RProxy is a simple reverse proxy server writen in Golang. It can replace substring in body of backend server responses. Replacing work only for responses with Content-Type header set in "text/plain" and "text/html".
go get github.com/arvinkulagin/rproxy
mkdir $GOPATH/src/github.com/arvinkulagin
cd $GOPATH/src/github.com/arvinkulagin
git clone https://github.com/arvinkulagin/rproxy.git
cd $GOPATH/src/github.com/arvinkulagin/rproxy
make build
cd $GOPATH/src/github.com/arvinkulagin/rproxy
make build-image
rproxy -config rproxy.conf
docker run -d --net "host" -v "/path/to/rproxy/donfig/dir:/config" rproxy
address - interface and port to listening incoming requests in
target - address of target server
pattern - regexp pattern to match substrings for replacing
replacement - replacement substring