matcher.go

package routing

import (
	"fmt"
	"net/http"
	"regexp"
	"sort"

	"github.com/dimfeld/httppath"
	"github.com/zalando/pathmux"
)

type leafRequestMatcher struct {
	r    *http.Request
	path string
}

func (m *leafRequestMatcher) Match(value interface{}) (bool, interface{}) {
	v, ok := value.(*pathMatcher)
	if !ok {
		return false, nil
	}

	l := matchLeaves(v.leaves, m.r, m.path)

	return l != nil, l
}

type leafMatcher struct {
	method        string
	hostRxs       []*regexp.Regexp
	pathRxs       []*regexp.Regexp
	headersExact  map[string]string
	headersRegexp map[string][]*regexp.Regexp
	predicates    []Predicate
	route         *Route
}

type leafMatchers []*leafMatcher

func leafWeight(l *leafMatcher) int {
	w := 0

	if l.method != "" {
		w++
	}

	w += len(l.hostRxs)
	w += len(l.pathRxs)
	w += len(l.headersExact)
	w += len(l.headersRegexp)
	w += len(l.predicates)

	return w
}

// Sorting of leaf matchers:
func (ls leafMatchers) Len() int           { return len(ls) }
func (ls leafMatchers) Swap(i, j int)      { ls[i], ls[j] = ls[j], ls[i] }
func (ls leafMatchers) Less(i, j int) bool { return leafWeight(ls[i]) > leafWeight(ls[j]) }

type pathMatcher struct {
	leaves            leafMatchers
	freeWildcardParam string
}

// root structure representing the routing tree.
type matcher struct {
	paths           *pathmux.Tree
	rootLeaves      leafMatchers
	matchingOptions MatchingOptions
}

// An error created if a route definition cannot be processed.
type definitionError struct {
	Id       string
	Index    int
	Original error
}

func (err *definitionError) Error() string {
	if err.Index < 0 {
		return err.Original.Error()
	}

	return fmt.Sprintf("%s [%d]: %v", err.Id, err.Index, err.Original)
}

// rx identifying the 'free form' wildcards at the end of the paths
var freeWildcardRx = regexp.MustCompile("/[*][^/]+$")

// compiles all rxs or fails
func compileRxs(exps []string) ([]*regexp.Regexp, error) {
	rxs := make([]*regexp.Regexp, len(exps))
	for i, exp := range exps {
		rx, err := regexp.Compile(exp)
		if err != nil {
			return nil, err
		}

		rxs[i] = rx
	}

	return rxs, nil
}

// canonicalizes the keys of the header conditions
func canonicalizeHeaders(h map[string]string) map[string]string {
	ch := make(map[string]string)
	for k, v := range h {
		ch[http.CanonicalHeaderKey(k)] = v
	}

	return ch
}

// canonicalizes the keys of the header regexp conditions
func canonicalizeHeaderRegexps(hrx map[string][]*regexp.Regexp) map[string][]*regexp.Regexp {
	chrx := make(map[string][]*regexp.Regexp)
	for k, v := range hrx {
		chrx[http.CanonicalHeaderKey(k)] = v
	}

	return chrx
}

// creates a new leaf matcher. preprocesses the
// Host, PathRegexp, Header and HeaderRegexp
// conditions.
func newLeaf(r *Route) (*leafMatcher, error) {
	hostRxs, err := compileRxs(r.HostRegexps)
	if err != nil {
		return nil, err
	}

	pathRxs, err := compileRxs(r.PathRegexps)
	if err != nil {
		return nil, err
	}

	headerExps := r.HeaderRegexps
	allHeaderRxs := make(map[string][]*regexp.Regexp)
	for k, exps := range headerExps {
		headerRxs, err := compileRxs(exps)
		if err != nil {
			return nil, err
		}

		allHeaderRxs[k] = headerRxs
	}

	return &leafMatcher{
		method:        r.Method,
		hostRxs:       hostRxs,
		pathRxs:       pathRxs,
		headersExact:  canonicalizeHeaders(r.Headers),
		headersRegexp: canonicalizeHeaderRegexps(allHeaderRxs),
		predicates:    r.Predicates,
		route:         r}, nil
}

