org.apache.commons.fileupload

Class MultipartStream


public class MultipartStream
extends java.lang.Object

Low level API for processing file uploads.

This class can be used to process data streams conforming to MIME 'multipart' format as defined in RFC 1867. Arbitrarily large amounts of data in the stream can be processed under constant memory usage.

The format of the stream is defined in the following way:
multipart-body := preamble 1*encapsulation close-delimiter epilogue
encapsulation := delimiter body CRLF
delimiter := "--" boundary CRLF
close-delimiter := "--" boudary "--"
preamble := <ignore>
epilogue := <ignore>
body := header-part CRLF body-part
header-part := 1*header CRLF
header := header-name ":" header-value
header-name := <printable ascii characters except ":">
header-value := <any ascii characters except CR & LF>
body-data := <arbitrary data>

Note that body-data can contain another mulipart entity. There is limited support for single pass processing of such nested streams. The nested stream is required to have a boundary token of the same length as the parent stream (see setBoundary(byte[])).

Here is an exaple of usage of this class.

    try {
        MultipartStream multipartStream = new MultipartStream(input,
                                                              boundary);
        boolean nextPart = malitPartStream.skipPreamble();
        OutputStream output;
        while(nextPart) {
            header = chunks.readHeader();
            // process headers
            // create some output stream
            multipartStream.readBodyPart(output);
            nextPart = multipartStream.readBoundary();
        }
    } catch(MultipartStream.MalformedStreamException e) {
          // the stream failed to follow required syntax
    } catch(IOException) {
          // a read or write error occurred
    }

 
Version:
$Id: MultipartStream.java,v 1.12 2003/06/01 00:18:13 martinc Exp $
Authors:
Rafal Krzewski
Martin Cooper
Sean C. Sullivan

Nested Class Summary

class
MultipartStream.IllegalBoundaryException
Thrown upon attempt of setting an invalid boundary token.
class
MultipartStream.MalformedStreamException
Thrown to indicate that the input stream fails to follow the required syntax.

Field Summary

protected static int
DEFAULT_BUFSIZE
The default length of the buffer used for processing a request.
protected static byte[]
FIELD_SEPARATOR
A byte sequence that that follows a delimiter that will be followed by an encapsulation (CRLF).
static int
HEADER_PART_SIZE_MAX
The maximum length of header-part that will be processed (10 kilobytes = 10240 bytes.).
protected static byte[]
HEADER_SEPARATOR
A byte sequence that marks the end of header-part (CRLFCRLF).
protected static byte[]
STREAM_TERMINATOR
A byte sequence that that follows a delimiter of the last encapsulation in the stream (--).
private byte[]
boundary
The byte sequence that partitions the stream.
private int
boundaryLength
The length of the boundary token plus the leading CRLF--.
private int
bufSize
The length of the buffer used for processing the request.
private byte[]
buffer
The buffer used for processing the request.
private int
head
The index of first valid character in the buffer.
private String
headerEncoding
The content encoding to use when reading headers.
private InputStream
input
The input stream from which data is read.
private int
keepRegion
The amount of data, in bytes, that must be kept in the buffer in order to detect delimiters reliably.
private int
tail
The index of last valid characer in the buffer + 1.

Constructor Summary

MultipartStream()
Default constructor.
MultipartStream(InputStream input, byte[] boundary)
Constructs a MultipartStream with a default size buffer.
MultipartStream(InputStream input, byte[] boundary, int bufSize)
Constructs a MultipartStream with a custom size buffer.

Method Summary

static boolean
arrayequals(byte[] a, byte[] b, int count)
Compares count first bytes in the arrays a and b.
int
discardBodyData()
Reads body-data from the current encapsulation and discards it.
protected int
findByte(byte value, int pos)
Searches for a byte of specified value in the buffer, starting at the specified position.
protected int
findSeparator()
Searches for the boundary in the buffer region delimited by head and tail.
String
getHeaderEncoding()
Retrieves the character encoding used when reading the headers of an individual part.
int
readBodyData(OutputStream output)
Reads body-data from the current encapsulation and writes its contents into the output Stream.
boolean
readBoundary()
Skips a boundary token, and checks whether more encapsulations are contained in the stream.
byte
readByte()
Reads a byte from the buffer, and refills it as necessary.
String
readHeaders()
Reads the header-part of the current encapsulation.
void
setBoundary(byte[] boundary)
Changes the boundary token used for partitioning the stream.
void
setHeaderEncoding(String encoding)
Specifies the character encoding to be used when reading the headers of individual parts.
boolean
skipPreamble()
Finds the beginning of the first encapsulation.
String
toString()
Returns a string representation of this object.

Field Details

DEFAULT_BUFSIZE

protected static final int DEFAULT_BUFSIZE
The default length of the buffer used for processing a request.
Field Value:
4096

FIELD_SEPARATOR

protected static final byte[] FIELD_SEPARATOR
A byte sequence that that follows a delimiter that will be followed by an encapsulation (CRLF).

HEADER_PART_SIZE_MAX

public static final int HEADER_PART_SIZE_MAX
The maximum length of header-part that will be processed (10 kilobytes = 10240 bytes.).
Field Value:
10240

HEADER_SEPARATOR

protected static final byte[] HEADER_SEPARATOR
A byte sequence that marks the end of header-part (CRLFCRLF).

