feat: add github_release_asset data source

This addresses issue integrations#2513 and adds support for a `github_release_asset`
data source.

Example of passing acceptance tests:

```
GITHUB_ORGANIZATION=mterwill \
GITHUB_OWNER=mterwill \
TF_ACC=1 \
  go test -v ./... -run ^TestAccGithubReleaseAssetDataSource
?       github.com/integrations/terraform-provider-github/v6    [no test files]
=== RUN   TestAccGithubReleaseAssetDataSource
=== RUN   TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID
=== RUN   TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_anonymous_account
    provider_utils.go:51: GITHUB_TOKEN environment variable should be empty
    provider_utils.go:74: Skipping TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_anonymous_account which requires anonymous mode
=== RUN   TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_individual_account
=== RUN   TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_organization_account
--- PASS: TestAccGithubReleaseAssetDataSource (11.65s)
    --- PASS: TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID (11.65s)
        --- SKIP: TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_anonymous_account (0.00s)
        --- PASS: TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_individual_account (8.90s)
        --- PASS: TestAccGithubReleaseAssetDataSource/queries_specified_asset_ID/with_an_organization_account (2.75s)
PASS
ok      github.com/integrations/terraform-provider-github/v6/github     12.434s
```

Signed-off-by: Mike Ball <mikedball@gmail.com>

github/config.go

@@ -186,7 +186,10 @@ func (injector *previewHeaderInjectorTransport) RoundTrip(req *http.Request) (*h
 		header := req.Header.Get(name)
 		if header == "" {
 			header = value
-		} else {
+			// NOTE: Some API endpoints expect a single Accept: application/octet-stream header.
+			// If one has been set, it's necessary to preserve it as-is, without
+			// appending previewHeaders value.
+		} else if !(strings.ToLower(name) == "accept" && header == "application/octet-stream") {
 			header = strings.Join([]string{header, value}, ",")
 		}
 		req.Header.Set(name, header)

github/data_source_github_release_asset.go

@@ -0,0 +1,147 @@
+package github
+
+import (
+	"context"
+	"io"
+	"strconv"
+	"strings"
+
+	"github.com/google/go-github/v66/github"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+)
+
+func dataSourceGithubReleaseAsset() *schema.Resource {
+	return &schema.Resource{
+		Read: dataSourceGithubReleaseAssetRead,
+
+		Schema: map[string]*schema.Schema{
+			"asset_id": {
+				Type:     schema.TypeInt,
+				Required: true,
+			},
+			"owner": {
+				Type:     schema.TypeString,
+				Required: true,
+			},
+			"repository": {
+				Type:     schema.TypeString,
+				Required: true,
+			},
+			"body": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"url": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"node_id": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"name": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"label": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"content_type": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"size": {
+				Type:     schema.TypeInt,
+				Computed: true,
+			},
+			"created_at": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"updated_at": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"browser_download_url": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+		},
+	}
+}
+
+func dataSourceGithubReleaseAssetRead(d *schema.ResourceData, meta interface{}) error {
+	repository := d.Get("repository").(string)
+	owner := d.Get("owner").(string)
+
+	client := meta.(*Owner).v3client
+	ctx := context.Background()
+
+	var err error
+	var asset *github.ReleaseAsset
+
+	assetID := int64(d.Get("asset_id").(int))
+	asset, _, err = client.Repositories.GetReleaseAsset(ctx, owner, repository, assetID)
+	if err != nil {
+		return err
+	}
+
+	var respBody io.ReadCloser
+	clientCopy := client.Client()
+	respBody, _, err = client.Repositories.DownloadReleaseAsset(ctx, owner, repository, assetID, clientCopy)
+	if err != nil {
+		return err
+	}
+	defer respBody.Close()
+
+	buf := new(strings.Builder)
+	_, err = io.Copy(buf, respBody)
+	if err != nil {
+		return err
+	}
+
+	d.SetId(strconv.FormatInt(asset.GetID(), 10))
+	err = d.Set("body", buf.String())
+	if err != nil {
+		return err
+	}
+	err = d.Set("url", asset.URL)
+	if err != nil {
+		return err
+	}
+	err = d.Set("node_id", asset.NodeID)
+	if err != nil {
+		return err
+	}
+	err = d.Set("name", asset.Name)
+	if err != nil {
+		return err
+	}
+	err = d.Set("label", asset.Label)
+	if err != nil {
+		return err
+	}
+	err = d.Set("content_type", asset.ContentType)
+	if err != nil {
+		return err
+	}
+	err = d.Set("size", asset.Size)
+	if err != nil {
+		return err
+	}
+	err = d.Set("created_at", asset.CreatedAt.String())
+	if err != nil {
+		return err
+	}
+	err = d.Set("created_at", asset.UpdatedAt.String())
+	if err != nil {
+		return err
+	}
+	err = d.Set("browser_download_url", asset.BrowserDownloadURL)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}

