rewrite

README

rewrite

rewrite performs internal message rewriting. Rewrites are invisible to the client. There are simple rewrites (fast) and complex rewrites (slower), but they're powerful enough to accommodate most dynamic back-end applications.

Syntax

rewrite from to

• from is the exact name of type to match
• to is the destination name or type to rewrite to

If from and to look like a DNS type (A, MX, etc.), the type of the message will be rewriten; e.g., to rewrite ANY queries to HINFO, use rewrite ANY HINFO.

If from and to look like a DNS class (IN, CH, or HS) the class of the message will be rewritten; e.g., to rewrite CH queries to IN use rewrite CH IN.

If it does not look like a type a name is assumed and the qname in the message is rewritten; this needs to be a full match of the name, e.g., rewrite miek.nl example.org.

If you specify multiple rules and an incoming query matches on multiple (simple) rules, only the first rewrite is applied.

Everything below this line has not been implemented, yet.

rewrite [basename] {
    regexp pattern
    ext    extensions...
    if     a cond b
    status code
    to     destinations...
}

• basepath is the base path to match before rewriting with a regular expression. Default is /.
• regexp (shorthand: r) will match the path with the given regular expression pattern. Extremely high-load servers should avoid using regular expressions.
• extensions... is a space-separated list of file extensions to include or ignore. Prefix an extension with ! to exclude an extension. The forward slash / symbol matches paths without file extensions.
• if specifies a rewrite condition. Multiple ifs are AND-ed together. a and b are any string and may use request placeholders. cond is the condition, with possible values explained below.
• status will respond with the given status code instead of performing a rewrite. In other words, use either "status" or "to" in your rule, but not both. The code must be a number in the format 2xx or 4xx.
• destinations... is one or more space-separated paths to rewrite to, with support for request placeholders as well as numbered regular expression captures such as {1}, {2}, etc. Rewrite will check each destination in order and rewrite to the first destination that exists. Each one is checked as a file or, if it ends with /, as a directory. The last destination will act as the default if no other destination exists. "if" Conditions

The if keyword is a powerful way to describe your rule. It takes the format a cond b, where the values a and b are separated by cond, a condition. The condition can be any of these:

is = a equals b
not = a does NOT equal b
has = a has b as a substring (b is a substring of a)
not_has = b is NOT a substring of a
starts_with = b is a prefix of a
ends_with = b is a suffix of a
match = a matches b, where b is a regular expression
not_match = a does NOT match b, where b is a regular expression

Examples

When requests come in for /mobile, actually serve /mobile/index. rewrite /mobile /mobile/index If the file is not favicon.ico and it is not a valid file or directory, serve the maintenance page if present, or finally, rewrite to index.php.

rewrite {
    if {file} not favicon.ico
    to {path} {path}/ /maintenance.html /index.php
}

If user agent includes "mobile" and path is not a valid file/directory, rewrite to the mobile index page.

rewrite {
    if if {>User-agent} has mobile
    to {path} {path}/ /mobile/index.php
}

If the request path starts with /source, respond with HTTP 403 Forbidden.

rewrite {
    regexp ^/source
    status 403
}

Rewrite /app to /index with a query string. {1} is the matched group (.*).

rewrite /app {
    r  (.*)
    to /index?path={1}
}

Documentation

Overview

Package rewrite is middleware for rewriting requests internally to something different.

Index

• Constants
• type If
  • func NewIf(a, operator, b string) (If, error)
  • func (i If) True(r *dns.Msg) bool
• type ResponseReverter
  • func NewResponseReverter(w dns.ResponseWriter, r *dns.Msg) *ResponseReverter
  • func (r *ResponseReverter) Hijack()
  • func (r *ResponseReverter) Write(buf []byte) (int, error)
  • func (r *ResponseReverter) WriteMsg(res *dns.Msg) error
• type Result
• type Rewrite
  • func (rw Rewrite) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)
• type Rule
• type SimpleRule
  • func NewSimpleRule(from, to string) SimpleRule
  • func (s SimpleRule) Rewrite(r *dns.Msg) Result

Constants

const (
	Is         = "is"
	Not        = "not"
	Has        = "has"
	NotHas     = "not_has"
	StartsWith = "starts_with"
	EndsWith   = "ends_with"
	Match      = "match"
	NotMatch   = "not_match"
)

Operators

Types

type If

type If struct {
	A        string
	Operator string
	B        string
}

If is statement for a rewrite condition.

func NewIf

func NewIf(a, operator, b string) (If, error)

NewIf creates a new If condition.

func (If) True

func (i If) True(r *dns.Msg) bool

True returns true if the condition is true and false otherwise. If r is not nil, it replaces placeholders before comparison.

type ResponseReverter

type ResponseReverter struct {
	dns.ResponseWriter
	// contains filtered or unexported fields
}

ResponseReverter reverses the operations done on the question section of a packet. This is need because the client will otherwise disregards the response, i.e. dig will complain with ';; Question section mismatch: got miek.nl/HINFO/IN'

func NewResponseReverter

func NewResponseReverter(w dns.ResponseWriter, r *dns.Msg) *ResponseReverter

NewResponseReverter returns a pointer to a new ResponseReverter.

func (*ResponseReverter) Hijack

func (r *ResponseReverter) Hijack()

Hijack implements dns.Hijacker. It simply wraps the underlying ResponseWriter's Hijack method if there is one, or returns an error.

func (*ResponseReverter) Write

func (r *ResponseReverter) Write(buf []byte) (int, error)

Write is a wrapper that records the size of the message that gets written.

func (*ResponseReverter) WriteMsg

func (r *ResponseReverter) WriteMsg(res *dns.Msg) error

WriteMsg records the status code and calls the underlying ResponseWriter's WriteMsg method.

type Result

type Result int

Result is the result of a rewrite

const (
	// RewriteIgnored is returned when rewrite is not done on request.
	RewriteIgnored Result = iota
	// RewriteDone is returned when rewrite is done on request.
	RewriteDone
	// RewriteStatus is returned when rewrite is not needed and status code should be set
	// for the request.
	RewriteStatus
)

type Rewrite

type Rewrite struct {
	Next  middleware.Handler
	Rules []Rule
	// contains filtered or unexported fields
}

Rewrite is middleware to rewrite requests internally before being handled.

func (Rewrite) ServeDNS

func (rw Rewrite) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)

ServeDNS implements the middleware.Handler interface.

type Rule

type Rule interface {
	// Rewrite rewrites the internal location of the current request.
	Rewrite(*dns.Msg) Result
}

Rule describes an internal location rewrite rule.

type SimpleRule

type SimpleRule struct {
	From, To string
	// contains filtered or unexported fields
}

SimpleRule is a simple rewrite rule. If the From and To look like a type the type of the request is rewritten, otherwise the name is. Note: TSIG signed requests will be invalid.

func NewSimpleRule

func NewSimpleRule(from, to string) SimpleRule

NewSimpleRule creates a new Simple Rule

func (SimpleRule) Rewrite

func (s SimpleRule) Rewrite(r *dns.Msg) Result

Rewrite rewrites the the current request.