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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 maphandler
import (
"fmt"
"net/http"
"regexp"
"strings"
"github.com/caddyserver/caddy/v2"
"github.com/caddyserver/caddy/v2/modules/caddyhttp"
)
func init() {
caddy.RegisterModule(Handler{})
}
// Handler implements a middleware that maps inputs to outputs. Specifically, it
// compares a source value against the map inputs, and for one that matches, it
// applies the output values to each destination. Destinations become placeholder
// names.
//
// Mapped placeholders are not evaluated until they are used, so even for very
// large mappings, this handler is quite efficient.
type Handler struct {
// Source is the placeholder from which to get the input value.
Source string `json:"source,omitempty"`
// Destinations are the names of placeholders in which to store the outputs.
// Destination values should be wrapped in braces, for example, {my_placeholder}.
Destinations []string `json:"destinations,omitempty"`
// Mappings from source values (inputs) to destination values (outputs).
// The first matching, non-nil mapping will be applied.
Mappings []Mapping `json:"mappings,omitempty"`
// If no mappings match or if the mapped output is null/nil, the associated
// default output will be applied (optional).
Defaults []string `json:"defaults,omitempty"`
}
// CaddyModule returns the Caddy module information.
func (Handler) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "http.handlers.map",
New: func() caddy.Module { return new(Handler) },
}
}
// Provision sets up h.
func (h *Handler) Provision(_ caddy.Context) error {
for j, dest := range h.Destinations {
if strings.Count(dest, "{") != 1 || !strings.HasPrefix(dest, "{") {
return fmt.Errorf("destination must be a placeholder and only a placeholder")
}
h.Destinations[j] = strings.Trim(dest, "{}")
}
for i, m := range h.Mappings {
if m.InputRegexp == "" {
continue
}
var err error
h.Mappings[i].re, err = regexp.Compile(m.InputRegexp)
if err != nil {
return fmt.Errorf("compiling regexp for mapping %d: %v", i, err)
}
}
// TODO: improve efficiency even further by using an actual map type
// for the non-regexp mappings, OR sort them and do a binary search
return nil
}
// Validate ensures that h is configured properly.
func (h *Handler) Validate() error {
nDest, nDef := len(h.Destinations), len(h.Defaults)
if nDef > 0 && nDef != nDest {
return fmt.Errorf("%d destinations != %d defaults", nDest, nDef)
}
seen := make(map[string]int)
for i, m := range h.Mappings {
// prevent confusing/ambiguous mappings
if m.Input != "" && m.InputRegexp != "" {
return fmt.Errorf("mapping %d has both input and input_regexp fields specified, which is confusing", i)
}
// prevent duplicate mappings
input := m.Input
if m.InputRegexp != "" {
input = m.InputRegexp
}
if prev, ok := seen[input]; ok {
return fmt.Errorf("mapping %d has a duplicate input '%s' previously used with mapping %d", i, input, prev)
}
seen[input] = i
// ensure mappings have 1:1 output-to-destination correspondence
nOut := len(m.Outputs)
if nOut != nDest {
return fmt.Errorf("mapping %d has %d outputs but there are %d destinations defined", i, nOut, nDest)
}
}
return nil
}
func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
// defer work until a variable is actually evaluated by using replacer's Map callback
repl.Map(func(key string) (any, bool) {
// return early if the variable is not even a configured destination
destIdx := h.destinationIndex(key)
if destIdx < 0 {
return nil, false
}
input := repl.ReplaceAll(h.Source, "")
// find the first mapping matching the input and return
// the requested destination/output value
for _, m := range h.Mappings {
output := m.Outputs[destIdx]
if output == nil {
continue
}
outputStr := caddy.ToString(output)
// evaluate regular expression if configured
if m.re != nil {
var result []byte
matches := m.re.FindStringSubmatchIndex(input)
if matches == nil {
continue
}
result = m.re.ExpandString(result, outputStr, input, matches)
return string(result), true
}
// otherwise simple string comparison
if input == m.Input {
return repl.ReplaceAll(outputStr, ""), true
}
}
// fall back to default if no match or if matched nil value
if len(h.Defaults) > destIdx {
return repl.ReplaceAll(h.Defaults[destIdx], ""), true
}
return nil, true
})
return next.ServeHTTP(w, r)
}
// destinationIndex returns the positional index of the destination
// is name is a known destination; otherwise it returns -1.
func (h Handler) destinationIndex(name string) int {
for i, dest := range h.Destinations {
if dest == name {
return i
}
}
return -1
}
// Mapping describes a mapping from input to outputs.
type Mapping struct {
// The input value to match. Must be distinct from other mappings.
// Mutually exclusive to input_regexp.
Input string `json:"input,omitempty"`
// The input regular expression to match. Mutually exclusive to input.
InputRegexp string `json:"input_regexp,omitempty"`
// Upon a match with the input, each output is positionally correlated
// with each destination of the parent handler. An output that is null
// (nil) will be treated as if it was not mapped at all.
Outputs []any `json:"outputs,omitempty"`
re *regexp.Regexp
}
// Interface guards
var (
_ caddy.Provisioner = (*Handler)(nil)
_ caddy.Validator = (*Handler)(nil)
_ caddyhttp.MiddlewareHandler = (*Handler)(nil)
)
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