<p>Hi guys,</p>
<p>This is my first project in Go, having experimented with it before. For this project I need to retrieve the licenses for GitHub repositories, so I'm using <a href="https://godoc.org/github.com/google/go-github/github" rel="nofollow">go-github</a>.</p>
<p>The <a href="https://godoc.org/github.com/google/go-github/github#Repository" rel="nofollow">Repository</a> type has a License field, but the documentation says <em>"// Only provided when using RepositoriesService.Get while in preview"</em>. Indeed, my application segfaults when I try to access a License's name field directly:</p>
<pre><code>license := repo.License.Name
</code></pre>
<p>Now the documentation says this field is available while in preview, but I have no idea what this is. There is no reference to "preview" in that page, and a Google search doesn't turn up anything useful either. Does anyone here know what I am to do?</p>
<hr/>**评论：**<br/><br/>gogroob: <pre><p>It means that particular API feature is in developer preview:
<a href="https://developer.github.com/v3/licenses/#get-a-repositorys-license" rel="nofollow">https://developer.github.com/v3/licenses/#get-a-repositorys-license</a></p>
<blockquote>
<p>The Licenses API is currently available for developers to preview. During the preview period, the API may change without advance notice. Please see the blog post for full details.</p>
<p>To access the API during the preview period, you must provide a custom media type in the Accept header:</p>
<p><code>application/vnd.github.drax-preview+json</code></p>
</blockquote>
<p>A lot of the go-github struct fields are pointers because the response objects from the github API are dynamic. You should check if each field you intend to use is not nil before accessing it''s value to avoid crashing your service. </p></pre>fallenunia: <pre><p>Thanks for your reply. I was actually aware of the GitHub preview mode but did not connect the dots. As a follow-up question, do you know how I can provide that custom media type when using go-github?</p>
<p><strong>Edit:</strong> As far as I can see, the media type is set by go-github: <a href="https://github.com/google/go-github/blob/a77ccc9a588d217ea8c8b069620a3a070ed201c3/github/repos.go#L176" rel="nofollow">https://github.com/google/go-github/blob/a77ccc9a588d217ea8c8b069620a3a070ed201c3/github/repos.go#L176</a></p></pre>fallenunia: <pre><p>Ah, never mind. I got it working. The API indeed sets the media type by default; <code>Repository.License</code> is however still <code>nil</code> if GitHub's API cannot find a license for it. The following code works:</p>
<pre><code>repos, _, err := client.Repositories.List(user, opt)
if err != nil {
log.Fatal(err)
}
for _, repo := range repos {
name := repo.Name
var license string
if repo.License != nil {
license = *repo.License.Name
} else {
license = "N/A"
}
fmt.Printf("Repository %q by %q has license: %q\n", *name, user, license)
}
</code></pre></pre>
