config/validate: add new config validator

This validator is still experimental and is going to need new rules in the
future. This lays out the general framework.

config/validate/context.go

@@ -0,0 +1,54 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   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 validate
+
+import (
+	"strings"
+)
+
+// context represents the current position within a newline-delimited string.
+// Each line is loaded, one by one, into currentLine (newline omitted) and
+// lineNumber keeps track of its position within the original string.
+type context struct {
+	currentLine    string
+	remainingLines string
+	lineNumber     int
+}
+
+// Increment moves the context to the next line (if available).
+func (c *context) Increment() {
+	if c.currentLine == "" && c.remainingLines == "" {
+		return
+	}
+
+	lines := strings.SplitN(c.remainingLines, "\n", 2)
+	c.currentLine = lines[0]
+	if len(lines) == 2 {
+		c.remainingLines = lines[1]
+	} else {
+		c.remainingLines = ""
+	}
+	c.lineNumber++
+}
+
+// NewContext creates a context from the provided data. It strips out all
+// carriage returns and moves to the first line (if available).
+func NewContext(content []byte) context {
+	c := context{remainingLines: strings.Replace(string(content), "\r", "", -1)}
+	c.Increment()
+	return c
+}