--- /dev/null
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+package main
+
+// This program generates table.go and table_test.go based on the authoritative
+// public suffix list at https://publicsuffix.org/list/effective_tld_names.dat
+//
+// The version is derived from
+// https://api.github.com/repos/publicsuffix/list/commits?path=public_suffix_list.dat
+// and a human-readable form is at
+// https://github.com/publicsuffix/list/commits/master/public_suffix_list.dat
+//
+// To fetch a particular git revision, such as 5c70ccd250, pass
+// -url "https://raw.githubusercontent.com/publicsuffix/list/5c70ccd250/public_suffix_list.dat"
+// and -version "an explicit version string".
+
+import (
+ "bufio"
+ "bytes"
+ "flag"
+ "fmt"
+ "go/format"
+ "io"
+ "io/ioutil"
+ "net/http"
+ "os"
+ "regexp"
+ "sort"
+ "strings"
+
+ "golang.org/x/net/idna"
+)
+
+const (
+ // These sum of these four values must be no greater than 32.
+ nodesBitsChildren = 9
+ nodesBitsICANN = 1
+ nodesBitsTextOffset = 15
+ nodesBitsTextLength = 6
+
+ // These sum of these four values must be no greater than 32.
+ childrenBitsWildcard = 1
+ childrenBitsNodeType = 2
+ childrenBitsHi = 14
+ childrenBitsLo = 14
+)
+
+var (
+ maxChildren int
+ maxTextOffset int
+ maxTextLength int
+ maxHi uint32
+ maxLo uint32
+)
+
+func max(a, b int) int {
+ if a < b {
+ return b
+ }
+ return a
+}
+
+func u32max(a, b uint32) uint32 {
+ if a < b {
+ return b
+ }
+ return a
+}
+
+const (
+ nodeTypeNormal = 0
+ nodeTypeException = 1
+ nodeTypeParentOnly = 2
+ numNodeType = 3
+)
+
+func nodeTypeStr(n int) string {
+ switch n {
+ case nodeTypeNormal:
+ return "+"
+ case nodeTypeException:
+ return "!"
+ case nodeTypeParentOnly:
+ return "o"
+ }
+ panic("unreachable")
+}
+
+const (
+ defaultURL = "https://publicsuffix.org/list/effective_tld_names.dat"
+ gitCommitURL = "https://api.github.com/repos/publicsuffix/list/commits?path=public_suffix_list.dat"
+)
+
+var (
+ labelEncoding = map[string]uint32{}
+ labelsList = []string{}
+ labelsMap = map[string]bool{}
+ rules = []string{}
+
+ // validSuffixRE is used to check that the entries in the public suffix
+ // list are in canonical form (after Punycode encoding). Specifically,
+ // capital letters are not allowed.
+ validSuffixRE = regexp.MustCompile(`^[a-z0-9_\!\*\-\.]+$`)
+
+ shaRE = regexp.MustCompile(`"sha":"([^"]+)"`)
+ dateRE = regexp.MustCompile(`"committer":{[^{]+"date":"([^"]+)"`)
+
+ comments = flag.Bool("comments", false, "generate table.go comments, for debugging")
+ subset = flag.Bool("subset", false, "generate only a subset of the full table, for debugging")
+ url = flag.String("url", defaultURL, "URL of the publicsuffix.org list. If empty, stdin is read instead")
+ v = flag.Bool("v", false, "verbose output (to stderr)")
+ version = flag.String("version", "", "the effective_tld_names.dat version")
+)
+
+func main() {
+ if err := main1(); err != nil {
+ fmt.Fprintln(os.Stderr, err)
+ os.Exit(1)
+ }
+}
+
+func main1() error {
+ flag.Parse()
+ if nodesBitsTextLength+nodesBitsTextOffset+nodesBitsICANN+nodesBitsChildren > 32 {
+ return fmt.Errorf("not enough bits to encode the nodes table")
+ }
+ if childrenBitsLo+childrenBitsHi+childrenBitsNodeType+childrenBitsWildcard > 32 {
+ return fmt.Errorf("not enough bits to encode the children table")
+ }
+ if *version == "" {
+ if *url != defaultURL {
