LF characters in container stdout are converted to CRLF

[tazle]

Description

Newlines in container stdout are converted to CRLF.

Example:

tuure ~  $ docker run --rm -it ubuntu:24.04 sh -c 'echo "a\nb"' | xxd                     
00000000: 610d 0a62 0d0a                           a..b..

If I instead base64-encode the stdout, the conversion doesn't happen

tuure ~  $ docker run --rm -it ubuntu:24.04 sh -c 'echo "a\nb" | base64' | base64 -d | xxd                                    
00000000: 610a 620a                                a.b.

The instance is a VZ instance (for Rosetta suppport), and was created like:

colima start --vz-rosetta --vm-type vz --cpu 10 -d 30 -m 7 --activate

Version

tuure ~ $ colima version && limactl --version && qemu-img --version
colima version 0.7.5
git commit: 1588c06

runtime: docker
arch: aarch64
client: v27.3.0
server: v27.1.1
limactl version 0.23.2
qemu-img version 9.1.0
Copyright (c) 2003-2024 Fabrice Bellard and the QEMU Project developers

Operating System

• macOS Intel <= 13 (Ventura)
• macOS Intel >= 14 (Sonoma)
• Apple Silicon <= 13 (Ventura)
• Apple Silicon >= 14 (Sonoma)
• Linux

Output of colima status

tuure ~ $ colima status
INFO[0000] colima is running using macOS Virtualization.Framework
INFO[0000] arch: aarch64
INFO[0000] runtime: docker
INFO[0000] mountType: virtiofs
INFO[0000] socket: unix:///Users/tuure/.colima/default/docker.sock

Reproduction Steps

1. docker run --rm -it ubuntu:24.04 sh -c 'echo "a\nb"' | xxd

Expected behaviour

Expected newlines not to get converted to CRLFs.

Additional context

The CRLFs can be observed coming from the docker daemon, i.e. they are not an artifact of the client:

Extract from socat dump showing the stdout request and initial response

> 2024/09/22 00:42:31.000202662  length=291 from=0 to=290
 50 4f 53 54 20 2f 76 31 2e 34 36 2f 63 6f 6e 74  POST /v1.46/cont
 61 69 6e 65 72 73 2f 66 33 39 64 36 66 32 31 33  ainers/f39d6f213
 66 61 37 66 36 38 65 62 65 66 35 63 65 61 66 34  fa7f68ebef5ceaf4
 32 63 65 61 33 30 65 30 32 38 30 39 33 62 32 39  2cea30e028093b29
 30 66 33 36 38 61 61 63 32 31 63 32 32 32 65 38  0f368aac21c222e8
 61 36 35 35 63 35 62 2f 61 74 74 61 63 68 3f 73  a655c5b/attach?s
 74 64 65 72 72 3d 31 26 73 74 64 69 6e 3d 31 26  tderr=1&stdin=1&
 73 74 64 6f 75 74 3d 31 26 73 74 72 65 61 6d 3d  stdout=1&stream=
 31 20 48 54 54 50 2f 31 2e 31 0d 0a              1 HTTP/1.1..
 48 6f 73 74 3a 20 61 70 69 2e 6d 6f 62 79 2e 6c  Host: api.moby.l
 6f 63 61 6c 68 6f 73 74 0d 0a                    ocalhost..
 55 73 65 72 2d 41 67 65 6e 74 3a 20 44 6f 63 6b  User-Agent: Dock
 65 72 2d 43 6c 69 65 6e 74 2f 32 37 2e 33 2e 30  er-Client/27.3.0
 20 28 64 61 72 77 69 6e 29 0d 0a                  (darwin)..
 43 6f 6e 74 65 6e 74 2d 4c 65 6e 67 74 68 3a 20  Content-Length: 
 30 0d 0a                                         0..
 43 6f 6e 6e 65 63 74 69 6f 6e 3a 20 55 70 67 72  Connection: Upgr
 61 64 65 0d 0a                                   ade..
 43 6f 6e 74 65 6e 74 2d 54 79 70 65 3a 20 74 65  Content-Type: te
 78 74 2f 70 6c 61 69 6e 0d 0a                    xt/plain..
 55 70 67 72 61 64 65 3a 20 74 63 70 0d 0a        Upgrade: tcp..
 0d 0a                                            ..
--
< 2024/09/22 00:42:31.000203964  length=109 from=0 to=108
 48 54 54 50 2f 31 2e 31 20 31 30 31 20 55 50 47  HTTP/1.1 101 UPG
 52 41 44 45 44 0d 0a                             RADED..
 43 6f 6e 74 65 6e 74 2d 54 79 70 65 3a 20 61 70  Content-Type: ap
 70 6c 69 63 61 74 69 6f 6e 2f 76 6e 64 2e 64 6f  plication/vnd.do
 63 6b 65 72 2e 72 61 77 2d 73 74 72 65 61 6d 0d  cker.raw-stream.
 0a                                               .
 43 6f 6e 6e 65 63 74 69 6f 6e 3a 20 55 70 67 72  Connection: Upgr
 61 64 65 0d 0a                                   ade..
 55 70 67 72 61 64 65 3a 20 74 63 70 0d 0a        Upgrade: tcp..
 0d 0a                                            ..

And later the contents:

--
< 2024/09/22 00:42:31.000365423  length=6 from=109 to=114
 61 0d 0a                                         a..
 62 0d 0a                                         b..
--

[tazle]

A random thought: HTTP headers are \r\n-terminated. Could it be that whatever is relaying the stdout stream over HTTP thinks it's writing HTTP headers and converting the newlines?