fix(openresty): 修复源站错误页「仅针对 GET 请求」未生效

error_page 的 URI 内部重定向会把请求方法改写成 GET，导致内部
Lua 中 ngx.req.get_method() 恒为 GET，get_only 判断永不命中，
POST/PUT 等请求仍返回自定义错误页。

改为命名 location（@__openflare_origin_error）承载错误页：
命名 location 保留原始请求方法与原始错误状态码，非 GET 请求
直接以原状态码退出、不再注入自定义 HTML。附带回归断言，禁止
回退到 URI 内部重定向形式。

docs/changelog/index.md

@@ -18,6 +18,9 @@ sidebar: false
 
 ## [Unreleased]
 
+### 🛠 修复
+- 修复源站错误页「仅针对 GET 请求」未生效：`error_page` 内部重定向会把请求方法改写成 GET，导致内部 Lua 无法识别 POST/PUT 等原始方法、仍返回自定义错误页；现改为命名 location（`@__openflare_origin_error`）承载错误页，保留原始请求方法与错误状态码，非 GET 请求不再返回自定义错误页。
+
 ## [v3.5.1] - 2026-08-09
 
 ### 新增

pkg/render/openresty/origin_error_page.go

@@ -10,8 +10,12 @@ const (
 	// OriginErrorPageSupportPath is the SupportFile path for the origin error HTML template.
 	OriginErrorPageSupportPath = "error_pages/origin_error.html.tmpl"
 
-	// OriginErrorPageInternalLocation is the internal nginx location that serves the error body.
-	OriginErrorPageInternalLocation = "/__openflare_origin_error"
+	// OriginErrorPageInternalLocation is the named nginx location that serves the error body.
+	// Must be a NAMED location (@...), not a URI internal redirect: error_page URI redirects
+	// rewrite the request method to GET, so the get_only Lua check (ngx.req.get_method() ~= "GET")
+	// would never fire and POST/PUT would still receive the custom HTML. Named locations preserve
+	// the original request method and the original error status (without the `=` form).
+	OriginErrorPageInternalLocation = "@__openflare_origin_error"
 
 	defaultOriginErrorPageStatusTag = "500-599"
 )
@@ -137,13 +141,13 @@ func renderOriginErrorPageIntercept(cfg ConfigSnapshot) string {
 	return "        proxy_intercept_errors on;\n"
 }
 
-// renderOriginErrorPageServerBits emits server-level error_page + internal location.
+// renderOriginErrorPageServerBits emits server-level error_page + named error location.
 // Returns empty string when disabled, expand fails, or no codes remain.
 //
-// IMPORTANT: do NOT use `error_page CODE = /uri` (equals without response code).
+// IMPORTANT: do NOT use `error_page CODE = @name` (equals without response code).
 // That form adopts the status returned by the error URI; content_by_lua defaults
 // to 200 and ngx.status is often 0, so clients saw 200 with body "{{status}}"→"0".
-// Without `=`, nginx keeps the original error status for the internal redirect.
+// Without `=`, nginx keeps the original error status for the redirect.
 func renderOriginErrorPageServerBits(cfg ConfigSnapshot) string {
 	if !cfg.OriginErrorPageEnabled {
 		return ""
@@ -164,21 +168,22 @@ func renderOriginErrorPageServerBits(cfg ConfigSnapshot) string {
 }
 
 func renderOriginErrorPageInternalLocation(getOnly bool) string {
-	// Resolve status from $status (set by error_page internal redirect), then
+	// Resolve status from $status (set by error_page redirect), then
 	// upstream_status, then ngx.status. Force ngx.status so the client receives
 	// the real error code. Use function replacers so host/status with `%` are safe.
 	//
 	// Note: fmt.Sprintf is used only for the path placeholders; Lua `%` must be
 	// written as `%%` so Sprintf does not treat them as format verbs.
 	//
-	// When getOnly is true, non-GET that still hit this location (e.g. nginx-local
-	// 502 without upstream body) exit with the original status and no HTML body.
+	// The location is NAMED (@...), not a URI internal redirect: URI redirects
+	// (location = /uri) rewrite the request method to GET, which defeats the
+	// get_only gate below. Named locations keep the original method, so a POST
+	// that reaches this location exits with the original status and no HTML body.
 	getOnlyLua := "false"
 	if getOnly {
 		getOnlyLua = "true"
 	}
-	return fmt.Sprintf(`    location = %s {
-        internal;
+	return fmt.Sprintf(`    location %s {
         default_type text/html;
         charset utf-8;
         content_by_lua_block {

