org.apache.tomcat.util.http.fileupload

## Class MultipartStream

- java.lang.Object
- - org.apache.tomcat.util.http.fileupload.MultipartStream

-     public class MultipartStream
      extends 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 := "--" boundary "--"
  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 example of usage of this class.

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

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `MultipartStream.IllegalBoundaryException` Thrown upon attempt of setting an invalid boundary token.
    `class` | `MultipartStream.ItemInputStream` An `InputStream` for reading an items contents.
    `static class` | `MultipartStream.MalformedStreamException` Thrown to indicate that the input stream fails to follow the required syntax.
    `static class` | `MultipartStream.ProgressNotifier` Internal class, which is used to invoke the `ProgressListener`.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected static byte[]` | `BOUNDARY_PREFIX` A byte sequence that precedes a boundary (`CRLF--`).
    `static byte` | `CR` The Carriage Return ASCII character value.
    `static byte` | `DASH` The dash (-) ASCII character value.
    `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`).
    `static byte` | `LF` The Line Feed ASCII character value.
    `protected static byte[]` | `STREAM_TERMINATOR` A byte sequence that that follows a delimiter of the last encapsulation in the stream (`--`).

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `MultipartStream(InputStream input, byte[] boundary, int bufSize, MultipartStream.ProgressNotifier pNotifier)` Constructs a `MultipartStream` with a custom size buffer.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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`.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### CR

          public static final byte CR

      The Carriage Return ASCII character value.
      See Also:
        Constant Field Values

    - #### LF

          public static final byte LF

      The Line Feed ASCII character value.
      See Also:
        Constant Field Values

    - #### DASH

          public static final byte DASH

      The dash (-) ASCII character value.
      See Also:
        Constant Field Values

    - #### 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.).
      See Also:
        Constant Field Values

    - #### DEFAULT_BUFSIZE

          protected static final int DEFAULT_BUFSIZE

      The default length of the buffer used for processing a request.
      See Also:
        Constant Field Values

    - #### HEADER_SEPARATOR

          protected static final byte[] HEADER_SEPARATOR

      A byte sequence that marks the end of `header-part` (`CRLFCRLF`).

    - #### FIELD_SEPARATOR

          protected static final byte[] FIELD_SEPARATOR

      A byte sequence that that follows a delimiter that will be followed by an encapsulation (`CRLF`).

    - #### STREAM_TERMINATOR

          protected static final byte[] STREAM_TERMINATOR

      A byte sequence that that follows a delimiter of the last encapsulation in the stream (`--`).

    - #### BOUNDARY_PREFIX

          protected static final byte[] BOUNDARY_PREFIX

      A byte sequence that precedes a boundary (`CRLF--`).

  - ### Constructor Detail

    - #### MultipartStream

          public MultipartStream(InputStream input,
                         byte[] boundary,
                         int bufSize,
                         MultipartStream.ProgressNotifier pNotifier)

      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.
        `pNotifier` - The notifier, which is used for calling the progress listener, if any.
      Throws:
        `IllegalArgumentException` - If the buffer size is too small
      Since:
        1.3.1

  - ### Method Detail

    - #### 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.

    - #### 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.

    - #### 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.
      Throws:
        `IOException` - if there is no more data available.

    - #### readBoundary

          public boolean readBoundary()
                               throws FileUploadBase.FileUploadIOException,
                                      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:
        `FileUploadBase.FileUploadIOException` - if the bytes read from the stream exceeded the size limits
        `MultipartStream.MalformedStreamException` - if the stream ends unexpectedly or fails to follow required syntax.

    - #### 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.

    - #### readHeaders

          public String readHeaders()
                             throws FileUploadBase.FileUploadIOException,
                                    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:
        `FileUploadBase.FileUploadIOException` - if the bytes read from the stream exceeded the size limits.
        `MultipartStream.MalformedStreamException` - if the stream ends unexpectedly.

    - #### 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. May be null, in which case this method is equivalent to `discardBodyData()`.
      Returns:
        the amount of data written.
      Throws:
        `MultipartStream.MalformedStreamException` - if the stream ends unexpectedly.
        `IOException` - if an i/o error occurs.

    - #### 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.
        `IOException` - if an i/o error occurs.

    - #### skipPreamble

          public boolean skipPreamble()
                               throws IOException

      Finds the beginning of the first `encapsulation`.
      Returns:
        `true` if an `encapsulation` was found in the stream.
      Throws:
        `IOException` - if an i/o error occurs.

    - #### 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.

    - #### 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.

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