Split "modules/context.go" to separate files (#24569)

The "modules/context.go" is too large to maintain.

This PR splits it to separate files, eg: context_request.go,
context_response.go, context_serve.go

This PR will help:

1. The future refactoring for Gitea's web context (eg: simplify the context)
2. Introduce proper "range request" support
3. Introduce context function

This PR only moves code, doesn't change any logic.

modules/context/context_model.go

@@ -0,0 +1,138 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"path"
+	"strings"
+
+	"code.gitea.io/gitea/models/unit"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/issue/template"
+	"code.gitea.io/gitea/modules/log"
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+// IsUserSiteAdmin returns true if current user is a site admin
+func (ctx *Context) IsUserSiteAdmin() bool {
+	return ctx.IsSigned && ctx.Doer.IsAdmin
+}
+
+// IsUserRepoOwner returns true if current user owns current repo
+func (ctx *Context) IsUserRepoOwner() bool {
+	return ctx.Repo.IsOwner()
+}
+
+// IsUserRepoAdmin returns true if current user is admin in current repo
+func (ctx *Context) IsUserRepoAdmin() bool {
+	return ctx.Repo.IsAdmin()
+}
+
+// IsUserRepoWriter returns true if current user has write privilege in current repo
+func (ctx *Context) IsUserRepoWriter(unitTypes []unit.Type) bool {
+	for _, unitType := range unitTypes {
+		if ctx.Repo.CanWrite(unitType) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// IsUserRepoReaderSpecific returns true if current user can read current repo's specific part
+func (ctx *Context) IsUserRepoReaderSpecific(unitType unit.Type) bool {
+	return ctx.Repo.CanRead(unitType)
+}
+
+// IsUserRepoReaderAny returns true if current user can read any part of current repo
+func (ctx *Context) IsUserRepoReaderAny() bool {
+	return ctx.Repo.HasAccess()
+}
+
+// IssueTemplatesFromDefaultBranch checks for valid issue templates in the repo's default branch,
+func (ctx *Context) IssueTemplatesFromDefaultBranch() []*api.IssueTemplate {
+	ret, _ := ctx.IssueTemplatesErrorsFromDefaultBranch()
+	return ret
+}
+
+// IssueTemplatesErrorsFromDefaultBranch checks for issue templates in the repo's default branch,
+// returns valid templates and the errors of invalid template files.
+func (ctx *Context) IssueTemplatesErrorsFromDefaultBranch() ([]*api.IssueTemplate, map[string]error) {
+	var issueTemplates []*api.IssueTemplate
+
+	if ctx.Repo.Repository.IsEmpty {
+		return issueTemplates, nil
+	}
+
+	if ctx.Repo.Commit == nil {
+		var err error
+		ctx.Repo.Commit, err = ctx.Repo.GitRepo.GetBranchCommit(ctx.Repo.Repository.DefaultBranch)
+		if err != nil {
+			return issueTemplates, nil
+		}
+	}
+
+	invalidFiles := map[string]error{}
+	for _, dirName := range IssueTemplateDirCandidates {
+		tree, err := ctx.Repo.Commit.SubTree(dirName)
+		if err != nil {
+			log.Debug("get sub tree of %s: %v", dirName, err)
+			continue
+		}
+		entries, err := tree.ListEntries()
+		if err != nil {
+			log.Debug("list entries in %s: %v", dirName, err)
+			return issueTemplates, nil
+		}
+		for _, entry := range entries {
+			if !template.CouldBe(entry.Name()) {
+				continue
+			}
+			fullName := path.Join(dirName, entry.Name())
+			if it, err := template.UnmarshalFromEntry(entry, dirName); err != nil {
+				invalidFiles[fullName] = err
+			} else {
+				if !strings.HasPrefix(it.Ref, "refs/") { // Assume that the ref intended is always a branch - for tags users should use refs/tags/<ref>
+					it.Ref = git.BranchPrefix + it.Ref
+				}
+				issueTemplates = append(issueTemplates, it)
+			}
+		}
+	}
+	return issueTemplates, invalidFiles
+}
+
+// IssueConfigFromDefaultBranch returns the issue config for this repo.
+// It never returns a nil config.
+func (ctx *Context) IssueConfigFromDefaultBranch() (api.IssueConfig, error) {
+	if ctx.Repo.Repository.IsEmpty {
+		return GetDefaultIssueConfig(), nil
+	}
+
+	commit, err := ctx.Repo.GitRepo.GetBranchCommit(ctx.Repo.Repository.DefaultBranch)
+	if err != nil {
+		return GetDefaultIssueConfig(), err
+	}
+
+	for _, configName := range IssueConfigCandidates {
+		if _, err := commit.GetTreeEntryByPath(configName + ".yaml"); err == nil {
+			return ctx.Repo.GetIssueConfig(configName+".yaml", commit)
+		}
+
+		if _, err := commit.GetTreeEntryByPath(configName + ".yml"); err == nil {
+			return ctx.Repo.GetIssueConfig(configName+".yml", commit)
+		}
+	}
+
+	return GetDefaultIssueConfig(), nil
+}
+
+func (ctx *Context) HasIssueTemplatesOrContactLinks() bool {
+	if len(ctx.IssueTemplatesFromDefaultBranch()) > 0 {
+		return true
+	}
+
+	issueConfig, _ := ctx.IssueConfigFromDefaultBranch()
+	return len(issueConfig.ContactLinks) > 0
+}