mime/quotedprintable: LWSP-char not accepted between = and CRLF

[emersion]

Go version

go version go1.23.4 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/simon/.cache/go-build'
GOENV='/home/simon/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/simon/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/simon/go'
GOPRIVATE=''
GOPROXY='direct'
GOROOT='/usr/lib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/lib/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.4'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/simon/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/simon/src/go-imap/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2161554395=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Try to decode the following MIME message:

https://github.com/dovecot/imaptest/blob/73dcb3ff9ae8b6859ceaf383f21c5b62a9fd7500/src/tests/fetch-binary-mime-qp.mbox

RFC 2045 section 6.7 allows a transport-padding (see details in #70951).

What did you see happen?

quotedprintable: invalid bytes after =: " \r\n"
quotedprintable: invalid bytes after =: "\t \r\n"

What did you expect to see?

No error.

[gabyhelp]

Related Issues

• mime/quotedprintable: single line with only period cause message truncation when used in SMTP DATA #61235
• mime/quotedprintable: Read() returns error when underlying string ends with soft-break ("=") #15486 (closed)
• mime/multipart: quoted-printable check is case sensitive #28674 (closed)
• mime/quotedprintable: support message with long lines #43194
• mime: WordDecoder#DecodeHeader accept space as a part of 'encoded-word' #19417 (closed)
• net/mail: ReadMessage returns EOF error when the body is not present #47886 (closed)
• net/mail: ReadMessage returns EOF in case of header-only messages. #47897 (closed)
• mime/multipart: add (*Reader).NextRawPart to bypass automatic quoted-printable handling #29090 (closed)
• net/textproto: can write binary header it can't read #60674

Related Code Changes

• mime/quotedprintable: accept LWSP-char after =

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/638276 mentions this issue: mime/quotedprintable: accept LWSP-char after =

[dr2chase]

@neild @minux