+ return fmt.Errorf("-version was not specified, and the -url is not the default one")
+ }
+ sha, date, err := gitCommit()
+ if err != nil {
+ return err
+ }
+ *version = fmt.Sprintf("publicsuffix.org's public_suffix_list.dat, git revision %s (%s)", sha, date)
+ }
+ var r io.Reader = os.Stdin
+ if *url != "" {
+ res, err := http.Get(*url)
+ if err != nil {
+ return err
+ }
+ if res.StatusCode != http.StatusOK {
+ return fmt.Errorf("bad GET status for %s: %d", *url, res.Status)
+ }
+ r = res.Body
+ defer res.Body.Close()
+ }
+
+ var root node
+ icann := false
+ br := bufio.NewReader(r)
+ for {
+ s, err := br.ReadString('\n')
+ if err != nil {
+ if err == io.EOF {
+ break
+ }
+ return err
+ }
+ s = strings.TrimSpace(s)
+ if strings.Contains(s, "BEGIN ICANN DOMAINS") {
+ icann = true
+ continue
+ }
+ if strings.Contains(s, "END ICANN DOMAINS") {
+ icann = false
+ continue
+ }
+ if s == "" || strings.HasPrefix(s, "//") {
+ continue
+ }
+ s, err = idna.ToASCII(s)
+ if err != nil {
+ return err
+ }
+ if !validSuffixRE.MatchString(s) {
+ return fmt.Errorf("bad publicsuffix.org list data: %q", s)
+ }
+
+ if *subset {
+ switch {
+ case s == "ac.jp" || strings.HasSuffix(s, ".ac.jp"):
+ case s == "ak.us" || strings.HasSuffix(s, ".ak.us"):
+ case s == "ao" || strings.HasSuffix(s, ".ao"):
+ case s == "ar" || strings.HasSuffix(s, ".ar"):
+ case s == "arpa" || strings.HasSuffix(s, ".arpa"):
+ case s == "cy" || strings.HasSuffix(s, ".cy"):
+ case s == "dyndns.org" || strings.HasSuffix(s, ".dyndns.org"):
+ case s == "jp":
+ case s == "kobe.jp" || strings.HasSuffix(s, ".kobe.jp"):
+ case s == "kyoto.jp" || strings.HasSuffix(s, ".kyoto.jp"):
+ case s == "om" || strings.HasSuffix(s, ".om"):
+ case s == "uk" || strings.HasSuffix(s, ".uk"):
+ case s == "uk.com" || strings.HasSuffix(s, ".uk.com"):
+ case s == "tw" || strings.HasSuffix(s, ".tw"):
+ case s == "zw" || strings.HasSuffix(s, ".zw"):
+ case s == "xn--p1ai" || strings.HasSuffix(s, ".xn--p1ai"):
+ // xn--p1ai is Russian-Cyrillic "рф".
+ default:
+ continue
+ }
+ }
+
+ rules = append(rules, s)
+
+ nt, wildcard := nodeTypeNormal, false
+ switch {
+ case strings.HasPrefix(s, "*."):
+ s, nt = s[2:], nodeTypeParentOnly
+ wildcard = true
+ case strings.HasPrefix(s, "!"):
+ s, nt = s[1:], nodeTypeException
+ }
+ labels := strings.Split(s, ".")
+ for n, i := &root, len(labels)-1; i >= 0; i-- {
+ label := labels[i]
+ n = n.child(label)
+ if i == 0 {
+ if nt != nodeTypeParentOnly && n.nodeType == nodeTypeParentOnly {
+ n.nodeType = nt
+ }
+ n.icann = n.icann && icann
+ n.wildcard = n.wildcard || wildcard
+ }
+ labelsMap[label] = true
+ }
+ }
+ labelsList = make([]string, 0, len(labelsMap))
+ for label := range labelsMap {
+ labelsList = append(labelsList, label)
+ }
+ sort.Strings(labelsList)
+
+ if err := generate(printReal, &root, "table.go"); err != nil {
+ return err
+ }
+ if err := generate(printTest, &root, "table_test.go"); err != nil {
+ return err
+ }
+ return nil
+}
+
+func generate(p func(io.Writer, *node) error, root *node, filename string) error {
+ buf := new(bytes.Buffer)
+ if err := p(buf, root); err != nil {
+ return err
+ }
+ b, err := format.Source(buf.Bytes())
+ if err != nil {
+ return err
+ }
+ return ioutil.WriteFile(filename, b, 0644)
+}
+
+func gitCommit() (sha, date string, retErr error) {
+ res, err := http.Get(gitCommitURL)
+ if err != nil {
+ return "", "", err
+ }
+ if res.StatusCode != http.StatusOK {
