Make invocation URL dynamic

The API endpoint in Amazon's implementation of Lambda used the path
`/2015-03-31/functions/[func]/invocations` to invoke the function.
`[func]` the name of the function and is set as the value of the
`AWS_LAMBDA_FUNCTION_NAME` environment variable when the function
is executing on AWS.

The emulator uses a hard coded endpoint of
`/2015-03-31/functions/function/invocations`. This is even the case
when the `AWS_LAMBDA_FUNCTION_NAME` environment variable is set to
another value.

This patch changes the endpoint URL when the `AWS_LAMBDA_FUNCTION_NAME`
environment variable is set. In this case the invocation URL will
be `/2015-03-31/functions/${AWS_LAMBDA_FUNCTION_NAME}/invocations`.
When the environment variable isn't set, the current behaviour
persists and the function name is set to `function`.

The end result is the emulator behaviour is closer to the real
environment the functions execute in.

This PR fixes aws#43 I raised a few weeks ago.

cmd/aws-lambda-rie/http.go

@@ -9,13 +9,15 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func startHTTPServer(ipport string, sandbox Sandbox) {
+func startHTTPServer(ipport string, sandbox Sandbox, funcName string) {
 	srv := &http.Server{
 		Addr: ipport,
 	}
 
+	url := "/2015-03-31/functions/" + funcName + "/invocations"
+
 	// Pass a channel
-	http.HandleFunc("/2015-03-31/functions/function/invocations", func(w http.ResponseWriter, r *http.Request) {
+	http.HandleFunc(url, func(w http.ResponseWriter, r *http.Request) {
 		InvokeHandler(w, r, sandbox)
 	})
 

cmd/aws-lambda-rie/main.go

@@ -41,7 +41,8 @@ func main() {
 	go sandbox.Create()
 
 	testAPIipport := "0.0.0.0:8080"
-	startHTTPServer(testAPIipport, sandbox)
+	funcName := GetenvWithDefault("AWS_LAMBDA_FUNCTION_NAME", "function")
+	startHTTPServer(testAPIipport, sandbox, funcName)
 }
 
 func getCLIArgs() (options, []string) {

test/integration/local_lambda/test_end_to_end.py

@@ -60,7 +60,7 @@ def tearDownClass(cls):
                 arch_tag = "" if arch == "" else f"-{arch}"
                 cmd = f"docker rm -f {image}{arch_tag}"
                 Popen(cmd.split(" ")).communicate()
-            
+
         for arch in ARCHS:
             arch_tag = "" if arch == "" else f"-{arch}"
             Popen(f"docker rmi {cls.image_name}{arch_tag}".split(" ")).communicate()
@@ -136,7 +136,7 @@ def test_lambda_function_arn_exists_with_defining_custom_name(self, arch, port):
         time.sleep(SLEEP_TIME)
 
         r = requests.post(
-            f"http://localhost:{port}/2015-03-31/functions/function/invocations", json={}
+            f"http://localhost:{port}/2015-03-31/functions/MyCoolName/invocations", json={}
         )
         self.assertEqual(b'"My lambda ran succesfully"', r.content)
 
@@ -260,7 +260,7 @@ def test_function_name_is_overriden(self, arch, port):
         time.sleep(SLEEP_TIME)
 
         r = requests.post(
-            f"http://localhost:{port}/2015-03-31/functions/function/invocations", json={}
+            f"http://localhost:{port}/2015-03-31/functions/MyCoolName/invocations", json={}
         )
         self.assertEqual(b'"My lambda ran succesfully"', r.content)