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package main
import (
"flag"
"fmt"
"io/ioutil"
"log"
"net/http"
"os"
"strings"
"time"
"github.com/nats-io/nats.go"
)
// printHelp outputs the usage information.
func printHelp() {
fmt.Println("Usage: HTTP-to-NATS proxy server")
fmt.Println("\nThe following environment variables are supported:")
fmt.Println(" NATS_URL - NATS connection URL (default: nats://127.0.0.1:4222)")
fmt.Println(" NATS_USER - NATS username for authentication (optional)")
fmt.Println(" NATS_PASSWORD - NATS password for authentication (optional)")
fmt.Println(" NATS_TOKEN - NATS token for authentication (optional)")
fmt.Println(" NATS_NKEY - NATS NKEY for authentication (optional)")
fmt.Println(" NATS_NKEY_SEED - NATS NKEY seed for authentication (optional)")
fmt.Println(" NATS_CREDS_FILE - Path to NATS credentials file (optional)")
fmt.Println(" HTTP_PORT - HTTP port to listen on (default: 8080)")
}
func main() {
helpFlag := flag.Bool("help", false, "Display help information about available environment variables")
flag.Parse()
if *helpFlag {
printHelp()
os.Exit(0)
}
// Read NATS connection info from environment variables
natsURL := os.Getenv("NATS_URL")
if natsURL == "" {
natsURL = nats.DefaultURL // defaults to "nats://127.0.0.1:4222"
}
natsUser := os.Getenv("NATS_USER")
natsPassword := os.Getenv("NATS_PASSWORD")
natsToken := os.Getenv("NATS_TOKEN")
natsNkey := os.Getenv("NATS_NKEY")
natsNkeySeed := os.Getenv("NATS_NKEY_SEED")
natsCredsFile := os.Getenv("NATS_CREDS_FILE")
// Read HTTP port from environment variables
httpPort := os.Getenv("HTTP_PORT")
if httpPort == "" {
httpPort = "8080"
}
// Set up NATS connection options
opts := []nats.Option{nats.Name("Web proxy")}
if natsUser != "" && natsPassword != "" {
opts = append(opts, nats.UserInfo(natsUser, natsPassword))
} else if natsToken != "" {
opts = append(opts, nats.Token(natsToken))
} else if natsNkey != "" && natsNkeySeed != "" {
log.Fatalln("NKEY connection not supported")
} else if natsCredsFile != "" {
opts = append(opts, nats.UserCredentials(natsCredsFile))
}
nc, err := nats.Connect(natsURL, opts...)
if err != nil {
log.Fatal("Error connecting to NATS:", err)
}
defer nc.Close()
// HTTP handler to proxy all requests to NATS
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
// Read the entire request body (if any)
body, err := ioutil.ReadAll(r.Body)
if err != nil {
http.Error(w, "Error reading request body", http.StatusInternalServerError)
return
}
defer r.Body.Close()
// Create the NATS subject.
// Remove the leading slash from the path and replace remaining slashes with dots.
// The subject is prefixed with "http.<method>.", where <method> is lower-case.
path := strings.TrimPrefix(r.URL.Path, "/")
subjectPath := strings.ReplaceAll(path, "/", ".")
subject := fmt.Sprintf("http.%s.%s", strings.ToLower(r.Method), subjectPath)
log.Println("Forwarding HTTP", r.Method, "request on", r.URL.Path, "to NATS subject:", subject)
// Create a new NATS message with the HTTP request body
msg := nats.Msg{
Subject: subject,
Data: body,
Header: nats.Header{},
}
// Copy over all the HTTP request headers to the NATS message headers
for key, values := range r.Header {
for _, value := range values {
msg.Header.Add(key, value)
}
}
// Add additional HTTP meta-data as headers
msg.Header.Set("X-HTTP-Method", r.Method)
msg.Header.Set("X-HTTP-Path", r.URL.Path)
msg.Header.Set("X-HTTP-Query", r.URL.RawQuery)
msg.Header.Set("X-Remote-Addr", r.RemoteAddr)
// Send the NATS request and wait synchronously for a reply (timeout: 30 seconds)
reply, err := nc.RequestMsg(&msg, 30*time.Second)
if err != nil {
http.Error(w, "Error processing request", http.StatusInternalServerError)
log.Println("NATS request error:", err)
return
}
// Set any response headers from the NATS reply on the HTTP response
for key, values := range reply.Header {
for _, value := range values {
w.Header().Add(key, value)
}
}
// Write the reply body (from NATS) back to the HTTP client
w.Write(reply.Data)
})
// Start the HTTP server
fmt.Println("Server is running on http://localhost:8080")
log.Fatal(http.ListenAndServe(":8080", nil))
}
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