Adds a link fixer/checker to mungedocs.

Links that don't work yet can be prefixed with "TODO:" to avoid the check.

cmd/mungedocs/links.go

@@ -0,0 +1,143 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 main
+
+import (
+	"fmt"
+	"net/url"
+	"os"
+	"path"
+	"regexp"
+	"strings"
+)
+
+var (
+	// Finds markdown links of the form [foo](bar "alt-text").
+	linkRE = regexp.MustCompile(`\[([^]]*)\]\(([^)]*)\)`)
+	// Splits the link target into link target and alt-text.
+	altTextRE = regexp.MustCompile(`(.*)( ".*")`)
+)
+
+// checkLinks assumes fileBytes has links in markdown syntax, and verifies that
+// any relative links actually point to files that exist.
+func checkLinks(filePath string, fileBytes []byte) ([]byte, error) {
+	dir := path.Dir(filePath)
+	errors := []string{}
+
+	output := linkRE.ReplaceAllFunc(fileBytes, func(in []byte) (out []byte) {
+		match := linkRE.FindSubmatch(in)
+		// match[0] is the entire expression; [1] is the visible text and [2] is the link text.
+		visibleText := string(match[1])
+		linkText := string(match[2])
+		altText := ""
+		if parts := altTextRE.FindStringSubmatch(linkText); parts != nil {
+			linkText = parts[1]
+			altText = parts[2]
+		}
+
+		// clean up some random garbage I found in our docs.
+		linkText = strings.Trim(linkText, " ")
+		linkText = strings.Trim(linkText, "\n")
+		linkText = strings.Trim(linkText, " ")
+
+		u, err := url.Parse(linkText)
+		if err != nil {
+			errors = append(
+				errors,
+				fmt.Sprintf("%v, link %q is unparsable: %v", filePath, linkText, err),
+			)
+			return in
+		}
+
+		if u.Host != "" {
+			// We only care about relative links.
+			return in
+		}
+
+		suggestedVisibleText := visibleText
+		if u.Path != "" && !strings.HasPrefix(linkText, "TODO:") {
+			newPath, targetExists := checkPath(filePath, path.Clean(u.Path))
+			if !targetExists {
+				errors = append(
+					errors,
+					fmt.Sprintf("%v, %q: target not found\n", filePath, linkText),
+				)
+			}
+			u.Path = newPath
+			// Make the visible text show the absolute path if it's
+			// not nested in or beneath the current directory.
+			if strings.HasPrefix(u.Path, "..") {
+				suggestedVisibleText = makeRepoRelative(path.Join(dir, u.Path))
+			} else {
+				suggestedVisibleText = u.Path
+			}
+			if unescaped, err := url.QueryUnescape(u.String()); err != nil {
+				// Remove %28 type stuff, be nice to humans.
+				// And don't fight with the toc generator.
+				linkText = unescaped
+			} else {
+				linkText = u.String()
+			}
+		}
+		// If the current visible text is trying to be a file name, use
+		// the correct file name.
+		if (strings.Contains(visibleText, ".md") || strings.Contains(visibleText, "/")) && !strings.ContainsAny(visibleText, ` '"`+"`") {
+			visibleText = suggestedVisibleText
+		}
+
+		return []byte(fmt.Sprintf("[%s](%s)", visibleText, linkText+altText))
+	})
+	err := error(nil)
+	if len(errors) != 0 {
+		err = fmt.Errorf("%s", strings.Join(errors, "\n"))
+	}
+	return output, err
+}
+
+func makeRepoRelative(path string) string {
+	parts := strings.Split(path, "github.com/GoogleCloudPlatform/kubernetes/")
+	if len(parts) > 1 {
+		// Take out anything that is specific to the local filesystem.
+		return parts[1]
+	}
+	return path
+}
+
+func checkPath(filePath, linkPath string) (newPath string, ok bool) {
+	dir := path.Dir(filePath)
+	if strings.HasPrefix(linkPath, "/") {
+		if !strings.HasPrefix(linkPath, "/GoogleCloudPlatform") {
+			// Any absolute paths that aren't relative to github.com are wrong.
+			// Try to fix.
+			linkPath = linkPath[1:]
+		}
+	}
+
+	newPath = linkPath
+	for i := 0; i < 5; i++ {
+		// The file must exist.
+		target := path.Join(dir, newPath)
+		if info, err := os.Stat(target); err == nil {
+			if info.IsDir() {
+				return newPath + "/", true
+			}
+			return newPath, true
+		}
+		newPath = path.Join("..", newPath)
+	}
+	return linkPath, false
+}