Go module proxy implemented in python/django

goproxy.py

import json
from django.http import HttpResponse

class Modules(APIView):
    """
    For documentation, see; https://github.com/golang/go/blob/master/src/cmd/go/internal/modfetch/proxy.go

    call this like;
        sudo rm -rf ~/go/src/mod/ && \
        export GOPROXY=http://localhost:4000 && \
        go get -v github.com/pkg/errors
       
    to use go mod without hitting network
        go mod -vendor && \
        go build -getmode=vendor
    """

    def get(self, request):

        path = request.path
        req_content_type = request.content_type
        req_GET = request.GET
        print(
            "\n path={0} \nreq_content_type={1} \nreq_GET={2}".format(
                path, req_content_type, req_GET
            )
        )

        if path == "/github.com/pkg/errors/@v/list":
            return HttpResponse(content_type="text/plain", content="v0.8.0")
        elif path == "/github.com/pkg/errors/@v/v0.8.0.info":
            # see; https://github.com/golang/go/blob/88aa208024f04845381a86f2d5679d2e520b1ff6/src/cmd/go/internal/modfetch/proxy.go#L64-L67
            resp = {"Version": "v0.8.0", "Time": "2016-09-29T01:48:01Z"}
            return HttpResponse(content_type="text/plain", content=json.dumps(resp))
        elif path == "/github.com/pkg/errors/@v/v0.8.0.mod":
            resp = "module github.com/pkg/errors\n"
            return HttpResponse(content_type="text/plain", content=resp)
        elif path == "/github.com/pkg/errors/@v/v0.8.0.zip":
            """
            zipped package in specified format here;
            https://github.com/golang/go/blob/master/src/cmd/go/internal/modfetch/proxy.go#L66-L73
            The archive uses slash-separated paths, and every file path in the archive must 
            begin with <module>@<version>/, where the module and version are
            substituted directly, not case-encoded. The root of the module
            file tree corresponds to the <module>@<version>/ prefix in the archive.
            so there is /github.com/pkg/errors/@v/v0.8.0.zip which if you opened up
            it should look like:
            github.com
                └── pkg
                    └── errors@v0.8.0
                        ├── LICENSE
                        ├── README.md
                        ├── appveyor.yml
                        ├── bench_test.go
                        ├── errors.go
                        ├── errors_test.go
                        ├── example_test.go
                        ├── format_test.go
                        ├── stack.go
                        └── stack_test.go
            
            if you download from https://github.com/pkg/errors/archive/v0.8.0.zip it looks like
            errors-0.8.0
                ├── LICENSE
                ├── README.md
                ├── appveyor.yml
                ├── bench_test.go
                ├── errors.go
                ├── errors_test.go
                ├── example_test.go
                ├── format_test.go
                ├── stack.go
                └── stack_test.go
            
            so we need to read that and reconstruct it into a new zip file that looks like;
            github.com
                └── pkg
                    └── errors@v0.8.0
                        ├── LICENSE
                        ├── README.md
                        └──etc
            """
            return HttpResponse(
                content_type="text/plain",
                status=599,
                content="endpoint /github.com/pkg/errors/@v/v0.8.0.zip is not implemented.",
            )

goproxy.sh

#!/usr/bin/env bash

# https://github.com/anordal/shellharden/blob/master/how_to_do_things_safely_in_bash.md

if test "$BASH" = "" || "$BASH" -uc "a=();true \"\${a[@]}\"" 2>/dev/null; then
    # Bash 4.4, Zsh
    set -euo pipefail
else
    # Bash 4.3 and older chokes on empty arrays with set -u.
    set -eo pipefail
fi

# usage:
printf """\n\n example usage: \n
bash goproxy.sh \
/tmp/myGoProxy \
/tmp/zipper \
github.com/pkg/errors \
v0.0.8"""

GOPROXY_LOCATION=${1:-/tmp/myGoProxy}
ZIPPING_LOCATION=${2:-/tmp/zipper}
printf "\n\n GOPROXY_LOCATION=$GOPROXY_LOCATION \n"
printf "\n\n ZIPPING_LOCATION=$ZIPPING_LOCATION \n"

MODULE_NAME=${3:-notSet}
if [ "$MODULE_NAME" == "notSet"  ]; then
    printf "\n\n MODULE_NAME should not be empty\n"
    exit
fi
MODULE_VERSION=${4:-notSet}
if [ "$MODULE_VERSION" == "notSet"  ]; then
    printf "\n\n MODULE_VERSION should not be empty\n"
    exit
fi


# 1.
printf "\n\n downloading: \nmodule=$MODULE_NAME \nversion=$MODULE_VERSION \n\n"
mkdir -p $ZIPPING_LOCATION
wget -nc --directory-prefix=$ZIPPING_LOCATION https://$MODULE_NAME/archive/$MODULE_VERSION.zip
unzip $ZIPPING_LOCATION/$MODULE_VERSION.zip -d $ZIPPING_LOCATION
mkdir -p $ZIPPING_LOCATION/$MODULE_VERSION
mv $ZIPPING_LOCATION/*/* $ZIPPING_LOCATION/$MODULE_VERSION
mkdir -p $ZIPPING_LOCATION/$MODULE_NAME@$MODULE_VERSION
cp -r $ZIPPING_LOCATION/$MODULE_VERSION/* $ZIPPING_LOCATION/$MODULE_NAME@$MODULE_VERSION
zip /tmp/$MODULE_VERSION.zip $ZIPPING_LOCATION/$MODULE_NAME@$MODULE_VERSION/*

# 2.
printf "\n\n adding module to $GOPROXY_LOCATION: \nmodule=$MODULE_NAME \nversion=$MODULE_VERSION \n\n"
mkdir -p $GOPROXY_LOCATION
mkdir -p $GOPROXY_LOCATION/$MODULE_NAME/@v
echo "${MODULE_VERSION}" >> $GOPROXY_LOCATION/$MODULE_NAME/@v/list
echo "{"\"Version"\":"\"$MODULE_VERSION"\", "\"Time"\":"\"2016-09-29T01:48:01Z"\"}" >> $GOPROXY_LOCATION/$MODULE_NAME/@v/$MODULE_VERSION.info
echo "module $MODULE_NAME" >> $GOPROXY_LOCATION/$MODULE_NAME/@v/$MODULE_VERSION.mod
cp /tmp/$MODULE_VERSION.zip $GOPROXY_LOCATION/$MODULE_NAME/@v/

# 3. clean up
printf "\n\n cleaning up \n\n"
rm -rf $ZIPPING_LOCATION/*

# 4. set proxy env
printf "\n\n setting up GOPROXY env variable for \n\n"
export GOPROXY=file:///$GOPROXY_LOCATION

urls.py

from django.urls import re_path
from django.views.decorators.csrf import csrf_exempt
from .goproxy import Modules

urlpatterns = [
    # allow any uri
    re_path(r"^.*", csrf_exempt(Modules.as_view()), name="modules"),
]

To create a file-based Go module proxy, you can run the following commands.
I turned it into a repo: https://github.com/komuw/goproxy

Note that the advice to use errexit, given in https://github.com/anordal/shellharden/blob/master/how_to_do_things_safely_in_bash.md, conflicts with BashFAQ #105. The general best practice from the bash community (as solidified in the #bash IRC channel formerly of Freenode, now of Libera) is to use explicit || return / || exit extensively.