本文主要是介绍Composer 踩坑之 require，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
异常一：file could not be downloaded
使用 composer require 安装依赖包时，出现 file could not be downloaded
Jason:package jason$ composer require "overtrue/package-builder" --prefer-source[Composer\Downloader\TransportException]The "https://packagist.phpcomposer.com/p/provider-2019-01%24fea7e532df036d6561316b44b5194b84d8bdb92b6c81cf8f07d0afb25b0a2b05.json" file could not be downloaded (HTTP/1.1 404 Not Found)require [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-suggest] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--update-with-all-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--apcu-autoloader] [--] [<packages>]...Jason:package jason$
这是切换 Compser 源引起的，
方式一（推荐）：可以切换下其它的 composer 源，如：切换到 packagist.laravel-china.org
composer config -g repo.packagist composer https://packagist.laravel-china.org
方式二：可以多次尝试下，无法解决时执行下 composer update；在这里通过 composer update 后可正常安装依赖。
Jason:package jason$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Nothing to install or update
Generating autoload files
Jason:package jason$
Jason:package jason$Jason:package jason$ composer require "overtrue/package-builder" --prefer-source
Using version ^1.0 for overtrue/package-builder
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 7 installs, 0 updates, 0 removals- Installing symfony/polyfill-ctype (v1.11.0): Cloning 82ebae0220 from cache
...
异常二：[Runtime Exception] vendor does not exist and could not be created
使用 root 进行 composer 安装时（尽量避免使用 root 执行，特别是生产环境），出现：
[root@vm shop]# composer require encore/laravel-admin "1.6.8"
Do not run Composer as root/super user! See https://getcomposer.org/root for details
^C
Installation failed, reverting ./composer.json to its original content.
[root@vm shop]#
切换到普通用户，又再次出现权限不够：
[jason@vm shop]$ composer require encore/laravel-admin "1.6.8"
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 5 installs, 0 updates, 0 removals[RuntimeException]/home/www/shop/vendor/doctrine/event-manager does not exist and could not be created.require [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-suggest] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--update-with-all-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--apcu-autoloader] [--] [<packages>]...[jason@vm shop]$
项目本身是由 FTP 用户上传上来的，所以普通用户 jason 对其权限不足，首先考虑为其添加 www，ftp 用户组：
sudo usermod -a -G www jason
sudo usermod -a -G ftp jason
仍然不行。
最后只好将 vendor 的属主改为普通用户 jason
[jason@vm shop]$ sudo chown -R jason:jason vendor/
[jason@vm shop]$
再次安装：
[jason@vm shop]$ composer require encore/laravel-admin "1.6.8"
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 5 installs, 0 updates, 0 removals- Installing doctrine/event-manager (v1.0.0): Downloading (100%)- Installing doctrine/cache (v1.8.0): Downloading (100%)- Installing doctrine/dbal (v2.9.2): Downloading (100%)- Installing symfony/dom-crawler (v4.2.5): Downloading (100%)- Installing encore/laravel-admin (v1.6.8): Downloading (100%)
doctrine/cache suggests installing alcaeus/mongo-php-adapter (Required to use legacy MongoDB driver)
encore/laravel-admin suggests installing intervention/image (Required to handling and manipulation upload images (~2.3).)
encore/laravel-admin suggests installing spatie/eloquent-sortable (Required to built orderable gird.)[ErrorException]file_put_contents(./composer.lock): failed to open stream: Permission deniedrequire [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-suggest] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--update-with-all-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--apcu-autoloader] [--] [<packages>]...[jason@vm shop]$
提示 composer.lock 文件没有权限，将 composer.lock 的属主也修改到 jason
[jason@vm shop]$ sudo chown -R jason:jason ./composer.lock
[jason@vm shop]$
[jason@vm shop]$ composer require encore/laravel-admin "1.6.8"
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Nothing to install or update
Writing lock file
Generating optimized autoload files
> Illuminate\Foundation\ComposerScripts::postAutoloadDump
> @php artisan package:discover --ansi
Discovered Package: beyondcode/laravel-dump-server
Discovered Package: encore/laravel-admin
Discovered Package: fideloper/proxy
Discovered Package: laravel/nexmo-notification-channel
Discovered Package: laravel/slack-notification-channel
Discovered Package: laravel/tinker
Discovered Package: nesbot/carbon
Discovered Package: nunomaduro/collision
Package manifest generated successfully.
[jason@vm shop]$
安装成功。
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