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Date: Tue, 21 Mar 2017 17:30:42 +0000 (UTC)
From: "John Flavin (JIRA)" <jira@apache.org>
To: dev@hc.apache.org
Message-ID: <JIRA.13046711.1488220934000.79703.1490117442334@Atlassian.JIRA>
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Subject: [jira] [Closed] (HTTPCORE-449) IdentityInputStream.available()
 erroneously returns 0
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archived-at: Tue, 21 Mar 2017 17:30:48 -0000


     [ https://issues.apache.org/jira/browse/HTTPCORE-449?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

John Flavin closed HTTPCORE-449.
--------------------------------

Reviewed commit here: https://github.com/apache/httpcore/commit/a5dbd14bc8ea64ff529c4651aaad9bd2d89b9f53

Looks perfect to me. {{IdentityInputStream#available}} checks if there is anything in the buffer, if so it returns the buffer length, if not it returns the underlying {{InputStream#available}}. That's exactly what I was asking for.

There is one improvement you could make to the test {{testAvailableInStream}}. Rather than calling {{in.read(tmp)}} before {{in.available()}}, you could call {{in.available()}} first and assert that it gives a non-zero value even before you have called {{read}}. It's certainly not necessary to do, but that test change would assure me that the code is doing what it should.

> IdentityInputStream.available() erroneously returns 0
> -----------------------------------------------------
>
>                 Key: HTTPCORE-449
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-449
>             Project: HttpComponents HttpCore
>          Issue Type: Improvement
>          Components: HttpCore
>    Affects Versions: 4.4.5, 4.4.6
>            Reporter: John Flavin
>            Priority: Minor
>             Fix For: 5.0-alpha3
>
>
> h5. BACKGROUND
> I have an application that reads data from a stream. When data is available, I can read from the stream perfectly fine. However, sometimes the stream will remain open with no data, in which case reading from the stream blocks. I would like to use the {{available()}} method on the stream to first check whether anything can be read before attempting to read.
> h5. PROBLEM
> When I attempt to use the {{available()}} method on my {{InputStream}} instance it returns {{0}}, i.e. no data available, even when I can successfully call {{read(...)}} and read data off the stream. 
> h5. INVESTIGATION INTO PROBLEM
> I have traced the {{available()}} method on my {{InputStream}} instance through several layers of wrapper classes around more {{InputStream}} instances. Each layer's {{available()}} method simply calls into its wrapped {{InputStream}}'s {{available()}} method. That is, until I reach the {{IdentityInputStream.available()}} method. The latter does this:
> {code:java}
>     @Override
>     public int available() throws IOException {
>         if (this.in instanceof BufferInfo) {
>             return ((BufferInfo) this.in).length();
>         } else {
>             return 0;
>         }
>     }
> {code}
> The {{in}} in the above code is a {{SessionInputBufferImpl}}, which has a few methods that are seemingly relevant to this:
> {code:java}
>     @Override
>     public int capacity() {
>         return this.buffer.length;
>     }
>     @Override
>     public int length() {
>         return this.bufferlen - this.bufferpos;
>     }
>     @Override
>     public int available() {
>         return capacity() - length();
>     }
> {code}
> h5. QUESTION
> Why does {{IdentityInputStream.available()}} call {{((BufferInfo) this.in).length()}} instead of {{((BufferInfo) this.in).available()}}? The former returns {{0}} when I call it on a stream that has data which can be read, but has not been; the latter returns a number greater than {{0}}.


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