feat(routing): implement router merging

src/http/lnm_http_router.c

@@ -28,6 +28,7 @@ void lnm_http_router_free(lnm_http_router *router) {
 
   for (size_t i = 0; i < lnm_http_method_total; i++) {
     lnm_http_route_free(router->routes[i]);
+    lnm_http_route_free(router->multi_segment_routes[i]);
   }
 
   free(router);
@@ -287,3 +288,145 @@ lnm_http_route_match_get(lnm_http_route_match *match, const char *key) {
 
   return &match->key_segments[trie->index];
 }
+
+bool lnm_http_router_conflicts(const lnm_http_router *r1,
+                               const lnm_http_router *r2) {
+  // First check the literal routes for the routers
+  for (lnm_http_method m = 0; m < lnm_http_method_total; m++) {
+    if ((r1->routes[m] != NULL && r2->routes[m] != NULL) ||
+        (r1->multi_segment_routes[m] != NULL &&
+         r2->multi_segment_routes[m] != NULL)) {
+      return true;
+    }
+  }
+
+  if ((r1->single_segment_child != NULL && r2->single_segment_child != NULL) &&
+      lnm_http_router_conflicts(r1->single_segment_child,
+                                r2->single_segment_child)) {
+    return true;
+  }
+
+  for (unsigned char c = 0; c < 128; c++) {
+    if ((r1->exact_children[c] != NULL && r2->exact_children[c] != NULL) &&
+        lnm_http_router_conflicts(r1->exact_children[c],
+                                  r2->exact_children[c])) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void __lnm_http_router_merge(lnm_http_router *r1, lnm_http_router *r2) {
+  for (lnm_http_method m = 0; m < lnm_http_method_total; m++) {
+    if (r2->routes[m] != NULL) {
+      r1->routes[m] = r2->routes[m];
+    }
+
+    if (r2->multi_segment_routes[m] != NULL) {
+      r1->multi_segment_routes[m] = r2->multi_segment_routes[m];
+    }
+  }
+
+  if (r1->single_segment_child != NULL && r2->single_segment_child != NULL) {
+    __lnm_http_router_merge(r1->single_segment_child, r2->single_segment_child);
+  } else if (r2->single_segment_child != NULL) {
+    r1->single_segment_child = r2->single_segment_child;
+  }
+
+  for (unsigned char c = 0; c < 128; c++) {
+    if (r1->exact_children[c] != NULL && r2->exact_children[c] != NULL) {
+      __lnm_http_router_merge(r1->exact_children[c], r2->exact_children[c]);
+    } else if (r2->exact_children[c] != NULL) {
+      r1->exact_children[c] = r2->exact_children[c];
+    }
+  }
+
+  r1->represents_route = r1->represents_route || r2->represents_route;
+
+  free(r2);
+}
+
+lnm_err lnm_http_router_merge(lnm_http_router *r1, lnm_http_router *r2) {
+  if (lnm_http_router_conflicts(r1, r2)) {
+    return lnm_err_overlapping_route;
+  }
+
+  __lnm_http_router_merge(r1, r2);
+
+  return lnm_err_ok;
+}
+
+lnm_err lnm_http_router_nest(lnm_http_router *parent, lnm_http_router *child,
+                             const char *prefix) {
+  size_t prefix_len = strlen(prefix);
+
+  if (!is_ascii(prefix) || prefix[0] != '/' || prefix[prefix_len - 1] == '/') {
+    return lnm_err_invalid_route;
+  }
+
+  lnm_http_router *merge_target = parent;
+
+  // The child router's routes are also mounted on '/', so we stop one earlier
+  // as we need to merge it with the router representing the '/'
+  while (*(prefix + 1) != '\0') {
+    unsigned char c = *prefix;
+
+    if (merge_target->exact_children[c] == NULL) {
+      LNM_RES(lnm_http_router_init(&merge_target->exact_children[c]));
+    }
+
+    merge_target = merge_target->exact_children[c];
+    prefix++;
+  }
+
+  // We check whether there are any conflicts between the child and the existing
+  // router
+  bool conflicting = merge_target->single_segment_child != NULL &&
+                     child->single_segment_child != NULL;
+
+  for (lnm_http_method m = 0; !conflicting && m < lnm_http_method_total; m++) {
+    conflicting =
+        conflicting ||
+        (merge_target->routes[m] != NULL && child->routes[m] != NULL) ||
+        (merge_target->multi_segment_routes[m] != NULL &&
+         child->multi_segment_routes[m] != NULL);
+  }
+
+  for (unsigned char c = 0; !conflicting && c < 128; c++) {
+    conflicting = conflicting || (merge_target->exact_children[c] != NULL &&
+                                  child->exact_children[c] != NULL);
+  }
+
+  if (conflicting) {
+    return lnm_err_overlapping_route;
+  }
+
+  // Merge routers
+  merge_target->represents_route =
+      merge_target->represents_route || child->represents_route;
+
+  if (child->single_segment_child != NULL) {
+    merge_target->single_segment_child = child->single_segment_child;
+  }
+
+  for (lnm_http_method m = 0; m < lnm_http_method_total; m++) {
+    if (child->routes[m] != NULL) {
+      merge_target->routes[m] = child->routes[m];
+    }
+
+    if (child->multi_segment_routes[m] != NULL) {
+      merge_target->multi_segment_routes[m] = child->multi_segment_routes[m];
+    }
+  }
+
+  for (unsigned char c = 0; c < 128; c++) {
+    if (child->exact_children[c] != NULL) {
+      merge_target->exact_children[c] = child->exact_children[c];
+    }
+  }
+
+  free(child);
+
+  return lnm_err_ok;
+}