From 8fb9eb2feeda8d60039e07688998264cd71980af Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Sun, 26 Mar 2023 16:55:03 +0100
Subject: [PATCH] sync: make --suffix-keep-extension preserve 2 part extensions
 like .tar.gz

If a file has two (or more) extensions and the second (or subsequent)
extension is recognised as a valid mime type, then the suffix will go
before that extension. So `file.tar.gz` would be backed up to
`file-2019-01-01.tar.gz` whereas `file.badextension.gz` would be
backed up to `file.badextension-2019-01-01.gz`

Fixes #6892
---
 docs/content/docs.md             |  6 ++++++
 fs/operations/operations.go      | 21 ++++++++++++++++++---
 fs/operations/operations_test.go |  7 ++++++-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/docs/content/docs.md b/docs/content/docs.md
index 9084a7b26..a23ec18f8 100644
--- a/docs/content/docs.md
+++ b/docs/content/docs.md
@@ -1840,6 +1840,12 @@ would be backed up to `file.txt-2019-01-01` and with the flag it would
 be backed up to `file-2019-01-01.txt`.  This can be helpful to make
 sure the suffixed files can still be opened.
 
+If a file has two (or more) extensions and the second (or subsequent)
+extension is recognised as a valid mime type, then the suffix will go
+before that extension. So `file.tar.gz` would be backed up to
+`file-2019-01-01.tar.gz` whereas `file.badextension.gz` would be
+backed up to `file.badextension-2019-01-01.gz`.
+
 ### --syslog ###
 
 On capable OSes (not Windows or Plan9) send all log output to syslog.
diff --git a/fs/operations/operations.go b/fs/operations/operations.go
index 55a24a2d0..3f6fb6e73 100644
--- a/fs/operations/operations.go
+++ b/fs/operations/operations.go
@@ -618,9 +618,24 @@ func SuffixName(ctx context.Context, remote string) string {
 		return remote
 	}
 	if ci.SuffixKeepExtension {
-		ext := path.Ext(remote)
-		base := remote[:len(remote)-len(ext)]
-		return base + ci.Suffix + ext
+		var (
+			base  = remote
+			exts  = ""
+			first = true
+			ext   = path.Ext(remote)
+		)
+		for ext != "" {
+			// Look second and subsequent extensions in mime types.
+			// If they aren't found then don't keep it as an extension.
+			if !first && mime.TypeByExtension(ext) == "" {
+				break
+			}
+			base = base[:len(base)-len(ext)]
+			exts = ext + exts
+			first = false
+			ext = path.Ext(base)
+		}
+		return base + ci.Suffix + exts
 	}
 	return remote + ci.Suffix
 }
diff --git a/fs/operations/operations_test.go b/fs/operations/operations_test.go
index 37ebe99c4..45a2259be 100644
--- a/fs/operations/operations_test.go
+++ b/fs/operations/operations_test.go
@@ -371,9 +371,14 @@ func TestSuffixName(t *testing.T) {
 		{"test.txt", "-suffix", false, "test.txt-suffix"},
 		{"test.txt", "-suffix", true, "test-suffix.txt"},
 		{"test.txt.csv", "-suffix", false, "test.txt.csv-suffix"},
-		{"test.txt.csv", "-suffix", true, "test.txt-suffix.csv"},
+		{"test.txt.csv", "-suffix", true, "test-suffix.txt.csv"},
 		{"test", "-suffix", false, "test-suffix"},
 		{"test", "-suffix", true, "test-suffix"},
+		{"test.html", "-suffix", true, "test-suffix.html"},
+		{"test.html.txt", "-suffix", true, "test-suffix.html.txt"},
+		{"test.csv.html.txt", "-suffix", true, "test-suffix.csv.html.txt"},
+		{"test.badext.csv.html.txt", "-suffix", true, "test.badext-suffix.csv.html.txt"},
+		{"test.badext", "-suffix", true, "test-suffix.badext"},
 	} {
 		ci.Suffix = test.suffix
 		ci.SuffixKeepExtension = test.keepExt