cmd/go: Use web2 to fetch secure import paths

This allows `go get` to use netrc files.

- Reimplement web.Get as a forwarded call to web2.Get.
- Replace secure half of web.GetMaybeInsecure with web2.Get and return
  the body through it instead of the HTTP response.

Related to golang#29888.

Author: nilium

src/cmd/go/internal/web/http.go

@@ -15,13 +15,13 @@ import (
 	"crypto/tls"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"net/url"
 	"time"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/web2"
 	"cmd/internal/browser"
 )
 
@@ -53,22 +53,9 @@ func (e *HTTPError) Error() string {
 }
 
 // Get returns the data from an HTTP GET request for the given URL.
-func Get(url string) ([]byte, error) {
-	resp, err := httpClient.Get(url)
-	if err != nil {
-		return nil, err
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode != 200 {
-		err := &HTTPError{status: resp.Status, StatusCode: resp.StatusCode, url: url}
-
-		return nil, err
-	}
-	b, err := ioutil.ReadAll(resp.Body)
-	if err != nil {
-		return nil, fmt.Errorf("%s: %v", url, err)
-	}
-	return b, nil
+func Get(url string) (body []byte, err error) {
+	err = web2.Get(url, web2.ReadAllBody(&body))
+	return body, err
 }
 
 // GetMaybeInsecure returns the body of either the importPath's
@@ -87,10 +74,16 @@ func GetMaybeInsecure(importPath string, security SecurityMode) (urlStr string,
 		if security == Insecure && scheme == "https" { // fail earlier
 			res, err = impatientInsecureHTTPClient.Get(urlStr)
 		} else {
-			res, err = httpClient.Get(urlStr)
+			res = nil
+			err = web2.Get(urlStr, web2.Body(&body))
 		}
 		return
 	}
+	closeReader := func(r io.ReadCloser) {
+		if r != nil {
+			r.Close()
+		}
+	}
 	closeBody := func(res *http.Response) {
 		if res != nil {
 			res.Body.Close()
@@ -103,19 +96,23 @@ func GetMaybeInsecure(importPath string, security SecurityMode) (urlStr string,
 		}
 		if security == Insecure {
 			closeBody(res)
+			closeReader(body)
 			urlStr, res, err = fetch("http")
 		}
 	}
 	if err != nil {
 		closeBody(res)
+		closeReader(body)
 		return "", nil, err
+	} else if body == nil {
+		body = res.Body
 	}
 	// Note: accepting a non-200 OK here, so people can serve a
 	// meta import in their http 404 page.
-	if cfg.BuildV {
+	if cfg.BuildV && res != nil {
 		log.Printf("Parsing meta tags from %s (status code %d)", urlStr, res.StatusCode)
 	}
-	return urlStr, res.Body, nil
+	return urlStr, body, nil
 }
 
 func QueryEscape(s string) string { return url.QueryEscape(s) }