simple, functional interface to add additional balancer lb selection methods

without requiring code changes to mod_proxy/mod_proxy_balancer;
these can be implemented via sub-modules now.

Let the games begin...


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@232282 13f79535-47bb-0310-9956-ffa450edef68

5 files changed, 134 insertions, 57 deletions

diff --git a/CHANGES b/CHANGES
index d995006e64..8a6571b44f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,6 +1,11 @@
                                                         -*- coding: utf-8 -*-
 Changes with Apache 2.3.0
 
+  *) mod_proxy/mod_proxy_balancer: Provide a simple, functional
+     interface to add additional balancer lb selection methods
+     without requiring code changes to mod_proxy/mod_proxy_balancer;
+     these can be implemented via sub-modules now. [Jim Jagielski]
+
   *) mod_cache: Fix incorrectly served 304 responses when expired cache
      entity is valid, but cache is unwritable and headers cannot be
      updated.  [Colm MacCarthaigh <colm stdlib.net>]
diff --git a/modules/proxy/mod_proxy.c b/modules/proxy/mod_proxy.c
index fc1171ed89..1f3de0c117 100644
--- a/modules/proxy/mod_proxy.c
+++ b/modules/proxy/mod_proxy.c
@@ -224,7 +224,8 @@ static const char *set_worker_param(apr_pool_t *p,
     return NULL;
 }
 
-static const char *set_balancer_param(apr_pool_t *p,
+static const char *set_balancer_param(proxy_server_conf *conf,
+                                      apr_pool_t *p,
                                       proxy_balancer *balancer,
                                       const char *key,
                                       const char *val)
@@ -272,13 +273,17 @@ static const char *set_balancer_param(apr_pool_t *p,
         balancer->max_attempts_set = 1;
     }
     else if (!strcasecmp(key, "lbmethod")) {
-        /* Which LB scheduler method */
-        if (!strcasecmp(val, "traffic"))
-            balancer->lbmethod = lbmethod_traffic;
-        else if (!strcasecmp(val, "requests"))
-            balancer->lbmethod = lbmethod_requests;
-        else
-            return "lbmethod must be Traffic|Requests";
+        struct proxy_balancer_method *ent =
+           (struct proxy_balancer_method *) conf->lbmethods->elts;
+        int i;
+        for (i = 0; i < conf->lbmethods->nelts; i++) {
+           if (!strcasecmp(val, ent->name)) {
+               balancer->lbmethod = ent;
+               return NULL;
+           }
+           ent++;
+        }
+        return "unknown lbmethod";
     }
     else {
         return "unknown Balancer parameter";
@@ -793,6 +798,7 @@ static void * create_proxy_config(apr_pool_t *p, server_rec *s)
     ps->allowed_connect_ports = apr_array_make(p, 10, sizeof(int));
     ps->workers = apr_array_make(p, 10, sizeof(proxy_worker));
     ps->balancers = apr_array_make(p, 10, sizeof(proxy_balancer));
+    ps->lbmethods = apr_array_make(p, 10, sizeof(proxy_balancer_method));
     ps->forward = NULL;
     ps->reverse = NULL;
     ps->domain = NULL;
@@ -815,6 +821,9 @@ static void * create_proxy_config(apr_pool_t *p, server_rec *s)
     ps->badopt = bad_error;
     ps->badopt_set = 0;
     ps->pool = p;
+    
+    proxy_run_load_lbmethods(ps);
+    
     return ps;
 }
 
@@ -832,6 +841,7 @@ static void * merge_proxy_config(apr_pool_t *p, void *basev, void *overridesv)
     ps->allowed_connect_ports = apr_array_append(p, base->allowed_connect_ports, overrides->allowed_connect_ports);
     ps->workers = apr_array_append(p, base->workers, overrides->workers);
     ps->balancers = apr_array_append(p, base->balancers, overrides->balancers);
+    ps->lbmethods = apr_array_append(p, base->lbmethods, overrides->lbmethods);
     ps->forward = overrides->forward ? overrides->forward : base->forward;
     ps->reverse = overrides->reverse ? overrides->reverse : base->reverse;
 
