UNDERTOW-2017: HttpRequestConduit state is correctly maintained

Previously, small buffers that required multiple events to write
would not save the correct header state, resulting in NPEs
and requests which failed to include all headers.

This PR removes the duplicated state between the method body
and HttpRequestConduit in favor of exclusively using
HttpRequestConduit fields. This way the behavior across state
changes is unlikely to be impacted at all.
Hotspot isn't able to optimize field access quite as well
as local method scoped variables, however this isn't likely
to have an impact in practice, and it's more important to
send all headers with every request.

core/src/main/java/io/undertow/client/http/HttpRequestConduit.java

@@ -100,12 +100,7 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
         }
         ClientRequest request = this.request;
         ByteBuffer buffer = pooledBuffer.getBuffer();
-        Iterator<HttpString> nameIterator = this.nameIterator;
-        Iterator<String> valueIterator = this.valueIterator;
-        int charIndex = this.charIndex;
         int length;
-        String string = this.string;
-        HttpString headerName = this.headerName;
         int res;
         // BUFFER IS FLIPPED COMING IN
         if (state != STATE_START && buffer.hasRemaining()) {
@@ -189,11 +184,6 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
                             do {
                                 res = next.write(buffer);
                                 if (res == 0) {
-                                    this.string = string;
-                                    this.headerName = headerName;
-                                    this.charIndex = charIndex;
-                                    this.valueIterator = valueIterator;
-                                    this.nameIterator = nameIterator;
                                     log.trace("Continuation");
                                     return STATE_HDR_NAME;
                                 }
@@ -210,11 +200,6 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
                             res = next.write(buffer);
                             if (res == 0) {
                                 log.trace("Continuation");
-                                this.string = string;
-                                this.headerName = headerName;
-                                this.charIndex = charIndex;
-                                this.valueIterator = valueIterator;
-                                this.nameIterator = nameIterator;
                                 return STATE_HDR_D;
                             }
                         } while (buffer.hasRemaining());
@@ -230,11 +215,6 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
                             res = next.write(buffer);
                             if (res == 0) {
                                 log.trace("Continuation");
-                                this.string = string;
-                                this.headerName = headerName;
-                                this.charIndex = charIndex;
-                                this.valueIterator = valueIterator;
-                                this.nameIterator = nameIterator;
                                 return STATE_HDR_DS;
                             }
                         } while (buffer.hasRemaining());
@@ -260,11 +240,6 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
                             do {
                                 res = next.write(buffer);
                                 if (res == 0) {
-                                    this.string = string;
-                                    this.headerName = headerName;
-                                    this.charIndex = charIndex;
-                                    this.valueIterator = valueIterator;
-                                    this.nameIterator = nameIterator;
                                     log.trace("Continuation");
                                     return STATE_HDR_VAL;
                                 }
@@ -467,7 +442,6 @@ private int processWrite(int state, final ByteBuffer userData) throws IOExceptio
                                 if (res == 0) {
                                     log.trace("Continuation");
                                     this.charIndex = i;
-                                    this.string = string;
                                     this.state = STATE_URL;
                                     return STATE_URL;
                                 }