+ return "", "", fmt.Errorf("bad GET status for %s: %d", gitCommitURL, res.Status)
+ }
+ defer res.Body.Close()
+ b, err := ioutil.ReadAll(res.Body)
+ if err != nil {
+ return "", "", err
+ }
+ if m := shaRE.FindSubmatch(b); m != nil {
+ sha = string(m[1])
+ }
+ if m := dateRE.FindSubmatch(b); m != nil {
+ date = string(m[1])
+ }
+ if sha == "" || date == "" {
+ retErr = fmt.Errorf("could not find commit SHA and date in %s", gitCommitURL)
+ }
+ return sha, date, retErr
+}
+
+func printTest(w io.Writer, n *node) error {
+ fmt.Fprintf(w, "// generated by go run gen.go; DO NOT EDIT\n\n")
+ fmt.Fprintf(w, "package publicsuffix\n\nvar rules = [...]string{\n")
+ for _, rule := range rules {
+ fmt.Fprintf(w, "%q,\n", rule)
+ }
+ fmt.Fprintf(w, "}\n\nvar nodeLabels = [...]string{\n")
+ if err := n.walk(w, printNodeLabel); err != nil {
+ return err
+ }
+ fmt.Fprintf(w, "}\n")
+ return nil
+}
+
+func printReal(w io.Writer, n *node) error {
+ const header = `// generated by go run gen.go; DO NOT EDIT
+
+package publicsuffix
+
+const version = %q
+
+const (
+ nodesBitsChildren = %d
+ nodesBitsICANN = %d
+ nodesBitsTextOffset = %d
+ nodesBitsTextLength = %d
+
+ childrenBitsWildcard = %d
+ childrenBitsNodeType = %d
+ childrenBitsHi = %d
+ childrenBitsLo = %d
+)
+
+const (
+ nodeTypeNormal = %d
+ nodeTypeException = %d
+ nodeTypeParentOnly = %d
+)
+
+// numTLD is the number of top level domains.
+const numTLD = %d
+
+`
+ fmt.Fprintf(w, header, *version,
+ nodesBitsChildren, nodesBitsICANN, nodesBitsTextOffset, nodesBitsTextLength,
+ childrenBitsWildcard, childrenBitsNodeType, childrenBitsHi, childrenBitsLo,
+ nodeTypeNormal, nodeTypeException, nodeTypeParentOnly, len(n.children))
+
+ text := combineText(labelsList)
+ if text == "" {
+ return fmt.Errorf("internal error: makeText returned no text")
+ }
+ for _, label := range labelsList {
+ offset, length := strings.Index(text, label), len(label)
+ if offset < 0 {
+ return fmt.Errorf("internal error: could not find %q in text %q", label, text)
+ }
+ maxTextOffset, maxTextLength = max(maxTextOffset, offset), max(maxTextLength, length)
+ if offset >= 1<<nodesBitsTextOffset {
+ return fmt.Errorf("text offset %d is too large, or nodeBitsTextOffset is too small", offset)
+ }
+ if length >= 1<<nodesBitsTextLength {
+ return fmt.Errorf("text length %d is too large, or nodeBitsTextLength is too small", length)
+ }
+ labelEncoding[label] = uint32(offset)<<nodesBitsTextLength | uint32(length)
+ }
+ fmt.Fprintf(w, "// Text is the combined text of all labels.\nconst text = ")
+ for len(text) > 0 {
+ n, plus := len(text), ""
+ if n > 64 {
+ n, plus = 64, " +"
+ }
+ fmt.Fprintf(w, "%q%s\n", text[:n], plus)
+ text = text[n:]
+ }
+
+ if err := n.walk(w, assignIndexes); err != nil {
+ return err
+ }
+
+ fmt.Fprintf(w, `
+
+// nodes is the list of nodes. Each node is represented as a uint32, which
+// encodes the node's children, wildcard bit and node type (as an index into
+// the children array), ICANN bit and text.
+//
+// If the table was generated with the -comments flag, there is a //-comment
+// after each node's data. In it is the nodes-array indexes of the children,
+// formatted as (n0x1234-n0x1256), with * denoting the wildcard bit. The
+// nodeType is printed as + for normal, ! for exception, and o for parent-only
+// nodes that have children but don't match a domain label in their own right.
+// An I denotes an ICANN domain.
