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Tutorial: Developing a RESTful API with Become and Gin

This tutorial introduces the basics of writing a RESTful web service API with Go and the Gin Web Framework (Gin).

You'll become the most out of this tutorial if yous accept a bones familiarity with Go and its tooling. If this is your kickoff exposure to Go, delight meet Tutorial: Become started with Go for a quick introduction.

Gin simplifies many coding tasks associated with edifice web applications, including web services. In this tutorial, you'll apply Gin to route requests, retrieve request details, and marshal JSON for responses.

In this tutorial, you will build a RESTful API server with 2 endpoints. Your instance project volition be a repository of information about vintage jazz records.

The tutorial includes the following sections:

1. Design API endpoints.
2. Create a binder for your lawmaking.
3. Create the data.
4. Write a handler to return all items.
5. Write a handler to add a new item.
6. Write a handler to return a specific item.

Note: For other tutorials, run across Tutorials.

To try this as an interactive tutorial yous consummate in Google Cloud Trounce, click the button below.

Prerequisites

• An installation of Go 1.16 or later. For installation instructions, see Installing Become.
• A tool to edit your code. Whatever text editor y'all have will piece of work fine.
• A command final. Get works well using any terminal on Linux and Mac, and on PowerShell or cmd in Windows.
• The curl tool. On Linux and Mac, this should already exist installed. On Windows, it's included on Windows 10 Insider build 17063 and later. For before Windows versions, you might need to install it. For more, meet Tar and Gyre Come to Windows.

Design API endpoints

Yous'll build an API that provides access to a store selling vintage recordings on vinyl. Then you'll need to provide endpoints through which a client tin go and add albums for users.

When developing an API, you typically begin by designing the endpoints. Your API'southward users will have more success if the endpoints are easy to understand.

Here are the endpoints you'll create in this tutorial.

/albums

• Become – Get a list of all albums, returned as JSON.
• Mail – Add a new album from request information sent as JSON.

/albums/:id

• GET – Get an album by its ID, returning the anthology data equally JSON.

Adjacent, yous'll create a folder for your code.

Create a folder for your lawmaking

To brainstorm, create a projection for the lawmaking you'll write.

1. Open up a control prompt and alter to your home directory.

   On Linux or Mac:

                   $ cd                              

   On Windows:

                   C:\> cd %HOMEPATH%                              

2. Using the command prompt, create a directory for your code called web-service-gin.

                   $ mkdir web-service-gin $ cd spider web-service-gin                              

3. Create a module in which y'all can manage dependencies.

   Run the go mod init command, giving it the path of the module your code volition be in.

                   $ go mod init example/spider web-service-gin go: creating new go.mod: module example/web-service-gin                              

   This command creates a get.modernistic file in which dependencies you add will be listed for tracking. For more about naming a module with a module path, come across Managing dependencies.

Next, y'all'll design information structures for handling information.

Create the data

To keep things simple for the tutorial, you'll shop information in memory. A more than typical API would interact with a database.

Note that storing data in memory ways that the set of albums will be lost each time you stop the server, then recreated when you start information technology.

Write the code

1. Using your text editor, create a file chosen main.get in the web-service directory. You'll write your Go lawmaking in this file.

2. Into main.become, at the top of the file, paste the following packet declaration.

                   package principal                              

   A standalone plan (equally opposed to a library) is e'er in package main.

3. Beneath the parcel declaration, paste the post-obit proclamation of an album struct. You lot'll use this to store album data in retentivity.

   Struct tags such as json:"artist" specify what a field's proper name should exist when the struct's contents are serialized into JSON. Without them, the JSON would use the struct's capitalized field names – a style non as common in JSON.

                   // anthology represents data virtually a record album. type album struct {     ID     string  `json:"id"`     Title  string  `json:"title"`     Artist string  `json:"artist"`     Cost  float64 `json:"price"` }                              

4. Beneath the struct declaration you just added, paste the post-obit slice of album structs containing data you'll use to start.