// returns the free form wildcard parameter of a path
func freeWildcardParam(path string) string {
	param := freeWildcardRx.FindString(path)
	if param == "" {
		return ""
	}

	// clip '/*' and return only the name
	return param[2:]
}

func cleanPath(path string, o MatchingOptions) string {
	path = httppath.Clean(path)
	if o.ignoreTrailingSlash() && len(path) > 1 && path[len(path)-1] == '/' {
		path = path[:len(path)-1]
	}

	return path
}

// add all required tree entries for a subtree with patching the path and
// the wildcard name if required
func addSubtreeMatcher(pathTree *pathmux.Tree, path string, m *pathMatcher) error {
	// if has named free wildcard, use its name and take the path only
	// otherwise set the free wildcard name by convention to "*", as in "/foo/**"
	fwp := m.freeWildcardParam
	if fwp == "" {
		fwp = "*"
		m.freeWildcardParam = "*"
	} else {
		path = path[:len(path)-len(fwp)-1]
	}

	// if ends with '/' then set one without
	// otherwise set one with '/'
	//
	// the subtree will be represented as "/foo/**" or "/foo/*wildcard"
	var pathAlt, pathSubtree string
	if path[len(path)-1] == '/' {
		pathAlt = path[:len(path)-1]
		pathSubtree = path + "*" + fwp
	} else {
		pathAlt = path + "/"
		pathSubtree = pathAlt + "*" + fwp
	}

	if err := pathTree.Add(path, m); err != nil {
		return err
	}

	if pathAlt != "" {
		if err := pathTree.Add(pathAlt, m); err != nil {
			return err
		}
	}

	return pathTree.Add(pathSubtree, m)
}

// add each path matcher to the path tree. If a matcher is a subtree, add it with the
// additional paths.
func addTreeMatchers(pathTree *pathmux.Tree, matchers map[string]*pathMatcher, subtree bool) []*definitionError {
	var errors []*definitionError
	for p, m := range matchers {

		// sort leaves during construction time, based on their priority
		sort.Stable(m.leaves)

		if p == "" {
			p = "/"
		}

		if subtree {
			if err := addSubtreeMatcher(pathTree, p, m); err != nil {
				errors = append(errors, &definitionError{Index: -1, Original: err})
			}
		} else {
			if err := pathTree.Add(p, m); err != nil {
				errors = append(errors, &definitionError{Index: -1, Original: err})
				continue
			}
		}
	}

	return errors
}

// constructs a matcher based on the provided definitions.
//
// If `ignoreTrailingSlash` is true, the matcher handles
// paths with or without a trailing slash equally.
//
// It constructs the route definition into a trie structure
// based on their path condition, if any, and puts the routes
// with the same path condition into a leaf matcher structure
// where they get evaluated after the leaf was matched based
// on the rest of the conditions so that most strict route
// definition matches first.
func newMatcher(rs []*Route, o MatchingOptions) (*matcher, []*definitionError) {
	var (
		errors     []*definitionError
		rootLeaves leafMatchers
	)

	pathMatchers := make(map[string]*pathMatcher)
	subtreeMatchers := make(map[string]*pathMatcher)

	for i, r := range rs {
		l, err := newLeaf(r)
		if err != nil {
			errors = append(errors, &definitionError{r.Id, i, err})
			continue
		}

		p := r.path
		m := pathMatchers

		if r.pathSubtree != "" {
			p = r.pathSubtree
			m = subtreeMatchers
		}

		if p == "" {
			rootLeaves = append(rootLeaves, l)
			continue
		}

		// normalize path
		// in case ignoring trailing slashes, store and match all paths
		// without the trailing slash
		p = cleanPath(p, o)

		pm := m[p]
		if pm == nil {
			pm = &pathMatcher{freeWildcardParam: freeWildcardParam(p)}
			m[p] = pm
		}

		pm.leaves = append(pm.leaves, l)
	}

	pathTree := &pathmux.Tree{}
	errors = append(errors, addTreeMatchers(pathTree, pathMatchers, false)...)
	errors = append(errors, addTreeMatchers(pathTree, subtreeMatchers, true)...)

