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API 资产治理：ETag/Cache-Control/分页/排序/投影的“契约基线” 🚀

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0. TL;DR 🧭

• 契约基线：命名/版本/鉴权 → 分页/过滤/排序/投影 → 缓存（ETag/条件请求/Cache-Control） → 错误（ProblemDetails） → 可观测/配额/变更管理。

• 关键语义：

  • If-Match 强比较（强 ETag），不匹配 → 412；
  • If-None-Match 弱比较（含 *），命中 → 304；
  • 304 必带可变元数据（ETag/Cache-Control/Vary/...）。

• 三件套：OpenAPI Lint（Spectral）🧪＋ 门户 OperationFilter 📘 ＋ 兼容性测试集（Newman/BDN）🧰。

• 亮点：列表弱 ETag 以“本页 RowVersion 摘要”生成 📈；Vary 合并追加（含 Accept & Accept-Encoding）；绝对 Link 由 LinkGenerator 生成（适配反向代理/CDN）。

合约基线鸟瞰

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1. 背景与目标 🎯

• 痛点：接口风格分裂、无上限分页、过取/欠取、弱缓存/无条件请求、错误契约不统一。
• 目标：在 ABP vNext 体系沉淀可执行的 HTTP 合约基线（可被 Lint/拦截/文档化/测试守门）；以游标分页+投影降带宽，以ETag+条件请求降尾延迟与负载。

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2. 适用范围 📐

• 适用：RESTful/HTTP API（Controller、Minimal API、OData 网关）。
• 非目标：领域建模与 GraphQL；本文专注HTTP 契约层。

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3. 资源命名与版本治理（ABP 落地） 🧩

• 命名：复数资源、层级：/orders/{id}/items；动作用副资源/作业资源（/exports、/jobs）。
• 版本：ABP 集成 ASP.NET API Versioning 与 ApiExplorer/Swagger 分组。

// ApiContractBaselineModule.ConfigureServices(...)
context.Services.AddAbpApiVersioning(o =>
{o.ReportApiVersions = true;o.AssumeDefaultVersionWhenUnspecified = true;
});

• 弃用与下线：文档与响应宣布 Deprecation/Sunset；门户提供时间线。 🗓️

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4. 查询契约：分页 / 过滤 / 排序 / 投影 🔎

4.1 分页（游标优先） 🧭

输出 Link 为绝对 URI，由 LinkGenerator 生成，适配代理/CDN。

4.2 排序（ThenBy 链式、字段白名单） 📑

public static class QueryableSortExtensions
{private static readonly HashSet<string> Allowed = new(StringComparer.OrdinalIgnoreCase){ "id", "name", "price", "createdAt" };public static IQueryable<Product> ApplySort(this IQueryable<Product> q, string? sort){if (string.IsNullOrWhiteSpace(sort)) return q.OrderByDescending(x => x.Id);IOrderedQueryable<Product>? ordered = null;foreach (var token in sort.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)){var desc = token.StartsWith("-");var key  = desc ? token[1..] : token;if (!Allowed.Contains(key)) continue;ordered = (ordered, key, desc) switch{(null, "price", false)     => q.OrderBy(x => x.Price),(null, "price", true)      => q.OrderByDescending(x => x.Price),(null, "createdAt", false) => q.OrderBy(x => x.CreatedAt),(null, "createdAt", true)  => q.OrderByDescending(x => x.CreatedAt),(null, "name", false)      => q.OrderBy(x => x.Name),(null, "name", true)       => q.OrderByDescending(x => x.Name),(null, _, false)           => q.OrderBy(x => x.Id),(null, _, true)            => q.OrderByDescending(x => x.Id),(not null, "price", false)     => ordered!.ThenBy(x => x.Price),(not null, "price", true)      => ordered!.ThenByDescending(x => x.Price),(not null, "createdAt", false) => ordered!.ThenBy(x => x.CreatedAt),(not null, "createdAt", true)  => ordered!.ThenByDescending(x => x.CreatedAt),(not null, "name", false)      => ordered!.ThenBy(x => x.Name),(not null, "name", true)       => ordered!.ThenByDescending(x => x.Name),_ => ordered!};}return ordered ?? q.OrderByDescending(x => x.Id);}
}

4.3 投影（fields） ✂️

public sealed record QuerySpec(string? Cursor = null,int     Limit  = 50,string? Sort   = null,string? Fields = null // "id,name,price"
)
{public int Take => Math.Clamp(Limit, 1, 200);
}