                   // albums slice to seed record album data. var albums = []album{     {ID: "ane", Title: "Blue Railroad train", Artist: "John Coltrane", Price: 56.99},     {ID: "two", Title: "Jeru", Creative person: "Gerry Mulligan", Toll: 17.99},     {ID: "three", Title: "Sarah Vaughan and Clifford Brownish", Artist: "Sarah Vaughan", Price: 39.99}, }                              

Next, you'll write code to implement your first endpoint.

Write a handler to render all items

When the client makes a request at Go /albums, you lot want to return all the albums as JSON.

To do this, you'll write the following:

• Logic to prepare a response
• Code to map the request path to your logic

Notation that this is the reverse of how they'll be executed at runtime, but you're calculation dependencies first, and so the code that depends on them.

Write the code

1. Below the struct lawmaking you added in the preceding section, paste the following code to get the album list.

   This getAlbums function creates JSON from the slice of album structs, writing the JSON into the response.

                   // getAlbums responds with the list of all albums as JSON. func getAlbums(c *gin.Context) {     c.IndentedJSON(http.StatusOK, albums) }                              

   In this code, you:

   • Write a getAlbums office that takes a gin.Context parameter. Note that you could have given this function whatever name – neither Gin nor Go crave a particular function proper name format.

     gin.Context is the well-nigh important part of Gin. It carries request details, validates and serializes JSON, and more. (Despite the similar name, this is different from Get's born context package.)

   • Call Context.IndentedJSON to serialize the struct into JSON and add it to the response.

     The function's first argument is the HTTP status code you want to ship to the client. Hither, you're passing the StatusOK constant from the internet/http parcel to indicate 200 OK.

     Notation that you tin can replace Context.IndentedJSON with a call to Context.JSON to send more than compact JSON. In practise, the indented form is much easier to work with when debugging and the size deviation is usually small.

2. Near the summit of main.go, simply beneath the albums slice declaration, paste the code beneath to assign the handler function to an endpoint path.

   This sets upward an association in which getAlbums handles requests to the /albums endpoint path.

                   func main() {     router := gin.Default()     router.Go("/albums", getAlbums)      router.Run("localhost:8080") }                              

   In this lawmaking, you:

   • Initialize a Gin router using Default.

   • Use the Get role to associate the Go HTTP method and /albums path with a handler function.

     Note that you're passing the proper name of the getAlbums function. This is different from passing the result of the function, which you would do by passing getAlbums() (notation the parenthesis).

   • Apply the Run part to attach the router to an http.Server and start the server.

3. Near the height of main.go, only beneath the package annunciation, import the packages you'll demand to support the code you've just written.

   The showtime lines of code should look like this:

                   package master  import (     "net/http"      "github.com/gin-gonic/gin" )                              

4. Save main.go.

Run the code

1. Brainstorm tracking the Gin module as a dependency.

   At the control line, use become get to add the github.com/gin-gonic/gin module as a dependency for your module. Employ a dot argument to hateful "go dependencies for code in the electric current directory."

                   $ get get . become become: added github.com/gin-gonic/gin v1.seven.2                              

   Go resolved and downloaded this dependency to satisfy the import declaration you added in the previous step.

2. From the control line in the directory containing main.go, run the lawmaking. Use a dot statement to mean "run lawmaking in the current directory."

                   $ go run .                              

   In one case the lawmaking is running, y'all accept a running HTTP server to which y'all can send requests.

3. From a new control line window, use curl to make a asking to your running web service.

                   $ curl http://localhost:8080/albums                              

   The control should display the data you seeded the service with.

                   [         {                 "id": "1",                 "title": "Blue Train",                 "artist": "John Coltrane",                 "cost": 56.99         },         {                 "id": "2",                 "title": "Jeru",                 "creative person": "Gerry Mulligan",                 "toll": 17.99         },         {                 "id": "three",                 "title": "Sarah Vaughan and Clifford Dark-brown",                 "artist": "Sarah Vaughan",                 "toll": 39.99         } ]                              

You've started an API! In the next section, you'll create another endpoint with code to handle a POST request to add an item.

Write a handler to add together a new item

When the client makes a POST request at /albums, y'all want to add the album described in the asking torso to the existing albums information.

