Make prefixer support multiple tags, chunked enc
The prefixer needs to not only replace `src="` attributes as it currently does because that is not the only place a relative URL can appear. It needs to also prefix URLs found in CSS which can also come from the downstream http.ResponseWriter. This adds support for an arbitrary list of patterns that will cause the prefixer to insert its configured prefix. This is currently set to look for `src`, `href`, and `url()` attributes. Also, because we are modifying the stream, we need to suppress the Content-Length generated by any downstream http.Handlers and instead enable Transfer-Encoding: chunked so that we can stream the modified response (we don't know apriori how many times we'll perform a prefixing, so we can't calculate a final Content-Length). This is accomplished by duplicating the Headers in the wrapResponseWriter that is handed to the `Next` handler. We also handle the chunking and Flushing that needs to happen as a result of using chunked transfer encoding.pull/10616/head
Tim Raymond
parent
4064817ac8
commit
14437af28d
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@ -56,6 +56,11 @@ func Assets(opts AssetsOpts) http.Handler {
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up := URLPrefixer{
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Prefix: "/chronograf",
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Next: assets.Handler(),
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Attrs: [][]byte{
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[]byte(`src="`),
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[]byte(`href="`),
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[]byte(`url(`),
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},
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}
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up.ServeHTTP(w, r)
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})
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@ -4,62 +4,136 @@ import (
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"bufio"
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"bytes"
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"io"
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"log"
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"net/http"
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)
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// URLPrefixer is a wrapper for an http.Handler that will prefix all occurrences of a relative URL with the configured Prefix
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type URLPrefixer struct {
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Prefix string
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Next http.Handler
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Prefix string // the prefix to be appended after any detected Attrs
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Next http.Handler // the http.Handler which will generate the content to be modified by this handler
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Attrs [][]byte // a list of attrs that should have their URLs prefixed. For example `src="` or `href="` would be valid
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}
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type wrapResponseWriter struct {
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http.ResponseWriter
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Substitute *io.PipeWriter
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headerWritten bool
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dupHeader http.Header
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}
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func (wrw wrapResponseWriter) Write(p []byte) (int, error) {
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outCount, err := wrw.Substitute.Write(p)
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if err != nil || outCount == len(p) {
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wrw.Substitute.Close()
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}
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return outCount, err
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return wrw.Substitute.Write(p)
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}
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func (wrw wrapResponseWriter) WriteHeader(code int) {
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if !wrw.headerWritten {
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wrw.ResponseWriter.Header().Set("Content-Type", wrw.Header().Get("Content-Type"))
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wrw.headerWritten = true
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}
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wrw.ResponseWriter.WriteHeader(code)
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}
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// Header() copies the Header map from the underlying ResponseWriter to prevent
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// modifications to it by callers
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func (wrw wrapResponseWriter) Header() http.Header {
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wrw.dupHeader = http.Header{}
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origHeader := wrw.ResponseWriter.Header()
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for k, v := range origHeader {
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wrw.dupHeader[k] = v
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}
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return wrw.dupHeader
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}
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const CHUNK_SIZE int = 512
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// ServeHTTP implements an http.Handler that prefixes relative URLs from the Next handler with the configured prefix
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func (up *URLPrefixer) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
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// chunked transfer because we're modifying the response on the fly, so we
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// won't know the final content-length
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rw.Header().Set("Connection", "Keep-Alive")
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rw.Header().Set("Transfer-Encoding", "chunked")
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//rw.Header().Set("X-Content-Type-Options", "nosniff")
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writtenCount := 0 // number of bytes written to rw
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flusher, ok := rw.(http.Flusher)
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if !ok {
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log.Fatalln("Exected http.ResponseWriter to be an http.Flusher, but wasn't")
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}
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nextRead, nextWrite := io.Pipe()
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go up.Next.ServeHTTP(wrapResponseWriter{rw, nextWrite}, r)
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go func() {
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defer nextWrite.Close()
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up.Next.ServeHTTP(wrapResponseWriter{ResponseWriter: rw, Substitute: nextWrite}, r)
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}()
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srctag := []byte(`src="`)
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// Locate src tags, flushing everything that isn't to rw
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b := make([]byte, len(srctag))
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// setup a buffer which is the max length of our target attrs
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b := make([]byte, up.maxlen(up.Attrs...))
