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If signer had to cap the AMP doc, don't sign and proxy full document. #444

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Jun 24, 2020
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If signer had to cap the AMP doc, don't sign and proxy full document. #444

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18 changes: 17 additions & 1 deletion packager/signer/signer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -466,13 +466,29 @@ func formatLinkHeader(preloads []*rpb.Metadata_Preload) (string, error) {

// serveSignedExchange does the actual work of transforming, packaging and signed and writing to the response.
func (this *Signer) serveSignedExchange(resp http.ResponseWriter, fetchResp *http.Response, signURL *url.URL, act string, transformVersion int64) {
// After this, fetchResp.Body is consumed, and attempts to read or proxy it will result in an empty body.
// Cap with maxBodyLength to limit the memory that serveSignedExchange
// consumes per request. The serveSignedExchange implementation requires all
// the response body in memory, and doesn't work on streamed data.
fetchBody, err := ioutil.ReadAll(io.LimitReader(fetchResp.Body, maxBodyLength))
if err != nil {
util.NewHTTPError(http.StatusBadGateway, "Error reading body: ", err).LogAndRespond(resp)
return
}

// If the cap has been applied, it means the document is too large. Signer
// won't load all the body into memory, and therefore won't sign the
// document. But signer can still proxy the document unsigned: first write
// the capped part of the body that signer has already read, and then call
// proxy to write headers and stream the rest of the body. ResponseWriter
// will make sure the headers are eventually sent before the body.
if len(fetchBody) == maxBodyLength {
resp.Write(fetchBody)
proxy(resp, fetchResp, nil)
return
}

// Now that fetchResp.Body is consumed, attempts to read or proxy it will result in an empty body.

// Perform local transformations.
r := getTransformerRequest(this.rtvCache, string(fetchBody), signURL.String())
r.Version = transformVersion
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20 changes: 20 additions & 0 deletions packager/signer/signer_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1035,3 +1035,23 @@ func (this *SignerSuite) TestPrometheusMetricGatewayRequestsLatency() {
}

}

func (this *SignerSuite) TestIfCappedDontSignAndProxyFullDocument() {
urlSets := []util.URLSet{{
Sign: &util.URLPattern{[]string{"https"}, "", this.httpsHost(), stringPtr("/amp/.*"), []string{}, stringPtr(""), false, 2000, nil}}}

const uncappedTailLength = 100
veryLongString := strings.Repeat("a", maxBodyLength+uncappedTailLength)
var customFakeBody = []byte("<html amp><body>" + veryLongString)

this.fakeHandler = func(resp http.ResponseWriter, req *http.Request) {
resp.Header().Set("Content-Type", "text/html")
resp.Write(customFakeBody)
}
resp := pkgt.NewRequest(this.T(), this.new(urlSets), "/priv/doc?sign="+url.QueryEscape(this.httpsURL()+fakePath)).SetHeaders("", header).Do()
this.Assert().Equal(http.StatusOK, resp.StatusCode, "incorrect status: %#v", resp)

body, err := ioutil.ReadAll(resp.Body)
this.Require().NoError(err)
this.Assert().Equal(customFakeBody, body, "incorrect body: %#v", resp)
}