RUST-1645 Fix AWS Lambda detection logic (#876)

Author: abr-egn

src/cmap/establish/handshake/mod.rs

@@ -223,7 +223,9 @@ impl FaasEnvironmentName {
     fn new() -> Option<Self> {
         use FaasEnvironmentName::*;
         let mut found: Option<Self> = None;
-        if var_set("AWS_EXECUTION_ENV") || var_set("AWS_LAMBDA_RUNTIME_API") {
+        let lambda_env = env::var_os("AWS_EXECUTION_ENV")
+            .map_or(false, |v| v.to_string_lossy().starts_with("AWS_Lambda_"));
+        if lambda_env || var_set("AWS_LAMBDA_RUNTIME_API") {
             found = Some(AwsLambda);
         }
         if var_set("VERCEL") {

src/test/spec/faas.rs

@@ -114,3 +114,9 @@ async fn invalid_wrong_type() -> Result<()> {
     ])
     .await
 }
+
+#[cfg_attr(feature = "tokio-runtime", tokio::test)]
+#[cfg_attr(feature = "async-std-runtime", async_std::test)]
+async fn invalid_aws_not_lambda() -> Result<()> {
+    check_faas_handshake(&[("AWS_EXECUTION_ENV", "EC2")]).await
+}