From 6abdb30f15cff6c911fa57b61def548844eaaf33 Mon Sep 17 00:00:00 2001
From: Steve Engledow <steve@offend.me.uk>
Date: Wed, 23 Jul 2025 21:12:21 +0100
Subject: [PATCH] #694 Add support for reading from stdin with '-' as a
 template file name

---
 cft/parse/parse.go                |  4 ++++
 cft/parse/parse_test.go           | 32 +++++++++++++++++++++++++
 internal/cmd/deploy/deploy.go     | 29 +++++++++++++++++++---
 internal/cmd/deploy/util.go       |  9 ++++++-
 internal/cmd/diff/diff.go         |  2 +-
 internal/cmd/fmt/fmt.go           | 40 ++++++++++++++++++-------------
 internal/cmd/forecast/forecast.go |  2 ++
 internal/cmd/merge/merge.go       |  2 +-
 internal/cmd/tree/tree.go         |  2 +-
 9 files changed, 98 insertions(+), 24 deletions(-)

diff --git a/cft/parse/parse.go b/cft/parse/parse.go
index 162ec5811..f1dd912cb 100644
--- a/cft/parse/parse.go
+++ b/cft/parse/parse.go
@@ -26,6 +26,10 @@ func Reader(r io.Reader) (*cft.Template, error) {
 
 // File returns a cft.Template parsed from a file specified by fileName
 func File(fileName string) (*cft.Template, error) {
+	if fileName == "-" {
+		return Reader(os.Stdin)
+	}
+
 	source, err := os.ReadFile(fileName)
 	if err != nil {
 		return &cft.Template{}, fmt.Errorf("unable to read file: %s", err)
diff --git a/cft/parse/parse_test.go b/cft/parse/parse_test.go
index 8bd2b8dbe..a2f9625e1 100644
--- a/cft/parse/parse_test.go
+++ b/cft/parse/parse_test.go
@@ -132,6 +132,38 @@ func TestReadFile(t *testing.T) {
 	}
 }
 
+func TestReadFile_stdin(t *testing.T) {
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Error(err)
+	}
+
+	_, err = w.WriteString(testTemplate)
+	if err != nil {
+		t.Error(err)
+	}
+
+	err = w.Close()
+	if err != nil {
+		t.Error(err)
+	}
+
+	oldStdin := os.Stdin
+	defer func() {
+		os.Stdin = oldStdin
+	}()
+	os.Stdin = r
+
+	actual, err := parse.File("-")
+	if err != nil {
+		t.Error(err)
+	}
+
+	if diff := cmp.Diff(actual.Map(), expected.Map()); diff != "" {
+		t.Errorf(diff)
+	}
+}
+
 func TestReadString(t *testing.T) {
 	actual, err := parse.String(testTemplate)
 	if err != nil {
diff --git a/internal/cmd/deploy/deploy.go b/internal/cmd/deploy/deploy.go
index d62b92bf7..895d74018 100644
--- a/internal/cmd/deploy/deploy.go
+++ b/internal/cmd/deploy/deploy.go
@@ -43,6 +43,7 @@ var Cmd = &cobra.Command{
 	Long: `Creates or updates a CloudFormation stack named <stack> from the template file <template>. 
 You can also create and execute changesets with this command.
 If you don't specify a stack name, rain will use the template filename minus its extension.
+You can use "-" as the template filename to read from stdin.
 
 If a template needs to be packaged before it can be deployed, rain will package the template first.
 Rain will attempt to create an S3 bucket to store artifacts that it packages and deploys.
@@ -103,7 +104,13 @@ To list and delete changesets, use the ls and rm commands.
 		} else {
 
 			fn = args[0]
-			base := filepath.Base(fn)
+			// Handle stdin case with "-" filename
+			var base string
+			if fn == "-" {
+				base = "stdin"
+			} else {
+				base = filepath.Base(fn)
+			}
 
 			var suppliedStackName string
 
@@ -133,8 +140,16 @@ To list and delete changesets, use the ls and rm commands.
 
 			// Process metadata Rain Content before (Run build scripts before deployment)
 			if !changeset {
+				// Use current directory for stdin input
+				var dir string
+				if fn == "-" {
+					dir = "."
+				} else {
+					dir = filepath.Dir(fn)
+				}
+
 				err := processMetadataBefore(cft.Template{Node: templateNode},
-					stackName, filepath.Dir(fn))
+					stackName, dir)
 				if err != nil {
 					panic(err)
 				}
@@ -273,8 +288,16 @@ To list and delete changesets, use the ls and rm commands.
 
 		// Process Rain Metadata commands (Content)
 		if !changeset {
+			// Use current directory for stdin input
+			var dir string
+			if fn == "-" {
+				dir = "."
+			} else {
+				dir = filepath.Dir(fn)
+			}
+
 			err := processMetadataAfter(cft.Template{Node: templateNode},
-				stackName, filepath.Dir(fn))
+				stackName, dir)
 			if err != nil {
 				panic(err)
 			}
diff --git a/internal/cmd/deploy/util.go b/internal/cmd/deploy/util.go
index ad8050f7d..7e48718c2 100644
--- a/internal/cmd/deploy/util.go
+++ b/internal/cmd/deploy/util.go
@@ -81,13 +81,20 @@ func formatChangeSet(stackName, changeSetName string) string {
 	return strings.TrimSpace(out.String())
 }
 
+// PackageTemplate reads and packages a template from a file or stdin
 func PackageTemplate(fn string, yes bool) *cft.Template {
 	// Call RainBucket for side-effects in case we want to force bucket creation
 	s3.RainBucket(yes)
 