To practice this, you'll write the post-obit:

• Logic to add together the new anthology to the existing listing.
• A fleck of code to route the POST asking to your logic.

Write the code

1. Add together lawmaking to add albums data to the list of albums.

   Somewhere after the import statements, paste the following code. (The end of the file is a good place for this code, just Go doesn't enforce the order in which you lot declare functions.)

                   // postAlbums adds an album from JSON received in the request body. func postAlbums(c *gin.Context) {     var newAlbum album      // Call BindJSON to bind the received JSON to     // newAlbum.     if err := c.BindJSON(&newAlbum); err != nil {         return     }      // Add the new anthology to the slice.     albums = suspend(albums, newAlbum)     c.IndentedJSON(http.StatusCreated, newAlbum) }                              

   In this lawmaking, you:

   • Employ Context.BindJSON to bind the request trunk to newAlbum.
   • Append the album struct initialized from the JSON to the albums slice.
   • Add a 201 status lawmaking to the response, along with JSON representing the anthology you added.

2. Change your main part so that it includes the router.POST part, as in the post-obit.

                   func main() {     router := gin.Default()     router.GET("/albums", getAlbums)     router.POST("/albums", postAlbums)      router.Run("localhost:8080") }                              

   In this code, you:

   • Acquaintance the Mail service method at the /albums path with the postAlbums function.

     With Gin, you can acquaintance a handler with an HTTP method-and-path combination. In this style, you tin can separately road requests sent to a unmarried path based on the method the customer is using.

Run the code

1. If the server is still running from the terminal department, stop it.

2. From the command line in the directory containing chief.get, run the code.

                   $ go run .                              

3. From a different command line window, employ curlicue to make a request to your running web service.

                   $ curl http://localhost:8080/albums \     --include \     --header "Content-Blazon: application/json" \     --request "Mail service" \     --information '{"id": "4","championship": "The Modern Audio of Betty Carter","artist": "Betty Carter","cost": 49.99}'                              

   The command should display headers and JSON for the added album.

                   HTTP/1.i 201 Created Content-Blazon: application/json; charset=utf-eight Appointment: Wed, 02 Jun 2022 00:34:12 GMT Content-Length: 116  {     "id": "4",     "title": "The Modern Sound of Betty Carter",     "artist": "Betty Carter",     "price": 49.99 }                              

4. Every bit in the previous section, use curl to retrieve the full list of albums, which you can utilise to confirm that the new anthology was added.

                   $ gyre http://localhost:8080/albums \     --header "Content-Blazon: application/json" \     --request "Go"                              

   The command should brandish the album listing.

                   [         {                 "id": "1",                 "title": "Blue Train",                 "artist": "John Coltrane",                 "price": 56.99         },         {                 "id": "2",                 "championship": "Jeru",                 "artist": "Gerry Mulligan",                 "cost": 17.99         },         {                 "id": "3",                 "title": "Sarah Vaughan and Clifford Dark-brown",                 "artist": "Sarah Vaughan",                 "price": 39.99         },         {                 "id": "iv",                 "title": "The Modern Sound of Betty Carter",                 "artist": "Betty Carter",                 "price": 49.99         } ]                              

In the adjacent section, yous'll add code to handle a GET for a specific particular.

Write a handler to return a specific item

When the client makes a asking to Become /albums/[id], you want to return the album whose ID matches the id path parameter.

To practise this, y'all volition:

• Add logic to retrieve the requested album.
• Map the path to the logic.

Write the lawmaking

1. Below the postAlbums office you added in the preceding department, paste the following code to retrieve a specific album.

   This getAlbumByID function will extract the ID in the request path, then locate an album that matches.

                   // getAlbumByID locates the anthology whose ID value matches the id // parameter sent by the client, then returns that album every bit a response. func getAlbumByID(c *gin.Context) {     id := c.Param("id")      // Loop over the listing of albums, looking for     // an album whose ID value matches the parameter.     for _, a := range albums {         if a.ID == id {             c.IndentedJSON(http.StatusOK, a)             return         }     }     c.IndentedJSON(http.StatusNotFound, gin.H{"message": "album not found"}) }                              

   In this lawmaking, you:

   • Utilise Context.Param to retrieve the id path parameter from the URL. When you lot map this handler to a path, you'll include a placeholder for the parameter in the path.

