再聊HttpClient的NoHttpResponseException

org.apache.http.NoHttpResponseException: xxx failed to respond
    at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)
    at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
    at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
    at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
    at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:157)
    at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
    at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
    at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
    at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
    at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
    at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
    at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)

    /**
     * Sends the request and obtain a response.
     *
     * @param request   the request to execute.
     * @param conn      the connection over which to execute the request.
     *
     * @return  the response to the request.
     *
     * @throws IOException in case of an I/O error.
     * @throws HttpException in case of HTTP protocol violation or a processing
     *   problem.
     */
    public HttpResponse execute(
            final HttpRequest request,
            final HttpClientConnection conn,
            final HttpContext context) throws IOException, HttpException {
        Args.notNull(request, "HTTP request");
        Args.notNull(conn, "Client connection");
        Args.notNull(context, "HTTP context");
        try {
            HttpResponse response = doSendRequest(request, conn, context);
            if (response == null) {
                response = doReceiveResponse(request, conn, context);
            }
            return response;
        } catch (final IOException ex) {
            closeConnection(conn);
            throw ex;
        } catch (final HttpException ex) {
            closeConnection(conn);
            throw ex;
        } catch (final RuntimeException ex) {
            closeConnection(conn);
            throw ex;
        }
    }

    /**
     * Waits for and receives a response.
     * This method will automatically ignore intermediate responses
     * with status code 1xx.
     *
     * @param request   the request for which to obtain the response
     * @param conn      the connection over which the request was sent
     * @param context   the context for receiving the response
     *
     * @return  the terminal response, not yet post-processed
     *
     * @throws IOException in case of an I/O error.
     * @throws HttpException in case of HTTP protocol violation or a processing
     *   problem.
     */
    protected HttpResponse doReceiveResponse(
            final HttpRequest request,
            final HttpClientConnection conn,
            final HttpContext context) throws HttpException, IOException {
        Args.notNull(request, "HTTP request");
        Args.notNull(conn, "Client connection");
        Args.notNull(context, "HTTP context");
        HttpResponse response = null;
        int statusCode = 0;

        while (response == null || statusCode < HttpStatus.SC_OK) {

            response = conn.receiveResponseHeader();
            statusCode = response.getStatusLine().getStatusCode();
            if (statusCode < HttpStatus.SC_CONTINUE) {
                throw new ProtocolException("Invalid response: " + response.getStatusLine());
            }
            if (canResponseHaveBody(request, response)) {
                conn.receiveResponseEntity(response);
            }

        } // while intermediate response

        return response;
    }

    public HttpResponse receiveResponseHeader() throws HttpException, IOException {
        ensureOpen();
        final HttpResponse response = this.responseParser.parse();
        onResponseReceived(response);
        if (response.getStatusLine().getStatusCode() >= HttpStatus.SC_OK) {
            incrementResponseCount();
        }
        return response;
    }

    public T parse() throws IOException, HttpException {
        final int st = this.state;
        switch (st) {
        case HEAD_LINE:
            try {
                this.message = parseHead(this.sessionBuffer);
            } catch (final ParseException px) {
                throw new ProtocolException(px.getMessage(), px);
            }
            this.state = HEADERS;
            //$FALL-THROUGH$
        case HEADERS:
            final Header[] headers = AbstractMessageParser.parseHeaders(
                    this.sessionBuffer,
                    this.messageConstraints.getMaxHeaderCount(),
                    this.messageConstraints.getMaxLineLength(),
                    this.lineParser,
                    this.headerLines);
            this.message.setHeaders(headers);
            final T result = this.message;
            this.message = null;
            this.headerLines.clear();
            this.state = HEAD_LINE;
            return result;
        default:
            throw new IllegalStateException("Inconsistent parser state");
        }
    }

    protected HttpResponse parseHead(
            final SessionInputBuffer sessionBuffer) throws IOException, HttpException {
        //read out the HTTP status string
        int count = 0;
        ParserCursor cursor = null;
        do {
            // clear the buffer
            this.lineBuf.clear();
            final int i = sessionBuffer.readLine(this.lineBuf);
            if (i == -1 && count == 0) {
                // The server just dropped connection on us
                throw new NoHttpResponseException("The target server failed to respond");
            }
            cursor = new ParserCursor(0, this.lineBuf.length());
            if (lineParser.hasProtocolVersion(this.lineBuf, cursor)) {
                // Got one
                break;
            } else if (i == -1 || reject(this.lineBuf, count)) {
                // Giving up
                throw new ProtocolException("The server failed to respond with a " +
                        "valid HTTP response");
            }
            if (this.log.isDebugEnabled()) {
                this.log.debug("Garbage in response: " + this.lineBuf.toString());
            }
            count++;
        } while(true);
        //create the status line from the status string
        final StatusLine statusline = lineParser.parseStatusLine(this.lineBuf, cursor);
        return this.responseFactory.newHttpResponse(statusline, null);
    }

    /**
     * Send the given request over the given connection.
     * <p>
     * This method also handles the expect-continue handshake if necessary.
     * If it does not have to handle an expect-continue handshake, it will
     * not use the connection for reading or anything else that depends on
     * data coming in over the connection.
     *
     * @param request   the request to send, already
     *                  {@link #preProcess preprocessed}
     * @param conn      the connection over which to send the request,
     *                  already established
     * @param context   the context for sending the request
     *
     * @return  a terminal response received as part of an expect-continue
     *          handshake, or
     *          {@code null} if the expect-continue handshake is not used
     *
     * @throws IOException in case of an I/O error.
     * @throws HttpException in case of HTTP protocol violation or a processing
     *   problem.
     */
    protected HttpResponse doSendRequest(
            final HttpRequest request,
            final HttpClientConnection conn,
            final HttpContext context) throws IOException, HttpException {
        Args.notNull(request, "HTTP request");
        Args.notNull(conn, "Client connection");
        Args.notNull(context, "HTTP context");

        HttpResponse response = null;

        context.setAttribute(HttpCoreContext.HTTP_CONNECTION, conn);
        context.setAttribute(HttpCoreContext.HTTP_REQ_SENT, Boolean.FALSE);

        conn.sendRequestHeader(request);
        if (request instanceof HttpEntityEnclosingRequest) {
            // Check for expect-continue handshake. We have to flush the
            // headers and wait for an 100-continue response to handle it.
            // If we get a different response, we must not send the entity.
            boolean sendentity = true;
            final ProtocolVersion ver =
                request.getRequestLine().getProtocolVersion();
            if (((HttpEntityEnclosingRequest) request).expectContinue() &&
                !ver.lessEquals(HttpVersion.HTTP_1_0)) {

                conn.flush();
                // As suggested by RFC 2616 section 8.2.3, we don't wait for a
                // 100-continue response forever. On timeout, send the entity.
                if (conn.isResponseAvailable(this.waitForContinue)) {
                    response = conn.receiveResponseHeader();
                    if (canResponseHaveBody(request, response)) {
                        conn.receiveResponseEntity(response);
                    }
                    final int status = response.getStatusLine().getStatusCode();
                    if (status < 200) {
                        if (status != HttpStatus.SC_CONTINUE) {
                            throw new ProtocolException(
                                    "Unexpected response: " + response.getStatusLine());
                        }
                        // discard 100-continue
                        response = null;
                    } else {
                        sendentity = false;
                    }
                }
            }
            if (sendentity) {
                conn.sendRequestEntity((HttpEntityEnclosingRequest) request);
            }
        }
        conn.flush();
        context.setAttribute(HttpCoreContext.HTTP_REQ_SENT, Boolean.TRUE);
        return response;
    }