ngx_http_limit_req_handler

1 定义

ngx_http_limit_req_handler 函数 定义在 ./nginx-1.24.0/src/http/modules/ngx_http_limit_req_module.c

staticngx_int_tngx_http_limit_req_handler(ngx_http_request_t*r){uint32_thash;ngx_str_tkey;ngx_int_trc;ngx_uint_tn,excess;ngx_msec_tdelay;ngx_http_limit_req_ctx_t*ctx;ngx_http_limit_req_conf_t*lrcf;ngx_http_limit_req_limit_t*limit,*limits;if(r->main->limit_req_status){returnNGX_DECLINED;}lrcf=ngx_http_get_module_loc_conf(r,ngx_http_limit_req_module);limits=lrcf->limits.elts;excess=0;rc=NGX_DECLINED;#if(NGX_SUPPRESS_WARN)limit=NULL;#endiffor(n=0;n<lrcf->limits.nelts;n++){limit=&limits[n];ctx=limit->shm_zone->data;if(ngx_http_complex_value(r,&ctx->key,&key)!=NGX_OK){ngx_http_limit_req_unlock(limits,n);returnNGX_HTTP_INTERNAL_SERVER_ERROR;}if(key.len==0){continue;}if(key.len>65535){ngx_log_error(NGX_LOG_ERR,r->connection->log,0,"the value of the \"%V\" key ""is more than 65535 bytes: \"%V\"",&ctx->key.value,&key);continue;}hash=ngx_crc32_short(key.data,key.len);ngx_shmtx_lock(&ctx->shpool->mutex);rc=ngx_http_limit_req_lookup(limit,hash,&key,&excess,(n==lrcf->limits.nelts-1));ngx_shmtx_unlock(&ctx->shpool->mutex);ngx_log_debug4(NGX_LOG_DEBUG_HTTP,r->connection->log,0,"limit_req[%ui]: %i %ui.%03ui",n,rc,excess/1000,excess%1000);if(rc!=NGX_AGAIN){break;}}if(rc==NGX_DECLINED){returnNGX_DECLINED;}if(rc==NGX_BUSY||rc==NGX_ERROR){if(rc==NGX_BUSY){ngx_log_error(lrcf->limit_log_level,r->connection->log,0,"limiting requests%s, excess: %ui.%03ui by zone \"%V\"",lrcf->dry_run?", dry run":"",excess/1000,excess%1000,&limit->shm_zone->shm.name);}ngx_http_limit_req_unlock(limits,n);if(lrcf->dry_run){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_REJECTED_DRY_RUN;returnNGX_DECLINED;}r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_REJECTED;returnlrcf->status_code;}/* rc == NGX_AGAIN || rc == NGX_OK */if(rc==NGX_AGAIN){excess=0;}delay=ngx_http_limit_req_account(limits,n,&excess,&limit);if(!delay){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_PASSED;returnNGX_DECLINED;}ngx_log_error(lrcf->delay_log_level,r->connection->log,0,"delaying request%s, excess: %ui.%03ui, by zone \"%V\"",lrcf->dry_run?", dry run":"",excess/1000,excess%1000,&limit->shm_zone->shm.name);if(lrcf->dry_run){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_DELAYED_DRY_RUN;returnNGX_DECLINED;}r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_DELAYED;if(r->connection->read->ready){ngx_post_event(r->connection->read,&ngx_posted_events);}else{if(ngx_handle_read_event(r->connection->read,0)!=NGX_OK){returnNGX_HTTP_INTERNAL_SERVER_ERROR;}}r->read_event_handler=ngx_http_test_reading;r->write_event_handler=ngx_http_limit_req_delay;r->connection->write->delayed=1;ngx_add_timer(r->connection->write,delay);returnNGX_AGAIN;}

ngx_http_limit_req_handler 函数是 请求频率限制（rate limiting） 的核心处理函数。 它根据配置的限速规则和请求标识（如客户端 IP）， 在共享内存中统计请求速率， 并据此决定放行请求、延迟请求（通过异步定时器挂起等待）或立即拒绝请求（返回指定错误码）。 该函数在 `NGX_HTTP_PREACCESS_PHASE` 阶段运行，确保在访问控制前完成流量整形。

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2 详解

1 函数签名

staticngx_int_tngx_http_limit_req_handler(ngx_http_request_t*r)

返回值 用于返回函数执行结果的状态码

参数 ngx_http_request_t *r 指向当前 HTTP 请求上下文结构体

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2 逻辑流程

1 局部变量 2 防重入校验 3 配置提取 4 初始化 5 遍历所有限速规则 6 所有规则均未命中 7 限流拦截或异常 8 处理需要延迟或放行的情况

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1 局部变量

{uint32_thash;ngx_str_tkey;ngx_int_trc;ngx_uint_tn,excess;ngx_msec_tdelay;ngx_http_limit_req_ctx_t*ctx;ngx_http_limit_req_conf_t*lrcf;ngx_http_limit_req_limit_t*limit,*limits;

