square/okhttp · error · IOException

Unexpected code

Error message

Unexpected code 

What it means

Thrown in the PostForm recipe: `if (!response.isSuccessful()) throw new IOException("Unexpected code " + response)`. It POSTs an application/x-www-form-urlencoded body (search=Jurassic Park) to Wikipedia's index.php. Wikipedia returns non-2xx (often a 200 with HTML, but 400/405/302 are possible) and the guard trips.

Solutions

1. Inspect response.code() and follow redirects explicitly if needed.
2. Match Wikipedia's actual search form fields (some endpoints need 'title'/'limit').
3. Use the MediaWiki Action API (api.php) for structured search instead of scraping index.php.
4. Branch on code rather than throwing so the HTML body can be inspected.

Example fix

// before
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

// after
if (!response.isSuccessful()) {
  System.err.println("wiki POST returned " + response.code());
  return;
}

// Match Wikipedia's expected form fields and branch on status/redirects.
RequestBody form = new FormBody.Builder().add("search", "Jurassic Park").add("ns0", "1").build();
...
if (!response.isSuccessful()) { /* code + body */ return; }

static boolean isHtmlResult(Response r) { return r.isSuccessful() && "text/html".equals(r.body().contentType().subtype()); }

try {
  // call
} catch (IOException e) {
  // includes 'Unexpected code' (HTTP status) and transport errors
}

When it happens

Trigger: POST to https://en.wikipedia.org/w/index.php returns 302 (Wikipedia commonly redirects form POSTs), 405 (method not allowed for that path), 400, or 5xx. Wikipedia's search endpoint may expect a different form field set or a GET.

Common situations: Wikipedia changing its form handling / anti-abuse rules; missing required hidden form fields; running behind a filter that blocks POST; expecting JSON but getting HTML (still 200, so usually does not throw).

Related errors

• Unexpected code
• Unexpected code
• Unexpected code
• Unexpected code
• Unexpected code

AI-assisted analysis of square/okhttp@91a8b34c6f (2026-08-10). Data as JSON: /api/errors/0b581834c41319d2. Report an issue: GitHub.

Appendix: source

Thrown at samples/guide/src/main/java/okhttp3/recipes/PostForm.java:38

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public final class PostForm {
  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    RequestBody formBody = new FormBody.Builder()
        .add("search", "Jurassic Park")
        .build();
    Request request = new Request.Builder()
        .url("https://en.wikipedia.org/w/index.php")
        .post(formBody)
        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      System.out.println(response.body().string());
    }
  }

  public static void main(String... args) throws Exception {
    new PostForm().run();
  }
}

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