proxy: add ring_hash builtin

this is ketama-based, with options for minor compat changes with major
libraries.

does _not_ support weights. The weights bits in the original ketama
broke the algorithm, as changing the number of points would shift
unrelated servers when the list changes.

this also changes backends to take a "name" specifically, instead of an
"ip address". Though note if supplying a hostname instead of an IP there
might be inline DNS lookups on reconnects.

1 files changed, 18 insertions, 17 deletions

diff --git a/proxy_lua.c b/proxy_lua.c
index 2431417..f5f49c7 100644
--- a/proxy_lua.c
+++ b/proxy_lua.c
@@ -67,21 +67,25 @@ static int mcplib_backend_gc(lua_State *L) {
 }
 
 static int mcplib_backend(lua_State *L) {
-    luaL_checkstring(L, -4); // label for indexing backends.
-    const char *ip = luaL_checkstring(L, -3);
-    const char *port = luaL_checkstring(L, -2);
-    double weight = luaL_checknumber(L, -1);
+    luaL_checkstring(L, -3); // label for indexing backends.
+    size_t nlen = 0;
+    const char *name = luaL_checklstring(L, -2, &nlen);
+    const char *port = luaL_checkstring(L, -1);
     // FIXME (v2): upvalue for global ctx.
     proxy_ctx_t *ctx = settings.proxy_ctx;
 
+    if (nlen > MAX_NAMELEN-1) {
+        proxy_lua_error(L, "backend name too long");
+        return 0;
+    }
+
     // first check our reference table to compare.
     lua_pushvalue(L, -4);
     int ret = lua_gettable(L, lua_upvalueindex(MCP_BACKEND_UPVALUE));
     if (ret != LUA_TNIL) {
         mcp_backend_t *be_orig = luaL_checkudata(L, -1, "mcp.backend");
-        if (strncmp(be_orig->ip, ip, MAX_IPLEN) == 0
-                && strncmp(be_orig->port, port, MAX_PORTLEN) == 0
-                && be_orig->weight == weight) {
+        if (strncmp(be_orig->name, name, MAX_NAMELEN) == 0
+                && strncmp(be_orig->port, port, MAX_PORTLEN) == 0) {
             // backend is the same, return it.
             return 1;
         } else {
@@ -97,9 +101,8 @@ static int mcplib_backend(lua_State *L) {
 
     // FIXME (v2): remove some of the excess zero'ing below?
     memset(be, 0, sizeof(mcp_backend_t));
-    strncpy(be->ip, ip, MAX_IPLEN);
+    strncpy(be->name, name, MAX_NAMELEN);
     strncpy(be->port, port, MAX_PORTLEN);
-    be->weight = weight;
     be->depth = 0;
     be->rbuf = NULL;
     be->failed_count = 0;
@@ -143,17 +146,17 @@ static int mcplib_backend(lua_State *L) {
     }
     STAT_UL(ctx);
     be->connect_flags = flags;
-    int status = mcmc_connect(be->client, be->ip, be->port, flags);
+    int status = mcmc_connect(be->client, be->name, be->port, flags);
     if (status == MCMC_CONNECTED) {
         // FIXME (v2): is this possible? do we ever want to allow blocking
         // connections?
-        proxy_lua_ferror(L, "unexpectedly connected to backend early: %s:%s\n", be->ip, be->port);
+        proxy_lua_ferror(L, "unexpectedly connected to backend early: %s:%s\n", be->name, be->port);
         return 0;
     } else if (status == MCMC_CONNECTING) {
         be->connecting = true;
         be->can_write = false;
     } else {
-        proxy_lua_ferror(L, "failed to connect to backend: %s:%s\n", be->ip, be->port);
+        proxy_lua_ferror(L, "failed to connect to backend: %s:%s\n", be->name, be->port);
         return 0;
     }
 
@@ -256,14 +259,10 @@ static void _mcplib_pool_dist(lua_State *L, mcp_pool_t *p) {
         lua_setfield(L, -2, "id");
         // we don't use the hostname for ketama hashing
         // so passing ip for hostname is fine
-        lua_pushstring(L, be->ip);
-        // FIXME: hostname should probably work...
-        lua_setfield(L, -2, "hostname");
-        lua_pushstring(L, be->ip);
+        lua_pushstring(L, be->name);
         lua_setfield(L, -2, "addr");
         lua_pushstring(L, be->port);
         lua_setfield(L, -2, "port");
-        // TODO (v2): weight/etc?
 
         // set the backend table into the new pool table.
         lua_rawseti(L, -2, x);
@@ -734,6 +733,8 @@ int proxy_register_libs(LIBEVENT_THREAD *t, void *ctx) {
     // pointer pointers :)
     mcplib_open_dist_jump_hash(L);
     lua_setfield(L, -2, "dist_jump_hash");
+    mcplib_open_dist_ring_hash(L);
+    lua_setfield(L, -2, "dist_ring_hash");
 
     lua_pushlightuserdata(L, (void *)t); // upvalue for original thread
     lua_newtable(L); // upvalue for mcp.attach() table.