@@ -1021,7 +1031,7 @@ static const char *
                 return apr_pstrcat(cmd->temp_pool, "ProxyPass ", err, NULL);
         }        
         for (i = 0; i < arr->nelts; i++) {
-            const char *err = set_balancer_param(cmd->pool, balancer, elts[i].key,
+            const char *err = set_balancer_param(conf, cmd->pool, balancer, elts[i].key,
                                                  elts[i].val);
             if (err)
                 return apr_pstrcat(cmd->temp_pool, "ProxyPass ", err, NULL);
@@ -1509,7 +1519,7 @@ static const char *
         if (worker)
             err = set_worker_param(cmd->pool, worker, word, val);
         else
-            err = set_balancer_param(cmd->pool, balancer, word, val);
+            err = set_balancer_param(conf, cmd->pool, balancer, word, val);
 
         if (err)
             return apr_pstrcat(cmd->temp_pool, "ProxySet ", err, " ", word, " ", name, NULL);
@@ -1754,9 +1764,7 @@ static int proxy_status_hook(request_rec *r, int flags)
         ap_rprintf(r, "</td><td>%" APR_TIME_T_FMT "</td>",
                    apr_time_sec(balancer->timeout));
         ap_rprintf(r, "<td>%s</td>\n",
-                   balancer->lbmethod == lbmethod_requests ? "Requests" :
-                   balancer->lbmethod == lbmethod_traffic ? "Traffic" :
-                   "Unknown");
+                   balancer->lbmethod->name);
         ap_rputs("</table>\n", r);
         ap_rputs("\n\n<table border=\"0\"><tr>"
                  "<th>Sch</th><th>Host</th><th>Stat</th>"
@@ -1917,6 +1925,7 @@ APR_HOOK_STRUCT(
     APR_HOOK_LINK(canon_handler)
     APR_HOOK_LINK(pre_request)
     APR_HOOK_LINK(post_request)
+    APR_HOOK_LINK(load_lbmethods)
     APR_HOOK_LINK(request_status)
 )
 
@@ -1942,6 +1951,10 @@ APR_IMPLEMENT_EXTERNAL_HOOK_RUN_FIRST(proxy, PROXY, int, post_request,
                                        request_rec *r,
                                        proxy_server_conf *conf),(worker,
                                        balancer,r,conf),DECLINED)
+APR_IMPLEMENT_EXTERNAL_HOOK_RUN_ALL(proxy, PROXY, int, load_lbmethods,
+                                    (proxy_server_conf *conf), 
+                                    (conf),
+                                    OK, DECLINED)
 APR_IMPLEMENT_OPTIONAL_HOOK_RUN_ALL(proxy, PROXY, int, fixups,
                                     (request_rec *r), (r),
                                     OK, DECLINED)
diff --git a/modules/proxy/mod_proxy.h b/modules/proxy/mod_proxy.h
index 55e1eaf7e3..43b3526617 100644
--- a/modules/proxy/mod_proxy.h
+++ b/modules/proxy/mod_proxy.h
@@ -120,6 +120,7 @@ struct noproxy_entry {
 typedef struct proxy_balancer  proxy_balancer;
 typedef struct proxy_worker    proxy_worker;
 typedef struct proxy_conn_pool proxy_conn_pool;
+typedef struct proxy_balancer_method proxy_balancer_method;
 
 typedef struct {
     apr_array_header_t *proxies;
@@ -179,6 +180,7 @@ typedef struct {
     } proxy_status;             /* Status display options */
     char proxy_status_set;
     apr_pool_t *pool;           /* Pool used for allocating this struct */
+    apr_array_header_t *lbmethods;
 } proxy_server_conf;
 
 
@@ -257,6 +259,7 @@ typedef struct {
     apr_size_t      elected;    /* Number of times the worker was elected */
     char            route[PROXY_WORKER_MAX_ROUTE_SIZ+1];
     char            redirect[PROXY_WORKER_MAX_ROUTE_SIZ+1];
+    void            *context;   /* general purpose storage */
 } proxy_worker_stat;
 
