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Return HTTP 403 for blocked CONNECT requests to stop client retry storms #14

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Merged
bbrowning merged 1 commit into from
Apr 2, 2026
Merged

Return HTTP 403 for blocked CONNECT requests to stop client retry storms #14

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13 changes: 10 additions & 3 deletions internal/proxy/proxy.go
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Original file line number Diff line number Diff line change
Expand Up @@ -174,6 +174,10 @@ func (cf *ClientFilter) String() string {
return strings.Join(parts, ", ")
}

// rejectMsg is the generic response body for all rejected requests (CONNECT and plain HTTP).
// Intentionally vague to avoid revealing why the request was blocked.
const rejectMsg = "Request blocked by proxy policy"

// Config holds proxy configuration.
type Config struct {
ListenAddr string
Expand Down Expand Up @@ -219,6 +223,7 @@ func New(cfg Config) *http.Server {
srcIP := parseClientIP(ctx)
if srcIP == nil || !cfg.ClientFilter.IsAllowed(srcIP) {
log.Printf("CLIENT_REJECTED CONNECT %s from %s (not in allowed clients)", host, clientIP(ctx))
ctx.Resp = goproxy.NewResponse(ctx.Req, goproxy.ContentTypeText, http.StatusForbidden, rejectMsg)
return rejectConnect, host
}
}
Expand All @@ -232,6 +237,7 @@ func New(cfg Config) *http.Server {
if cfg.BlockedLogger != nil {
cfg.BlockedLogger.Log(clientIP(ctx), "CONNECT", host)
}
ctx.Resp = goproxy.NewResponse(ctx.Req, goproxy.ContentTypeText, http.StatusForbidden, rejectMsg)
return rejectConnect, host
}

Expand All @@ -240,6 +246,7 @@ func New(cfg Config) *http.Server {
if cfg.BlockedLogger != nil {
cfg.BlockedLogger.Log(clientIP(ctx), "CONNECT", host)
}
ctx.Resp = goproxy.NewResponse(ctx.Req, goproxy.ContentTypeText, http.StatusForbidden, rejectMsg)
return rejectConnect, host
}

Expand All @@ -264,7 +271,7 @@ func New(cfg Config) *http.Server {
return req, goproxy.NewResponse(req,
goproxy.ContentTypeText,
http.StatusForbidden,
"Client IP not allowed by proxy policy",
rejectMsg,
)
}
}
Expand All @@ -284,7 +291,7 @@ func New(cfg Config) *http.Server {
return req, goproxy.NewResponse(req,
goproxy.ContentTypeText,
http.StatusForbidden,
"Port not allowed by proxy policy",
rejectMsg,
)
}
}
Expand All @@ -298,7 +305,7 @@ func New(cfg Config) *http.Server {
return req, goproxy.NewResponse(req,
goproxy.ContentTypeText,
http.StatusForbidden,
"Domain not allowed by proxy policy",
rejectMsg,
)
}

Expand Down