生产建议：在 IQueryable 层 Select 到瘦 DTO（或 AutoMapper ProjectTo），避免过取与二次分配。

4.4 OData（可选，限幅一致） 🧱

services.AddControllers().AddOData(opt => opt.Select().OrderBy().Count().SetMaxTop(200));[EnableQuery(MaxTop = 200,MaxExpansionDepth = 2,AllowedQueryOptions =AllowedQueryOptions.Select |AllowedQueryOptions.Filter |AllowedQueryOptions.OrderBy |AllowedQueryOptions.Top |AllowedQueryOptions.Skip |AllowedQueryOptions.Count)]
public IQueryable<ProductDto> Get() => _svc.Query();

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5. 缓存契约：ETag / 条件请求 / Cache-Control ⚡

5.1 强/弱 ETag 与比较语义 🧠

• 强 ETag：Base64(RowVersion)，用于 If-Match（强比较）。
• 弱 ETag：W/"..."，建议用于列表/聚合，If-None-Match（弱比较）可命中。
• 304：必须携带可变元数据（如 ETag/Cache-Control/Vary/...）。

5.2 统一 ETag 生成与 Vary 合并 🧩

public interface IETagProvider
{string CreateStrongEtag(byte[] rowVersion);string CreateWeakEtag(string composite); // e.g., page RowVersions
}public sealed class DefaultETagProvider : IETagProvider
{public string CreateStrongEtag(byte[] rowVersion)=> $"\"{Convert.ToBase64String(rowVersion)}\""; // 强 ETag（无 W/）public string CreateWeakEtag(string composite){using var sha1 = System.Security.Cryptography.SHA1.Create();var hash = sha1.ComputeHash(System.Text.Encoding.UTF8.GetBytes(composite));return $"W/\"{Convert.ToBase64String(hash)}\"";}
}static void AddVary(HttpResponse res, params string[] tokens)
{var existing = res.Headers[HeaderNames.Vary].ToString().Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToHashSet(StringComparer.OrdinalIgnoreCase);foreach (var t in tokens) existing.Add(t);res.Headers[HeaderNames.Vary] = string.Join(", ", existing);
}

5.3 条件 GET/HEAD（含 *）与并发写 🔒

using Microsoft.Net.Http.Headers;[ApiController, Route("api/products")]
public class ProductsController : ControllerBase
{private readonly AppDbContext _db;private readonly IETagProvider _etag;private readonly LinkGenerator _links;public ProductsController(AppDbContext db, IETagProvider etag, LinkGenerator links){ _db = db; _etag = etag; _links = links; }[HttpGet("{id:long}")][HttpHead("{id:long}")] // HEAD 支持：与 GET 共用条件判定与头public async Task<IActionResult> GetById(long id, CancellationToken ct){var e = await _db.Products.AsNoTracking().Select(x => new { x.Id, x.Name, x.Price, x.UpdatedAt, x.RowVersion }).FirstOrDefaultAsync(x => x.Id == id, ct);if (e is null) return NotFound();var strong = new EntityTagHeaderValue(_etag.CreateStrongEtag(e.RowVersion));// If-None-Match: * 或 标签列表（弱比较）if (Request.Headers.TryGetValue(HeaderNames.IfNoneMatch, out var inm)){if (inm.Count == 1 && inm[0].Trim() == "*")return NotModifiedWithMetadata(strong); // 资源存在即命中if (EntityTagHeaderValue.TryParseList(inm, out var etags) &&etags.Any(tag => EntityTagHeaderValue.Compare(tag, strong, useStrongComparison: false)))return NotModifiedWithMetadata(strong);}WithCacheMetadata(Response, strong, maxAgeSeconds: 60);return Ok(e);}[HttpPut("{id:long}")]public async Task<IActionResult> Update(long id, [FromBody] UpdateProduct dto, CancellationToken ct){var entity = await _db.Products.FirstOrDefaultAsync(x => x.Id == id, ct);if (entity is null) return NotFound();var current = new EntityTagHeaderValue(_etag.CreateStrongEtag(entity.RowVersion));// If-Match（强比较）保护并发if (!Request.Headers.TryGetValue(HeaderNames.IfMatch, out var ifm) ||!EntityTagHeaderValue.TryParseList(ifm, out var candidates) ||!candidates.Any(tag => EntityTagHeaderValue.Compare(tag, current, useStrongComparison: true))){return StatusCode(StatusCodes.Status412PreconditionFailed,new ProblemDetails { Title = "Precondition Failed", Status = 412, Detail = "ETag mismatch." });}// ... mutate entity & SaveChangesawait _db.SaveChangesAsync(ct);return NoContent();}// ---- helpers ----IActionResult NotModifiedWithMetadata(EntityTagHeaderValue etag){WithCacheMetadata(Response, etag, maxAgeSeconds: 60);return StatusCode(StatusCodes.Status304NotModified);}static void WithCacheMetadata(HttpResponse res, EntityTagHeaderValue etag, int maxAgeSeconds){var headers = res.GetTypedHeaders();headers.ETag = etag;headers.CacheControl = new CacheControlHeaderValue { Private = true, MaxAge = TimeSpan.FromSeconds(maxAgeSeconds) };AddVary(res, "Accept", "Accept-Encoding"); // 合并追加// Date 由服务器自动写入}
}

