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// Copyright 2015 Matthew Holt and The Caddy Authors
//
// 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 rewrite
import (
"fmt"
"net/http"
"net/url"
"regexp"
"strconv"
"strings"
"go.uber.org/zap"
"github.com/caddyserver/caddy/v2"
"github.com/caddyserver/caddy/v2/modules/caddyhttp"
)
func init() {
caddy.RegisterModule(Rewrite{})
}
// Rewrite is a middleware which can rewrite/mutate HTTP requests.
//
// The Method and URI properties are "setters" (the request URI
// will be overwritten with the given values). Other properties are
// "modifiers" (they modify existing values in a differentiable
// way). It is atypical to combine the use of setters and
// modifiers in a single rewrite.
//
// To ensure consistent behavior, prefix and suffix stripping is
// performed in the URL-decoded (unescaped, normalized) space by
// default except for the specific bytes where an escape sequence
// is used in the prefix or suffix pattern.
//
// For all modifiers, paths are cleaned before being modified so that
// multiple, consecutive slashes are collapsed into a single slash,
// and dot elements are resolved and removed. In the special case
// of a prefix, suffix, or substring containing "//" (repeated slashes),
// slashes will not be merged while cleaning the path so that
// the rewrite can be interpreted literally.
type Rewrite struct {
// Changes the request's HTTP verb.
Method string `json:"method,omitempty"`
// Changes the request's URI, which consists of path and query string.
// Only components of the URI that are specified will be changed.
// For example, a value of "/foo.html" or "foo.html" will only change
// the path and will preserve any existing query string. Similarly, a
// value of "?a=b" will only change the query string and will not affect
// the path. Both can also be changed: "/foo?a=b" - this sets both the
// path and query string at the same time.
//
// You can also use placeholders. For example, to preserve the existing
// query string, you might use: "?{http.request.uri.query}&a=b". Any
// key-value pairs you add to the query string will not overwrite
// existing values (individual pairs are append-only).
//
// To clear the query string, explicitly set an empty one: "?"
URI string `json:"uri,omitempty"`
// Strips the given prefix from the beginning of the URI path.
// The prefix should be written in normalized (unescaped) form,
// but if an escaping (`%xx`) is used, the path will be required
// to have that same escape at that position in order to match.
StripPathPrefix string `json:"strip_path_prefix,omitempty"`
// Strips the given suffix from the end of the URI path.
// The suffix should be written in normalized (unescaped) form,
// but if an escaping (`%xx`) is used, the path will be required
// to have that same escape at that position in order to match.
StripPathSuffix string `json:"strip_path_suffix,omitempty"`
// Performs substring replacements on the URI.
URISubstring []substrReplacer `json:"uri_substring,omitempty"`
// Performs regular expression replacements on the URI path.
PathRegexp []*regexReplacer `json:"path_regexp,omitempty"`
// Mutates the query string of the URI.
Query *queryOps `json:"query,omitempty"`
logger *zap.Logger
}
// CaddyModule returns the Caddy module information.
func (Rewrite) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "http.handlers.rewrite",
New: func() caddy.Module { return new(Rewrite) },
}
}
// Provision sets up rewr.
func (rewr *Rewrite) Provision(ctx caddy.Context) error {
rewr.logger = ctx.Logger()
for i, rep := range rewr.PathRegexp {
if rep.Find == "" {
return fmt.Errorf("path_regexp find cannot be empty")
}
re, err := regexp.Compile(rep.Find)
if err != nil {
return fmt.Errorf("compiling regular expression %d: %v", i, err)
}
rep.re = re
}
if rewr.Query != nil {
for _, replacementOp := range rewr.Query.Replace {
err := replacementOp.Provision(ctx)
if err != nil {
return fmt.Errorf("compiling regular expression %s in query rewrite replace operation: %v", replacementOp.SearchRegexp, err)
}
}
}
return nil
}
func (rewr Rewrite) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
const message = "rewrote request"
if rewr.logger.Check(zap.DebugLevel, message) == nil {
rewr.Rewrite(r, repl)
return next.ServeHTTP(w, r)
}
logger := rewr.logger.With(
zap.Object("request", caddyhttp.LoggableHTTPRequest{Request: r}),
)
changed := rewr.Rewrite(r, repl)
if changed {
logger.Debug(message,
zap.String("method", r.Method),
zap.String("uri", r.RequestURI),
)
}
return next.ServeHTTP(w, r)
}
// rewrite performs the rewrites on r using repl, which should
// have been obtained from r, but is passed in for efficiency.