 /* Worker configuration */
@@ -293,6 +296,7 @@ struct proxy_worker {
 #if APR_HAS_THREADS
     apr_thread_mutex_t  *mutex;  /* Thread lock for updating address cache */
 #endif
+    void            *context;   /* general purpose storage */
 };
 
 struct proxy_balancer {
@@ -303,10 +307,7 @@ struct proxy_balancer {
     apr_interval_time_t timeout; /* Timeout for waiting on free connection */
     int                 max_attempts; /* Number of attempts before failing */
     char                max_attempts_set;
-    enum {
-       lbmethod_requests = 1,
-       lbmethod_traffic = 2
-    } lbmethod;
+    proxy_balancer_method *lbmethod;
 
     /* XXX: Perhaps we will need the proc mutex too.
      * Altrough we are only using arithmetic operations
@@ -316,6 +317,14 @@ struct proxy_balancer {
 #if APR_HAS_THREADS
     apr_thread_mutex_t  *mutex;  /* Thread lock for updating lb params */
 #endif
+    void            *context;   /* general purpose storage */
+};
+
+struct proxy_balancer_method {
+    const char *name;            /* name of the load balancer method*/
+    proxy_worker *(*finder)(proxy_balancer *balancer,
+                            request_rec *r);
+    void            *context;   /* general purpose storage */
 };
 
 #if APR_HAS_THREADS
@@ -365,6 +374,14 @@ APR_DECLARE_EXTERNAL_HOOK(proxy, PROXY, int, canon_handler, (request_rec *r,
 APR_DECLARE_EXTERNAL_HOOK(proxy, PROXY, int, create_req, (request_rec *r, request_rec *pr))
 APR_DECLARE_EXTERNAL_HOOK(proxy, PROXY, int, fixups, (request_rec *r)) 
 
+/*
+ * Useful hook run within the create per-server phase which
+ * adds the required lbmethod structs, so they exist at
+ * configure time
+ */
+APR_DECLARE_EXTERNAL_HOOK(proxy, PROXY, int, load_lbmethods,
+                                     (proxy_server_conf *conf))
+
 /**
  * pre request hook.
  * It will return the most suitable worker at the moment
diff --git a/modules/proxy/mod_proxy_balancer.c b/modules/proxy/mod_proxy_balancer.c
index 28e03bbc8d..38314b26df 100644
--- a/modules/proxy/mod_proxy_balancer.c
+++ b/modules/proxy/mod_proxy_balancer.c
@@ -21,6 +21,7 @@
 #include "mod_proxy.h"
 #include "ap_mpm.h"
 #include "apr_version.h"
+#include "apr_hooks.h"
 
 module AP_MODULE_DECLARE_DATA proxy_balancer_module;
 
@@ -262,13 +263,14 @@ static proxy_worker *find_session_route(proxy_balancer *balancer,
  *   b a d c d a c d b d ...
  *
  */
+ 
 static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
-                                      request_rec *r)
+                                request_rec *r)
 {
     int i;
     int total_factor = 0;
     proxy_worker *worker = (proxy_worker *)balancer->workers->elts;
-    proxy_worker *candidate = NULL;
+    proxy_worker *mycandidate = NULL;
     
     /* First try to see if we have available candidate */
     for (i = 0; i < balancer->workers->nelts; i++) {
@@ -286,18 +288,18 @@ static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
         if (PROXY_WORKER_IS_USABLE(worker)) {
             worker->s->lbstatus += worker->s->lbfactor;
             total_factor += worker->s->lbfactor;
-            if (!candidate || worker->s->lbstatus > candidate->s->lbstatus)
-                candidate = worker;
+            if (!mycandidate || worker->s->lbstatus > mycandidate->s->lbstatus)
+                mycandidate = worker;
         }
         worker++;
     }
 
-    if (candidate) {
-        candidate->s->lbstatus -= total_factor;
-        candidate->s->elected++;
+    if (mycandidate) {
+        mycandidate->s->lbstatus -= total_factor;
+        mycandidate->s->elected++;
     }
 
-    return candidate;
+    return mycandidate;
 }
 
 /*
@@ -318,13 +320,13 @@ static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
  * chosen more often, to even things out.
  */
 static proxy_worker *find_best_bytraffic(proxy_balancer *balancer,
-                                          request_rec *r)
+                                         request_rec *r)
 {
     int i;
     apr_off_t mytraffic = 0;
     apr_off_t curmin = 0;
     proxy_worker *worker = (proxy_worker *)balancer->workers->elts;
-    proxy_worker *candidate = NULL;
+    proxy_worker *mycandidate = NULL;
     
