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opensend Go SDK

Minimal first-party Go SDK for OpenSend transactional email sends with a Resend-shaped first send surface.

Use your OpenSend API key (os_...) with the Resend-compatible API surface.

Installation

From a Go module, install the package from this repository:

bash
go get github.com/namuh-eng/opensend/packages/go-sdk

Setup

Use environment variables instead of hardcoding API keys:

bash
export OPENSEND_API_KEY="os_your_api_key"

For self-hosted OpenSend, point the SDK at your deployment origin. The default hosted origin is https://api.opensend.com.

bash
export OPENSEND_BASE_URL="http://localhost:3026"

Send an email

go
package main

import (
	"context"
	"fmt"
	"log"
	"os"

	opensend "github.com/namuh-eng/opensend/packages/go-sdk"
)

func main() {
	options := []opensend.Option{}
	if baseURL := os.Getenv("OPENSEND_BASE_URL"); baseURL != "" {
		options = append(options, opensend.WithBaseURL(baseURL))
	}

	client, err := opensend.NewClient(os.Getenv("OPENSEND_API_KEY"), options...)
	if err != nil {
		log.Fatal(err)
	}

	email, err := client.Send(context.Background(), opensend.SendRequest{
		From:    "hello@yourdomain.com",
		To:      []string{"recipient@example.com"},
		Subject: "Hello from OpenSend",
		HTML:    "# It works!",
	})
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(email.ID)
}

Send posts to OpenSend's Resend-compatible POST /emails endpoint and returns the accepted email id.

Custom HTTP client

go
httpClient := &http.Client{Timeout: 10 * time.Second}
client, err := opensend.NewClient(
	os.Getenv("OPENSEND_API_KEY"),
	opensend.WithHTTPClient(httpClient),
)

Errors

Non-2xx API responses return *opensend.APIError. The error keeps the HTTP status and raw response body so callers can branch on validation/auth failures. When OpenSend returns its public error envelope, Name, Code, Message, and Details are populated too.

go
email, err := client.Send(ctx, params)
if err != nil {
	var apiErr *opensend.APIError
	if errors.As(err, &apiErr) {
		fmt.Println(apiErr.StatusCode, apiErr.Code, apiErr.Body)
		return
	}
	return
}
fmt.Println(email.ID)

Supported first slice

  • client.Send(ctx, opensend.SendRequest{...}) → POST /emails
  • Bearer API key auth
  • Configurable base URL
  • Optional custom *http.Client
  • Typed request fields for from, to, subject, html, text, cc, bcc, and reply_to

This first package intentionally does not implement attachments, templates, audiences, domains, framework examples, provider infrastructure, or the full Resend resource surface yet.

Tests

bash
cd packages/go-sdk
go test ./...
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