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io.ReadFull(nextRead, b) // prime the buffer with the start of the input
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buf := bytes.NewBuffer(b)
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// Read next handler's response byte by byte
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src := bufio.NewScanner(nextRead)
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src.Split(bufio.ScanBytes)
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for {
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window := buf.Bytes()
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// advance a byte if window is not a src attr
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if !bytes.Equal(window, srctag) {
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if matchlen, match := up.match(window, up.Attrs...); matchlen == 0 {
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if src.Scan() {
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// shift the next byte into buf
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rw.Write(buf.Next(1))
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writtenCount++
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buf.Write(src.Bytes())
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if writtenCount >= CHUNK_SIZE {
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flusher.Flush()
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writtenCount = 0
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}
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} else {
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if err := src.Err(); err != nil {
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log.Println("Error encountered while scanning: err:", err)
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}
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rw.Write(window)
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flusher.Flush()
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break
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}
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continue
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} else {
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buf.Next(len(srctag)) // advance to the relative URL
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for i := 0; i < len(srctag); i++ {
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buf.Next(matchlen) // advance to the relative URL
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for i := 0; i < matchlen; i++ {
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src.Scan()
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buf.Write(src.Bytes())
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}
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rw.Write(srctag) // add the src attr to the output
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rw.Write(match) // add the src attr to the output
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io.WriteString(rw, up.Prefix) // write the prefix
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}
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}
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}
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// match compares the subject against a list of targets. If there is a match
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// between any of them a non-zero value is returned. The returned value is the
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// length of the match. It is assumed that subject's length > length of all
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// targets. The matching []byte is also returned as the second return parameter
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func (up *URLPrefixer) match(subject []byte, targets ...[]byte) (int, []byte) {
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for _, target := range targets {
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if bytes.Equal(subject[:len(target)], target) {
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return len(target), target
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}
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}
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return 0, []byte{}
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}
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// maxlen returns the length of the largest []byte provided to it as an argument
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func (up *URLPrefixer) maxlen(targets ...[]byte) int {
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max := 0
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for _, tgt := range targets {
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if tlen := len(tgt); tlen > max {
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max = tlen
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}
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}
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return max
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}
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@ -15,18 +15,63 @@ var prefixerTests = []struct {
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subject string
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expected string
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shouldErr bool
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attrs [][]byte
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}{
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{
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`One script tag`,
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`<script type="text/javascript" src="/loljavascript.min.js">`,
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`<script type="text/javascript" src="/arbitraryprefix/loljavascript.min.js">`,
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false,
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[][]byte{
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[]byte(`src="`),
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},
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},
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{
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`Two script tags`,
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`<script type="text/javascript" src="/loljavascript.min.js"><script type="text/javascript" src="/anotherscript.min.js">`,
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`<script type="text/javascript" src="/arbitraryprefix/loljavascript.min.js"><script type="text/javascript" src="/arbitraryprefix/anotherscript.min.js">`,
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false,
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[][]byte{
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[]byte(`src="`),
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},
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},
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{
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`Link href`,
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`<link rel="shortcut icon" href="/favicon.ico">`,
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`<link rel="shortcut icon" href="/arbitraryprefix/favicon.ico">`,
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false,
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[][]byte{
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[]byte(`src="`),
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[]byte(`href="`),
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},
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},
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{
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`Trailing HTML`,
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`<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="Content-type" content="text/html; charset=utf-8"/>
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<title>Chronograf</title>
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<link rel="shortcut icon" href="/favicon.ico"><link href="/chronograf.css" rel="stylesheet"></head>
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<body>
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<div id='react-root'></div>
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<script type="text/javascript" src="/manifest.7489452b099f9581ca1b.dev.js"></script><script type="text/javascript" src="/vendor.568c0101d870a13ecff9.dev.js"></script><script type="text/javascript" src="/app.13d0ce0b33609be3802b.dev.js"></script></body>
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</html>`,
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`<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="Content-type" content="text/html; charset=utf-8"/>
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<title>Chronograf</title>
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<link rel="shortcut icon" href="/arbitraryprefix/favicon.ico"><link href="/arbitraryprefix/chronograf.css" rel="stylesheet"></head>
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<body>
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<div id='react-root'></div>
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<script type="text/javascript" src="/arbitraryprefix/manifest.7489452b099f9581ca1b.dev.js"></script><script type="text/javascript" src="/arbitraryprefix/vendor.568c0101d870a13ecff9.dev.js"></script><script type="text/javascript" src="/arbitraryprefix/app.13d0ce0b33609be3802b.dev.js"></script></body>
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</html>`,
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false,
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[][]byte{
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[]byte(`src="`),
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[]byte(`href="`),
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},
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},
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}
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@ -41,7 +86,7 @@ func Test_Server_Prefixer_RewritesURLs(t *testing.T) {
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fmt.Fprintln(w, subject)
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})
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pfx := &server.URLPrefixer{Prefix: "/arbitraryprefix", Next: backend}
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pfx := &server.URLPrefixer{Prefix: "/arbitraryprefix", Next: backend, Attrs: test.attrs}
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ts := httptest.NewServer(pfx)
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defer ts.Close()
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@ -57,7 +102,7 @@ func Test_Server_Prefixer_RewritesURLs(t *testing.T) {
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}
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if string(actual) != expected+"\n" {
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t.Error(test.name, ":\n Unsuccessful prefixing.\n\tWant:", expected, "\n\tGot:", string(actual))
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t.Error(test.name, ":\n Unsuccessful prefixing.\n\tWant:", fmt.Sprintf("%+q", expected), "\n\tGot: ", fmt.Sprintf("%+q", string(actual)))
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}
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}
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}
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@ -7,4 +7,4 @@
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<body>
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<div id='react-root'></div>
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</body>
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</html
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</html>
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