golang-microservices-rest: A Go repository from shubhamd99

Go Lang Microservices

Golang - Go is a statically typed, compiled programming language designed at Google by Robert Griesemer, Rob Pike, and Ken Thompson. Go is syntactically similar to C, but with memory safety, garbage collection, structural typing, and CSP-style concurrency.
Concurrency - In computer programming, concurrency is ability of a computer to deal with multiple things at once. A general purpose PC might have just one CPU core which does all the processing and computation.
Docs - https://golang.org/doc/
Download Gorilla go get github.com/gorilla/mux - https://www.gorillatoolkit.org/
Microservice architecture, or simply microservices, is a distinctive method of developing software systems that tries to focus on building single-function modules with well-defined interfaces and operations. The trend has grown popular in recent years as Enterprises look to become more Agile and move towards a DevOps and continuous testing.
Swagger

brew tap go-swagger/go-swagger
brew install go-swagger

OR 

go get -u github.com/go-swagger/go-swagger/cmd/swagger

Generate API Client with Swagger (It will create client inside client folder)

swagger generate client -f ./swagger.yaml

Advantages

Developed at Google
Statically Typed language
Community Support
Simplicity
Faster Compile Time
Garbage Collection
Builtin Concurrency
Standard Libraries - In the end you will get standalone binary file to run the code

Tips

We cannot declare unused variables, go will throw compliation error

Run

RUN - go run main.go
Check Connection - curl -v -d 'Shubham' localhost:9090
Create binary exe - go build

Data Types

In the Go programming language, data types refer to an extensive system used for declaring variables or functions of different types.

Boolean types - (a) true (b) false
Numeric types - a) integer types or b) floating point values
String types - Strings are immutable types that is once created, it is not possible to change the contents of a string.
Derived types

(a) Pointer types (b) Array types (c) Structure types (d) Union types and (e) Function types f) Slice types g) Interface types h) Map types i) Channel Types

A variable is nothing but a name given to a storage area that the programs can manipulate. Each variable in Go has a specific type, which determines the size and layout of the variable's memory, the range of values that can be stored within that memory, and the set of operations that can be applied to the variable.

var  i, j, k int;
var  c, ch byte;
var  f, salary float32;
d =  42;

Integers Types

Arrays

Go programming language provides a data structure called the array, which can store a fixed-size sequential collection of elements of the same type.

var variable_name [SIZE] variable_type

var balance = [5]float32{1000.0, 2.0, 3.4, 7.0, 50.0}

Slices

Go Slice is an abstraction over Go Array. Go Array allows you to define variables that can hold several data items of the same kind but it does not provide any inbuilt method to increase its size dynamically or get a sub-array of its own. Slices overcome this limitation.

var numbers []int /* a slice of unspecified size */
/* numbers == []int{0,0,0,0,0}*/
numbers = make([]int,5,5) /* a slice of length 5 and capacity 5*/

Maps

Go provides another important data type named map which maps unique keys to values. A key is an object that you use to retrieve a value at a later date.

var map_variable map[key_data_type]value_data_type

var countryCapitalMap map[string]string
/* create a map*/
countryCapitalMap = make(map[string]string)

/* insert key-value pairs in the map*/
countryCapitalMap["France"] = "Paris"
countryCapitalMap["Italy"] = "Rome"
countryCapitalMap["Japan"] = "Tokyo"
countryCapitalMap["India"] = "New Delhi"

/* print map using keys*/
for country := range countryCapitalMap {
    fmt.Println("Capital of",country,"is",countryCapitalMap[country])
}

/* test if entry is present in the map or not*/
capital, ok := countryCapitalMap["United States"]

/* if ok is true, entry is present otherwise entry is absent*/
if(ok){
    fmt.Println("Capital of United States is", capital)  
} else {
    fmt.Println("Capital of United States is not present") 
}

Struct

Collection of data types. Go arrays allow you to define variables that can hold several data items of the same kind. Structure is another user-defined data type available in Go programming, which allows you to combine data items of different kinds.

type Books struct {
   title string
   author string
   subject string
   book_id int
}

Loops

arr := []int{1, 2, 3, 4, 5, 6, 7}

for key, value := range arr {
	fmt.Println(key, value)
}

If and Switch

if i >= 0 || j >= 0 {
    fmt.Println("i, j is greater than 0")
}
	

switch o := 2 + 3; o {
case 1, 3, 5, 7, 9:
   fmt.Println("Odd")
case 2, 4, 8:
   fmt.Println("Even")
default:
   fmt.Println("default")
}

Defer, Panic and Recover

A defer statement defers the execution of a function until the surrounding function returns. The deferred call's arguments are evaluated immediately, but the function call is not executed until the surrounding function returns.

Panic is a built-in function that stops the ordinary flow of control and begins panicking.

Recover is a built-in function that regains control of a panicking goroutine. Recover is only useful inside deferred functions. During normal execution, a call to recover will return nil and have no other effect.

Pointers

As you know, every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory.

A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location.

var var_name *var-type

var ip *int        /* pointer to an integer */
var fp *float32    /* pointer to a float */

var  ptr *int

fmt.Printf("The value of ptr is : %x\n", ptr  )

Functions

A function is a group of statements that together perform a task.

/* function returning the max between two numbers */

func max(num1, num2 int) int {
   /* local variable declaration */
   result int

   if (num1 > num2) {
      result = num1
   } else {
      result = num2
   }
   return result 
}

Interfaces

Collection of behaviours. Go programming provides another data type called interfaces which represents a set of method signatures.

Goroutines

A goroutine is a lightweight thread of execution.

Suppose we have a function call f(s). Here’s how we’d call that in the usual way, running it synchronously.

f("direct")

To invoke this function in a goroutine, use go f(s). This new goroutine will execute concurrently with the calling one.

To Identify Race Conditions run go run -race .\Main.go

Channels

Channels are a typed conduit through which you can send and receive values with the channel operator, <-.

ch <- v    // Send v to channel ch.
v := <-ch  // Receive from ch, and assign value to v.

Like maps and slices, channels must be created before use:

ch := make(chan int)

By default, sends and receives block until the other side is ready. This allows goroutines to synchronize without explicit locks or condition variables.

shubhamd99/golang-microservices-rest