fix proxy retry loop (air-verse#635)

This addresses two bugs:
1) The loop could exit with an error condition present and fail to
   inform the user.
2) On Windows 11, syscall.ECONNREFUSED is not returned. Instead we
   receive net.OpError with a message similar to:

"unable to reach app: Get "http://localhost:7000/": dial tcp [::1]:7000: connectex: No connection could be made because the target machine actively refused it."

The Fix:
Since the retry loop is short; just 1 second maximum, we retry until no
error happens. If an error does occur, we inform the user.

runner/proxy.go

@@ -2,14 +2,12 @@ package runner
 
 import (
  "bytes"
- "errors"
  "fmt"
  "io"
  "log"
  "net/http"
  "strconv"
  "strings"
- "syscall"
  "time"
 )
 
@@ -106,18 +104,20 @@ func (p *Proxy) proxyHandler(w http.ResponseWriter, r *http.Request) {
  }
  req.Header.Set("X-Forwarded-For", r.RemoteAddr)
 
- // retry on connection refused error since after a file change air will restart the server and it may take a few milliseconds for the server to be up-and-running.
+ // air will restart the server. it may take a few milliseconds for it to start back up.
+ // therefore, we retry until the server becomes available or this retry loop exits with an error.
  var resp *http.Response
+ resp, err = p.client.Do(req)
  for i := 0; i < 10; i++ {
- resp, err = p.client.Do(req)
  if err == nil {
  break
  }
- if !errors.Is(err, syscall.ECONNREFUSED) {
- http.Error(w, "proxy handler: unable to reach app", http.StatusInternalServerError)
- return
- }
  time.Sleep(100 * time.Millisecond)
+ resp, err = p.client.Do(req)
+ }
+ if err != nil {
+ http.Error(w, "proxy handler: unable to reach app", http.StatusInternalServerError)
+ return
  }
  defer resp.Body.Close()