反向代理提示：在 Program.cs 配置 app.UseForwardedHeaders() 以尊重 X-Forwarded-*，并在 Kestrel/反代层正确设置可信代理。

5.4 列表端点：弱 ETag（本页摘要）与 304 元数据、绝对 Link 🔁

[HttpGet]
public async Task<IActionResult> List([FromQuery] QuerySpec q, CancellationToken ct)
{var baseQuery = _db.Products.AsNoTracking();var items = await baseQuery.ApplySort(q.Sort).Take(q.Take + 1).ToListAsync(ct);var hasMore    = items.Count > q.Take;var page       = hasMore ? items.Take(q.Take).ToList() : items;var nextCursor = hasMore ? items.Last().Id.ToString() : null;// 弱 ETag：仅反映**本页** RowVersion 摘要（提升命中率）var rvConcat = page.Count == 0? "empty" // 空页稳定 ETag: string.Join('|', page.Select(p => Convert.ToBase64String(p.RowVersion)));var weak = new EntityTagHeaderValue(_etag.CreateWeakEtag(rvConcat));// If-None-Match: * 或 标签列表（弱比较）if (Request.Headers.TryGetValue(HeaderNames.IfNoneMatch, out var inm)){if (inm.Count == 1 && inm[0].Trim() == "*"){WithCacheMetadata(Response, weak, 30);return StatusCode(StatusCodes.Status304NotModified);}if (EntityTagHeaderValue.TryParseList(inm, out var etags) &&etags.Any(tag => EntityTagHeaderValue.Compare(tag, weak, useStrongComparison: false))){WithCacheMetadata(Response, weak, 30);return StatusCode(StatusCodes.Status304NotModified);}}WithCacheMetadata(Response, weak, 30);if (nextCursor != null){// 使用 LinkGenerator 生成绝对 URL（适配反代）var nextUrl = _links.GetUriByAction(httpContext: HttpContext,action: nameof(List),controller: "Products",values: new { cursor = nextCursor, limit = q.Limit });Response.Headers.Append(HeaderNames.Link, $"<{nextUrl}>; rel=\"next\"");}return Ok(new { data = page, nextCursor });
}

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6. 错误与一致性：ProblemDetails + Trace Context 🆘

builder.Services.AddProblemDetails();app.UseForwardedHeaders(); // 反向代理/负载均衡场景建议启用
app.Use(async (ctx, next) =>
{var id = System.Diagnostics.Activity.Current?.Id;if (!string.IsNullOrEmpty(id))ctx.Response.Headers["traceparent"] = id; // 进入时写await next();
});
app.UseExceptionHandler(); // 未处理异常 → problem+json

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7. 安全与最小暴露 🛡️

• 仅绑定 DTO 字段；输出投影最小化、敏感字段脱敏；
• 速率限制头 RateLimit/RateLimit-Policy（草案）可选，不做强制门禁；
• OData：限制 AllowedQueryOptions/MaxTop/MaxExpansionDepth，必要时限制表达式复杂度。

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8. 可观测与 SLO 🔭

• 指标：304_ratio、avg_body_bytes、p95_latency、etag_missing_total、projection_hit_ratio；
• 日志：记录分页/过滤/排序/投影与条件请求命中/落空原因；
• 告警：分页无上限、投影缺失导致响应过大、ETag 漏配、条件请求无效。

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9. “契约校验器”与门禁（Spectral + 代码级） 🧪

9.1 OpenAPI Lint（规则节选）

extends: "spectral:oas"
rules:get-must-document-etag:description: "GET 响应需声明 ETag 或 304 分支"given: "$.paths[*][get].responses"then:function: schemafunctionOptions:schema:type: objectanyOf:- required: ["304"]- properties:"200":properties:headers:type: objectpatternProperties:"(?i)^etag$": {}write-must-require-if-match:description: "PUT/PATCH/DELETE 需文档化 If-Match 请求头"given: "$.paths[*][put,patch,delete]"then:field: parametersfunction: truthyproblem-details-on-4xx-5xx:description: "4xx/5xx 必须提供 application/problem+json"given: "$.paths[*][*].responses[?(@key.match(/^[45]\\d\\d$/))].content"then:field: application/problem+jsonfunction: truthy