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2 防重入校验

if(r->main->limit_req_status){returnNGX_DECLINED;}

检查主请求状态 如果主请求的 limit_req_status 已被设置， 说明请求已经过本模块处理并得出了最终结果（拒绝、延迟或通过）， 直接返回 NGX_DECLINED 表示不再处理。

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3 配置提取

lrcf=ngx_http_get_module_loc_conf(r,ngx_http_limit_req_module);limits=lrcf->limits.elts;

lrcf： 从当前请求的 location 配置中取出 ngx_http_limit_req_module 的配置结构。 limits：将配置中存储限速规则的动态数组 (lrcf->limits) 取出为 C 数组指针，便于遍历。

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4 初始化

excess=0;rc=NGX_DECLINED;

初始化超出量为 0。 将最终返回值预设为 NGX_DECLINED， 表示“未匹配任何规则，放行”。 后续根据查找结果修改。

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#if(NGX_SUPPRESS_WARN)limit=NULL;#endif

抑制编译器警告 如果编译时定义了 NGX_SUPPRESS_WARN（通常用于消除未初始化警告）， 则将 limit 显式初始化为 NULL。避免某些编译器在优化时误报 limit 可能未被初始化。

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5 遍历所有限速规则

for(n=0;n<lrcf->limits.nelts;n++){limit=&limits[n];ctx=limit->shm_zone->data;if(ngx_http_complex_value(r,&ctx->key,&key)!=NGX_OK){ngx_http_limit_req_unlock(limits,n);returnNGX_HTTP_INTERNAL_SERVER_ERROR;}if(key.len==0){continue;}if(key.len>65535){ngx_log_error(NGX_LOG_ERR,r->connection->log,0,"the value of the \"%V\" key ""is more than 65535 bytes: \"%V\"",&ctx->key.value,&key);continue;}hash=ngx_crc32_short(key.data,key.len);ngx_shmtx_lock(&ctx->shpool->mutex);rc=ngx_http_limit_req_lookup(limit,hash,&key,&excess,(n==lrcf->limits.nelts-1));ngx_shmtx_unlock(&ctx->shpool->mutex);ngx_log_debug4(NGX_LOG_DEBUG_HTTP,r->connection->log,0,"limit_req[%ui]: %i %ui.%03ui",n,rc,excess/1000,excess%1000);if(rc!=NGX_AGAIN){break;}}

循环遍历配置的所有限速规则

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6 所有规则均未命中

if(rc==NGX_DECLINED){returnNGX_DECLINED;}

如果最终 rc 仍为 NGX_DECLINED，说明没有任何规则限制此请求，直接放行

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7 限流拦截或异常

if(rc==NGX_BUSY||rc==NGX_ERROR){if(rc==NGX_BUSY){ngx_log_error(lrcf->limit_log_level,r->connection->log,0,"limiting requests%s, excess: %ui.%03ui by zone \"%V\"",lrcf->dry_run?", dry run":"",excess/1000,excess%1000,&limit->shm_zone->shm.name);}ngx_http_limit_req_unlock(limits,n);if(lrcf->dry_run){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_REJECTED_DRY_RUN;returnNGX_DECLINED;}r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_REJECTED;returnlrcf->status_code;}

处理拒绝情况 当返回 NGX_BUSY（请求超限）或 NGX_ERROR（内部错误）时，准备拒绝请求。

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8 处理需要延迟或放行的情况

/* rc == NGX_AGAIN || rc == NGX_OK */if(rc==NGX_AGAIN){excess=0;}delay=ngx_http_limit_req_account(limits,n,&excess,&limit);if(!delay){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_PASSED;returnNGX_DECLINED;}ngx_log_error(lrcf->delay_log_level,r->connection->log,0,"delaying request%s, excess: %ui.%03ui, by zone \"%V\"",lrcf->dry_run?", dry run":"",excess/1000,excess%1000,&limit->shm_zone->shm.name);if(lrcf->dry_run){r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_DELAYED_DRY_RUN;returnNGX_DECLINED;}r->main->limit_req_status=NGX_HTTP_LIMIT_REQ_DELAYED;if(r->connection->read->ready){ngx_post_event(r->connection->read,&ngx_posted_events);}else{if(ngx_handle_read_event(r->connection->read,0)!=NGX_OK){returnNGX_HTTP_INTERNAL_SERVER_ERROR;}}r->read_event_handler=ngx_http_test_reading;r->write_event_handler=ngx_http_limit_req_delay;r->connection->write->delayed=1;ngx_add_timer(r->connection->write,delay);returnNGX_AGAIN;}