feat(server): Implement microhttpd framework (#241)

* feat(server): Implement server core functions with microhttpd

* feat(server): Implement signal handler to terminate TA

- Add signal handler for SIGINT and SIGTERM
- Add logger when error occurred, starting and destroying TA

* feat(server): Implement URL parser

* Match request URL with regular expression
* Parse parameter to use with strtok

* feat(server): Implement generate_address API callback function

* feat(server): Implement find_txn_by_tag API callback function

* feat(server): Implement find_txn_obj_by_tag API callback function

* feat(server): Implement get_txn_obj API callback function

* feat(server): Implement get_tips_pair API callback function

* feat(server): Implement get_tips API callback function

* feat(server): Implement send_transfer API callback function

* feat(server): Implement recv_mam_msg API callback function

* feat(server): Implement send_mam_msg API callback function

* feat(server): Implement invalid path handling callback function

* feat(server): Implement OPTIONS request handling callback function

* feat(server): Implement send_trytes API callback function

* fix(server): Rename POST and OPTIONS flag

* fix: Refactor codelines to meet coding style

* feat(server): Implement req / res log message

* fix(server): Fix wrong url length in ta_get_url_parameter

* fix(api): Update find txn related apis (#237)

* fix(server): Check request body in POST api callback functions (#239)

If the GET request has the same url with the POST apis, it should return
a method_not_allowed response. Thus we should check if body is empty or not
in the callback functions before execution.

* fix(server): Modify error code switch case in set_response_content (#240)

accelerator/BUILD

@@ -13,6 +13,18 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "accelerator_microhttpd",
+    srcs = ["main.c"],
+    copts = ["-DLOGGER_ENABLE"],
+    deps = [
+        ":http",
+        ":ta_config",
+        ":ta_errors",
+        "@entangled//utils/handles:signal",
+    ],
+)
+
 cc_image(
     name = "ta_image",
     binary = ":accelerator",
@@ -34,6 +46,19 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "http",
+    srcs = ["http.c"],
+    hdrs = ["http.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":apis",
+        ":ta_config",
+        ":ta_errors",
+        "@libmicrohttpd",
+    ],
+)
+
 cc_library(
     name = "common_core",
     srcs = ["common_core.c"],

accelerator/errors.h

@@ -51,6 +51,7 @@ extern "C" {
 #define SC_MODULE_RES (0x06 << SC_MODULE_SHIFT)
 #define SC_MODULE_CONF (0x07 << SC_MODULE_SHIFT)
 #define SC_MODULE_UTILS (0x08 << SC_MODULE_SHIFT)
+#define SC_MODULE_HTTP (0x09 << SC_MODULE_SHIFT)
 /** @} */
 
 /** @name serverity code */
@@ -147,9 +148,22 @@ typedef enum {
   SC_CONF_UNKNOWN_OPTION = 0x03 | SC_MODULE_CONF | SC_SEVERITY_FATAL,
   /**< undefined option in CLI */
 
+  // UTILS module
   SC_UTILS_NULL = 0x01 | SC_MODULE_UTILS | SC_SEVERITY_FATAL,
   SC_UTILS_WRONG_REQUEST_OBJ = 0x02 | SC_MODULE_UTILS | SC_SEVERITY_FATAL,
   /**< wrong TA request object */
+
+  // HTTP module
+  SC_HTTP_OOM = 0x01 | SC_MODULE_HTTP | SC_SEVERITY_FATAL,
+  /**< Fail to create http object */
+  SC_HTTP_NULL = 0x02 | SC_MODULE_HTTP | SC_SEVERITY_FATAL,
+  /**< NULL object in http */
+  SC_HTTP_INVALID_REGEX = 0x03 | SC_MODULE_HTTP | SC_SEVERITY_MAJOR,
+  /**< Invalid URL regular expression rule in http */
+  SC_HTTP_URL_NOT_MATCH = 0x04 | SC_MODULE_HTTP | SC_SEVERITY_MAJOR,
+  /**< URL doesn't match regular expression rule */
+  SC_HTTP_URL_PARSE_ERROR = 0x05 | SC_MODULE_HTTP | SC_SEVERITY_MAJOR,
+  /**< URL parameter parsing error */
 } status_t;
 
 typedef enum {