From 5b5fdc6bc5df29fd85cd1449c43425f4e0810d02 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Fri, 28 Oct 2022 23:23:29 +0100
Subject: [PATCH] s3: add provider quirk --s3-might-gzip to fix corrupted on
 transfer: sizes differ

Before this change, some files were giving this error when downloaded
from Cloudflare and other providers.

    ERROR corrupted on transfer: sizes differ NNN vs MMM

This is because these providers auto gzips the object when rclone
wasn't expecting it to. (AWS does not gzip objects without their being
uploaded gzipped).

This patch adds a quirk to for fix the problem and a flag to control
it. The quirk `might_gzip` is set to `true` for all providers except
AWS.

See: https://forum.rclone.org/t/s3-error-corrupted-on-transfer-sizes-differ-nnn-vs-mmm/33694/
Fixes: #6533
---
 backend/s3/s3.go | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/backend/s3/s3.go b/backend/s3/s3.go
index 388adeb4b..8be8307ce 100644
--- a/backend/s3/s3.go
+++ b/backend/s3/s3.go
@@ -2174,6 +2174,31 @@ can't check the size and hash but the file contents will be decompressed.
 `,
 			Advanced: true,
 			Default:  false,
+		}, {
+			Name: "might_gzip",
+			Help: strings.ReplaceAll(`Set this if the backend might gzip objects.
+
+Normally providers will not alter objects when they are downloaded. If
+an object was not uploaded with |Content-Encoding: gzip| then it won't
+be set on download.
+
+However some providers may gzip objects even if they weren't uploaded
+with |Content-Encoding: gzip| (eg Cloudflare).
+
+A symptom of this would be receiving errors like
+
+    ERROR corrupted on transfer: sizes differ NNN vs MMM
+
+If you set this flag and rclone downloads an object with
+Content-Encoding: gzip set and chunked transfer encoding, then rclone
+will decompress the object on the fly.
+
+If this is set to unset (the default) then rclone will choose
+according to the provider setting what to apply, but you can override
+rclone's choice here.
+`, "|", "`"),
+			Default:  fs.Tristate{},
+			Advanced: true,
 		}, {
 			Name:     "no_system_metadata",
 			Help:     `Suppress setting and reading of system metadata`,
@@ -2305,6 +2330,7 @@ type Options struct {
 	Versions              bool                 `config:"versions"`
 	VersionAt             fs.Time              `config:"version_at"`
 	Decompress            bool                 `config:"decompress"`
+	MightGzip             fs.Tristate          `config:"might_gzip"`
 	NoSystemMetadata      bool                 `config:"no_system_metadata"`
 }
 
@@ -2665,10 +2691,12 @@ func setQuirks(opt *Options) {
 		virtualHostStyle  = true
 		urlEncodeListings = true
 		useMultipartEtag  = true
+		mightGzip         = true // assume all providers might gzip until proven otherwise
 	)
 	switch opt.Provider {
 	case "AWS":
 		// No quirks
+		mightGzip = false // Never auto gzips objects
 	case "Alibaba":
 		useMultipartEtag = false // Alibaba seems to calculate multipart Etags differently from AWS
 	case "HuaweiOBS":
@@ -2782,6 +2810,12 @@ func setQuirks(opt *Options) {
 		opt.UseMultipartEtag.Valid = true
 		opt.UseMultipartEtag.Value = useMultipartEtag
 	}
+
+	// set MightGzip if not manually set
+	if !opt.MightGzip.Valid {
+		opt.MightGzip.Valid = true
+		opt.MightGzip.Value = mightGzip
+	}
 }
 
 // setRoot changes the root of the Fs
@@ -4867,7 +4901,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 
 	// Decompress body if necessary
 	if aws.StringValue(resp.ContentEncoding) == "gzip" {
-		if o.fs.opt.Decompress {
+		if o.fs.opt.Decompress || (resp.ContentLength == nil && o.fs.opt.MightGzip.Value) {
 			return readers.NewGzipReader(resp.Body)
 		}
 		o.fs.warnCompressed.Do(func() {