// It returns true if any changes were made to r.
func (rewr Rewrite) Rewrite(r *http.Request, repl *caddy.Replacer) bool {
oldMethod := r.Method
oldURI := r.RequestURI
// method
if rewr.Method != "" {
r.Method = strings.ToUpper(repl.ReplaceAll(rewr.Method, ""))
}
// uri (path, query string and... fragment, because why not)
if uri := rewr.URI; uri != "" {
// find the bounds of each part of the URI that exist
pathStart, qsStart, fragStart := -1, -1, -1
pathEnd, qsEnd := -1, -1
loop:
for i, ch := range uri {
switch {
case ch == '?' && qsStart < 0:
pathEnd, qsStart = i, i+1
case ch == '#' && fragStart < 0: // everything after fragment is fragment (very clear in RFC 3986 section 4.2)
if qsStart < 0 {
pathEnd = i
} else {
qsEnd = i
}
fragStart = i + 1
break loop
case pathStart < 0 && qsStart < 0:
pathStart = i
}
}
if pathStart >= 0 && pathEnd < 0 {
pathEnd = len(uri)
}
if qsStart >= 0 && qsEnd < 0 {
qsEnd = len(uri)
}
// isolate the three main components of the URI
var path, query, frag string
if pathStart > -1 {
path = uri[pathStart:pathEnd]
}
if qsStart > -1 {
query = uri[qsStart:qsEnd]
}
if fragStart > -1 {
frag = uri[fragStart:]
}
// build components which are specified, and store them
// in a temporary variable so that they all read the
// same version of the URI
var newPath, newQuery, newFrag string
if path != "" {
// replace the `path` placeholder to escaped path
pathPlaceholder := "{http.request.uri.path}"
if strings.Contains(path, pathPlaceholder) {
path = strings.ReplaceAll(path, pathPlaceholder, r.URL.EscapedPath())
}
newPath = repl.ReplaceAll(path, "")
}
// before continuing, we need to check if a query string
// snuck into the path component during replacements
if before, after, found := strings.Cut(newPath, "?"); found {
// recompute; new path contains a query string
var injectedQuery string
newPath, injectedQuery = before, after
// don't overwrite explicitly-configured query string
if query == "" {
query = injectedQuery
}
}
if query != "" {
newQuery = buildQueryString(query, repl)
}
if frag != "" {
newFrag = repl.ReplaceAll(frag, "")
}
// update the URI with the new components
// only after building them
if pathStart >= 0 {
if path, err := url.PathUnescape(newPath); err != nil {
r.URL.Path = newPath
} else {
r.URL.Path = path
}
}
if qsStart >= 0 {
r.URL.RawQuery = newQuery
}
if fragStart >= 0 {
r.URL.Fragment = newFrag
}
}
// strip path prefix or suffix
if rewr.StripPathPrefix != "" {
prefix := repl.ReplaceAll(rewr.StripPathPrefix, "")
mergeSlashes := !strings.Contains(prefix, "//")
changePath(r, func(escapedPath string) string {
escapedPath = caddyhttp.CleanPath(escapedPath, mergeSlashes)
return trimPathPrefix(escapedPath, prefix)
})
}
if rewr.StripPathSuffix != "" {
suffix := repl.ReplaceAll(rewr.StripPathSuffix, "")
mergeSlashes := !strings.Contains(suffix, "//")
changePath(r, func(escapedPath string) string {
escapedPath = caddyhttp.CleanPath(escapedPath, mergeSlashes)
return reverse(trimPathPrefix(reverse(escapedPath), reverse(suffix)))
})
}
// substring replacements in URI
for _, rep := range rewr.URISubstring {
rep.do(r, repl)
}
// regular expression replacements on the path
for _, rep := range rewr.PathRegexp {
rep.do(r, repl)
}
// apply query operations
if rewr.Query != nil {
rewr.Query.do(r, repl)
}
// update the encoded copy of the URI
r.RequestURI = r.URL.RequestURI()
// return true if anything changed
return r.Method != oldMethod || r.RequestURI != oldURI
}
// buildQueryString takes an input query string and
// performs replacements on each component, returning
// the resulting query string. This function appends
// duplicate keys rather than replaces.
func buildQueryString(qs string, repl *caddy.Replacer) string {
var sb strings.Builder
// first component must be key, which is the same
// as if we just wrote a value in previous iteration
wroteVal := true
for len(qs) > 0 {
// determine the end of this component, which will be at
// the next equal sign or ampersand, whichever comes first
nextEq, nextAmp := strings.Index(qs, "="), strings.Index(qs, "&")
ampIsNext := nextAmp >= 0 && (nextAmp < nextEq || nextEq < 0)
end := len(qs) // assume no delimiter remains...
if ampIsNext {
end = nextAmp // ...unless ampersand is first...
