add middleware for request prioritization #33951
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add middleware for request prioritization
This adds a middleware for overload protection, that is intended to help protect against malicious scrapers. It does this by via [`codel`](https://github.com/bohde/codel), which will perform the following: 1. Limit the number of in-flight requests to some user defined max 2. When in-flight requests have reached their max, begin queuing requests, with logged in requests having priority above logged out requests 3. Once a request has been queued for too long, it has a percentage chance to be rejected based upon how overloaded the entire system is. When a server experiences more traffic than it can handle, this has the effect of keeping latency low for logged in users, while rejecting just enough requests from logged out users to keep the service from being overloaded. Below are benchmarks showing a system at 100% capacity and 200% capacity in a few different configurations. The 200% capacity is shown to highlight an extreme case. I used [hey](https://github.com/rakyll/hey) to simulate the bot traffic: ``` hey -z 1m -c 10 "http://localhost:3000/rowan/demo/issues?state=open&type=all&labels=&milestone=0&project=0&assignee=0&poster=0&q=fix" ``` The concurrency of 10 was chosen from experiments where my local server began to experience higher latency. Results | Method | Concurrency | p95 latency | Successful RPS | Requests Dropped | |--------|--------|--------|--------|--------| | QoS Off | 10 | 0.2960s | 44 rps | 0% | | QoS Off | 20 | 0.5667s | 44 rps | 0%| | QoS On | 20 | 0.4409s | 48 rps | 10% | | QoS On 50% Logged In* | 10 | 0.3891s | 33 rps | 7% | | QoS On 50% Logged Out* | 10 | 2.0388s | 13 rps | 6% | Logged in users were given the additional parameter ` -H "Cookie: i_like_gitea=<session>`. Tests with `*` were run at the same time, representing a workload with mixed logged in & logged out users. Results are separated to show prioritization, and how logged in users experience a 100ms latency increase under load, compared to the 1.6 seconds logged out users see.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,121 @@ | ||
| // Copyright 2025 The Gitea Authors. All rights reserved. | ||
| // SPDX-License-Identifier: MIT | ||
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| package common | ||
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| import ( | ||
| "fmt" | ||
| "net/http" | ||
| "strings" | ||
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| user_model "code.gitea.io/gitea/models/user" | ||
| "code.gitea.io/gitea/modules/setting" | ||
| "code.gitea.io/gitea/modules/web/middleware" | ||
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| "github.com/bohde/codel" | ||
| ) | ||
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| type Priority int | ||
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| func (p Priority) String() string { | ||
| switch p { | ||
| case HighPriority: | ||
| return "high" | ||
| case DefaultPriority: | ||
| return "default" | ||
| case LowPriority: | ||
| return "low" | ||
| default: | ||
| return fmt.Sprintf("%d", p) | ||
| } | ||
| } | ||
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| const ( | ||
| LowPriority = Priority(-10) | ||
| DefaultPriority = Priority(0) | ||
| HighPriority = Priority(10) | ||
| ) | ||
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| // QoS implements quality of service for requests, based upon whether | ||
| 1E80 | // or not the user is logged in. All traffic may get dropped, and | |
| // anonymous users are deprioritized. | ||
| func QoS() func(next http.Handler) http.Handler { | ||
| maxOutstanding := setting.Service.QoS.MaxInFlightRequests | ||
| if maxOutstanding <= 0 { | ||
| maxOutstanding = 10 | ||
| } | ||
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| c := codel.NewPriority(codel.Options{ | ||
| // The maximum number of waiting requests. | ||
| MaxPending: setting.Service.QoS.MaxWaitingRequests, | ||
| // The maximum number of in-flight requests. | ||
| MaxOutstanding: maxOutstanding, | ||
| // The target latency that a blocked request should wait | ||
| // for. After this, it might be dropped. | ||
| TargetLatency: setting.Service.QoS.TargetWaitTime, | ||
| }) | ||
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| return func(next http.Handler) http.Handler { | ||
| return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) { | ||
| ctx := req.Context() | ||
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| priority := DefaultPriority | ||
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| // If the user is logged in, assign high priority. | ||
| data := middleware.GetContextData(req.Context()) | ||
| if _, ok := data[middleware.ContextDataKeySignedUser].(*user_model.User); ok { | ||
| priority = HighPriority | ||
| } else if IsGitContents(req.URL.Path) { | ||
| // Otherwise, if the path would is accessing git contents directly, mark as low priority | ||
| priority = LowPriority | ||
| } | ||
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| // Check if the request can begin processing. | ||
| err := c.Acquire(ctx, int(priority)) | ||
| if err != nil { | ||
| // If it failed, the service is over capacity and should error | ||
| http.Error(w, "Service Unavailable", http.StatusServiceUnavailable) | ||
| return | ||
| } | ||
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| // Release long-polling immediately, so they don't always | ||
| // take up an in-flight request | ||
| if strings.Contains(req.URL.Path, "/user/events") { | ||
| c.Release() | ||
| } else { | ||
| defer c.Release() | ||
| } | ||
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| next.ServeHTTP(w, req) | ||
| }) | ||
| } | ||
| } | ||
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| func IsGitContents(path string) bool { | ||
| parts := []string{ | ||
| "refs", | ||
| "archive", | ||
| "commit", | ||
| "graph", | ||
| "blame", | ||
| "branches", | ||
| "tags", | ||
| "labels", | ||
| "stars", | ||
| "search", | ||
| "activity", | ||
| "wiki", | ||
| "watchers", | ||
| "compare", | ||
| "raw", | ||
| "src", | ||
| "commits", | ||
| } | ||
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| for _, p := range parts { | ||
| if strings.Contains(path, p) { | ||
| return true | ||
| } | ||
| } | ||
| return false | ||
| } |
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