http-message
                                The purpose of this PSR is to provide a set of common interfaces for HTTP messages as described in RFC 7230 and RFC 7231
                            
                        How to download and setup http-message
Open terminal and run command
                                            git clone https://github.com/php-fig/http-message.git
                                        
                                        git clone is used to create a copy or clone of http-message repositories.
                                        You pass git clone a repository URL. it supports a few different network protocols and corresponding URL formats.
Also you may download zip file with http-message https://github.com/php-fig/http-message/archive/master.zip
Or simply clone http-message with SSH
                                            [email protected]:php-fig/http-message.git                                    
                                    If you have some problems with http-message
You may open issue on http-message support forum (system) here: https://github.com/php-fig/http-message/issuesSimilar to http-message repositories
Here you may see http-message alternatives and analogs
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