Multiple response headers with same name combined to a single comma-separated list

[stuartio]

Checklist

• I've searched for similar issues.
• I'm using the latest version of HTTPie.

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Minimal reproduction code and steps

1. Request from any endpoint which produces multiple response headers with the same name

Current result

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 2
Content-Type: text/plain
Date: Mon, 13 Jun 2022 11:17:01 GMT
Server: nginx/1.22.0
edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-17-01.933Z
not-edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-17-01.933Z
testheader: 1, 2, 3

Expected result

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 2
Content-Type: text/plain
Date: Mon, 13 Jun 2022 11:17:01 GMT
Server: nginx/1.22.0
edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-17-01.933Z
not-edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-17-01.933Z
testheader: 1
testheader: 2
testheader: 3

Debug output

PS C:\code> http https://origin.stuartmacleod.net/httpie --debug
HTTPie 3.2.1
Requests 2.27.1
Pygments 2.11.2
Python 3.8.10 (tags/v3.8.10:3d8993a, May 3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)]
C:\code\Python\Python38\python.exe
Windows 10

<Environment {'apply_warnings_filter': <function Environment.apply_warnings_filter at 0x000001EC361D6310>,
'args': Namespace(),
'as_silent': <function Environment.as_silent at 0x000001EC361D61F0>,
'colors': 256,
'config': {'default_options': ['--style=xcode']},
'config_dir': WindowsPath('C:/Users/Stuart/AppData/Roaming/httpie'),
'devnull': <property object at 0x000001EC3616B4A0>,
'is_windows': True,
'log_error': <function Environment.log_error at 0x000001EC361D6280>,
'program_name': 'http',
'quiet': 0,
'rich_console': <functools.cached_property object at 0x000001EC36168E20>,
'rich_error_console': <functools.cached_property object at 0x000001EC361764C0>,
'show_displays': True,
'stderr': <colorama.ansitowin32.StreamWrapper object at 0x000001EC36148E50>,
'stderr_isatty': True,
'stdin': <_io.TextIOWrapper name='' mode='r' encoding='utf-8'>,
'stdin_encoding': 'utf-8',
'stdin_isatty': True,
'stdout': <colorama.ansitowin32.StreamWrapper object at 0x000001EC3612FFA0>,
'stdout_encoding': 'utf-8',
'stdout_isatty': True}>

<PluginManager {'adapters': [],
'auth': [<class 'httpie.plugins.builtin.BasicAuthPlugin'>,
<class 'httpie.plugins.builtin.DigestAuthPlugin'>,
<class 'httpie.plugins.builtin.BearerAuthPlugin'>],
'converters': [],
'formatters': [<class 'httpie.output.formatters.headers.HeadersFormatter'>,
<class 'httpie.output.formatters.json.JSONFormatter'>,
<class 'httpie.output.formatters.xml.XMLFormatter'>,
<class 'httpie.output.formatters.colors.ColorFormatter'>]}>

requests.request(**{'auth': None,
'data': RequestJSONDataDict(),
'headers': <HTTPHeadersDict('User-Agent': b'HTTPie/3.2.1')>,
'method': 'get',
'params': <generator object MultiValueOrderedDict.items at 0x000001EC36543200>,
'url': 'https://origin.stuartmacleod.net/httpie'})

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 2
Content-Type: text/plain
Date: Mon, 13 Jun 2022 11:18:15 GMT
Server: nginx/1.22.0
edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-18-15.040Z
not-edge-cache-tag: origin.stuartmacleod.net-2022-06-13T11-18-15.040Z
testheader: 1, 2, 3

ok

Additional information, screenshots, or code examples

This behaviour was changed after version 2.4.0. With 2.4.0 and earlier it outputs as expected, so I assume this was a deliberate move. If so, is there an option to use the previous output behaviour I could add to my config.json?