gzip compression for requests

Application Insights supports gzip compression for requests to `POST
/v2/track`. When sending lots of telemetry items, network time starts
to be the limiting factor and compression helps with this.

Gzip compression is turned on by default and cannot be disabled. As far
as I can tell this is the same behaviour as the Application Insights
.NET SDK. If compression turns out to be an issue for some users, it
could be made optional in the future.

Author: frigus02

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+- Use gzip compression (`Content-Encoding: gzip`) for `POST /v2/track` HTTP request.
+
 ## [0.19.0] - 2022-01-23
 
 - Upgrade to `v0.17.0` of `opentelemetry`.

Cargo.toml

@@ -34,6 +34,7 @@ metrics = ["opentelemetry/metrics", "ureq"]
 async-trait = "0.1"
 bytes = "1"
 chrono = "0.4"
+flate2 = "1"
 http = "0.2"
 once_cell = "1"
 opentelemetry = "0.17"

src/lib.rs

@@ -511,6 +511,13 @@ pub enum Error {
     #[error("serializing upload request failed with {0}")]
     UploadSerializeRequest(serde_json::Error),
 
+    /// Application Insights telemetry data failed serialize or compress. Telemetry reporting failed
+    /// because of this.
+    ///
+    /// Note: This is an error in this crate. If you spot this, please open an issue.
+    #[error("compressing upload request failed with {0}")]
+    UploadCompressRequest(std::io::Error),
+
     /// Application Insights telemetry response failed to deserialize from JSON.
     ///
     /// Telemetry reporting may have worked. But since we could not look into the response, we

src/uploader.rs

@@ -1,5 +1,7 @@
 use crate::{models::Envelope, Error, HttpClient};
 use bytes::Bytes;
+use flate2::write::GzEncoder;
+use flate2::Compression;
 use http::{Request, Response, Uri};
 use serde::Deserialize;
 #[cfg(feature = "metrics")]
@@ -33,9 +35,10 @@ pub(crate) async fn send(
     endpoint: &Uri,
     items: Vec<Envelope>,
 ) -> Result<(), Error> {
-    let payload = serde_json::to_vec(&items).map_err(Error::UploadSerializeRequest)?;
+    let payload = serialize_request_body(items)?;
     let request = Request::post(endpoint)
         .header(http::header::CONTENT_TYPE, "application/json")
+        .header(http::header::CONTENT_ENCODING, "gzip")
         .body(payload)
         .expect("request should be valid");
 
@@ -50,11 +53,12 @@ pub(crate) async fn send(
 /// Sends a telemetry items to the server.
 #[cfg(feature = "metrics")]
 pub(crate) fn send_sync(endpoint: &Uri, items: Vec<Envelope>) -> Result<(), Error> {
-    let payload = serde_json::to_vec(&items).map_err(Error::UploadSerializeRequest)?;
+    let payload = serialize_request_body(items)?;
 
     // TODO Implement retries
     let response = match ureq::post(&endpoint.to_string())
         .set(http::header::CONTENT_TYPE.as_str(), "application/json")
+        .set(http::header::CONTENT_ENCODING.as_str(), "gzip")
         .send_bytes(&payload)
     {
         Ok(response) => response,
@@ -79,6 +83,12 @@ pub(crate) fn send_sync(endpoint: &Uri, items: Vec<Envelope>) -> Result<(), Erro
     )
 }
 
+fn serialize_request_body(items: Vec<Envelope>) -> Result<Vec<u8>, Error> {
+    let mut gzip_encoder = GzEncoder::new(Vec::new(), Compression::default());
+    serde_json::to_writer(&mut gzip_encoder, &items).map_err(Error::UploadSerializeRequest)?;
+    gzip_encoder.finish().map_err(Error::UploadCompressRequest)
+}
+
 fn handle_response(response: Response<Bytes>) -> Result<(), Error> {
     match response.status().as_u16() {
         STATUS_OK => Ok(()),

tests/http_requests.rs

@@ -206,6 +206,7 @@ mod tick {
 }
 
 mod format {
+    use flate2::read::GzDecoder;
     use http::Request;
     use regex::Regex;
 
@@ -250,7 +251,9 @@ mod format {
     }
 
     fn pretty_print_json(body: &[u8]) -> String {
-        let json: serde_json::Value = serde_json::from_slice(body).expect("body is valid json");
+        let gzip_decoder = GzDecoder::new(body);
+        let json: serde_json::Value =
+            serde_json::from_reader(gzip_decoder).expect("body is valid json");
         serde_json::to_string_pretty(&json).unwrap()
     }
 }

tests/snapshots/http_requests__traces_batch_async_std.snap

@@ -1,12 +1,13 @@
 ---
 source: tests/http_requests.rs
-assertion_line: 131
+assertion_line: 100
 expression: traces_batch_async_std
 
 ---
 POST /v2/track HTTP/1.1
 host: dc.services.visualstudio.com
 content-type: application/json
+content-encoding: gzip
 
 [
   {

tests/snapshots/http_requests__traces_batch_tokio.snap

@@ -1,12 +1,13 @@
 ---
 source: tests/http_requests.rs
-assertion_line: 145
+assertion_line: 114
 expression: traces_batch_tokio
 
 ---
 POST /v2/track HTTP/1.1
 host: dc.services.visualstudio.com
 content-type: application/json
+content-encoding: gzip
 
 [
   {

tests/snapshots/http_requests__traces_simple.snap

@@ -7,6 +7,7 @@ expression: traces_simple
 POST /v2/track HTTP/1.1
 host: dc.services.visualstudio.com
 content-type: application/json
+content-encoding: gzip
 
 [
   {
@@ -92,6 +93,7 @@ content-type: application/json
 POST /v2/track HTTP/1.1
 host: dc.services.visualstudio.com
 content-type: application/json
+content-encoding: gzip
 
 [
   {