Workaround for #33 - go sub-modules

README.md

@@ -299,3 +299,54 @@ func Handle(w http.ResponseWriter, r *http.Request) {
 	w.Write([]byte(result))
 }
 ```
+
+#### Advanced usage - Go sub-modules via `GO_REPLACE.txt`
+
+For this example you will need to be using Go 1.13 or newer and Go modules, enable this via `faas-cli build --build-arg GO111MODULE=on`.
+
+Imagine you have a package which you want to store outside of the `handler.go` file, it's another middleware which can perform an echo of the user's input.
+
+```Golang
+package handlers
+
+import (
+	"io/ioutil"
+	"net/http"
+)
+
+func Echo(w http.ResponseWriter, r *http.Request) {
+	if r.Body != nil {
+		defer r.Body.Close()
+		b, _ := ioutil.ReadAll(r.Body)
+		w.Write(b)
+	}
+}
+```
+
+To include a relative module such as this new `handlers` package, you should create a `GO_REPLACE.txt` file as follows:
+
+```
+replace github.com/alexellis/vault/purchase/handlers => ./function/handlers
+```
+
+How did we get to that? Let's say your GOPATH for your GitHub repo is: `github.com/alexellis/vault/` and your OpenFaaS function is `purchase` generated by `faas-cli new purchase --lang golang-middleware`.
+
+Your relative GOPATH is: `github.com/alexellis/vault/purchase`, so add a redirect as per below to redirect the "handlers" package to where it exists in the build container.
+
+
+Now if you want to reference the handlers package from within your `handler.go` write the following:
+
+```golang
+package function
+
+import (
+	"net/http"
+
+	"github.com/alexellis/vault/purchase/handlers"
+)
+
+func Handle(w http.ResponseWriter, r *http.Request) {
+
+	handlers.Echo(w, r)
+}
+```

template/golang-middleware/Dockerfile

@@ -12,14 +12,22 @@ RUN mkdir -p /go/src/handler
 WORKDIR /go/src/handler
 COPY . .
 
+# Add user overrides to the root go.mod, which is the only place "replace" can be used
+RUN cat function/GO_REPLACE.txt >> ./go.mod || exit 0
+
 # Run a gofmt and exclude all vendored code.
 RUN test -z "$(gofmt -l $(find . -type f -name '*.go' -not -path "./vendor/*" -not -path "./function/vendor/*"))" || { echo "Run \"gofmt -s -w\" on your Golang code"; exit 1; }
 
 ARG GO111MODULE="off"
 ARG GOPROXY=""
+ARG GOFLAGS=""
+
+WORKDIR /go/src/handler/function
+
+RUN go test ./... -cover
 
+WORKDIR /go/src/handler
 RUN go build --ldflags "-s -w" -a -installsuffix cgo -o handler .
-RUN go test handler/function/... -cover
 
 FROM alpine:3.11
 # Add non root user and certs
@@ -30,11 +38,9 @@ RUN apk --no-cache add ca-certificates \
 
 WORKDIR /home/app
 
-COPY --from=build /go/src/handler/handler    .
-COPY --from=build /usr/bin/fwatchdog         .
-COPY --from=build /go/src/handler/function/  .
-
-RUN chown -R app /home/app
+COPY --from=build --chown=app /go/src/handler/handler    .
+COPY --from=build --chown=app /usr/bin/fwatchdog         .
+COPY --from=build --chown=app /go/src/handler/function/  .
 
 USER app