} else if nextEq >= 0 && (nextEq < nextAmp || nextAmp < 0) {
end = nextEq // ...or unless equal is first.
}
// consume the component and write the result
comp := qs[:end]
comp, _ = repl.ReplaceFunc(comp, func(name string, val any) (any, error) {
if name == "http.request.uri.query" && wroteVal {
return val, nil // already escaped
}
var valStr string
switch v := val.(type) {
case string:
valStr = v
case fmt.Stringer:
valStr = v.String()
case int:
valStr = strconv.Itoa(v)
default:
valStr = fmt.Sprintf("%+v", v)
}
return url.QueryEscape(valStr), nil
})
if end < len(qs) {
end++ // consume delimiter
}
qs = qs[end:]
// if previous iteration wrote a value,
// that means we are writing a key
if wroteVal {
if sb.Len() > 0 && len(comp) > 0 {
sb.WriteRune('&')
}
} else {
sb.WriteRune('=')
}
sb.WriteString(comp)
// remember for the next iteration that we just wrote a value,
// which means the next iteration MUST write a key
wroteVal = ampIsNext
}
return sb.String()
}
// trimPathPrefix is like strings.TrimPrefix, but customized for advanced URI
// path prefix matching. The string prefix will be trimmed from the beginning
// of escapedPath if escapedPath starts with prefix. Rather than a naive 1:1
// comparison of each byte to determine if escapedPath starts with prefix,
// both strings are iterated in lock-step, and if prefix has a '%' encoding
// at a particular position, escapedPath must also have the same encoding
// representation for that character. In other words, if the prefix string
// uses the escaped form for a character, escapedPath must literally use the
// same escape at that position. Otherwise, all character comparisons are
// performed in normalized/unescaped space.
func trimPathPrefix(escapedPath, prefix string) string {
var iPath, iPrefix int
for {
if iPath >= len(escapedPath) || iPrefix >= len(prefix) {
break
}
prefixCh := prefix[iPrefix]
ch := string(escapedPath[iPath])
if ch == "%" && prefixCh != '%' && len(escapedPath) >= iPath+3 {
var err error
ch, err = url.PathUnescape(escapedPath[iPath : iPath+3])
if err != nil {
// should be impossible unless EscapedPath() is returning invalid values!
return escapedPath
}
iPath += 2
}
// prefix comparisons are case-insensitive to consistency with
// path matcher, which is case-insensitive for good reasons
if !strings.EqualFold(ch, string(prefixCh)) {
return escapedPath
}
iPath++
iPrefix++
}
// if we iterated through the entire prefix, we found it, so trim it
if iPath >= len(prefix) {
return escapedPath[iPath:]
}
// otherwise we did not find the prefix
return escapedPath
}
func reverse(s string) string {
r := []rune(s)
for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
r[i], r[j] = r[j], r[i]
}
return string(r)
}
// substrReplacer describes either a simple and fast substring replacement.
type substrReplacer struct {
// A substring to find. Supports placeholders.
Find string `json:"find,omitempty"`
// The substring to replace with. Supports placeholders.
Replace string `json:"replace,omitempty"`
// Maximum number of replacements per string.
// Set to <= 0 for no limit (default).
Limit int `json:"limit,omitempty"`
}
// do performs the substring replacement on r.
func (rep substrReplacer) do(r *http.Request, repl *caddy.Replacer) {
if rep.Find == "" {
return
}
lim := rep.Limit
if lim == 0 {
lim = -1
}
find := repl.ReplaceAll(rep.Find, "")
replace := repl.ReplaceAll(rep.Replace, "")
mergeSlashes := !strings.Contains(rep.Find, "//")
changePath(r, func(pathOrRawPath string) string {
return strings.Replace(caddyhttp.CleanPath(pathOrRawPath, mergeSlashes), find, replace, lim)
})
r.URL.RawQuery = strings.Replace(r.URL.RawQuery, find, replace, lim)
}
// regexReplacer describes a replacement using a regular expression.
type regexReplacer struct {
// The regular expression to find.
Find string `json:"find,omitempty"`
// The substring to replace with. Supports placeholders and
// regular expression capture groups.
