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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 16458] - HttpClient enter 100% for endless time
Date Thu, 20 Feb 2003 17:00:40 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=16458

HttpClient enter 100% for endless time





------- Additional Comments From olegk@apache.org  2003-02-20 17:00 -------
The bug appears to have been found by Sam Maloney <sam.maloney@filogix.com>

===========================================================================
Here is the problem:

        at 
org.apache.commons.httpclient.HttpParser.readRawLine(HttpParser.java:46)
        at 
org.apache.commons.httpclient.HttpParser.readLine(HttpParser.java:81)
        at 
org.apache.commons.httpclient.HttpConnection.readLine(HttpConnection.java:878)
        at 
org.apache.commons.httpclient.HttpConnectionAdapter.readLine(MultiThreadedHttpConnectionManager_fixed.java:730)
        at 
org.apache.commons.httpclient.HttpMethodBase.readStatusLine(HttpMethodBase.java:1917)

You can see that readStatusLine looks like this:

<SNIP>
        //read out the HTTP status string
        String statusString = conn.readLine();
        while ((statusString != null) && !statusString.startsWith("HTTP/")) {
                statusString = conn.readLine();
        }
        if (statusString == null) {
                // A null statusString means the connection was lost before we got a
                // response.  Try again.
                throw new HttpRecoverableException("Error in parsing the status "
                        + " line from the response: unable to find line starting
with"
                        + " \"HTTP/\"");
        }
</SNIP>

You can see from the above code, that until conn.readLine() returns null or a 
string starting with "HTTP/", this piece of code will keep looping 
indefinatly (what is taking 100% CPU). Right now, readLine never will return 
null, only empty strings.

I'm guessing readLine must have returned null at one point, as every place 
that calls it expects null to be returned on closed connection.

The way readLine must work for the calling code to work is:

1) Read data upto \r\n, return line. (currently happens)
2) if EOF before finding \r\n, but we have data in our buffer, return the 
buffer. (also happens)

3) if EOF before finding any data (buf.size()==0), then return null to signal 
that no more data is possible, and caller should NOT call again. (this is 
what patch adds)

If we return empty string like is happening currently, then the caller will 
not know NOT to call again. In this bugs case, the caller keeps reading lines 
until it finds 'HTTP/'. Since the empty string doesn't match that, the caller 
will keep trying to get the next line, and they will just keep getting "".

Here is my patch again, updated to apply to HttpParser (where the readLine 
code has been moved to since my last patch). I have retested the new patch 
and it is working in all my test cases, including the one to reproduce the 
bug.

Index: HttpParser.java
===================================================================
RCS file: 
/home/cvspublic/jakarta-commons/httpclient/src/java/org/apache/commons/httpclient/HttpParser.java,v
retrieving revision 1.1
diff -u -r1.1 HttpParser.java
--- HttpParser.java     16 Feb 2003 13:10:16 -0000      1.1
+++ HttpParser.java     20 Feb 2003 15:51:51 -0000
@@ -58,6 +58,10 @@
                 }
             }
         }
+        if (buf.size() <= 0) {
+            // Then we just started reading, but the stream is EOF (closed).
+            return null; // Let caller know we got EOF BEFORE any data.
+        }
         if (WIRE_LOG.isDebugEnabled()) {
             WIRE_LOG.debug("<< \"" + buf.toString() + (ch>0 ? "\" [\\r\\n]" : 
""));
         }
@@ -79,6 +83,12 @@
     public static String readLine(InputStream inputStream) throws IOException 
{
         LOG.trace("enter HttpConnection.readLine()");
         byte[] rawdata = readRawLine(inputStream);
+
+        if (rawdata == null) {
+            // Then there was EOF before any data was read, we must let 
caller know.
+            return null;
+        }
+
         int len = rawdata.length;
         if (( len >= 2) && (rawdata[len - 2] == '\r') && (rawdata[len
- 1] == 
'\n')) {
             return HttpConstants.getString(rawdata, 0, rawdata.length - 2);

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