Add an option to set the expect 100 timeout (#376)

For larger request bodies, `curl` will use an `Expect` header to first validate
the request headers before sending the actual body. However, if the server does not
reply within `CURLOPT_EXPECT_100_TIMEOUT_MS` then the server will send the request anyways.

This behaviour can sometimes lead to higher total latency since in the best case, an additional
server roundtrip is required and in the worst case, the request is delayed by `CURLOPT_EXPECT_100_TIMEOUT_MS`.

The best-case scenario is where the request is invalid and the server replies with a `417 Expectation Failed`
without having to wait for or process the request body at all.

This commit adds the ability to define a custom timeout or override it by setting it to zero.

.gitignore

@@ -1,2 +1,3 @@
 Cargo.lock
 target/
+.idea/

curl-sys/lib.rs

@@ -574,6 +574,7 @@ pub const CURLOPT_SSL_OPTIONS: CURLoption = CURLOPTTYPE_LONG + 216;
 // pub const CURLOPT_DNS_LOCAL_IP4: CURLoption = CURLOPTTYPE_OBJECTPOINT + 222;
 // pub const CURLOPT_DNS_LOCAL_IP6: CURLoption = CURLOPTTYPE_OBJECTPOINT + 223;
 // pub const CURLOPT_LOGIN_OPTIONS: CURLoption = CURLOPTTYPE_OBJECTPOINT + 224;
+pub const CURLOPT_EXPECT_100_TIMEOUT_MS: CURLoption = CURLOPTTYPE_LONG + 227;
 pub const CURLOPT_UNIX_SOCKET_PATH: CURLoption = CURLOPTTYPE_OBJECTPOINT + 231;
 pub const CURLOPT_PIPEWAIT: CURLoption = CURLOPTTYPE_LONG + 237;
 pub const CURLOPT_CONNECT_TO: CURLoption = CURLOPTTYPE_OBJECTPOINT + 243;

src/easy/handler.rs

@@ -2290,6 +2290,33 @@ impl<H> Easy2<H> {
     // =========================================================================
     // getters
 
+    /// Set maximum time to wait for Expect 100 request before sending body.
+    ///
+    /// `curl` has internal heuristics that trigger the use of a `Expect`
+    /// header for large enough request bodies where the client first sends the
+    /// request header along with an `Expect: 100-continue` header. The server
+    /// is supposed to validate the headers and respond with a `100` response
+    /// status code after which `curl` will send the actual request body.
+    ///
+    /// However, if the server does not respond to the initial request
+    /// within `CURLOPT_EXPECT_100_TIMEOUT_MS` then `curl` will send the
+    /// request body anyways.
+    ///
+    /// The best-case scenario is where the request is invalid and the server
+    /// replies with a `417 Expectation Failed` without having to wait for or process
+    /// the request body at all. However, this behaviour can also lead to higher
+    /// total latency since in the best case, an additional server roundtrip is required
+    /// and in the worst case, the request is delayed by `CURLOPT_EXPECT_100_TIMEOUT_MS`.
+    ///
+    /// More info: https://curl.se/libcurl/c/CURLOPT_EXPECT_100_TIMEOUT_MS.html
+    ///
+    /// By default this option is not set and corresponds to
+    /// `CURLOPT_EXPECT_100_TIMEOUT_MS`.
+    pub fn expect_100_timeout(&mut self, timeout: Duration) -> Result<(), Error> {
+        let ms = timeout.as_secs() * 1000 + (timeout.subsec_nanos() / 1_000_000) as u64;
+        self.setopt_long(curl_sys::CURLOPT_EXPECT_100_TIMEOUT_MS, ms as c_long)
+    }
+
     /// Get info on unmet time conditional
     ///
     /// Returns if the condition provided in the previous request didn't match