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Poc router stack backtracking (#1791)
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Router: PoC stack based backtracking

Co-authored-by: stffabi <stffabi@users.noreply.github.com>
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@aldas @stffabi
aldas and stffabi authored Mar 2, 2021
1 parent b2444d8 commit 6f9b71c
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Showing 2 changed files with 243 additions and 127 deletions.
194 changes: 77 additions & 117 deletions router.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@ package echo

import (
"net/http"
"strings"
)

type (
Expand Down Expand Up @@ -334,21 +333,48 @@ func (r *Router) Find(method, path string, c Context) {
cn := r.tree // Current node as root

var (
search = path
child *node // Child node
n int // Param counter
nk kind // Next kind
nn *node // Next node
ns string // Next search
pvalues = ctx.pvalues // Use the internal slice so the interface can keep the illusion of a dynamic slice
search = path
searchIndex = 0
n int // Param counter
pvalues = ctx.pvalues // Use the internal slice so the interface can keep the illusion of a dynamic slice
)

// Search order static > param > any
for {
if search == "" {
break
// Backtracking is needed when a dead end (leaf node) is reached in the router tree.
// To backtrack the current node will be changed to the parent node and the next kind for the
// router logic will be returned based on fromKind or kind of the dead end node (static > param > any).
// For example if there is no static node match we should check parent next sibling by kind (param).
// Backtracking itself does not check if there is a next sibling, this is done by the router logic.
backtrackToNextNodeKind := func(fromKind kind) (nextNodeKind kind, valid bool) {
previous := cn
cn = previous.parent
valid = cn != nil

// Next node type by priority
// NOTE: With the current implementation we never backtrack from an `any` route, so `previous.kind` is
// always `static` or `any`
// If this is changed then for any route next kind would be `static` and this statement should be changed
nextNodeKind = previous.kind + 1

if fromKind == skind {
// when backtracking is done from static kind block we did not change search so nothing to restore
return
}

// restore search to value it was before we move to current node we are backtracking from.
if previous.kind == skind {
searchIndex -= len(previous.prefix)
} else {
n--
// for param/any node.prefix value is always `:` so we can not deduce searchIndex from that and must use pValue
// for that index as it would also contain part of path we cut off before moving into node we are backtracking from
searchIndex -= len(pvalues[n])
}
search = path[searchIndex:]
return
}

// Search order static > param > any
for {
pl := 0 // Prefix length
l := 0 // LCP length

Expand All @@ -365,148 +391,82 @@ func (r *Router) Find(method, path string, c Context) {
}
}

if l == pl {
// Continue search
search = search[l:]
// Finish routing if no remaining search and we are on an leaf node
if search == "" && (nn == nil || cn.parent == nil || cn.ppath != "") {
break
}
// Handle special case of trailing slash route with existing any route (see #1526)
if search == "" && path[len(path)-1] == '/' && cn.anyChildren != nil {
goto Any
if l != pl {
// No matching prefix, let's backtrack to the first possible alternative node of the decision path
nk, ok := backtrackToNextNodeKind(skind)
if !ok {
return // No other possibilities on the decision path
} else if nk == pkind {
goto Param
// NOTE: this case (backtracking from static node to previous any node) can not happen by current any matching logic. Any node is end of search currently
//} else if nk == akind {
// goto Any
} else {
// Not found (this should never be possible for static node we are looking currently)
return
}
}

// Attempt to go back up the tree on no matching prefix or no remaining search
if l != pl || search == "" {
if nn == nil { // Issue #1348
return // Not found
}
cn = nn
search = ns
if nk == pkind {
goto Param
} else if nk == akind {
goto Any
}
// The full prefix has matched, remove the prefix from the remaining search
search = search[l:]
searchIndex = searchIndex + l

// Finish routing if no remaining search and we are on an leaf node
if search == "" && cn.ppath != "" {
break
}

// Static node
if child = cn.findStaticChild(search[0]); child != nil {
// Save next
if cn.prefix[len(cn.prefix)-1] == '/' { // Issue #623
nk = pkind
nn = cn
ns = search
if search != "" {
if child := cn.findStaticChild(search[0]); child != nil {
cn = child
continue
}
cn = child
continue
}

Param:
// Param node
if child = cn.paramChildren; child != nil {
// Issue #378
if len(pvalues) == n {
continue
}

// Save next
if cn.prefix[len(cn.prefix)-1] == '/' { // Issue #623
nk = akind
nn = cn
ns = search
}

if child := cn.paramChildren; search != "" && child != nil {
cn = child
i, l := 0, len(search)
for ; i < l && search[i] != '/'; i++ {
}
pvalues[n] = search[:i]
n++
search = search[i:]
searchIndex = searchIndex + i
continue
}

Any:
// Any node
if cn = cn.anyChildren; cn != nil {
if child := cn.anyChildren; child != nil {
// If any node is found, use remaining path for pvalues
cn = child
pvalues[len(cn.pnames)-1] = search
break
}

// No node found, continue at stored next node
// or find nearest "any" route
if nn != nil {
// No next node to go down in routing (issue #954)
// Find nearest "any" route going up the routing tree
search = ns
np := nn.parent
// Consider param route one level up only
if cn = nn.paramChildren; cn != nil {
pos := strings.IndexByte(ns, '/')
if pos == -1 {
// If no slash is remaining in search string set param value
if len(cn.pnames) > 0 {
pvalues[len(cn.pnames)-1] = search
}
break
} else if pos > 0 {
// Otherwise continue route processing with restored next node
cn = nn
nn = nil
ns = ""
goto Param
}
}
// No param route found, try to resolve nearest any route
for {
np = nn.parent
if cn = nn.anyChildren; cn != nil {
break
}
if np == nil {
break // no further parent nodes in tree, abort
}
var str strings.Builder
str.WriteString(nn.prefix)
str.WriteString(search)
search = str.String()
nn = np
}
if cn != nil { // use the found "any" route and update path
pvalues[len(cn.pnames)-1] = search
break
}
// Let's backtrack to the first possible alternative node of the decision path
nk, ok := backtrackToNextNodeKind(akind)
if !ok {
return // No other possibilities on the decision path
} else if nk == pkind {
goto Param
} else if nk == akind {
goto Any
} else {
// Not found
return
}
return // Not found

}

ctx.handler = cn.findHandler(method)
ctx.path = cn.ppath
ctx.pnames = cn.pnames

// NOTE: Slow zone...
if ctx.handler == nil {
ctx.handler = cn.checkMethodNotAllowed()

// Dig further for any, might have an empty value for *, e.g.
// serving a directory. Issue #207.
if cn = cn.anyChildren; cn == nil {
return
}
if h := cn.findHandler(method); h != nil {
ctx.handler = h
} else {
ctx.handler = cn.checkMethodNotAllowed()
}
ctx.path = cn.ppath
ctx.pnames = cn.pnames
pvalues[len(cn.pnames)-1] = ""
}

return
}
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