Merge pull request #2 from etsy/write-executable-atomically

fix: write downloaded executable atomically

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/google/btree v1.0.1 // indirect
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79
 	github.com/hashicorp/terraform-config-inspect v0.0.0-20210318070130-9a80970d6b34
+	github.com/natefinch/atomic v1.0.1 // indirect
 	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
 	github.com/pkg/errors v0.9.1
 )

go.sum

@@ -36,6 +36,8 @@ github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+
 github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7/go.mod h1:ZXFpozHsX6DPmq2I0TCekCxypsnAUbP2oI0UX1GXzOo=
 github.com/mitchellh/go-wordwrap v1.0.0 h1:6GlHJ/LTGMrIJbwgdqdl2eEH8o+Exx/0m8ir9Gns0u4=
 github.com/mitchellh/go-wordwrap v1.0.0/go.mod h1:ZXFpozHsX6DPmq2I0TCekCxypsnAUbP2oI0UX1GXzOo=
+github.com/natefinch/atomic v1.0.1 h1:ZPYKxkqQOx3KZ+RsbnP/YsgvxWQPGxjC0oBt2AhwV0A=
+github.com/natefinch/atomic v1.0.1/go.mod h1:N/D/ELrljoqDyT3rZrsUmtsuzvHkeB/wWjHV22AZRbM=
 github.com/peterbourgon/diskv v2.0.1+incompatible h1:UBdAOUP5p4RWqPBg048CAvpKN+vxiaj6gdUUzhl4XmI=
 github.com/peterbourgon/diskv v2.0.1+incompatible/go.mod h1:uqqh8zWWbv1HBMNONnaR/tNboyR3/BZd58JJSHlUSCU=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
@@ -54,10 +56,8 @@ github.com/vmihailenco/msgpack v3.3.3+incompatible/go.mod h1:fy3FlTQTDXWkZ7Bh6Ac
 github.com/zclconf/go-cty v1.1.0 h1:uJwc9HiBOCpoKIObTQaLR+tsEXx1HBHnOsOOpcdhZgw=
 github.com/zclconf/go-cty v1.1.0/go.mod h1:xnAOWiHeOqg2nWS62VtQ7pbOu17FtxJNW8RLEih+O3s=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20190426145343-a29dc8fdc734 h1:p/H982KKEjUnLJkM3tt/LemDnOc1GiZL5FCVlORJ5zo=
 golang.org/x/crypto v0.0.0-20190426145343-a29dc8fdc734/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/net v0.0.0-20180811021610-c39426892332/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 h1:0GoQqolDA55aaLxZyTzK/Y2ePZzZTUrRacwib7cNsYQ=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

internal/releaseapi/client.go

@@ -14,6 +14,7 @@ import (
 	"github.com/Masterminds/semver/v3"
 	"github.com/gregjones/httpcache"
 	"github.com/gregjones/httpcache/diskcache"
+	"github.com/natefinch/atomic"
 	"github.com/pkg/errors"
 )
 
@@ -122,47 +123,39 @@ func (c *Client) downloadBuild(build Build) (string, error) {
 		return "", err
 	}
 
+	defer zipFile.Close()
+
 	zipReader, err := zip.NewReader(zipFile, zipLength)
 
 	if err != nil {
 		return "", errors.Wrap(err, "could not unzip release archive")
 	}
 
-	destination, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0755)
-
-	defer destination.Close()
-
-	if err != nil {
-		return "", errors.Wrap(err, "could not create destination file for executable")
-	}
-
-	var found bool
-
 	for _, f := range zipReader.File {
 		if filepath.Base(f.Name) != "terraform" {
 			continue
 		}
 
 		source, err := f.Open()
 
-		defer source.Close()
-
 		if err != nil {
-			return "", errors.Wrap(err, "could not read executable in release archive")
+			return "", errors.Wrap(err, "could not read binary in release archive")
 		}
 
-		if _, err := io.Copy(destination, source); err != nil {
-			return "", errors.Wrap(err, "could not copy executable to destination")
+		defer source.Close()
+
+		if err := atomic.WriteFile(path, source); err != nil {
+			return "", errors.Wrap(err, "could not write binary to the cache directory")
 		}
 
-		found = true
-	}
+		if err := os.Chmod(path, 0700); err != nil {
+			return "", errors.Wrap(err, "could not make binary executable")
+		}
 
-	if !found {
-		return "", errors.New("could not find executable named 'terraform' in release archive")
+		return path, nil
 	}
 
-	return path, nil
+	return "", errors.New("could not find executable named 'terraform' in release archive")
 }
 
 func (c *Client) downloadReleaseArchive(build Build) (*os.File, int64, error) {
@@ -176,11 +169,13 @@ func (c *Client) downloadReleaseArchive(build Build) (*os.File, int64, error) {
 
 	response, err := c.httpClient.Do(request)
 
-	defer response.Body.Close()
-
 	if err != nil {
 		return nil, 0, errors.Wrap(err, "could not download release archive")
-	} else if response.StatusCode != http.StatusOK {
+	}
+
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
 		return nil, 0, errors.Errorf("unexpected status code '%s' in response", response.StatusCode)
 	}
 
@@ -197,10 +192,6 @@ func (c *Client) downloadReleaseArchive(build Build) (*os.File, int64, error) {
 	return tmp, response.ContentLength, nil
 }
 
-func cachedReleaseListPath(cacheDir string) string {
-	return filepath.Join(cacheDir, "terraform-releases")
-}
-
 func cachedExecutablePath(cacheDir string, b Build) string {
 	return filepath.Join(cacheDir, executableName(b))
 }