Move context from modules to services (#29440)

Since `modules/context` has to depend on `models` and many other
packages, it should be moved from `modules/context` to
`services/context` according to design principles. There is no logic
code change on this PR, only move packages.

- Move `code.gitea.io/gitea/modules/context` to
`code.gitea.io/gitea/services/context`
- Move `code.gitea.io/gitea/modules/contexttest` to
`code.gitea.io/gitea/services/contexttest` because of depending on
context
- Move `code.gitea.io/gitea/modules/upload` to
`code.gitea.io/gitea/services/context/upload` because of depending on
context

services/context/response.go

@@ -0,0 +1,103 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"net/http"
+
+	web_types "code.gitea.io/gitea/modules/web/types"
+)
+
+// ResponseWriter represents a response writer for HTTP
+type ResponseWriter interface {
+	http.ResponseWriter
+	http.Flusher
+	web_types.ResponseStatusProvider
+
+	Before(func(ResponseWriter))
+
+	Status() int // used by access logger template
+	Size() int   // used by access logger template
+}
+
+var _ ResponseWriter = &Response{}
+
+// Response represents a response
+type Response struct {
+	http.ResponseWriter
+	written        int
+	status         int
+	befores        []func(ResponseWriter)
+	beforeExecuted bool
+}
+
+// Write writes bytes to HTTP endpoint
+func (r *Response) Write(bs []byte) (int, error) {
+	if !r.beforeExecuted {
+		for _, before := range r.befores {
+			before(r)
+		}
+		r.beforeExecuted = true
+	}
+	size, err := r.ResponseWriter.Write(bs)
+	r.written += size
+	if err != nil {
+		return size, err
+	}
+	if r.status == 0 {
+		r.status = http.StatusOK
+	}
+	return size, nil
+}
+
+func (r *Response) Status() int {
+	return r.status
+}
+
+func (r *Response) Size() int {
+	return r.written
+}
+
+// WriteHeader write status code
+func (r *Response) WriteHeader(statusCode int) {
+	if !r.beforeExecuted {
+		for _, before := range r.befores {
+			before(r)
+		}
+		r.beforeExecuted = true
+	}
+	if r.status == 0 {
+		r.status = statusCode
+		r.ResponseWriter.WriteHeader(statusCode)
+	}
+}
+
+// Flush flushes cached data
+func (r *Response) Flush() {
+	if f, ok := r.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
+// WrittenStatus returned status code written
+func (r *Response) WrittenStatus() int {
+	return r.status
+}
+
+// Before allows for a function to be called before the ResponseWriter has been written to. This is
+// useful for setting headers or any other operations that must happen before a response has been written.
+func (r *Response) Before(f func(ResponseWriter)) {
+	r.befores = append(r.befores, f)
+}
+
+func WrapResponseWriter(resp http.ResponseWriter) *Response {
+	if v, ok := resp.(*Response); ok {
+		return v
+	}
+	return &Response{
+		ResponseWriter: resp,
+		status:         0,
+		befores:        make([]func(ResponseWriter), 0),
+	}
+}