     /* First try to see if we have available candidate */
     for (i = 0; i < balancer->workers->nelts; i++) {
@@ -342,19 +344,19 @@ static proxy_worker *find_best_bytraffic(proxy_balancer *balancer,
         if (PROXY_WORKER_IS_USABLE(worker)) {
             mytraffic = (worker->s->transferred/worker->s->lbfactor) +
                         (worker->s->read/worker->s->lbfactor);
-            if (!candidate || mytraffic < curmin) {
-                candidate = worker;
+            if (!mycandidate || mytraffic < curmin) {
+                mycandidate = worker;
                 curmin = mytraffic;
             }
         }
         worker++;
     }
     
-    if (candidate) {
-        candidate->s->elected++;
+    if (mycandidate) {
+        mycandidate->s->elected++;
     }
 
-    return candidate;
+    return mycandidate;
 }
 
 static proxy_worker *find_best_worker(proxy_balancer *balancer,
@@ -365,14 +367,12 @@ static proxy_worker *find_best_worker(proxy_balancer *balancer,
     if (PROXY_THREAD_LOCK(balancer) != APR_SUCCESS)
         return NULL;    
 
-    if (balancer->lbmethod == lbmethod_requests) {
-        candidate = find_best_byrequests(balancer, r);
-    } else if (balancer->lbmethod == lbmethod_traffic) {
-        candidate = find_best_bytraffic(balancer, r);
-    } else {
+    candidate = (*balancer->lbmethod->finder)(balancer, r);
+
+/*    
         PROXY_THREAD_UNLOCK(balancer);
         return NULL;
-    }
+*/
 
     PROXY_THREAD_UNLOCK(balancer);
 
@@ -657,18 +657,15 @@ static int balancer_handler(request_rec *r)
             bsel->max_attempts_set = 1;
         }
         if ((val = apr_table_get(params, "lm"))) {
-            int ival = atoi(val);
-            switch(ival) {
-                case 0:
-                    break;
-                case lbmethod_traffic:
-                    bsel->lbmethod = lbmethod_traffic;
-                    break;
-                case lbmethod_requests:
-                    bsel->lbmethod = lbmethod_requests;
-                    break;
-                default:
+            struct proxy_balancer_method *ent =
+               (struct proxy_balancer_method *) conf->lbmethods->elts;
+            int i;
+            for (i = 0; i < conf->lbmethods->nelts; i++) {
+                if (!strcasecmp(val, ent->name)) {
+                    bsel->lbmethod = ent;
                     break;
+                }
+                ent++;
             }
         }
     }
@@ -755,8 +752,7 @@ static int balancer_handler(request_rec *r)
                 apr_time_sec(balancer->timeout));
             ap_rprintf(r, "<td>%d</td>\n", balancer->max_attempts);
             ap_rprintf(r, "<td>%s</td>\n",
-                       balancer->lbmethod == lbmethod_requests ? "Requests" :
-                       balancer->lbmethod == lbmethod_traffic  ? "Traffic" : "Unknown");
+                       balancer->lbmethod->name);
             ap_rputs("</table>\n", r);
             ap_rputs("\n\n<table border=\"0\"><tr>"
                 "<th>Scheme</th><th>Host</th>"
@@ -834,10 +830,17 @@ static int balancer_handler(request_rec *r)
             ap_rprintf(r, "value=\"%d\"></td></tr>\n",
                        bsel->max_attempts);
             ap_rputs("<tr><td>LB Method:</td><td><select name=\"lm\">", r);
-            ap_rprintf(r, "<option value=\"%d\" %s>Requests</option>", lbmethod_requests,
-                       bsel->lbmethod == lbmethod_requests ? "selected" : "");
-            ap_rprintf(r, "<option value=\"%d\" %s>Traffic</option>", lbmethod_traffic,
-                       bsel->lbmethod == lbmethod_traffic ? "selected" : "");
+            {
+                struct proxy_balancer_method *ent =
+                   (struct proxy_balancer_method *) conf->lbmethods->elts;
+                int i;
+                for (i = 0; i < conf->lbmethods->nelts; i++) {
+                    ap_rprintf(r, "<option value=\"%s\" %s>%s</option>", ent->name,
+                       (!strcasecmp(bsel->lbmethod->name, ent->name)) ? "selected" : "",
+                       ent->name);
+                    ent++;
+                }
+            }
             ap_rputs("</select></td></tr>\n", r);
             ap_rputs("<tr><td colspan=2><input type=submit value=\"Submit\"></td></tr>\n", r);
             ap_rvputs(r, "</table>\n<input type=hidden name=\"b\" ", NULL);
@@ -871,6 +874,30 @@ static void child_init(apr_pool_t *p, server_rec *s)
 
