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

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.

Start at the setHttpHeader entry point and the doRequestAsync path described in the issue, then reproduce the request with the Chinese carrier value. Compare header construction with the referenced Headers.Builder behavior and verify that the request completes without an IllegalArgumentException.