Step by Step Guide to Building a pdfFiller API Integration in Go

Introduction

Hey there, fellow Go enthusiast! Ready to supercharge your document handling capabilities? Let's dive into integrating the pdfFiller API into your Go project. This powerful tool will let you manipulate PDFs like a pro, from filling forms to managing templates. Buckle up, because we're about to make your document workflow smoother than ever!

Prerequisites

Before we jump in, make sure you've got:

• Go installed (I know, obvious, right?)
• pdfFiller API credentials (grab 'em from the pdfFiller developer portal)
• Your favorite Go package manager (we'll be using go mod)

Setting up the project

Let's kick things off by setting up our project:

mkdir pdffiller-integration
cd pdffiller-integration
go mod init github.com/yourusername/pdffiller-integration

Easy peasy! Now we've got our project structure ready to rock.

Authentication

First things first, let's tackle authentication. pdfFiller uses OAuth 2.0, so let's implement that flow:

import (
    "golang.org/x/oauth2"
)

func getClient() *http.Client {
    config := &oauth2.Config{
        ClientID:     "YOUR_CLIENT_ID",
        ClientSecret: "YOUR_CLIENT_SECRET",
        Endpoint:     oauth2.Endpoint{
            AuthURL:  "https://api.pdffiller.com/v1/oauth/authorize",
            TokenURL: "https://api.pdffiller.com/v1/oauth/token",
        },
    }

    token := &oauth2.Token{
        AccessToken: "YOUR_ACCESS_TOKEN",
    }

    return config.Client(context.Background(), token)
}

Pro tip: In a real-world scenario, you'd want to securely store and refresh these tokens. But for now, this'll get us rolling!

Core API Integration

Now, let's create a client to handle our API requests:

type PDFFillerClient struct {
    BaseURL    string
    HTTPClient *http.Client
}

func NewPDFFillerClient(baseURL string, httpClient *http.Client) *PDFFillerClient {
    return &PDFFillerClient{
        BaseURL:    baseURL,
        HTTPClient: httpClient,
    }
}

func (c *PDFFillerClient) makeRequest(method, endpoint string, body io.Reader) (*http.Response, error) {
    url := c.BaseURL + endpoint
    req, err := http.NewRequest(method, url, body)
    if err != nil {
        return nil, err
    }

    return c.HTTPClient.Do(req)
}

Implementing key pdfFiller features

Let's implement some core features:

Document upload

func (c *PDFFillerClient) UploadDocument(filePath string) (string, error) {
    file, err := os.Open(filePath)
    if err != nil {
        return "", err
    }
    defer file.Close()

    body := &bytes.Buffer{}
    writer := multipart.NewWriter(body)
    part, err := writer.CreateFormFile("file", filepath.Base(filePath))
    if err != nil {
        return "", err
    }
    io.Copy(part, file)
    writer.Close()

    resp, err := c.makeRequest("POST", "/api/v1/document", body)
    if err != nil {
        return "", err
    }
    defer resp.Body.Close()

    // Parse response and return document ID
    // ...
}

Filling forms

func (c *PDFFillerClient) FillForm(documentID string, data map[string]string) error {
    jsonData, err := json.Marshal(data)
    if err != nil {
        return err
    }

    _, err = c.makeRequest("POST", fmt.Sprintf("/api/v1/document/%s/fill", documentID), bytes.NewBuffer(jsonData))
    return err
}

Error handling and logging

Don't forget to implement robust error handling and logging. Here's a quick example:

import (
    "log"
)

func (c *PDFFillerClient) makeRequest(method, endpoint string, body io.Reader) (*http.Response, error) {
    // ... previous code ...

    resp, err := c.HTTPClient.Do(req)
    if err != nil {
        log.Printf("Error making request: %v", err)
        return nil, err
    }

    if resp.StatusCode >= 400 {
        log.Printf("API error: %s", resp.Status)
        // Handle API errors accordingly
    }

    return resp, nil
}

Testing the integration

Always test your code! Here's a simple test to get you started:

func TestUploadDocument(t *testing.T) {
    client := NewPDFFillerClient("https://api.pdffiller.com", getClient())
    docID, err := client.UploadDocument("test.pdf")
    if err != nil {
        t.Fatalf("Failed to upload document: %v", err)
    }
    if docID == "" {
        t.Fatal("Expected a document ID, got empty string")
    }
}

Best practices and optimization

Remember to implement rate limiting to stay within API constraints, consider caching responses for frequently accessed data, and use Go's concurrency features for parallel requests when appropriate.

Conclusion

And there you have it! You've just built a solid foundation for integrating pdfFiller into your Go projects. With this setup, you're ready to take on any document-related challenge that comes your way.

Remember, this is just the beginning. Explore the pdfFiller API docs to discover even more features you can add to your integration. Happy coding, and may your PDFs always be perfectly filled!