	// sort root leaves during construction time, based on their priority
	sort.Stable(rootLeaves)

	return &matcher{pathTree, rootLeaves, o}, errors
}

// matches a path in the path trie structure.
func matchPathTree(tree *pathmux.Tree, path string, lrm *leafRequestMatcher) (map[string]string, *leafMatcher) {
	v, params, value := tree.LookupMatcher(path, lrm)
	if v == nil {
		return nil, nil
	}

	// prepend slash in case of free form wildcards path segments (`/*name`),
	pm := v.(*pathMatcher)
	if pm.freeWildcardParam != "" {
		freeParam := params[pm.freeWildcardParam]
		freeParam = "/" + freeParam
		params[pm.freeWildcardParam] = freeParam
	}

	return params, value.(*leafMatcher)
}

// matches the path regexp conditions in a leaf matcher.
func matchRegexps(rxs []*regexp.Regexp, s string) bool {
	for _, rx := range rxs {
		if !rx.MatchString(s) {
			return false
		}
	}

	return true
}

// matches a set of request headers to a fix and regexp header condition
func matchHeader(h http.Header, key string, check func(string) bool) bool {
	vals, has := h[key]
	if !has {
		return false
	}

	for _, val := range vals {
		if check(val) {
			return true
		}
	}

	return false
}

// matches a set of request headers to the fix and regexp header conditions
func matchHeaders(exact map[string]string, hrxs map[string][]*regexp.Regexp, h http.Header) bool {
	// todo: would be better to allow any that match, even if slower

	for k, v := range exact {
		if !matchHeader(h, k, func(val string) bool { return val == v }) {
			return false
		}
	}

	for k, rxs := range hrxs {
		for _, rx := range rxs {
			if !matchHeader(h, k, rx.MatchString) {
				return false
			}
		}
	}

	return true
}

// check if all defined custom predicates are matched
func matchPredicates(cps []Predicate, req *http.Request) bool {
	for _, cp := range cps {
		if !cp.Match(req) {
			return false
		}
	}

	return true
}

// matches a request to the conditions in a leaf matcher
func matchLeaf(l *leafMatcher, req *http.Request, path string) bool {
	if l.method != "" && l.method != req.Method {
		return false
	}

	if !matchRegexps(l.hostRxs, req.Host) {
		return false
	}

	if !matchRegexps(l.pathRxs, path) {
		return false
	}

	if !matchHeaders(l.headersExact, l.headersRegexp, req.Header) {
		return false
	}

	if !matchPredicates(l.predicates, req) {
		return false
	}

	return true
}

// matches a request to a set of leaf matchers
func matchLeaves(leaves leafMatchers, req *http.Request, path string) *leafMatcher {
	for _, l := range leaves {
		if matchLeaf(l, req, path) {
			return l
		}
	}

	return nil
}

// tries to match a request against the available definitions. If a match is found,
// returns the associated value, and the wildcard parameters from the path definition,
// if any.
func (m *matcher) match(r *http.Request) (*Route, map[string]string) {
	// normalize path before matching
	// in case ignoring trailing slashes, match without the trailing slash
	path := cleanPath(r.URL.Path, m.matchingOptions)
	lrm := &leafRequestMatcher{r, path}

	// first match fixed and wildcard paths
	params, l := matchPathTree(m.paths, path, lrm)

	if l != nil {
		return l.route, params
	}

	// if no path match, match root leaves for other conditions
	l = matchLeaves(m.rootLeaves, r, path)
	if l != nil {
		return l.route, nil
	}

	return nil, nil
}