pkg/render/openresty/origin_error_page_test.go

@@ -24,22 +24,27 @@ func TestRenderOriginErrorPageEnabled(t *testing.T) {
 	if !strings.Contains(out, "proxy_intercept_errors on") {
 		t.Fatal("missing intercept")
 	}
-	if !strings.Contains(out, "error_page") || !strings.Contains(out, "/__openflare_origin_error") {
+	if !strings.Contains(out, "error_page") || !strings.Contains(out, "@__openflare_origin_error") {
 		t.Fatal("missing error_page")
 	}
 	if !strings.Contains(out, "error_page 500") {
 		t.Fatalf("expected expanded status codes in error_page, got:\n%s", out)
 	}
-	// Must NOT use `error_page … = /uri` (adopts error-URI status → often 200).
-	// `location = /path` is unrelated and expected.
+	// Must NOT use `error_page … = @name` (adopts error-URI status → often 200).
 	for _, line := range strings.Split(out, "\n") {
 		trimmed := strings.TrimSpace(line)
 		if strings.HasPrefix(trimmed, "error_page ") && strings.Contains(trimmed, " = ") {
 			t.Fatalf("error_page must not use '=' form, got: %s", trimmed)
 		}
 	}
-	if !strings.Contains(out, "error_page ") || !strings.Contains(out, " /__openflare_origin_error;") {
-		t.Fatal("error_page must redirect to internal location without '='")
+	if !strings.Contains(out, "error_page ") || !strings.Contains(out, " @__openflare_origin_error;") {
+		t.Fatal("error_page must redirect to the named error location without '='")
+	}
+	if !strings.Contains(out, "location @__openflare_origin_error {") {
+		t.Fatal("error location must be a named location (@...) that preserves the request method")
+	}
+	if strings.Contains(out, "location = /__openflare_origin_error") {
+		t.Fatal("error location must NOT be a URI internal redirect (error_page URI redirects rewrite the method to GET, breaking the get_only gate)")
 	}
 	if !strings.Contains(out, "resolve_error_status") || !strings.Contains(out, "ngx.status = code") {
 		t.Fatal("internal location must resolve and set ngx.status to the original error code")
@@ -103,6 +108,16 @@ func TestRenderOriginErrorPageGetOnly(t *testing.T) {
 	if !strings.Contains(out, `ngx.req.get_method() ~= "GET"`) {
 		t.Fatal("internal location must skip HTML for non-GET")
 	}
+	// Regression: error_page must target the NAMED location. URI internal redirects
+	// (location = /uri) rewrite the request method to GET, so ngx.req.get_method()
+	// would always return "GET" and the get_only gate would never skip HTML for
+	// POST/PUT. Named locations preserve the original method.
+	if !strings.Contains(out, "error_page 500") || !strings.Contains(out, " @__openflare_origin_error;") {
+		t.Fatalf("error_page must target the named location, got:\n%s", out)
+	}
+	if strings.Contains(out, "location = /__openflare_origin_error") {
+		t.Fatal("get_only must not use URI internal redirect (rewrites method to GET, breaking the gate)")
+	}
 }
 
 func TestRenderOriginErrorPageDisabled(t *testing.T) {
@@ -121,8 +136,8 @@ func TestRenderOriginErrorPageDisabled(t *testing.T) {
 	if strings.Contains(out, "proxy_intercept_errors") {
 		t.Fatal("should not intercept when disabled")
 	}
-	if strings.Contains(out, "/__openflare_origin_error") {
-		t.Fatal("should not emit internal error location when disabled")
+	if strings.Contains(out, "@__openflare_origin_error") {
+		t.Fatal("should not emit error location when disabled")
 	}
 	res, err := Render(doc, nil)
 	if err != nil {
@@ -199,7 +214,7 @@ func TestRenderOriginErrorPageCustomHTMLInSupportFile(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !strings.Contains(out, "error_page 502 /__openflare_origin_error;") {
+	if !strings.Contains(out, "error_page 502 @__openflare_origin_error;") {
 		t.Fatalf("expected single 502 error_page without '=', got:\n%s", out)
 	}
 }
@@ -227,7 +242,7 @@ func TestRenderOriginErrorPageSkipsPagesRoutes(t *testing.T) {
 	if strings.Contains(out, "proxy_intercept_errors") {
 		t.Fatal("pages routes must not get proxy_intercept_errors")
 	}
-	if strings.Contains(out, "/__openflare_origin_error") {
+	if strings.Contains(out, "@__openflare_origin_error") {
 		t.Fatal("pages routes must not get origin error location")
 	}
 }