How to modify HTTP response body? #19

soraliu · 2020-06-02T09:54:51Z

I found that there are a lot of materials about modifying HTTP response headers. I want to inject some static codes into the HTTP response body, and how can I do it?

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width" />
    <title>title</title>
  </head>
  <body>
    body
  </body>
</html>

I want to inject some codes into HTML.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width" />
    <title>title</title>
    <!-- the following codes are injected by envoy-filter -->
    <meta name="custom" content="value" />
  </head>
  <body>
    body
  </body>
</html>

I would be very appreciative if somebody can help me.

soraliu · 2020-06-03T02:45:18Z

@yuval-k Hi man, may I ask for your help? 😂

yuval-k · 2020-06-16T12:43:24Z

Hi!
I'm not sure if it is possible with the current ABI; will have to check if the upstream ABI has updated to allow for this...

RichiCoder1 · 2020-08-25T22:28:04Z

Would be very interested in this. Could potentially enable something like https://github.com/inikulin/parse5/blob/master/packages/parse5-html-rewriting-stream/docs/index.md or https://github.com/cloudflare/lol-html at the proxy level (assuming there's also a way to get body chunks)

esnible · 2020-08-30T17:01:27Z

My guess is that we are expected to return StopIterationAndBuffer from onResponseBody(), then later use the buffers in a call to send_local_response(). I haven't gotten this working yet but that is the route I am attempting.

RichiCoder1 · 2020-08-30T17:08:56Z

@esnible The appropriate APIs exists it looks like. See the Rust sdk for an example. https://github.com/proxy-wasm/proxy-wasm-rust-sdk/blob/master/examples/http_body.rs

Specifically set_response_body which appears to just be an abstraction of set_buffer which may or may not exist in this SDK?

yuval-k · 2020-08-31T02:16:18Z

i would not use send_local_reply for this purpose; i believe send_local_reply also sends the headers, so not sure if it can be called when orResponseBody happens;

what you probably want to do is manipulate the buffer as it goes through onResponseBody. this way you also minimize memory footprint

esnible · 2020-08-31T12:03:47Z

@yuval-k I have a user who wants to use WASM to recreate his current NGINX configuration which uses error_page and proxy_pass to fetch UI from one microservice to replace the error page generated by a different microservice.

I'm not an NGINX guy. We thought maybe an EnvoyFilter could detect HTTP status codes on text/html pages, and if it saw a problem do httpCall() and use the results of that call as the body to the original call, keeping the original headers.

What do you think?

ceastman-ibm · 2020-08-31T14:59:46Z

Here is the current workaround that I have: @esnible and I are working on this together:

function envoy_on_response(response_handle)
headers = response_handle:headers()
streamInfo = response_handle:streamInfo()
dynamicMetadata = streamInfo:dynamicMetadata()
requestData = dynamicMetadata:get("request_headers")

-- This section of code is for redirecting to maintenance if a 4xx or 5xx status code is detected

if string.match(headers:get(":status"), '[4-5].*') and requestData["accept"] ~= nil and string.find(string.lower(requestData["accept"]), "application/json") == nil then
maintenance_url = "https://"..requestData["request_authority"].."/maintenance/"..headers:get(":status")
headers:replace("location", maintenance_url)
headers:replace(":status", "302")
end

basically the goal is that the browser url doesn't change(redirect), it just displays a nice custom html page instead of the enovy test status page.

the maintenance microservice is inside the istio mesh.

cortex93 · 2021-07-24T13:08:33Z

Hi, any news on that ?

All other sdks (cpp, rust, go, zig) are importing proxy_set_buffer_bytes to allow to modify the BufferTypeValues.HttpResponseBody.

The goal is to be able to do the same thing as in this envoy sample https://github.com/envoyproxy/envoy/blob/6834081f835d609606e77ef84d734e30fc403d58/examples/wasm-cc/envoy_filter_http_wasm_updated_example.cc#L83

yuval-k · 2021-07-29T00:43:21Z

@cortex93 whatever you can do with other WASM envoy runtime, you should be able to do with this one as well.

cortex93 · 2021-07-29T19:17:19Z

@cortex93 whatever you can do with other WASM envoy runtime, you should be able to do with this one as well.

I may have missed something but https://github.com/solo-io/proxy-runtime/blob/master/assembly/imports.ts is not importing proxy_set_buffer_bytes and this sdk is not exporting some helper as others sdk.

It seems clear to you but this thread is all about that and after more than a year, no one come with a working solution. Maybe you can share a sample ?

kathuriasumit · 2023-06-21T10:43:42Z

Hi @yuval-k, I am trying out the proxy_set_buffer_bytes implementation, This basically overrides the bytes in existing buffer, What if there is a need to enrich response body and required additional bytes in buffer? Do you have any suggestion for this use case?

kathuriasumit · 2023-06-22T10:39:37Z

Hi @yuval-k, I am trying out the proxy_set_buffer_bytes implementation, This basically overrides the bytes in existing buffer, What if there is a need to enrich response body and required additional bytes in buffer? Do you have any suggestion for this use case?

Sharing below one of working approach.

onResponseBody(body_buffer_length: usize, end_of_stream: bool): FilterDataStatusValues {
   if (!end_of_stream) {
     this.upstream_response_size = this.upstream_response_size + u32(body_buffer_length);
     return FilterDataStatusValues.StopIterationAndBuffer;
   }
   // read the response
   let original_response_body_buffer = get_buffer_bytes(BufferTypeValues.HttpResponseBody, 0, 
   this.upstream_response_size);
   let response_body_buffer = ...;
   // update the buffer
   set_buffer_bytes(BufferTypeValues.HttpResponseBody, 0, response_body_buffer.byteLength, response_body_buffer);
   return FilterDataStatusValues.Continue
   }
 
onResponseHeaders(a: u32, end_of_stream: bool): FilterHeadersStatusValues {
  // update the content length header
  stream_context.headers.response.replace("content-length", new_response_content_length.toString());
  }
   ```

yuval-k mentioned this issue Jun 16, 2020

how would I go about writing a filter to transform the response body #20

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How to modify HTTP response body? #19

How to modify HTTP response body? #19

soraliu commented Jun 2, 2020 •

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soraliu commented Jun 3, 2020 •

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yuval-k commented Jun 16, 2020

RichiCoder1 commented Aug 25, 2020

esnible commented Aug 30, 2020

RichiCoder1 commented Aug 30, 2020

yuval-k commented Aug 31, 2020

esnible commented Aug 31, 2020

ceastman-ibm commented Aug 31, 2020 •

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cortex93 commented Jul 24, 2021

yuval-k commented Jul 29, 2021

cortex93 commented Jul 29, 2021

kathuriasumit commented Jun 21, 2023

kathuriasumit commented Jun 22, 2023

How to modify HTTP response body? #19

How to modify HTTP response body? #19

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soraliu commented Jun 2, 2020 • edited Loading

soraliu commented Jun 3, 2020 • edited Loading

yuval-k commented Jun 16, 2020

RichiCoder1 commented Aug 25, 2020

esnible commented Aug 30, 2020

RichiCoder1 commented Aug 30, 2020

yuval-k commented Aug 31, 2020

esnible commented Aug 31, 2020

ceastman-ibm commented Aug 31, 2020 • edited Loading

cortex93 commented Jul 24, 2021

yuval-k commented Jul 29, 2021

cortex93 commented Jul 29, 2021

kathuriasumit commented Jun 21, 2023

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soraliu commented Jun 2, 2020 •

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soraliu commented Jun 3, 2020 •

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ceastman-ibm commented Aug 31, 2020 •

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