Parse ENV vars for run config

Previously we were translating them in the `Dockerfile`, but that was
requiring running the command in a shell, which interferes with signals.
Also it means it only works when running in Docker.

Instead, we can check the environment variables when setting up the
default values.

We allow them to be set with or without a prefix, to avoid name clashes.
For example, `--http-port` can be set in the environment as either
`HTTP_PORT` or `MPROXY_HTTP_PORT`.

Dockerfile

@@ -6,11 +6,6 @@ RUN make
 FROM ubuntu as base
 COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=build /app/bin/mproxy /usr/local/bin/
+EXPOSE 80 443
 
-ENV HTTP_PORT=80
-ENV HTTPS_PORT=443
-ENV DEBUG=false
-
-EXPOSE $HTTP_PORT $HTTPS_PORT
-
-CMD mproxy run --http-port=${HTTP_PORT} --https-port=${HTTPS_PORT} --debug=${DEBUG}
+CMD [ "mproxy", "run" ]

internal/cmd/run.go

@@ -24,9 +24,9 @@ func newRunCommand() *runCommand {
 		RunE:  runCommand.run,
 	}
 
-	runCommand.cmd.Flags().BoolVar(&runCommand.debugLogsEnabled, "debug", false, "Include debugging logs")
-	runCommand.cmd.Flags().IntVar(&globalConfig.HttpPort, "http-port", server.DefaultHttpPort, "Port to serve HTTP traffic on")
-	runCommand.cmd.Flags().IntVar(&globalConfig.HttpsPort, "https-port", server.DefaultHttpsPort, "Port to serve HTTPS traffic on")
+	runCommand.cmd.Flags().BoolVar(&runCommand.debugLogsEnabled, "debug", getEnvBool("DEBUG", false), "Include debugging logs")
+	runCommand.cmd.Flags().IntVar(&globalConfig.HttpPort, "http-port", getEnvInt("HTTP_PORT", server.DefaultHttpPort), "Port to serve HTTP traffic on")
+	runCommand.cmd.Flags().IntVar(&globalConfig.HttpsPort, "https-port", getEnvInt("HTTPS_PORT", server.DefaultHttpsPort), "Port to serve HTTPS traffic on")
 
 	return runCommand
 }

internal/cmd/util.go

@@ -2,6 +2,12 @@ package cmd
 
 import (
 	"net/rpc"
+	"os"
+	"strconv"
+)
+
+const (
+	ENV_PREFIX = "MPROXY_"
 )
 
 func withRPCClient(socketPath string, fn func(client *rpc.Client) error) error {
@@ -12,3 +18,45 @@ func withRPCClient(socketPath string, fn func(client *rpc.Client) error) error {
 	defer client.Close()
 	return fn(client)
 }
+
+func findEnv(key string) (string, bool) {
+	value, ok := os.LookupEnv(ENV_PREFIX + key)
+	if ok {
+		return value, true
+	}
+
+	value, ok = os.LookupEnv(key)
+	if ok {
+		return value, true
+	}
+
+	return "", false
+}
+
+func getEnvInt(key string, defaultValue int) int {
+	value, ok := findEnv(key)
+	if !ok {
+		return defaultValue
+	}
+
+	intValue, err := strconv.Atoi(value)
+	if err != nil {
+		return defaultValue
+	}
+
+	return intValue
+}
+
+func getEnvBool(key string, defaultValue bool) bool {
+	value, ok := findEnv(key)
+	if !ok {
+		return defaultValue
+	}
+
+	boolValue, err := strconv.ParseBool(value)
+	if err != nil {
+		return defaultValue
+	}
+
+	return boolValue
+}