core: add XCADDY_GO_MOD_FLAGS env var to allow passing custom go mod flags

README.md

@@ -157,7 +157,9 @@ Because the subcommands and flags are constrained to benefit rapid plugin protot
 - `XCADDY_SKIP_BUILD=1` causes xcaddy to not compile the program, it is used in conjunction with build tools such as [GoReleaser](https://goreleaser.com). Implies `XCADDY_SKIP_CLEANUP=1`.
 - `XCADDY_SKIP_CLEANUP=1` causes xcaddy to leave build artifacts on disk after exiting.
 - `XCADDY_WHICH_GO` sets the go command to use when for example more then 1 version of go is installed.
-- `XCADDY_GO_BUILD_FLAGS` overrides default build arguments. Supports Unix-style shell quoting, for example: XCADDY_GO_BUILD_FLAGS="-ldflags '-w s'".
+- `XCADDY_GO_BUILD_FLAGS` overrides default build arguments. Supports Unix-style shell quoting, for example: XCADDY_GO_BUILD_FLAGS="-ldflags '-w s'". The provided flags are applied to `go` commands: build, clean, get, install, list, run, and test
+- `XCADDY_GO_MOD_FLAGS` overrides default `go mod` arguments. Supports Unix-style shell quoting.
+
 ---
 
 © 2020 Matthew Holt

builder.go

@@ -45,6 +45,7 @@ type Builder struct {
 	SkipBuild    bool          `json:"skip_build,omitempty"`
 	Debug        bool          `json:"debug,omitempty"`
 	BuildFlags   string        `json:"build_flags,omitempty"`
+	ModFlags     string        `json:"mod_flags,omitempty"`
 }
 
 // Build builds Caddy at the configured version with the
@@ -102,13 +103,13 @@ func (b Builder) Build(ctx context.Context, outputFile string) error {
 	log.Println("[INFO] Building Caddy")
 
 	// tidy the module to ensure go.mod and go.sum are consistent with the module prereq
-	tidyCmd := buildEnv.newGoCommand("mod", "tidy")
+	tidyCmd := buildEnv.newGoModCommand("tidy")
 	if err := buildEnv.runCommand(ctx, tidyCmd, b.TimeoutGet); err != nil {
 		return err
 	}
 
 	// compile
-	cmd := buildEnv.newGoCommand("build",
+	cmd := buildEnv.newGoBuildCommand("build",
 		"-o", absOutputFile,
 	)
 	if b.Debug {

cmd/main.go

@@ -41,6 +41,7 @@ var (
 	skipCleanup      = os.Getenv("XCADDY_SKIP_CLEANUP") == "1" || skipBuild
 	buildDebugOutput = os.Getenv("XCADDY_DEBUG") == "1"
 	buildFlags       = os.Getenv("XCADDY_GO_BUILD_FLAGS")
+	modFlags         = os.Getenv("XCADDY_GO_MOD_FLAGS")
 )
 
 func Main() {
@@ -136,6 +137,7 @@ func runBuild(ctx context.Context, args []string) error {
 		SkipCleanup:  skipCleanup,
 		Debug:        buildDebugOutput,
 		BuildFlags:   buildFlags,
+		ModFlags:     modFlags,
 	}
 	err := builder.Build(ctx, output)
 	if err != nil {

environment.go

@@ -100,11 +100,12 @@ func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
 		timeoutGoGet:    b.TimeoutGet,
 		skipCleanup:     b.SkipCleanup,
 		buildFlags:      b.BuildFlags,
+		modFlags:        b.ModFlags,
 	}
 
 	// initialize the go module
 	log.Println("[INFO] Initializing Go module")
-	cmd := env.newGoCommand("mod", "init")
+	cmd := env.newGoModCommand("init")
 	cmd.Args = append(cmd.Args, "caddy")
 	err = env.runCommand(ctx, cmd, 10*time.Second)
 	if err != nil {
@@ -115,7 +116,7 @@ func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
 	replaced := make(map[string]string)
 	for _, r := range b.Replacements {
 		log.Printf("[INFO] Replace %s => %s", r.Old.String(), r.New.String())
-		cmd := env.newGoCommand("mod", "edit",
+		cmd := env.newGoModCommand("edit",
 			"-replace", fmt.Sprintf("%s=%s", r.Old.Param(), r.New.Param()))
 		err := env.runCommand(ctx, cmd, 10*time.Second)
 		if err != nil {
@@ -181,6 +182,7 @@ type environment struct {
 	timeoutGoGet    time.Duration
 	skipCleanup     bool
 	buildFlags      string
+	modFlags        string
 }
 
 // Close cleans up the build environment, including deleting
@@ -194,22 +196,40 @@ func (env environment) Close() error {
 	return os.RemoveAll(env.tempFolder)
 }
 
-func (env environment) newGoCommand(args ...string) *exec.Cmd {
-	cmd := exec.Command(utils.GetGo(), args...)
+func (env environment) newCommand(command string, args ...string) *exec.Cmd {
+	cmd := exec.Command(command, args...)
 	cmd.Dir = env.tempFolder
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
+	return cmd
+}
+
+// newGoBuildCommand creates a new *exec.Cmd which assumes the first element in `args` is one of: build, clean, get, install, list, run, or test. The
+// created command will also have the value of `XCADDY_GO_BUILD_FLAGS` appended to its arguments, if set.
+func (env environment) newGoBuildCommand(args ...string) *exec.Cmd {
+	cmd := env.newCommand(utils.GetGo(), args...)
+	return parseAndAppendFlags(cmd, env.buildFlags)
+}
+
+// newGoModCommand creates a new *exec.Cmd which assumes `args` are the args for `go mod` command. The
+// created command will also have the value of `XCADDY_GO_MOD_FLAGS` appended to its arguments, if set.
+func (env environment) newGoModCommand(args ...string) *exec.Cmd {
+	args = append([]string{"mod"}, args...)
+	cmd := env.newCommand(utils.GetGo(), args...)
+	return parseAndAppendFlags(cmd, env.modFlags)
+}
 
-	if env.buildFlags == "" {
+func parseAndAppendFlags(cmd *exec.Cmd, flags string) *exec.Cmd {
+	if strings.TrimSpace(flags) == "" {
 		return cmd
 	}
 
-	flags, err := shlex.Split(env.buildFlags)
+	fs, err := shlex.Split(flags)
 	if err != nil {
-		log.Printf("[ERROR] Splitting arguments failed: %s", env.buildFlags)
+		log.Printf("[ERROR] Splitting arguments failed: %s", flags)
 		return cmd
 	}
-	cmd.Args = append(cmd.Args, flags...)
+	cmd.Args = append(cmd.Args, fs...)
 
 	return cmd
 }
@@ -276,7 +296,7 @@ func (env environment) execGoGet(ctx context.Context, modulePath, moduleVersion,
 		caddy += "@" + caddyVersion
 	}
 
-	cmd := env.newGoCommand("get", "-d", "-v")
+	cmd := env.newGoBuildCommand("get", "-d", "-v")
 	// using an empty string as an additional argument to "go get"
 	// breaks the command since it treats the empty string as a
 	// distinct argument, so we're using an if statement to avoid it.