STREAM_TERMINATOR

protected static final byte[] STREAM_TERMINATOR
A byte sequence that that follows a delimiter of the last encapsulation in the stream (--).

boundary

private byte[] boundary
The byte sequence that partitions the stream.

boundaryLength

private int boundaryLength
The length of the boundary token plus the leading CRLF--.

bufSize

private int bufSize
The length of the buffer used for processing the request.

buffer

private byte[] buffer
The buffer used for processing the request.

head

private int head
The index of first valid character in the buffer.
0 <= head <32bufSize

headerEncoding

private String headerEncoding
The content encoding to use when reading headers.

input

private InputStream input
The input stream from which data is read.

keepRegion

private int keepRegion
The amount of data, in bytes, that must be kept in the buffer in order to detect delimiters reliably.

tail

private int tail
The index of last valid characer in the buffer + 1.
0 <= tail <= bufSize

Constructor Details

MultipartStream

public MultipartStream()
Default constructor.

MultipartStream

public MultipartStream(InputStream input,
                       byte[] boundary)
            throws IOException
Constructs a MultipartStream with a default size buffer.
Parameters:
input - The InputStream to serve as a data source.
boundary - The token used for dividing the stream into encapsulations.

MultipartStream

public MultipartStream(InputStream input,
                       byte[] boundary,
                       int bufSize)
Constructs a MultipartStream with a custom size buffer.

Note that the buffer must be at least big enough to contain the boundary string, plus 4 characters for CR/LF and double dash, plus at least one byte of data. Too small a buffer size setting will degrade performance.

Parameters:
input - The InputStream to serve as a data source.
boundary - The token used for dividing the stream into encapsulations.
bufSize - The size of the buffer to be used, in bytes.

Method Details

arrayequals

public static boolean arrayequals(byte[] a,
                                  byte[] b,
                                  int count)
Compares count first bytes in the arrays a and b.
Parameters:
a - The first array to compare.
b - The second array to compare.
count - How many bytes should be compared.
Returns:
true if count first bytes in arrays a and b are equal.

discardBodyData

public int discardBodyData()
            throws MultipartStream.MalformedStreamException,
                   IOException
Reads body-data from the current encapsulation and discards it.

Use this method to skip encapsulations you don't need or don't understand.

Returns:
The amount of data discarded.
Throws:
MultipartStream.MalformedStreamException - if the stream ends unexpectedly.

findByte

protected int findByte(byte value,
                       int pos)
Searches for a byte of specified value in the buffer, starting at the specified position.
Parameters:
value - The value to find.
pos - The starting position for searching.
Returns:
The position of byte found, counting from beginning of the buffer, or -1 if not found.

findSeparator

protected int findSeparator()
Searches for the boundary in the buffer region delimited by head and tail.
Returns:
The position of the boundary found, counting from the beginning of the buffer, or -1 if not found.

getHeaderEncoding

public String getHeaderEncoding()
Retrieves the character encoding used when reading the headers of an individual part. When not specified, or null, the platform default encoding is used.
Returns:
The encoding used to read part headers.

readBodyData

public int readBodyData(OutputStream output)
            throws MultipartStream.MalformedStreamException,
                   IOException
Reads body-data from the current encapsulation and writes its contents into the output Stream.

Arbitrary large amounts of data can be processed by this method using a constant size buffer. (see constructor).

Parameters:
output - The Stream to write data into.
Returns:
the amount of data written.
Throws:
MultipartStream.MalformedStreamException - if the stream ends unexpectedly.

readBoundary

public boolean readBoundary()
            throws MultipartStream.MalformedStreamException
Skips a boundary token, and checks whether more encapsulations are contained in the stream.
Returns:
true if there are more encapsulations in this stream; false otherwise.
Throws:
MultipartStream.MalformedStreamException - if the stream ends unexpecetedly or fails to follow required syntax.

readByte

public byte readByte()
            throws IOException
Reads a byte from the buffer, and refills it as necessary.
Returns:
The next byte from the input stream.

readHeaders

public String readHeaders()
            throws MultipartStream.MalformedStreamException
Reads the header-part of the current encapsulation.

Headers are returned verbatim to the input stream, including the trailing CRLF marker. Parsing is left to the application.

TODO allow limiting maximum header size to protect against abuse.

Returns:
The header-part of the current encapsulation.
Throws:
MultipartStream.MalformedStreamException - if the stream ends unexpecetedly.

setBoundary

public void setBoundary(byte[] boundary)
            throws MultipartStream.IllegalBoundaryException
Changes the boundary token used for partitioning the stream.

This method allows single pass processing of nested multipart streams.

The boundary token of the nested stream is required to be of the same length as the boundary token in parent stream.

Restoring the parent stream boundary token after processing of a nested stream is left to the application.

Parameters:
boundary - The boundary to be used for parsing of the nested stream.
Throws:
MultipartStream.IllegalBoundaryException - if the boundary has a different length than the one being currently parsed.

setHeaderEncoding

public void setHeaderEncoding(String encoding)
Specifies the character encoding to be used when reading the headers of individual parts. When not specified, or null, the platform default encoding is used.
Parameters:
encoding - The encoding used to read part headers.

skipPreamble

public boolean skipPreamble()
            throws IOException
Finds the beginning of the first encapsulation.
Returns:
true if an encapsulation was found in the stream.

toString

public String toString()
Returns a string representation of this object.
Returns:
The string representation of this object.

Copyright © 2002-2003 Apache Software Foundation. All Rights Reserved.