Fall back to source install only when binary URL is 404

When the install from a binary package fails it falls back to installing from source. Tthe only case where the fallback
should occur is when the server responds with a 404 that no binary package exists. Otherwise it's falling back on
various IO or permissions errors.

Fixes #30

Author: andrewkroh

CHANGELOG.md

@@ -7,7 +7,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fix errors with renames failing across disks by falling back to a copy/delete. [#31](https://github.com/andrewkroh/gvm/pull/31)
-
+- Fall back to a source code based install only when binary package URL returns
+  with HTTP 404. [#30](https://github.com/andrewkroh/gvm/issues/30) [#32](https://github.com/andrewkroh/gvm/pull/32)
+  
 ## [0.2.3]
 
 ### Changed 

common/common.go

@@ -15,23 +15,26 @@ import (
 
 var log = logrus.WithField("package", "common")
 
+// ErrNotFound is returned when the download fails due to HTTP 404 Not Found.
+var ErrNotFound = errors.New("not found")
+
 func DownloadFile(url, destinationDir string) (string, error) {
-	log.WithField("url", url).Debug("downloading file")
+	log.WithField("url", url).Debug("Downloading file")
 	var name string
 	var err error
 	var retry bool
 	for a := 1; a <= 3; a++ {
 		name, err, retry = downloadFile(url, destinationDir)
 		if err != nil && retry {
-			log.WithError(err).Debugf("Attempt %d failed", a)
+			log.WithError(err).Debugf("Download attempt %d failed", a)
 			continue
 		}
 		break
 	}
 	return name, err
 }
 
-func downloadFile(url, destinationDir string) (string, error, bool) {
+func downloadFile(url, destinationDir string) (path string, err error, retryable bool) {
 	client := http.Client{
 		Timeout: time.Duration(3 * time.Minute),
 	}
@@ -42,7 +45,10 @@ func downloadFile(url, destinationDir string) (string, error, bool) {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return "", errors.Errorf("download failed with http status %v", resp.StatusCode), resp.StatusCode != http.StatusNotFound
+		if resp.StatusCode == http.StatusNotFound {
+			return "", ErrNotFound, false
+		}
+		return "", errors.Errorf("download failed with http status %v", resp.StatusCode), true
 	}
 
 	name := filepath.Join(destinationDir, filepath.Base(url))
@@ -55,7 +61,7 @@ func downloadFile(url, destinationDir string) (string, error, bool) {
 	if err != nil {
 		return "", errors.Wrap(err, "failed to write file to disk"), true
 	}
-	log.WithFields(logrus.Fields{"file": name, "size_bytes": numBytes}).Debug("download complete")
+	log.WithFields(logrus.Fields{"file": name, "size_bytes": numBytes}).Debug("Download complete")
 
 	return name, nil, false
 }

gvm.go

@@ -1,6 +1,7 @@
 package gvm
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -9,6 +10,8 @@ import (
 	"strings"
 
 	"github.com/sirupsen/logrus"
+
+	"github.com/andrewkroh/gvm/common"
 )
 
 type Manager struct {
@@ -214,9 +217,10 @@ func (m *Manager) Install(version *GoVersion) (string, error) {
 		if err == nil {
 			return dir, nil
 		}
-		m.Logger.WithFields(logrus.Fields{"version": version, "error": err}).
-			Warn("Failed to install Go from binary package. Trying to " +
-				"install from source.")
+		// Only continue to installing from source if the server confirms 404.
+		if !errors.Is(err, common.ErrNotFound) {
+			return "", err
+		}
 	}
 
 	return m.installSrc(version)