src: refactor method parsing

Use a switch and a macro to branch parsing of HTTP methods.
Easier to read and much shorter.

In this commit, the order of branches dispatching is the same as in the
original code, to ease review. Reordering branches by descending
frequency will improve speed too.

PR-URL: https://github.com/nodejs/http-parser/pull/273
Reviewed-By: Fedor Indutny <fedor@indutny.com>

http_parser.c

@@ -1007,89 +1007,40 @@ reexecute:
           UPDATE_STATE(s_req_spaces_before_url);
         } else if (ch == matcher[parser->index]) {
           ; /* nada */
-        } else if (parser->method == HTTP_CONNECT) {
-          if (parser->index == 1 && ch == 'H') {
-            parser->method = HTTP_CHECKOUT;
-          } else if (parser->index == 2  && ch == 'P') {
-            parser->method = HTTP_COPY;
-          } else {
-            SET_ERRNO(HPE_INVALID_METHOD);
-            goto error;
-          }
-        } else if (parser->method == HTTP_MKCOL) {
-          if (parser->index == 1 && ch == 'O') {
-            parser->method = HTTP_MOVE;
-          } else if (parser->index == 1 && ch == 'E') {
-            parser->method = HTTP_MERGE;
-          } else if (parser->index == 1 && ch == '-') {
-            parser->method = HTTP_MSEARCH;
-          } else if (parser->index == 2 && ch == 'A') {
-            parser->method = HTTP_MKACTIVITY;
-          } else if (parser->index == 3 && ch == 'A') {
-            parser->method = HTTP_MKCALENDAR;
-          } else {
-            SET_ERRNO(HPE_INVALID_METHOD);
-            goto error;
-          }
-        } else if (parser->method == HTTP_SUBSCRIBE) {
-          if (parser->index == 1 && ch == 'E') {
-            parser->method = HTTP_SEARCH;
-          } else {
-            SET_ERRNO(HPE_INVALID_METHOD);
-            goto error;
-          }
-        } else if (parser->method == HTTP_REPORT) {
-            if (parser->index == 2 && ch == 'B') {
-              parser->method = HTTP_REBIND;
-            } else {
-              SET_ERRNO(HPE_INVALID_METHOD);
-              goto error;
-            }
-        } else if (parser->index == 1) {
-          if (parser->method == HTTP_POST) {
-            if (ch == 'R') {
-              parser->method = HTTP_PROPFIND; /* or HTTP_PROPPATCH */
-            } else if (ch == 'U') {
-              parser->method = HTTP_PUT; /* or HTTP_PURGE */
-            } else if (ch == 'A') {
-              parser->method = HTTP_PATCH;
-            } else {
-              SET_ERRNO(HPE_INVALID_METHOD);
-              goto error;
-            }
-          } else if (parser->method == HTTP_LOCK) {
-            if (ch == 'I') {
-              parser->method = HTTP_LINK;
-            } else {
-              SET_ERRNO(HPE_INVALID_METHOD);
-              goto error;
-            }
-          }
-        } else if (parser->index == 2) {
-          if (parser->method == HTTP_PUT) {
-            if (ch == 'R') {
-              parser->method = HTTP_PURGE;
-            } else {
-              SET_ERRNO(HPE_INVALID_METHOD);
-              goto error;
-            }
-          } else if (parser->method == HTTP_UNLOCK) {
-            if (ch == 'S') {
-              parser->method = HTTP_UNSUBSCRIBE;
-            } else if(ch == 'B') {
-              parser->method = HTTP_UNBIND;
-            } else {
+        } else if (IS_ALPHA(ch)) {
+
+          switch (parser->method << 16 | parser->index << 8 | ch) {
+#define XX(meth, pos, ch, new_meth) \
+            case (HTTP_##meth << 16 | pos << 8 | ch): \
+              parser->method = HTTP_##new_meth; break;
+
+            XX(POST,      1, 'U', PUT)
+            XX(POST,      1, 'A', PATCH)
+            XX(CONNECT,   1, 'H', CHECKOUT)
+            XX(CONNECT,   2, 'P', COPY)
+            XX(MKCOL,     1, 'O', MOVE)
+            XX(MKCOL,     1, 'E', MERGE)
+            XX(MKCOL,     2, 'A', MKACTIVITY)
+            XX(MKCOL,     3, 'A', MKCALENDAR)
+            XX(SUBSCRIBE, 1, 'E', SEARCH)
+            XX(REPORT,    2, 'B', REBIND)
+            XX(POST,      1, 'R', PROPFIND)
+            XX(PROPFIND,  4, 'P', PROPPATCH)
+            XX(PUT,       2, 'R', PURGE)
+            XX(LOCK,      1, 'I', LINK)
+            XX(UNLOCK,    2, 'S', UNSUBSCRIBE)
+            XX(UNLOCK,    2, 'B', UNBIND)
+            XX(UNLOCK,    3, 'I', UNLINK)
+#undef XX
+
+            default:
               SET_ERRNO(HPE_INVALID_METHOD);
               goto error;
-            }
-          } else {
-            SET_ERRNO(HPE_INVALID_METHOD);
-            goto error;
           }
-        } else if (parser->index == 4 && parser->method == HTTP_PROPFIND && ch == 'P') {
-          parser->method = HTTP_PROPPATCH;
-        } else if (parser->index == 3 && parser->method == HTTP_UNLOCK && ch == 'I') {
-          parser->method = HTTP_UNLINK;
+        } else if (ch == '-' &&
+                   parser->index == 1 &&
+                   parser->method == HTTP_MKCOL) {
+          parser->method = HTTP_MSEARCH;
         } else {
           SET_ERRNO(HPE_INVALID_METHOD);
           goto error;