API process and code structure

One 、HTTP API The server starts the process

1.  Starting a  API  After the command ,API  The command will first load the configuration file , Do the following processing according to the configuration .
2.  Usually, log related configurations are recorded in the configuration file , After parsing the configuration file , You can load the log package initialization function , To initialize the log instance , For later programs to call .
3.  Next , Initialize database instance , Establish a database connection , For later facing the database  CRUD  Operation and use .
4.  After establishing the database connection , Need to set up  HTTP, Usually include  3  Aspect settings ：
	4.1  Set up  Header
	4.2  Registered routing 
	4.3  Register middleware 
5.  And then it will call  net/http  Bag  ListenAndServe()  Method start up  HTTP  The server .
6.  Start up  HTTP  Before port , Program meeting  go  An agreement , Come on ping HTTP  Server's  /sd/health  Interface , If the program starts successfully ,ping  Assist in  timeout  It will return successfully before , If the program fails to start , be  ping  The process will eventually  timeout, And terminate the whole program .

Two 、HTTP Request processing flow

1. Establishing a connection

1. The client sends  HTTP  After the request , The server will resolve the domain name according to the domain name , Is to change the website name into  IP  Address ：localhost ->127.0.0.1,Linux hosts file 、DNS  Domain name resolution can realize this function .
2. Then launch  TCP  Three handshakes to establish a connection , After the connection is established, you can send  HTTP  Request the .

2. Receiving request

1.HTTP  Server software process , This means  API  The server , After receiving the request ,
2. First of all, according to the  HTTP  Request line information to parse to  HTTP Methods and paths , Then according to  API  The server registers the routing information and finds the specific processing function .（ It might be understood as ：HTTP  Method  +  Mapping of path and specific processing function ）

3. Processing requests

1. After receiving the request ,HTTP  Frameworks generally have their own analytic functions , Just input  HTTP  Request message , You can parse the required request header and message body , And then deal with the business logic .
2. Usually , Business logic processing can be divided into two types ： Including the operation on the database and excluding the operation on the data . In large systems, there are usually both ：
	1.  Including operations on the database ： Need to access the database （ Additions and deletions ）, Then get the specified data , After data processing , Return the response package .
	2.  Does not include operations on the database ： After business logic processing , Return the response package .

4. Record the processing of things

1. In the process of business logic processing , Some key information needs to be recorded , Convenient later stage  Debug  use .
2. stay  Go  There are a variety of log packages in the to record this information .

3、 ... and 、HTTP Request message

One HTTP The request message is sent by the request line （request line）、 Request header （header）、 Blank line and request data are composed of four parts .

1、 Composition of request header

1.  The first line must be a request line （request line）
	 Used to describe the request type 、 The resources to be accessed and the  HTTP  edition 
2.  Then there is a head （header） Section 
	 Used to describe additional information to be used by the server 
3.  Then there is an empty line 
4.  Finally, request data （ Call it the subject ：body）
	 You can add any other data 
	
 Be careful ：
	 Request any website , Use F12 You can view the request header and response header information 
	HTTP  The response format is similar to the request format , Also by  4  Component composition ： Status line 、 The message header 、 Blank lines and response data .

Four 、 Directory structure

stay Go API In the project , It usually includes many functions .
1、 Common function items

Makefile  file （ Compile the file ）、 Profile directory 、RESTful API Server's handler Catalog 、model  Catalog 、 Tool catalog 、vendor  Catalog , And the actual processing business logic function service  Catalog .

2、 Specific directory structure

gin Does not provide a standardized directory structure 
admin.sh --  One button stop 
conf --  Profile directory 
config --  Code for reading and parsing configuration files 
db.sql --  Create library table 
docs --  Document directory 
router --  route  -- url
hander --  Processing function  -- go Code 
main.go --  Entrance file 
model --  Data model  -- ORM
pkg --  Write some general processing code 
util