The abstract InputStream.read() method reads a single byte from an input source, and returns its value as an int, in the range 0 to 255. It will return -1 only if when the end of the input stream has been reached. The similar Reader.read() method reads a single character, and returns its value as an int, in the range 0-65,535. It also returns -1 only if when the end of the stream has been reached. Both methods are meant to be overridden by subclasses.
These methods are often used to read a byte or character from a stream. Unfortunately many programmers prematurely convert the resulting int back to a byte or char before checking whether they have reached the end of the value for stream (signaled by a return value of -1. It is vital to check the return value for -1 before narrowing it ). Programs must check for end of stream (e.g., -1) before narrowing the return value to a byte or char.
This guideline applies to any InputStream or Reader subclass that provide an implementation of the read() method. This guideline is a specific instance of NUM15-J. Ensure conversions of numeric types to narrower types do not result in lost or misinterpreted data.
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FileInputStream in;
// initialize stream
byte data;
while ((data = (byte) in.read()) != -1) {
// ...
}
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If When the read() method in this noncompliant code example returns the byte value 0xFF, it will be indistinguishable from the -1 value used to indicate the end of stream, because the byte value is promoted and sign extended to an int before being compared with -1.
Compliant Solution (byte)
Use and value a variable of type int to capture the return value of the byte input method. If When the value returned by read() is not -1, it can be safely cast to type byte. If When read() returns 0XFF, the comparison will test 0x000000FF against 0xFFFFFFFF and fail.
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This noncompliant code example casts the value of type int returned by the read() method directly to a value of type char, which is then compared with -1 in an attempt to detect the end of stream. This conversion leaves the value of c as 0xffff (e.g., Character.MAX_VALUE) instead of -1. As a resultConsequently, the test for the end of stream never evaluates to true.
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Compliant Solution (char)
Use and value a variable of type int to capture the return value of the character input method. When the value of returned by read() is not -1, it can be safely cast to type char.
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Historically, using a narrow type to capture the return value of a byte input function has resulted in significant vulnerabilities, including command injection attacks. (See the ; see CA-1996-22 advisory. ) As a resultConsequently, the severity of this error is high.
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