http_body.rs

// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use proxy_wasm::traits::*;
use proxy_wasm::types::*;

#[no_mangle]
pub fn _start() {
    proxy_wasm::set_log_level(LogLevel::Trace);
    proxy_wasm::set_root_context(|_| -> Box<dyn RootContext> { Box::new(HttpBodyRoot) });
}

struct HttpBodyRoot;

impl Context for HttpBodyRoot {}

impl RootContext for HttpBodyRoot {
    fn on_create_child_context(&mut self, _context_id: u32) -> Option<ChildContext> {
        Some(ChildContext::HttpContext(Box::new(HttpBody)))
    }
}

struct HttpBody;

impl Context for HttpBody {}

impl HttpContext for HttpBody {
    fn on_http_response_headers(&mut self, _: usize) -> Action {
        // If there is a Content-Length header and we change the length of
        // the body later, then clients will break. So remove it.
        // We must do this here, because once we exit this function we
        // can no longer modify the response headers.
        self.set_http_response_header("content-length", None);
        Action::Continue
    }

    fn on_http_response_body(&mut self, body_size: usize, end_of_stream: bool) -> Action {
        if !end_of_stream {
            // Wait -- we'll be called again when the complete body is buffered
            // at the host side.
            return Action::Pause;
        }

        // Replace the message body if it contains the text "secret".
        // Since we returned "Pause" previuously, this will return the whole body.
        if let Some(body_bytes) = self.get_http_response_body(0, body_size) {
            let body_str = String::from_utf8(body_bytes).unwrap();
            if body_str.contains("secret") {
                let new_body = format!("Original message body ({} bytes) redacted.", body_size);
                self.set_http_response_body(0, body_size, &new_body.into_bytes());
            }
        }
        Action::Continue
    }
}