+	// Handle stdin case with "-" filename
+	templateName := fn
+	if fn == "-" {
+		templateName = "stdin"
+	}
+
 	t, err := pkg.File(fn)
 	if err != nil {
-		panic(ui.Errorf(err, "error packaging template '%s'", fn))
+		panic(ui.Errorf(err, "error packaging template '%s'", templateName))
 	}
 
 	return t
diff --git a/internal/cmd/diff/diff.go b/internal/cmd/diff/diff.go
index 9a7e25350..df917d4ae 100644
--- a/internal/cmd/diff/diff.go
+++ b/internal/cmd/diff/diff.go
@@ -16,7 +16,7 @@ var longDiff = false
 var Cmd = &cobra.Command{
 	Use:                   "diff <from> <to>",
 	Short:                 "Compare CloudFormation templates",
-	Long:                  "Outputs a summary of the changes necessary to transform the CloudFormation template named <from> into the template named <to>.",
+	Long:                  "Outputs a summary of the changes necessary to transform the CloudFormation template named <from> into the template named <to>.\n\nYou can use \"-\" as a filename to read from stdin.",
 	Args:                  cobra.ExactArgs(2),
 	DisableFlagsInUseLine: true,
 	Run: func(cmd *cobra.Command, args []string) {
diff --git a/internal/cmd/fmt/fmt.go b/internal/cmd/fmt/fmt.go
index 0154e445c..2bcbd6039 100644
--- a/internal/cmd/fmt/fmt.go
+++ b/internal/cmd/fmt/fmt.go
@@ -120,11 +120,19 @@ func formatFile(filename string) result {
 		return res
 	}
 
-	r, err := os.Open(filename)
-	if err != nil {
-		return result{
-			name: filename,
-			err:  ui.Errorf(err, "unable to read '%s'", filename),
+	var r *os.File
+	var err error
+
+	if filename == "-" {
+		r = os.Stdin
+		filename = "stdin"
+	} else {
+		r, err = os.Open(filename)
+		if err != nil {
+			return result{
+				name: filename,
+				err:  ui.Errorf(err, "unable to read '%s'", filename),
+			}
 		}
 	}
 
@@ -145,24 +153,22 @@ var Cmd = &cobra.Command{
 			// Check there's data on stdin
 			stat, err := os.Stdin.Stat()
 			if err != nil {
-				panic(ui.Errorf(err, "unable to open stdin"))
+				cmd.Help()
+				os.Exit(0)
 			}
 
 			if stat.Mode()&os.ModeNamedPipe == 0 && stat.Size() == 0 {
-				fmt.Println("CAKES")
-				panic(cmd.Help())
+				cmd.Help()
+				os.Exit(0)
 			}
 
-			writeFlag = false // Can't write back to stdin ;)
+			// There is data on stdin, assume the user intends to format it
+			args = []string{"-"}
+		}
 
-			results = []result{
-				formatReader("<stdin>", os.Stdin),
-			}
-		} else {
-			results = make([]result, len(args))
-			for i, filename := range args {
-				results[i] = formatFile(filename)
-			}
+		results = make([]result, len(args))
+		for i, filename := range args {
+			results[i] = formatFile(filename)
 		}
 
 		hasErr := false
diff --git a/internal/cmd/forecast/forecast.go b/internal/cmd/forecast/forecast.go
index 8f399a4bd..f15366e6e 100644
--- a/internal/cmd/forecast/forecast.go
+++ b/internal/cmd/forecast/forecast.go
@@ -343,6 +343,8 @@ template has been checked to make sure it has a valid syntax.
 
 This command checks for some common issues across all resources, and 
 resource-specific checks. See the README for more details.
+
+You can use "-" as a filename to read the template from stdin.
 `,
 	Args:                  cobra.RangeArgs(1, 2),
 	DisableFlagsInUseLine: true,
diff --git a/internal/cmd/merge/merge.go b/internal/cmd/merge/merge.go
index dace5320d..f70133a4a 100644
--- a/internal/cmd/merge/merge.go
+++ b/internal/cmd/merge/merge.go
@@ -21,7 +21,7 @@ var outFn = ""
 var Cmd = &cobra.Command{
 	Use:                   "merge <template> <template> ...",
 	Short:                 "Merge two or more CloudFormation templates",
-	Long:                  "Merges all specified CloudFormation templates, print the resultant template to standard out",
+	Long:                  "Merges all specified CloudFormation templates, print the resultant template to standard out.\n\nYou can use \"-\" as a filename to read from stdin for any of the template arguments.",
 	Args:                  cobra.MinimumNArgs(2),
 	DisableFlagsInUseLine: true,
 	Run: func(cmd *cobra.Command, args []string) {
diff --git a/internal/cmd/tree/tree.go b/internal/cmd/tree/tree.go
index e7d32250f..a6875717f 100644
--- a/internal/cmd/tree/tree.go
+++ b/internal/cmd/tree/tree.go
@@ -16,7 +16,7 @@ var twoWayTree = false
 var Cmd = &cobra.Command{
 	Use:                   "tree [template]",
 	Short:                 "Find dependencies of Resources and Outputs in a local template",
-	Long:                  "Find and display the dependencies between Parameters, Resources, and Outputs in a CloudFormation template.",
+	Long:                  "Find and display the dependencies between Parameters, Resources, and Outputs in a CloudFormation template.\n\nYou can use \"-\" as a filename to read from stdin.",
 	Args:                  cobra.ExactArgs(1),
 	Aliases:               []string{"graph"},
 	DisableFlagsInUseLine: true,