cmd: Add caddy fmt command. (#3090)

This takes the config file as input and formats it.
Prints the result to stdout. Can write changes to
file if `--write` flag is passed.

Fixes #3020

Signed-off-by: Vaibhav <vrongmeal@gmail.com>

caddyconfig/caddyfile/formatter.go

@@ -0,0 +1,137 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddyfile
+
+import (
+	"bytes"
+	"io"
+	"unicode"
+)
+
+// Format formats a Caddyfile to conventional standards.
+func Format(body []byte) []byte {
+	reader := bytes.NewReader(body)
+	result := new(bytes.Buffer)
+
+	var (
+		commented,
+		quoted,
+		escaped,
+		block,
+		environ,
+		lineBegin bool
+
+		firstIteration = true
+
+		prev,
+		curr,
+		next rune
+
+		err error
+	)
+
+	for {
+		prev = curr
+		curr = next
+
+		if curr < 0 {
+			break
+		}
+
+		next, _, err = reader.ReadRune()
+		if err != nil {
+			if err == io.EOF {
+				next = -1
+			} else {
+				panic(err)
+			}
+		}
+
+		if firstIteration {
+			firstIteration = false
+			lineBegin = true
+			continue
+		}
+
+		if quoted {
+			if escaped {
+				escaped = false
+			} else {
+				if curr == '\\' {
+					escaped = true
+				}
+				if curr == '"' {
+					quoted = false
+				}
+			}
+			if curr == '\n' {
+				quoted = false
+			}
+		} else if commented {
+			if curr == '\n' {
+				commented = false
+			}
+		} else {
+			if curr == '"' {
+				quoted = true
+			}
+			if curr == '#' {
+				commented = true
+			}
+			if curr == '}' {
+				if environ {
+					environ = false
+				} else if block {
+					block = false
+				}
+			}
+			if curr == '{' {
+				if unicode.IsSpace(next) {
+					block = true
+
+					if !unicode.IsSpace(prev) {
+						result.WriteRune(' ')
+					}
+				} else {
+					environ = true
+				}
+			}
+			if lineBegin {
+				if curr == ' ' || curr == '\t' {
+					continue
+				} else {
+					lineBegin = false
+					if block {
+						result.WriteRune('\t')
+					}
+				}
+			} else {
+				if prev == '{' &&
+					(curr == ' ' || curr == '\t') &&
+					(next != '\n' && next != '\r') {
+					curr = '\n'
+				}
+			}
+		}
+
+		if curr == '\n' {
+			lineBegin = true
+		}
+
+		result.WriteRune(curr)
+	}
+
+	return result.Bytes()
+}