 }
 
+/*
+ * How to add additional lbmethods:
+ *   1. Create func which determines "best" candidate worker
+ *      (eg: find_best_bytraffic, above)
+ *   2. Create proxy_balancer_method struct which
+ *      defines the method and add it to
+ *      available server methods using
+ *      the proxy_hook_load_lbmethods hook
+ *      (eg: add_lbmethods below).
+ */
+static int add_lbmethods(proxy_server_conf *conf)
+{
+    proxy_balancer_method *new;
+
+    new  = apr_array_push(conf->lbmethods);
+    new->name = "byrequests";
+    new->finder = find_best_byrequests;
+    new  = apr_array_push(conf->lbmethods);
+    new->name = "bytraffic";
+    new->finder = find_best_bytraffic;
+
+    return OK;
+}
+
 static void ap_proxy_balancer_register_hook(apr_pool_t *p)
 {
     /* Only the mpm_winnt has child init hook handler.
@@ -880,10 +907,11 @@ static void ap_proxy_balancer_register_hook(apr_pool_t *p)
     static const char *const aszPred[] = { "mpm_winnt.c", "mod_proxy.c", NULL};
      /* manager handler */
     ap_hook_handler(balancer_handler, NULL, NULL, APR_HOOK_FIRST);
-    ap_hook_child_init(child_init, aszPred, NULL, APR_HOOK_MIDDLE); 
+    ap_hook_child_init(child_init, aszPred, NULL, APR_HOOK_MIDDLE);
     proxy_hook_pre_request(proxy_balancer_pre_request, NULL, NULL, APR_HOOK_FIRST);    
     proxy_hook_post_request(proxy_balancer_post_request, NULL, NULL, APR_HOOK_FIRST);    
     proxy_hook_canon_handler(proxy_balancer_canon, NULL, NULL, APR_HOOK_FIRST);
+    proxy_hook_load_lbmethods(add_lbmethods, NULL, NULL, APR_HOOK_FIRST);
 }
 
 module AP_MODULE_DECLARE_DATA proxy_balancer_module = {
diff --git a/modules/proxy/proxy_util.c b/modules/proxy/proxy_util.c
index f975dc0ea2..6bcb559b55 100644
--- a/modules/proxy/proxy_util.c
+++ b/modules/proxy/proxy_util.c
@@ -1155,6 +1155,8 @@ PROXY_DECLARE(const char *) ap_proxy_add_balancer(proxy_balancer **balancer,
                                                   const char *url)
 {
     char *c, *q, *uri = apr_pstrdup(p, url);
+    int i;
+    proxy_balancer_method *lbmethod;
 
     c = strchr(uri, ':');   
     if (c == NULL || c[1] != '/' || c[2] != '/' || c[3] == '\0')
@@ -1167,8 +1169,20 @@ PROXY_DECLARE(const char *) ap_proxy_add_balancer(proxy_balancer **balancer,
     *balancer = apr_array_push(conf->balancers);
     memset(*balancer, 0, sizeof(proxy_balancer));
 
+    /*
+     * NOTE: The default method is byrequests, which we assume
+     * exists!
+     */
+    lbmethod = (proxy_balancer_method *)conf->lbmethods->elts;
+    for (i = 0; i < conf->lbmethods->nelts; i++) {
+        if (!strcasecmp(lbmethod->name, "byrequests")) {
+            break;
+        }
+        lbmethod++;
+    }
+
     (*balancer)->name = uri;
-    (*balancer)->lbmethod = lbmethod_requests;
+    (*balancer)->lbmethod = lbmethod;
     (*balancer)->workers = apr_array_make(p, 5, sizeof(proxy_worker));
     /* XXX Is this a right place to create mutex */
 #if APR_HAS_THREADS