github/data_source_github_release_asset_test.go

@@ -0,0 +1,84 @@
+package github
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
+)
+
+func TestAccGithubReleaseAssetDataSource(t *testing.T) {
+
+	testReleaseRepository := "go-github-issue-demo-1"
+	if os.Getenv("GITHUB_TEMPLATE_REPOSITORY") != "" {
+		testReleaseRepository = os.Getenv("GITHUB_TEMPLATE_REPOSITORY")
+	}
+
+	testReleaseAssetID := "151970555"
+	if os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_ID") != "" {
+		testReleaseAssetID = os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_ID")
+	}
+
+	testReleaseAssetName := "foo.txt"
+	if os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_NAME") != "" {
+		testReleaseAssetName = os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_NAME")
+	}
+
+	testReleaseAssetContent := "Hello, world!\n"
+	if os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_CONTENT") != "" {
+		testReleaseAssetContent = os.Getenv("GITHUB_TEMPLATE_REPOSITORY_RELEASE_ASSET_CONTENT")
+	}
+
+	testReleaseOwner := testOrganizationFunc()
+
+	t.Run("queries specified asset ID", func(t *testing.T) {
+
+		config := fmt.Sprintf(`
+			data "github_release_asset" "test" {
+				repository = "%s"
+				owner = "%s"
+				asset_id = "%s"
+			}
+		`, testReleaseRepository, testReleaseOwner, testReleaseAssetID)
+
+		check := resource.ComposeTestCheckFunc(
+			resource.TestCheckResourceAttr(
+				"data.github_release_asset.test", "asset_id", testReleaseAssetID,
+			),
+			resource.TestCheckResourceAttr(
+				"data.github_release_asset.test", "name", testReleaseAssetName,
+			),
+			resource.TestCheckResourceAttr(
+				"data.github_release_asset.test", "body", testReleaseAssetContent,
+			),
+		)
+
+		testCase := func(t *testing.T, mode string) {
+			resource.Test(t, resource.TestCase{
+				PreCheck:  func() { skipUnlessMode(t, mode) },
+				Providers: testAccProviders,
+				Steps: []resource.TestStep{
+					{
+						Config: config,
+						Check:  check,
+					},
+				},
+			})
+		}
+
+		t.Run("with an anonymous account", func(t *testing.T) {
+			testCase(t, anonymous)
+		})
+
+		t.Run("with an individual account", func(t *testing.T) {
+			testCase(t, individual)
+		})
+
+		t.Run("with an organization account", func(t *testing.T) {
+			testCase(t, organization)
+		})
+
+	})
+
+}

github/provider.go

@@ -237,6 +237,7 @@ func Provider() *schema.Provider {
 			"github_organization_webhooks":                                          dataSourceGithubOrganizationWebhooks(),
 			"github_ref":                                                            dataSourceGithubRef(),
 			"github_release":                                                        dataSourceGithubRelease(),
+			"github_release_asset":                                                  dataSourceGithubReleaseAsset(),
 			"github_repositories":                                                   dataSourceGithubRepositories(),
 			"github_repository":                                                     dataSourceGithubRepository(),
 			"github_repository_autolink_references":                                 dataSourceGithubRepositoryAutolinkReferences(),

website/docs/d/release_asset.html.markdown

@@ -0,0 +1,84 @@
+---
+layout: "github"
+page_title: "GitHub: github_release_asset"
+description: |-
+  Get information on a GitHub release asset.
+---
+
+# github\_release\_asset
+
+Use this data source to retrieve information about a GitHub release asset associated with a specific GitHub release.
+
+## Example Usage
+To retrieve the latest release that is present in a repository:
+
+```hcl
+data "github_release" "example" {
+    repository  = "example-repository"
+    owner       = "example-owner"
+    retrieve_by = "latest"
+}
+```
+
+To retrieve a specific release asset from a repository based on its ID:
+
+```hcl
+data "github_release_asset" "example" {
+    repository  = "example-repository"
+    owner       = "example-owner"
+    asset_id    = 12345
+}
+```
+
+To retrieve the first release asset associated with the the latest release in a repository:
+
+```hcl
+data "github_release" "example" {
+    repository  = "example-repository"
+    owner       = "example-owner"
+    retrieve_by = "latest"
+}
+
+data "github_release_asset" "example" {
+    repository  = "example-repository"
+    owner       = "example-owner"
+    asset_id    = data.github_release.example.assets[0].id
+}
+```
+
+To retrieve all release assets associated with the the latest release in a repository:
+
+```hcl
+data "github_release" "example" {
+    repository  = "example-repository"
+    owner       = "example-owner"
+    retrieve_by = "latest"
+}
+
+data "github_release_asset" "example" {
+    count       = length(data.github_release.example.assets)
+    repository  = "example-repository"
+    owner       = "example-owner"
+    asset_id    = data.github_release.example.assets[count.index].id
+}
+```
+
+## Argument Reference
+
+*  `repository`  -  (Required) Name of the repository to retrieve the release from.
+*  `owner`  -  (Required) Owner of the repository.
+*  `asset_id`  -  (Required) ID of the release asset to retrieve.
+
+## Attributes Reference
+
+* `id` - ID of the asset
+* `url` - URL of the asset
+* `node_id` - Node ID of the asset
+* `name` - The file name of the asset
+* `label` - Label for the asset
+* `content_type` - MIME type of the asset
+* `size` - Size in byte
+* `created_at` - Date the asset was created
+* `updated_at` - Date the asset was last updated
+* `browser_download_url` - Browser download URL
+* `body` - The release asset body