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Add precondition.go.
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2 changed files with 224 additions and 0 deletions
110
webserver/precondition.go
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110
webserver/precondition.go
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package webserver
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import (
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"net/http"
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"strings"
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)
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// This is partly based on the Go standard library file net/http/fs.go.
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// scanETag determines if a syntactically valid ETag is present at s. If so,
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// the ETag and remaining text after consuming ETag is returned. Otherwise,
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// it returns "", "".
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func scanETag(s string) (etag string, remain string) {
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s = strings.TrimLeft(s, " \t\n\r")
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start := 0
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if strings.HasPrefix(s, "W/") {
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start = 2
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}
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if len(s[start:]) < 2 || s[start] != '"' {
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return "", ""
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}
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// ETag is either W/"text" or "text".
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// See RFC 7232 2.3.
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for i := start + 1; i < len(s); i++ {
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c := s[i]
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switch {
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// Character values allowed in ETags.
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case c == 0x21 || c >= 0x23 && c <= 0x7E || c >= 0x80:
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case c == '"':
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return s[:i+1], s[i+1:]
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default:
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return "", ""
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}
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}
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return "", ""
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}
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// etagMatch returns whether the given eTag matches an IM/INM header value.
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// The empty string in etag is interpreted as a non-existent object.
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func etagMatch(etag, header string) bool {
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if header == "" {
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return false
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}
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if header == etag {
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return true
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}
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for {
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header = strings.TrimLeft(header, " \t\n\r")
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if len(header) == 0 {
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break
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}
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if header[0] == ',' {
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header = header[1:]
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continue
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}
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if header[0] == '*' {
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return etag != ""
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}
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e, remain := scanETag(header)
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if e == "" {
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break
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}
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if e == etag {
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return true
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}
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header = remain
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}
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return false
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}
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func writeNotModified(w http.ResponseWriter) {
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// RFC 7232 section 4.1:
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// a sender SHOULD NOT generate representation metadata other than the
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// above listed fields unless said metadata exists for the purpose of
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// guiding cache updates (e.g., Last-Modified might be useful if the
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// response does not have an ETag field).
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h := w.Header()
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delete(h, "Content-Type")
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delete(h, "Content-Length")
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delete(h, "Content-Encoding")
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if h.Get("Etag") != "" {
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delete(h, "Last-Modified")
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}
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w.WriteHeader(http.StatusNotModified)
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}
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// checkPreconditions evaluates request preconditions.
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// It interprets an empty etag as a non-existent object.
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func checkPreconditions(w http.ResponseWriter, r *http.Request, etag string) (done bool) {
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// RFC 7232 section 6.
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im := r.Header.Get("If-Match")
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if im != "" && !etagMatch(etag, im) {
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w.WriteHeader(http.StatusPreconditionFailed)
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return true
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}
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inm := r.Header.Get("If-None-Match")
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if inm != "" && etagMatch(etag, inm) {
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if r.Method == "GET" || r.Method == "HEAD" {
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writeNotModified(w)
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return true
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} else {
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w.WriteHeader(http.StatusPreconditionFailed)
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return true
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}
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}
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return false
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}
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114
webserver/precondition_test.go
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114
webserver/precondition_test.go
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package webserver
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import (
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"net/http"
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"testing"
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)
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type testWriter struct {
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statusCode int
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}
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func (w *testWriter) Header() http.Header {
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return nil
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}
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func (w *testWriter) Write(buf []byte) (int, error) {
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return len(buf), nil
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}
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func (w *testWriter) WriteHeader(statusCode int) {
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if w.statusCode != 0 {
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panic("WriteHeader called twice")
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}
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w.statusCode = statusCode
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}
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func TestEtagMatch(t *testing.T) {
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type tst struct {
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etag, header string
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}
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var match = []tst{
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{`"foo"`, `"foo"`},
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{`"foo"`, ` "foo"`},
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{`"foo"`, `"foo" `},
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{`"foo"`, ` "foo" `},
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{`"foo"`, `"foo", "bar"`},
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{`"foo"`, `"bar", "foo"`},
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{`W/"foo"`, `W/"foo"`},
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}
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var mismatch = []tst{
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{``, ``},
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{``, `*`},
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{``, `"foo"`},
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{`"foo"`, ``},
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{`"foo"`, `"bar"`},
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{`"foo"`, `"bar", "baz"`},
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{`"foo"`, `"baz", "bar"`},
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{`"foo"`, `W/"foo"`},
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{`W/"foo"`, `"foo"`},
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}
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for _, tst := range match {
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m := etagMatch(tst.etag, tst.header)
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if !m {
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t.Errorf("%#v %#v: got %v, expected true",
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tst.etag, tst.header, m,
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)
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}
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}
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for _, tst := range mismatch {
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m := etagMatch(tst.etag, tst.header)
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if m {
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t.Errorf("%#v %#v: got %v, expected false",
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tst.etag, tst.header, m,
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)
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}
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}
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}
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func TestCheckPreconditions(t *testing.T) {
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var tests = []struct {
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method, etag, im, inm string
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result int
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}{
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{"GET", ``, ``, ``, 0},
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{"GET", ``, `*`, ``, 412},
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{"GET", ``, ``, `*`, 0},
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{"POST", ``, `*`, ``, 412},
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{"POST", ``, ``, `*`, 0},
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{"GET", `"123"`, ``, ``, 0},
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{"GET", `"123"`, `"123"`, ``, 0},
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{"GET", `"123"`, `"124"`, ``, 412},
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{"POST", `"123"`, `"124"`, ``, 412},
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{"GET", `"123"`, `*`, ``, 0},
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{"GET", `"123"`, ``, `"123"`, 304},
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{"POST", `"123"`, ``, `"123"`, 412},
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{"GET", `"123"`, ``, `"124"`, 0},
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{"GET", `"123"`, ``, `*`, 304},
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}
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for _, tst := range tests {
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var w testWriter
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h := make(http.Header)
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if tst.im != "" {
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h.Set("If-Match", tst.im)
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}
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if tst.inm != "" {
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h.Set("If-None-Match", tst.inm)
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}
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r := http.Request{
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Method: tst.method,
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Header: h,
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}
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done := checkPreconditions(&w, &r, tst.etag)
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if done != (tst.result != 0) || w.statusCode != tst.result {
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t.Errorf("%#v %#v %#v: got %v, expected %v",
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tst.etag, tst.im, tst.inm,
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w.statusCode, tst.result)
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}
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}
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}
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