Reapply: Relax validation of HTTP header values to retain L/M behavior

This reapplies AOSP commit 3c28a13
There is a chance that we may want to revert this change in future.

Previous commit message:

This relaxes some validation logic newly introduced in the version
of OkHttp used in N.

This change leaves the character code validation stricter
than it was in M by still preventing control codes like \n, \r,
backspace and delete. It does allow developers to pass
Java characters > 7F to addRequestProperty() and also receive
headers from servers which contain characters > 7F.

Android's HttpURLConnection does not follow the HTTP spec as
it encodes request header values and interprets response
headers as UTF-8 and not ISO-8859-1.

If a server is expecting or sending ISO-8859-1 encoded characters
>7F in headers then these will still be corrupted or misinterpreted
by Android. However, this has been the behavior since L and is not
changed here.

The OkHttp change which caused characters >7F to generate an
IllegalArgumentException and partially reverted here:
square/okhttp#1785

See also: square/okhttp#1998
square/okhttp#2016
for recent upstream bugs.

Bug: 28867041
Bug: https://code.google.com/p/android/issues/detail?id=210205
(cherry picked from commit 75687ca5ae54f417afb4c02ba04767da6786d829)

Change-Id: Id683ec13142f1d7d8792143066f1dd2e5f62cf86

okhttp-tests/src/test/java/com/squareup/okhttp/RequestTest.java

@@ -188,8 +188,11 @@ public final class RequestTest {
     assertForbiddenHeader("\t");
     assertForbiddenHeader("\u001f");
     assertForbiddenHeader("\u007f");
-    assertForbiddenHeader("\u0080");
-    assertForbiddenHeader("\ud83c\udf69");
+
+    // ANDROID-BEGIN Workaround for http://b/28867041
+    // assertForbiddenHeader("\u0080");
+    // assertForbiddenHeader("\ud83c\udf69");
+    // ANDROID-END
   }
 
   private void assertForbiddenHeader(String s) {

okhttp-tests/src/test/java/com/squareup/okhttp/URLConnectionTest.java

@@ -2839,11 +2839,14 @@ private void reusedConnectionFailsWithPost(TransferKind transferKind, int reques
       fail();
     } catch (IllegalArgumentException expected) {
     }
-    try {
-      connection.addRequestProperty("Name", "\u2615\ufe0f");
-      fail();
-    } catch (IllegalArgumentException expected) {
-    }
+
+    // ANDROID-BEGIN Disabled for http://b/28867041
+    // try {
+    //   connection.addRequestProperty("Name", "\u2615\ufe0f");
+    //   fail();
+    // } catch (IllegalArgumentException expected) {
+    // }
+    // ANDROID-END
   }
 
   @Test public void responseHeaderParsingIsLenient() throws Exception {

okhttp/src/main/java/com/squareup/okhttp/Headers.java

@@ -304,7 +304,12 @@ private void checkNameAndValue(String name, String value) {
 
       for (int i = 0, length = value.length(); i < length; i++) {
         char c = value.charAt(i);
-        if (c <= '\u001f' || c >= '\u007f') {
+        // ANDROID-BEGIN
+        // http://b/28867041 - keep things working for apps that rely on Android's (out of spec)
+        // UTF-8 header encoding behavior.
+        // if (c <= '\u001f' || c >= '\u007f') {
+        if (c <= '\u001f' || c == '\u007f') {
+        // ANDROID-END
           throw new IllegalArgumentException(String.format(
               "Unexpected char %#04x at %d in header value: %s", (int) c, i, value));
         }