Issue and proposed fix. Non ascii characters in header causes a IllegalArgumentException

setHttpHeaderのエントリポイントと、issueで説明されているdoRequestAsyncのパスから開始し、中国のキャリア値を使ってリクエストを再現します。ヘッダーの構築を参照されているHeaders.Builderの動作と比較し、リクエストがIllegalArgumentExceptionなしで完了することを確認します。

No pending exception expected: java.lang.IllegalArgumentException: Unexpected char

https://github.com/square/okhttp/issues/6347
https://github.com/square/okhttp/issues/4008
https://github.com/square/okhttp/issues/7275
https://github.com/square/okhttp/pull/4296

In the case of using setHttpHeader("carrier", ""中国电信"").
Note: 中国电信 is a Chinese telecommunications (cell phone provider carrier).

No pending exception expected: java.lang.IllegalArgumentException: Unexpected char 0x4e2d at 243 in User-Agent value

at void okhttp3.Headers$Companion.checkValue(java.lang.String, java.lang.String) (Headers.kt:450)
at void okhttp3.Headers$Companion.access$checkValue(okhttp3.Headers$Companion, java.lang.String, java.lang.String) (Headers.kt:362)
at okhttp3.Headers$Builder okhttp3.Headers$Builder.add(java.lang.String, java.lang.String) (Headers.kt:261)
at okhttp3.Request$Builder okhttp3.Request$Builder.addHeader(java.lang.String, java.lang.String) (Request.kt:210)
at <snipped>.setHttpHeader(java.lang.String, java.lang.String) (HttpClientRequest.java

The currently existing code snippet causes an issue.

 public void setHttpHeader(String name, String value) {
        this.requestBuilder = requestBuilder.addHeader(name, value);
    }

I believe the possible fix is to add a
this.headersBuilder = new Headers.Builder();
and then switch setHttpHeader to
this.headersBuilder = headersBuilder.addUnsafeNonAscii(name, value);
Then in the doRequestAsync add this.requestBuilder.headers(this.headersBuilder.build()); before the OK_Client call
or to 'build and set' in every set. Just depends if you want to do a lot of duplicate work or not.

We are running a modified version of libhttpclient, so our fix is applied there. I'll see if/when I have time to PR this change into libHttpClient proper, but if not, above should help anyone who comes across similar issue.