse HTTP/1.0 or HTTP/1.1 TCP connections ("keep-alive") unless the Body is read to completion and is
closed.
It's mean: if I use http.Get and don't call resp.Body.Close() then it will not resue HTTP/1.0 or HTTP/1.1 TCP connections ("keep-alive") yeah?
so I write some code:
package main
import (
"time"
"fmt"
"io/ioutil"
"net/http"
)
func main() {
resp, err := http.Get("http://127.0.0.1:8588")
if err != nil {
panic(err)
}
_, err = ioutil.ReadAll(resp.Body)
if err != nil {
panic(err)
}
resp2, err := http.Get("http://127.0.0.1:8588")
if err != nil {
panic(err)
}
_, err = ioutil.ReadAll(resp2.Body)
if err != nil {
panic(err)
}
fmt.Println("before time sleep")
time.Sleep(time.Second * 35)
}
and I only see ONE tcp connection build in wireshark, why?
I don't close res.Body so the http client should't be reuse the tcp connection.
this problem has been solved in
https://github.com/golang/go/issues/22954.
You have read it till the end in first occurence of line:
_, err = ioutil.ReadAll(resp.Body)
So the connection is ready to be resused. Try not to read and run again.
I'm having trouble with socket programming.
I have a program that reads from localhost:7777 and writes to localhost:8000.
I use netcat from the command line to write and read to 7777 and 8000 respectively.
This is the reader:
netcat -l -p 8000
And this is the writer:
printf "asti||" | netcat localhost 7777
But my program gets network errors when it tries to write to port 8000 for the second
time. The error is Fatal error: dial tcp 127.0.0.1:8000: getsockopt: connection refused.
What's happening? Why on the second write the error appears?
Furthermore, I noticed that if I kill the netcat reader and restart it then there's no network errors. So to reiterate, the program writes once to 8000 and netcat reads it. Then I kill netcat reader and restart it. At this point the program can write again to 8000. But if the program tries to write two successive times to 8000 without me restarting netcat, then the error appears.
Here is the entire program (it's short). If you like, you experience this mystical behaviour yourself:
package main
import (
"fmt"
"net"
"os"
"strings"
// "io/ioutil"
)
func main() {
end_of_message_terminator := "||"
beginning_of_next_message := ""
request := make([]byte, 512)
service_port := ":7777"
tcpAddr, err := net.ResolveTCPAddr("tcp4", service_port)
checkError(err)
listener, err := net.ListenTCP("tcp", tcpAddr)
checkError(err)
for {
conn, err := listener.Accept()
if err != nil {
continue
}
read_len, err := conn.Read(request)
if read_len == 0 {
continue
}
request_string := string(request[:read_len])
fmt.Printf("Request String %s\\END", request_string)
messages := strings.Split(request_string, end_of_message_terminator)
fmt.Printf("%q\n", messages)
messages[0] = beginning_of_next_message + messages[0]
if messages[len(messages) - 1] != "" {
beginning_of_next_message = messages[len(messages) - 1]
messages[len(messages) - 1] = ""
fmt.Printf("was here 00\n")
}
if len(messages) == 1 {
continue
}
for i := range messages {
go func(){
fmt.Printf("was here 04\n")
respond_to_message(messages[i])
}()
fmt.Printf("was here 01\n")
}
conn.Close()
}
}
func respond_to_message(message string){
message_parameters := strings.Split(message, "|")
response_port := "localhost:8000"
tcpAddr_res, err := net.ResolveTCPAddr("tcp4", response_port)
checkError(err)
response_writer, err := net.DialTCP("tcp", nil, tcpAddr_res)
for i := range message_parameters {
fmt.Printf("was here03\n")
param_parts := strings.Split(message_parameters[i], "=")
fmt.Printf("message: %s\n", message)
fmt.Printf("message_parameters%q\n", message_parameters)
fmt.Printf("params_parts: %q\n", param_parts)
//param_name := param_parts[0]
//param_value := param_parts[1]
checkError(err)
response_writer.Write([]byte("asti de crhis"))
checkError(err)
//result, err := ioutil.ReadAll(response_writer)
//checkError(err)
//fmt.Println(string(result))
}
//response_writer.Close()
}
func checkError(err error) {
if err != nil {
fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
os.Exit(1)
}
}