Infer content type in alloc fs stat endpoint

api/fs.go

@@ -20,11 +20,12 @@ const (
 
 // AllocFileInfo holds information about a file inside the AllocDir
 type AllocFileInfo struct {
-	Name     string
-	IsDir    bool
-	Size     int64
-	FileMode string
-	ModTime  time.Time
+	Name        string
+	IsDir       bool
+	Size        int64
+	FileMode    string
+	ModTime     time.Time
+	ContentType string
 }
 
 // StreamFrame is used to frame data of a file when streaming

client/allocdir/alloc_dir.go

@@ -11,6 +11,9 @@ import (
 	"sync"
 	"time"
 
+	"net/http"
+	"strings"
+
 	hclog "github.com/hashicorp/go-hclog"
 	multierror "github.com/hashicorp/go-multierror"
 	cstructs "github.com/hashicorp/nomad/client/structs"
@@ -392,15 +395,41 @@ func (d *AllocDir) Stat(path string) (*cstructs.AllocFileInfo, error) {
 		return nil, err
 	}
 
+	contentType := detectContentType(info, p)
+
 	return &cstructs.AllocFileInfo{
-		Size:     info.Size(),
-		Name:     info.Name(),
-		IsDir:    info.IsDir(),
-		FileMode: info.Mode().String(),
-		ModTime:  info.ModTime(),
+		Size:        info.Size(),
+		Name:        info.Name(),
+		IsDir:       info.IsDir(),
+		FileMode:    info.Mode().String(),
+		ModTime:     info.ModTime(),
+		ContentType: contentType,
 	}, nil
 }
 
+// detectContentType tries to infer the file type by reading the first
+// 512 bytes of the file. Json file extensions are special cased.
+func detectContentType(fileInfo os.FileInfo, path string) string {
+	contentType := "unknown"
+	if !fileInfo.IsDir() {
+		f, err := os.Open(path)
+		// Best effort content type detection
+		// We ignore errors because this is optional information
+		if err == nil {
+			fileBytes := make([]byte, 512)
+			_, err := f.Read(fileBytes)
+			if err == nil {
+				contentType = http.DetectContentType(fileBytes)
+			}
+		}
+	}
+	// Special case json files
+	if strings.HasSuffix(path, ".json") {
+		contentType = "application/json"
+	}
+	return contentType
+}
+
 // ReadAt returns a reader for a file at the path relative to the alloc dir
 func (d *AllocDir) ReadAt(path string, offset int64) (io.ReadCloser, error) {
 	if escapes, err := structs.PathEscapesAllocDir("", path); err != nil {

client/allocdir/alloc_dir_test.go

@@ -472,3 +472,18 @@ func TestPathFuncs(t *testing.T) {
 		t.Errorf("%q is not empty. empty=%v error=%v", dir, empty, err)
 	}
 }
+
+func TestAllocDir_DetectContentType(t *testing.T) {
+	require := require.New(t)
+	imgPath := "input/image.png"
+	fileInfo, err := os.Stat(imgPath)
+	require.Nil(err)
+	res := detectContentType(fileInfo, imgPath)
+	require.Equal("image/png", res)
+
+	jsonPath := "input/test.json"
+	fileInfo, err = os.Stat(jsonPath)
+	require.Nil(err)
+	res = detectContentType(fileInfo, jsonPath)
+	require.Equal("application/json", res)
+}

client/allocdir/input/test.json

@@ -0,0 +1,3 @@
+{
+"test":"test"
+}

client/fs_endpoint_test.go

@@ -98,7 +98,7 @@ func TestFS_Stat(t *testing.T) {
 	// Wait for alloc to be running
 	alloc := testutil.WaitForRunning(t, s.RPC, job)[0]
 
-	// Make the request with bad allocation id
+	// Make the request
 	req := &cstructs.FsStatRequest{
 		AllocID:      alloc.ID,
 		Path:         "/",

client/structs/structs.go

@@ -36,11 +36,12 @@ type ClientStatsResponse struct {
 
 // AllocFileInfo holds information about a file inside the AllocDir
 type AllocFileInfo struct {
-	Name     string
-	IsDir    bool
-	Size     int64
-	FileMode string
-	ModTime  time.Time
+	Name        string
+	IsDir       bool
+	Size        int64
+	FileMode    string
+	ModTime     time.Time
+	ContentType string `json:"contenttype,omitempty"`
 }
 
 // FsListRequest is used to list an allocation's directory.

command/alloc_fs.go

@@ -213,7 +213,7 @@ func (f *AllocFSCommand) Run(args []string) int {
 	if stat {
 		// Display the file information
 		out := make([]string, 2)
-		out[0] = "Mode|Size|Modified Time|Name"
+		out[0] = "Mode|Size|Modified Time|Content Type|Name"
 		if file != nil {
 			fn := file.Name
 			if file.IsDir {
@@ -225,8 +225,8 @@ func (f *AllocFSCommand) Run(args []string) int {
 			} else {
 				size = humanize.IBytes(uint64(file.Size))
 			}
-			out[1] = fmt.Sprintf("%s|%s|%s|%s", file.FileMode, size,
-				formatTime(file.ModTime), fn)
+			out[1] = fmt.Sprintf("%s|%s|%s|%s|%s", file.FileMode, size,
+				formatTime(file.ModTime), file.ContentType, fn)
 		}
 		f.Ui.Output(formatList(out))
 		return 0