Replace string `json:"replace,omitempty"`
re *regexp.Regexp
}
func (rep regexReplacer) do(r *http.Request, repl *caddy.Replacer) {
if rep.Find == "" || rep.re == nil {
return
}
replace := repl.ReplaceAll(rep.Replace, "")
changePath(r, func(pathOrRawPath string) string {
return rep.re.ReplaceAllString(pathOrRawPath, replace)
})
}
func changePath(req *http.Request, newVal func(pathOrRawPath string) string) {
req.URL.RawPath = newVal(req.URL.EscapedPath())
if p, err := url.PathUnescape(req.URL.RawPath); err == nil && p != "" {
req.URL.Path = p
} else {
req.URL.Path = newVal(req.URL.Path)
}
// RawPath is only set if it's different from the normalized Path (std lib)
if req.URL.RawPath == req.URL.Path {
req.URL.RawPath = ""
}
}
// queryOps describes the operations to perform on query keys: add, set, rename and delete.
type queryOps struct {
// Renames a query key from Key to Val, without affecting the value.
Rename []queryOpsArguments `json:"rename,omitempty"`
// Sets query parameters; overwrites a query key with the given value.
Set []queryOpsArguments `json:"set,omitempty"`
// Adds query parameters; does not overwrite an existing query field,
// and only appends an additional value for that key if any already exist.
Add []queryOpsArguments `json:"add,omitempty"`
// Replaces query parameters.
Replace []*queryOpsReplacement `json:"replace,omitempty"`
// Deletes a given query key by name.
Delete []string `json:"delete,omitempty"`
}
// Provision compiles the query replace operation regex.
func (replacement *queryOpsReplacement) Provision(_ caddy.Context) error {
if replacement.SearchRegexp != "" {
re, err := regexp.Compile(replacement.SearchRegexp)
if err != nil {
return fmt.Errorf("replacement for query field '%s': %v", replacement.Key, err)
}
replacement.re = re
}
return nil
}
func (q *queryOps) do(r *http.Request, repl *caddy.Replacer) {
query := r.URL.Query()
for _, renameParam := range q.Rename {
key := repl.ReplaceAll(renameParam.Key, "")
val := repl.ReplaceAll(renameParam.Val, "")
if key == "" || val == "" {
continue
}
query[val] = query[key]
delete(query, key)
}
for _, setParam := range q.Set {
key := repl.ReplaceAll(setParam.Key, "")
if key == "" {
continue
}
val := repl.ReplaceAll(setParam.Val, "")
query[key] = []string{val}
}
for _, addParam := range q.Add {
key := repl.ReplaceAll(addParam.Key, "")
if key == "" {
continue
}
val := repl.ReplaceAll(addParam.Val, "")
query[key] = append(query[key], val)
}
for _, replaceParam := range q.Replace {
key := repl.ReplaceAll(replaceParam.Key, "")
search := repl.ReplaceKnown(replaceParam.Search, "")
replace := repl.ReplaceKnown(replaceParam.Replace, "")
// replace all query keys...
if key == "*" {
for fieldName, vals := range query {
for i := range vals {
if replaceParam.re != nil {
query[fieldName][i] = replaceParam.re.ReplaceAllString(query[fieldName][i], replace)
} else {
query[fieldName][i] = strings.ReplaceAll(query[fieldName][i], search, replace)
}
}
}
continue
}
for fieldName, vals := range query {
for i := range vals {
if replaceParam.re != nil {
query[fieldName][i] = replaceParam.re.ReplaceAllString(query[fieldName][i], replace)
} else {
query[fieldName][i] = strings.ReplaceAll(query[fieldName][i], search, replace)
}
}
}
}
for _, deleteParam := range q.Delete {
param := repl.ReplaceAll(deleteParam, "")
if param == "" {
continue
}
delete(query, param)
}
r.URL.RawQuery = query.Encode()
}
type queryOpsArguments struct {
// A key in the query string. Note that query string keys may appear multiple times.
Key string `json:"key,omitempty"`
// The value for the given operation; for add and set, this is
// simply the value of the query, and for rename this is the
// query key to rename to.
Val string `json:"val,omitempty"`
}
type queryOpsReplacement struct {
// The key to replace in the query string.
Key string `json:"key,omitempty"`
// The substring to search for.
Search string `json:"search,omitempty"`
// The regular expression to search with.
SearchRegexp string `json:"search_regexp,omitempty"`
// The string with which to replace matches.
Replace string `json:"replace,omitempty"`
re *regexp.Regexp
}
// Interface guard
var _ caddyhttp.MiddlewareHandler = (*Rewrite)(nil)
|