User can initiate a connection close. (#22)

include/aws/http/connection.h

@@ -127,6 +127,13 @@ AWS_EXTERN_C_BEGIN
 AWS_HTTP_API
 int aws_http_client_connect(const struct aws_http_client_connection_options *options);
 
+/**
+ * Begin shutdown sequence of the connection if it hasn't already started. It's safe to call this
+ * function regardless of the connection state as long as you hold a reference to the connection.
+ */
+AWS_HTTP_API
+int aws_http_client_connection_close(struct aws_http_connection *connection);
+
 /**
  * Users must release the connection when they are done with it.
  * The connection's memory cannot be reclaimed until this is done.

source/connection.c

@@ -166,7 +166,13 @@ static struct aws_http_connection *s_connection_new(
     return NULL;
 }
 
-/* TODO: probably should have a aws_http_connection_close(int error_code) function */
+int aws_http_client_connection_close(struct aws_http_connection *connection) {
+    if (connection->channel_slot->channel) {
+        return aws_channel_shutdown(connection->channel_slot->channel, AWS_ERROR_SUCCESS);
+    }
+
+    return AWS_OP_SUCCESS;
+}
 
 void aws_http_connection_release(struct aws_http_connection *connection) {
     assert(connection);