stack: Do not use templates for env files

This commit removes the templating logic for writing .env files.
Instead it simply writes a key-value directory directly to the destined
file.

pkg/compose/env.go

@@ -0,0 +1,142 @@
+package compose
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/tkw1536/pkglib/collection"
+)
+
+const (
+	EnvFileHeader = "# THIS FILE IS AUTOMATICALLY GENERATED. DO NOT EDIT. \n\n"
+
+	EnvEqualChar   = '='  // assignment
+	EnvReplaceChar = '#'  // replacement for invalid characters
+	EnvEscapeChar  = '\\' // escaping
+	EnvQuoteChar   = '"'  // quoting
+)
+
+type errInvalidName string
+
+func (ei errInvalidName) Error() string {
+	return fmt.Sprintf("invalid variable name: %q", string(ei))
+}
+
+// WriteEnvFile writes a .env file to io.Writer.
+// Variables are written in consistent order.
+//
+// Variable names may only contain ascii letters, numbers or the character "_".
+// Invalid variable names are an error.
+//
+// Variables values are escaped using EscapeEnvValue.
+//
+// count contains the number of bytes written to writer.
+// In case of an error, partial content may already have been written to writer, as indicated by count.
+func WriteEnvFile(writer io.Writer, env map[string]string) (count int, err error) {
+	var n int
+
+	// write the header to the file
+	n, err = fmt.Fprint(writer, EnvFileHeader)
+	count += n
+	if err != nil {
+		return
+	}
+
+	collection.IterateSorted(env, func(key, value string) {
+		// if we already had an error, break
+		if err != nil {
+			return
+		}
+
+		// if we don't have a valid name, break
+		if !isValidVariable(key) {
+			err = errInvalidName(key)
+			return
+		}
+
+		// write write key = EscapeEnvValue(value) followed by a new line
+		n, err = fmt.Fprintf(writer, "%s%s%s\n", key, string(EnvEqualChar), EscapeEnvValue(value))
+		count += n
+		if err != nil {
+			return
+		}
+	})
+	return
+}
+
+// isValidVariable checks if name is a valid variable name.
+func isValidVariable(name string) bool {
+	for _, r := range name {
+		if !(r == '_' || (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9')) {
+			return false
+		}
+	}
+	return true
+}
+
+// Escape escapes the given value to be written to an environment variable.
+// If the value does not need escaping, it may return it unchanged.
+//
+// EscapeEnvValue allows ASCII characters from ' ' to '~' (inclusive) as well as  '\t', '\r', '\n'.
+// Other characters are automatically replaced by EnvReplaceChar.
+func EscapeEnvValue(value string) (escaped string) {
+	// first check if we need to escape at all.
+	var changed bool
+	for _, r := range value {
+		if !isValidEnvChar(r) || r == '\n' || r == '\r' || r == '\t' || r == '$' || r == EnvEscapeChar || r == EnvQuoteChar {
+			changed = true
+		}
+	}
+	if !changed {
+		return value
+	}
+
+	// make a new builder and make space for the original value
+	var builder strings.Builder
+	builder.Grow(len(value) + 2)
+
+	// begin the quoting
+	builder.WriteRune(EnvQuoteChar)
+
+	// iterate over it
+	for _, r := range value {
+		// if the character is invalid, it is replaced with an '_'
+		if !isValidEnvChar(r) {
+			builder.WriteRune(EnvReplaceChar)
+			continue
+		}
+
+		switch r {
+		// custom escape for '\n', '\r', '\t'
+		case '\n':
+			builder.WriteRune(EnvEscapeChar)
+			builder.WriteRune('n')
+		case '\r':
+			builder.WriteRune(EnvEscapeChar)
+			builder.WriteRune('r')
+		case '\t':
+			builder.WriteRune(EnvEscapeChar)
+			builder.WriteRune('t')
+
+		// standard escape for special characters
+		case '$', EnvEscapeChar, EnvQuoteChar:
+			builder.WriteRune(EnvEscapeChar)
+			fallthrough
+
+		// that's it
+		default:
+			builder.WriteRune(r)
+		}
+	}
+
+	// close the quote
+	builder.WriteRune(EnvQuoteChar)
+
+	return builder.String()
+}
+
+// isValidEnvChar checks if the rune r is allowed in environment variables.
+func isValidEnvChar(r rune) bool {
+	return r == '\n' || r == '\r' || r == '\t' || (r >= ' ' && r <= '~')
+}

pkg/unpack/resource.go

@@ -10,7 +10,6 @@ import (
 	"github.com/tkw1536/pkglib/fsx/umaskfree"
 )
 
-var errExpectedFileButGotDirectory = errors.New("expected a file, but got a directory")
 var errExpectedDirectoryButGotFile = errors.New("expected a directory, but got a file")
 
 // InstallDir installs the directory at src within fsys to dst.

pkg/unpack/template.go

@@ -5,10 +5,8 @@ import (
 	"bufio"
 	"fmt"
 	"io"
-	"io/fs"
 	"strings"
 
-	"github.com/tkw1536/pkglib/fsx/umaskfree"
 	"golang.org/x/exp/maps"
 	"golang.org/x/exp/slices"
 )
@@ -196,38 +194,3 @@ parseloop:
 
 	return nil
 }
-
-// InstallTemplate unpacks the resource located at src in fsys, then processes it as a template, and eventually writes it to dst.
-// Any existing file is truncated and overwritten.
-//
-// See [WriteTemplate] for possible errors.
-func InstallTemplate(dst string, context map[string]string, src string, fsys fs.FS) error {
-
-	// open the srcFile
-	srcFile, err := fsys.Open(src)
-	if err != nil {
-		return err
-	}
-	defer srcFile.Close()
-
-	// stat it
-	srcInfo, err := srcFile.Stat()
-	if err != nil {
-		return err
-	}
-
-	// check if it is a directory
-	if srcInfo.IsDir() {
-		return errExpectedFileButGotDirectory
-	}
-
-	// open the destination file
-	file, err := umaskfree.Create(dst, srcInfo.Mode())
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-
-	// write the file!
-	return WriteTemplate(file, context, srcFile)
-}