+//
+// The layout within the uint32, from MSB to LSB, is:
+// [%2d bits] unused
+// [%2d bits] children index
+// [%2d bits] ICANN bit
+// [%2d bits] text index
+// [%2d bits] text length
+var nodes = [...]uint32{
+`,
+ 32-nodesBitsChildren-nodesBitsICANN-nodesBitsTextOffset-nodesBitsTextLength,
+ nodesBitsChildren, nodesBitsICANN, nodesBitsTextOffset, nodesBitsTextLength)
+ if err := n.walk(w, printNode); err != nil {
+ return err
+ }
+ fmt.Fprintf(w, `}
+
+// children is the list of nodes' children, the parent's wildcard bit and the
+// parent's node type. If a node has no children then their children index
+// will be in the range [0, 6), depending on the wildcard bit and node type.
+//
+// The layout within the uint32, from MSB to LSB, is:
+// [%2d bits] unused
+// [%2d bits] wildcard bit
+// [%2d bits] node type
+// [%2d bits] high nodes index (exclusive) of children
+// [%2d bits] low nodes index (inclusive) of children
+var children=[...]uint32{
+`,
+ 32-childrenBitsWildcard-childrenBitsNodeType-childrenBitsHi-childrenBitsLo,
+ childrenBitsWildcard, childrenBitsNodeType, childrenBitsHi, childrenBitsLo)
+ for i, c := range childrenEncoding {
+ s := "---------------"
+ lo := c & (1<<childrenBitsLo - 1)
+ hi := (c >> childrenBitsLo) & (1<<childrenBitsHi - 1)
+ if lo != hi {
+ s = fmt.Sprintf("n0x%04x-n0x%04x", lo, hi)
+ }
+ nodeType := int(c>>(childrenBitsLo+childrenBitsHi)) & (1<<childrenBitsNodeType - 1)
+ wildcard := c>>(childrenBitsLo+childrenBitsHi+childrenBitsNodeType) != 0
+ if *comments {
+ fmt.Fprintf(w, "0x%08x, // c0x%04x (%s)%s %s\n",
+ c, i, s, wildcardStr(wildcard), nodeTypeStr(nodeType))
+ } else {
+ fmt.Fprintf(w, "0x%x,\n", c)
+ }
+ }
+ fmt.Fprintf(w, "}\n\n")
+ fmt.Fprintf(w, "// max children %d (capacity %d)\n", maxChildren, 1<<nodesBitsChildren-1)
+ fmt.Fprintf(w, "// max text offset %d (capacity %d)\n", maxTextOffset, 1<<nodesBitsTextOffset-1)
+ fmt.Fprintf(w, "// max text length %d (capacity %d)\n", maxTextLength, 1<<nodesBitsTextLength-1)
+ fmt.Fprintf(w, "// max hi %d (capacity %d)\n", maxHi, 1<<childrenBitsHi-1)
+ fmt.Fprintf(w, "// max lo %d (capacity %d)\n", maxLo, 1<<childrenBitsLo-1)
+ return nil
+}
+
+type node struct {
+ label string
+ nodeType int
+ icann bool
+ wildcard bool
+ // nodesIndex and childrenIndex are the index of this node in the nodes
+ // and the index of its children offset/length in the children arrays.
+ nodesIndex, childrenIndex int
+ // firstChild is the index of this node's first child, or zero if this
+ // node has no children.
+ firstChild int
+ // children are the node's children, in strictly increasing node label order.
+ children []*node
+}
+
+func (n *node) walk(w io.Writer, f func(w1 io.Writer, n1 *node) error) error {
+ if err := f(w, n); err != nil {
+ return err
+ }
+ for _, c := range n.children {
+ if err := c.walk(w, f); err != nil {
+ return err
+ }
+ }
+ return nil
+}
+
+// child returns the child of n with the given label. The child is created if
+// it did not exist beforehand.
+func (n *node) child(label string) *node {
+ for _, c := range n.children {
+ if c.label == label {
+ return c
+ }
+ }
+ c := &node{
+ label: label,
+ nodeType: nodeTypeParentOnly,
+ icann: true,
+ }
+ n.children = append(n.children, c)
+ sort.Sort(byLabel(n.children))
+ return c
+}
+
+type byLabel []*node
+
+func (b byLabel) Len() int { return len(b) }
+func (b byLabel) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
+func (b byLabel) Less(i, j int) bool { return b[i].label < b[j].label }
+
+var nextNodesIndex int
+
+// childrenEncoding are the encoded entries in the generated children array.