   • Loop over the album structs in the slice, looking for ane whose ID field value matches the id parameter value. If it's constitute, you lot serialize that album struct to JSON and render information technology as a response with a 200 OK HTTP lawmaking.

     As mentioned to a higher place, a real-earth service would probable use a database query to perform this lookup.

   • Return an HTTP 404 error with http.StatusNotFound if the album isn't constitute.

2. Finally, modify your master and then that it includes a new call to router.GET, where the path is now /albums/:id, equally shown in the following case.

                   func main() {     router := gin.Default()     router.Become("/albums", getAlbums)     router.GET("/albums/:id", getAlbumByID)     router.Postal service("/albums", postAlbums)      router.Run("localhost:8080") }                              

   In this code, y'all:

   • Associate the /albums/:id path with the getAlbumByID function. In Gin, the colon preceding an item in the path signifies that the item is a path parameter.

Run the code

1. If the server is however running from the final section, stop it.

2. From the command line in the directory containing master.get, run the code to start the server.

                   $ become run .                              

3. From a different control line window, apply curl to make a request to your running web service.

                   $ curl http://localhost:8080/albums/two                              

   The command should display JSON for the anthology whose ID y'all used. If the album wasn't constitute, yous'll become JSON with an error message.

                   {         "id": "2",         "title": "Jeru",         "creative person": "Gerry Mulligan",         "price": 17.99 }                              

Conclusion

Congratulations! You lot've just used Go and Gin to write a simple RESTful spider web service.

Suggested next topics:

• If you're new to Go, you'll find useful best practices described in Effective Go and How to write Get code.
• The Get Tour is a great step-by-step introduction to Become fundamentals.
• For more than about Gin, run into the Gin Spider web Framework package documentation or the Gin Spider web Framework docs.

Completed code

This section contains the code for the application you build with this tutorial.

            package chief  import (     "net/http"      "github.com/gin-gonic/gin" )  // anthology represents data about a tape album. type album struct {     ID     string  `json:"id"`     Title  string  `json:"title"`     Artist cord  `json:"creative person"`     Toll  float64 `json:"price"` }  // albums slice to seed record anthology information. var albums = []album{     {ID: "1", Title: "Blueish Railroad train", Artist: "John Coltrane", Price: 56.99},     {ID: "2", Championship: "Jeru", Artist: "Gerry Mulligan", Price: 17.99},     {ID: "3", Title: "Sarah Vaughan and Clifford Brown", Artist: "Sarah Vaughan", Cost: 39.99}, }  func primary() {     router := gin.Default()     router.GET("/albums", getAlbums)     router.GET("/albums/:id", getAlbumByID)     router.POST("/albums", postAlbums)      router.Run("localhost:8080") }  // getAlbums responds with the list of all albums equally JSON. func getAlbums(c *gin.Context) {     c.IndentedJSON(http.StatusOK, albums) }  // postAlbums adds an album from JSON received in the request body. func postAlbums(c *gin.Context) {     var newAlbum album      // Call BindJSON to bind the received JSON to     // newAlbum.     if err := c.BindJSON(&newAlbum); err != nil {         return     }      // Add the new album to the slice.     albums = append(albums, newAlbum)     c.IndentedJSON(http.StatusCreated, newAlbum) }  // getAlbumByID locates the anthology whose ID value matches the id // parameter sent past the client, then returns that album as a response. func getAlbumByID(c *gin.Context) {     id := c.Param("id")      // Loop through the list of albums, looking for     // an album whose ID value matches the parameter.     for _, a := range albums {         if a.ID == id {             c.IndentedJSON(http.StatusOK, a)             return         }     }     c.IndentedJSON(http.StatusNotFound, gin.H{"message": "album not constitute"}) }                      

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Source: https://go.dev/doc/tutorial/web-service-gin

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