contented: replace octet-stream mime types with autodetected one, if possible; add timestamp to filenames

contented.go

@@ -11,8 +11,10 @@ import (
 	"mime/multipart"
 	"net/http"
 	"net/textproto"
+	"time"
 
 	telegram "github.com/go-telegram-bot-api/telegram-bot-api"
+	filetype "gopkg.in/h2non/filetype.v1"
 )
 
 func (this *NTFServer) ContentedEnabled() bool {
@@ -79,19 +81,41 @@ func (this *NTFServer) ContentedUploadSync(fileId string, expectSizeBytes int64)
 	}
 	defer resp.Body.Close()
 
-	// Determine a suitable pseudo-filename from the telegram content-type
-
-	fileContentType := resp.Header.Get("Content-Type") // is it blank? who knows?
-
 	if this.verbose {
 		log.Printf("Downloaded telegram file response headers: %#v\n", resp.Header)
 	}
 
-	fileName := "telegram-upload"
+	// Download
+	fileBuff := bytes.Buffer{}
+	_, err = io.CopyN(&fileBuff, resp.Body, expectSizeBytes) // CopyN asserts either err!=nil, or copiedBytes == expectSizeBytes. So we're safe
+	if err != nil {
+		return "", fmt.Errorf("CopyN: %s", err.Error())
+	}
+
+	// Determine a suitable pseudo-filename from the telegram content-type
+	// Telegram seems to always supply application/octet-stream
+	// If Telegram gives us something else, trust it; but otherwise, we can probably do better
+
+	fileName := fmt.Sprintf("telegram-upload-%d", time.Now().Unix())
+	fileContentType := resp.Header.Get("Content-Type") // is it blank? who knows?
+
+	if fileContentType == `application/octet-stream` || fileContentType == `` {
+
+		// Autodetect something better, if possible
+		if contentTypeMatches, err := filetype.Match(fileBuff.Bytes()); err == nil {
+			fileContentType = contentTypeMatches.MIME.Value
+			fileName += `.` + contentTypeMatches.Extension // no leading period
+		}
+
+	} else {
+
+		// We were supplied a good mime type, just need to find a good file extension
 		if fileExts, err := mime.ExtensionsByType(fileContentType); err == nil && len(fileExts) > 0 {
 			fileName += fileExts[0] // Just pick the first one. They all contain a leading period
 		}
 
+	}
+
 	// Contented uploads are in multipart mime format
 	uploadBody := bytes.Buffer{}
 	formValues := multipart.NewWriter(&uploadBody)
@@ -105,10 +129,9 @@ func (this *NTFServer) ContentedUploadSync(fileId string, expectSizeBytes int64)
 		return "", err
 	}
 
-	// Download
-	_, err = io.CopyN(filePart, resp.Body, expectSizeBytes) // CopyN asserts either err!=nil, or copiedBytes == expectSizeBytes. So we're safe
+	_, err = io.CopyN(filePart, bytes.NewReader(fileBuff.Bytes()), expectSizeBytes)
 	if err != nil {
-		return "", fmt.Errorf("CopyN: %s", err.Error())
+		return "", err
 	}
 
 	// Upload