9.2 CI/门禁流水线（Mermaid）

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10. 开发者门户（Swagger/Redoc） 📘

• OperationFilter：为 GET 增加 If-None-Match 参数、304 头；为 PUT/PATCH/DELETE 增加 If-Match 参数与 412 说明；统一 ProblemDetails Schema。

using Microsoft.OpenApi.Models;
using Swashbuckle.AspNetCore.SwaggerGen;public class ETagOperationFilter : IOperationFilter
{public void Apply(OpenApiOperation op, OperationFilterContext ctx){var method = ctx.ApiDescription.HttpMethod?.ToUpperInvariant();op.Parameters ??= new List<OpenApiParameter>();if (method == "GET"){op.Parameters.Add(new OpenApiParameter{Name = "If-None-Match", In = ParameterLocation.Header,Schema = new OpenApiSchema{ Type = "string" },Description = "ETag for conditional GET (supports weak compare and *)"});op.Responses.TryAdd("304", new OpenApiResponse{Description = "Not Modified",Headers = new Dictionary<string, OpenApiHeader>{["ETag"]          = new(){ Schema = new() { Type = "string" } },["Cache-Control"] = new(){ Schema = new() { Type = "string" } },["Vary"]          = new(){ Schema = new() { Type = "string" } }}});}if (method is "PUT" or "PATCH" or "DELETE"){op.Parameters.Add(new OpenApiParameter{Name = "If-Match", In = ParameterLocation.Header, Required = true,Schema = new OpenApiSchema{ Type = "string" },Description = "Strong ETag required (strong comparison)"});op.Responses.TryAdd("412", new OpenApiResponse{Description = "Precondition Failed (ProblemDetails)",Content = new Dictionary<string, OpenApiMediaType>{["application/problem+json"] = new() {Schema = new OpenApiSchema {Reference = new OpenApiReference{ Id="ProblemDetails", Type=ReferenceType.Schema } } }}});}}
}

若需要在 Swagger 中显式 ProblemDetails Schema，可在 AddSwaggerGen 中 MapType<ProblemDetails>(_ => new OpenApiSchema{ ... }) 或引入共享 Schema。

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11. 兼容性测试集（Newman/Playwright/BDN） 🧪🧪

• 条件 GET：首 GET 取 ETag → If-None-Match（含 *）→ 304；断言 ETag/Cache-Control/Vary。
• 并发写：用旧强 ETag → 412；用新强 ETag → 204/200。
• 游标分页：极值/去重/不回退；Link 绝对 URI 校验。
• 投影：fields 不含字段不返回且不报错。
• ProblemDetails：4xx/5xx 均为 application/problem+json。

# 条件 GET + 304
etag=$(curl -sI http://localhost:5000/api/products/1 | awk -F': ' '/^ETag:/{print $2}' | tr -d '\r')
curl -i -H "If-None-Match: $etag" http://localhost:5000/api/products/1
curl -i -H "If-None-Match: *"    http://localhost:5000/api/products/1   # 通配命中# 并发写 412
curl -i -X PUT -H "If-Match: \"stale-etag\"" -H "Content-Type: application/json" \-d '{"name":"N","price":1}' http://localhost:5000/api/products/1

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12. ABP vNext 工程化落地 🧱

• 配置项（appsettings.json）：分页上限/字段白名单/缓存策略/OData QueryOptions；
• CI 门禁：Spectral + 单测 + 回归集；
• 门户：定制 Swagger UI 页签展示契约基线、弃用时间线与复制片段。
• 反向代理：UseForwardedHeaders + 可信代理列表 + LinkGenerator 生成绝对 URI。

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13. 路线图 🗺️

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常见误区 ✅

• If-None-Match: * 已覆盖到详情与列表（GET/HEAD 命中 304）。
• 列表弱 ETag 使用“本页摘要”，命中率更高；空页稳定弱 ETag。
• Vary 合并追加（默认含 Accept, Accept-Encoding）。
• 绝对 Link 由 LinkGenerator 生成（适配反代）。
• OData MaxTop 全局=局部一致。
• 坚持：If-Match 强比较、If-None-Match 弱比较、304 必带元数据。

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可复现指南（最小步骤） 🧰

dotnet new webapi -n ApiBaselineDemo
cd ApiBaselineDemodotnet add package Swashbuckle.AspNetCore
dotnet add package Asp.Versioning.Mvc
dotnet add package Asp.Versioning.Mvc.ApiExplorer
dotnet add package Microsoft.AspNetCore.OData# 将本文中的：
# - IETagProvider/DefaultETagProvider/AddVary/WithCacheMetadata
# - QuerySpec/QueryableSortExtensions
# - ProductsController（含 If-None-Match:*、本页弱 ETag、LinkGenerator 绝对 Link、HEAD 支持）
# - OperationFilter/ProblemDetails 中间件
# 复制进项目，net8.0 编译运行
dotnet run