+// All these pre-defined entries have no children.
+var childrenEncoding = []uint32{
+ 0 << (childrenBitsLo + childrenBitsHi), // Without wildcard bit, nodeTypeNormal.
+ 1 << (childrenBitsLo + childrenBitsHi), // Without wildcard bit, nodeTypeException.
+ 2 << (childrenBitsLo + childrenBitsHi), // Without wildcard bit, nodeTypeParentOnly.
+ 4 << (childrenBitsLo + childrenBitsHi), // With wildcard bit, nodeTypeNormal.
+ 5 << (childrenBitsLo + childrenBitsHi), // With wildcard bit, nodeTypeException.
+ 6 << (childrenBitsLo + childrenBitsHi), // With wildcard bit, nodeTypeParentOnly.
+}
+
+var firstCallToAssignIndexes = true
+
+func assignIndexes(w io.Writer, n *node) error {
+ if len(n.children) != 0 {
+ // Assign nodesIndex.
+ n.firstChild = nextNodesIndex
+ for _, c := range n.children {
+ c.nodesIndex = nextNodesIndex
+ nextNodesIndex++
+ }
+
+ // The root node's children is implicit.
+ if firstCallToAssignIndexes {
+ firstCallToAssignIndexes = false
+ return nil
+ }
+
+ // Assign childrenIndex.
+ maxChildren = max(maxChildren, len(childrenEncoding))
+ if len(childrenEncoding) >= 1<<nodesBitsChildren {
+ return fmt.Errorf("children table size %d is too large, or nodeBitsChildren is too small", len(childrenEncoding))
+ }
+ n.childrenIndex = len(childrenEncoding)
+ lo := uint32(n.firstChild)
+ hi := lo + uint32(len(n.children))
+ maxLo, maxHi = u32max(maxLo, lo), u32max(maxHi, hi)
+ if lo >= 1<<childrenBitsLo {
+ return fmt.Errorf("children lo %d is too large, or childrenBitsLo is too small", lo)
+ }
+ if hi >= 1<<childrenBitsHi {
+ return fmt.Errorf("children hi %d is too large, or childrenBitsHi is too small", hi)
+ }
+ enc := hi<<childrenBitsLo | lo
+ enc |= uint32(n.nodeType) << (childrenBitsLo + childrenBitsHi)
+ if n.wildcard {
+ enc |= 1 << (childrenBitsLo + childrenBitsHi + childrenBitsNodeType)
+ }
+ childrenEncoding = append(childrenEncoding, enc)
+ } else {
+ n.childrenIndex = n.nodeType
+ if n.wildcard {
+ n.childrenIndex += numNodeType
+ }
+ }
+ return nil
+}
+
+func printNode(w io.Writer, n *node) error {
+ for _, c := range n.children {
+ s := "---------------"
+ if len(c.children) != 0 {
+ s = fmt.Sprintf("n0x%04x-n0x%04x", c.firstChild, c.firstChild+len(c.children))
+ }
+ encoding := labelEncoding[c.label]
+ if c.icann {
+ encoding |= 1 << (nodesBitsTextLength + nodesBitsTextOffset)
+ }
+ encoding |= uint32(c.childrenIndex) << (nodesBitsTextLength + nodesBitsTextOffset + nodesBitsICANN)
+ if *comments {
+ fmt.Fprintf(w, "0x%08x, // n0x%04x c0x%04x (%s)%s %s %s %s\n",
+ encoding, c.nodesIndex, c.childrenIndex, s, wildcardStr(c.wildcard),
+ nodeTypeStr(c.nodeType), icannStr(c.icann), c.label,
+ )
+ } else {
+ fmt.Fprintf(w, "0x%x,\n", encoding)
+ }
+ }
+ return nil
+}
+
+func printNodeLabel(w io.Writer, n *node) error {
+ for _, c := range n.children {
+ fmt.Fprintf(w, "%q,\n", c.label)
+ }
+ return nil
+}
+
+func icannStr(icann bool) string {
+ if icann {
+ return "I"
+ }
+ return " "
+}
+
+func wildcardStr(wildcard bool) string {
+ if wildcard {
+ return "*"
+ }
+ return " "
+}
+
+// combineText combines all the strings in labelsList to form one giant string.
+// Overlapping strings will be merged: "arpa" and "parliament" could yield
+// "arparliament".
+func combineText(labelsList []string) string {
+ beforeLength := 0
+ for _, s := range labelsList {
+ beforeLength += len(s)
+ }
+
+ text := crush(removeSubstrings(labelsList))
+ if *v {
+ fmt.Fprintf(os.Stderr, "crushed %d bytes to become %d bytes\n", beforeLength, len(text))
+ }
+ return text
+}
+
+type byLength []string
+
+func (s byLength) Len() int { return len(s) }
+func (s byLength) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s byLength) Less(i, j int) bool { return len(s[i]) < len(s[j]) }
+
+// removeSubstrings returns a copy of its input with any strings removed
+// that are substrings of other provided strings.
+func removeSubstrings(input []string) []string {
+ // Make a copy of input.
+ ss := append(make([]string, 0, len(input)), input...)
+ sort.Sort(byLength(ss))
+
+ for i, shortString := range ss {
+ // For each string, only consider strings higher than it in sort order, i.e.
+ // of equal length or greater.
+ for _, longString := range ss[i+1:] {
+ if strings.Contains(longString, shortString) {
+ ss[i] = ""
+ break
+ }
+ }
+ }
+
+ // Remove the empty strings.
+ sort.Strings(ss)
+ for len(ss) > 0 && ss[0] == "" {
+ ss = ss[1:]
+ }
+ return ss
+}
+
+// crush combines a list of strings, taking advantage of overlaps. It returns a
+// single string that contains each input string as a substring.
+func crush(ss []string) string {
+ maxLabelLen := 0
+ for _, s := range ss {
+ if maxLabelLen < len(s) {
+ maxLabelLen = len(s)
+ }
+ }
+
+ for prefixLen := maxLabelLen; prefixLen > 0; prefixLen-- {
+ prefixes := makePrefixMap(ss, prefixLen)
+ for i, s := range ss {
+ if len(s) <= prefixLen {
+ continue
+ }
+ mergeLabel(ss, i, prefixLen, prefixes)
+ }
+ }
+
+ return strings.Join(ss, "")
+}
+
+// mergeLabel merges the label at ss[i] with the first available matching label
+// in prefixMap, where the last "prefixLen" characters in ss[i] match the first
+// "prefixLen" characters in the matching label.
+// It will merge ss[i] repeatedly until no more matches are available.
+// All matching labels merged into ss[i] are replaced by "".
+func mergeLabel(ss []string, i, prefixLen int, prefixes prefixMap) {
+ s := ss[i]
+ suffix := s[len(s)-prefixLen:]
+ for _, j := range prefixes[suffix] {
+ // Empty strings mean "already used." Also avoid merging with self.
+ if ss[j] == "" || i == j {
+ continue
+ }
+ if *v {
+ fmt.Fprintf(os.Stderr, "%d-length overlap at (%4d,%4d): %q and %q share %q\n",
+ prefixLen, i, j, ss[i], ss[j], suffix)
+ }
+ ss[i] += ss[j][prefixLen:]
+ ss[j] = ""
+ // ss[i] has a new suffix, so merge again if possible.
+ // Note: we only have to merge again at the same prefix length. Shorter
+ // prefix lengths will be handled in the next iteration of crush's for loop.
+ // Can there be matches for longer prefix lengths, introduced by the merge?
+ // I believe that any such matches would by necessity have been eliminated
+ // during substring removal or merged at a higher prefix length. For
+ // instance, in crush("abc", "cde", "bcdef"), combining "abc" and "cde"
+ // would yield "abcde", which could be merged with "bcdef." However, in
+ // practice "cde" would already have been elimintated by removeSubstrings.
+ mergeLabel(ss, i, prefixLen, prefixes)
+ return
+ }
+}
+
+// prefixMap maps from a prefix to a list of strings containing that prefix. The
+// list of strings is represented as indexes into a slice of strings stored
+// elsewhere.
+type prefixMap map[string][]int
+
+// makePrefixMap constructs a prefixMap from a slice of strings.
+func makePrefixMap(ss []string, prefixLen int) prefixMap {
+ prefixes := make(prefixMap)
+ for i, s := range ss {
+ // We use < rather than <= because if a label matches on a prefix equal to
+ // its full length, that's actually a substring match handled by
+ // removeSubstrings.
+ if prefixLen < len(s) {
+ prefix := s[:prefixLen]
+ prefixes[prefix] = append(prefixes[prefix], i)
+ }
+ }
+
+ return prefixes
+}
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