Stream API Functions

This document lists most useful (and most often needed) functions. Be aware, that there are many more to be found in either the class references or via the builtin class browser.

See also "Stream Handling" in Expecco_API.
Reference: Stream and ExternalStream and Socket

Back to Useful API Functions

Creation

Internal Streams

These are streams on an internal (in memory) collection. Typically these are strings, byteArrays or regular arrays. But actually, any sequenceable collection (ie. one which is indexed by an integer) can be streamed upon.

In addition, there are generator streams such as Random number generators or cryptographic HashStreams, among others, and wrapping streams for filtering, decoding or line numbering.

aCollection readStream => Stream

aString readStream => Stream

ReadStream on: aCollection => Stream

returns a stream to read from a general collection or especially from a string (which is a collection of characters). Notice that a a stream on a collection which contains non-characters will return its elements when reading. Thus, you can also open stream on integers, floats, or whatever the collection contains.

aCollection writeStream => Stream

aString writeStream => Stream

WriteStream on: aCollection => Stream

returns a stream to write to a general collection or especially a string stream. The stream will write initially into the given collection, but will reallocate a bigger collection if required. Usually, the given collection will be empty so the stream will immediately allocate a new container and return that at the end (see "contents" below).

External Streams

pathString asFilename readStream => Stream

pathString asFilename writeStream => Stream

pathString asFilename appendingWriteStream => Stream

returns a stream to read / write the file named aFilenameString

Socket newTCPclientToHost: hostNameOrAddress port: aPortOrServiceName => SocketStream

returns a connected socket for reading and writing.
Browse the Socket class for many more socket creation operations.

PipeStream readingFrom: OS-command => PipeStream

returns a stream reading the output from an operating system command.

For example, on Unix, you can read the output of the " ls " command via "PipeStream readingFrom:'ls'".
The corresponding code for Windows would be "PipeStream readingFrom:'dir'".
Notice that the PipeStream class provides additional protocol to control eg. how to handle stderr wrt. stdout.

PipeStream writingTo: OS-command => PipeStream

returns a stream writing to the input of an operating system command

PipeStream bidirectionalFor: OS-command => PipeStream (Unix/Linux only)

returns a read/write stream to an operating system command. Writes will feed the program's input, whereas the program's output can be read from the pipe stream.

Wellknown Streams

Transcript

the Smalltalk console window also supports the stream protocol

Stdin

the standard input (notice: if started as "exe" on Windows, there will be no stdin; if started via desktop double click on unix, it will report End-of-File).
If started as "com" on Windows and/or in a command window, stdin is reading your command window input.

Stdout

the standard output (notice: if started as "exe" on Windows, there will be no stdout; if started via desktop double click on unix, it will typically be redirected to either a log file or to /dev/null).
If started as "com" on Windows and/or in a command window, stdout is shown in the command window.

Stderr

the standard error (notice: if started as "exe" on Windows, there will be no stderr; if started via desktop double click on unix, it will typically be redirected to either a log file or to /dev/null)
If started as "com" on Windows and/or in a command window, stdout is shown in the command window.

Testing

aStream atEnd => Boolean

aStream.atEnd() [JS]

returns true if no more elements are to be read

aStream isPositionable => Boolean

returns true if the stream supports positioning. Not all streams support this (e.g. Sockets, PipeStreams, StdOut etc. do not).

aStream size => Integer

returns the number of bytes written to a writeStream or the overall size of a readStream's contents. Not all streams know their size and will report an error (e.g. Sockets, PipeStreams, StdOut etc. do not).

Mode Settings

By default, external character streams (in particular: file streams) are in text mode, meaning that the read functions retrieve characters or strings.
If the mode is switched to binary mode, bytes (integers) and byteArrays are retrieved.

aStream binary

aStream.binary() [JS]

aStream text

aStream.text() [JS]

switches to binary or text mode

aStream buffered: aBoolean

for external write streams: turns buffering on/off.
By default, terminal stream are line buffered, while file streams use a larger buffer. When writing, buffers are filled first and then bigger chunks are written en-bloc. Notice that buffering may lead to characters written to a file being unseen by other programs until the buffer is flushed or the file stream is closed (see flush below).

Reading

Characters

aStream next => Character | nil

aStream.next() [JS]

returns the next element (as character object if text stream) or byte if in binary mode or arbitrary object if streaming other collections.

Example:

 s := 'data.txt' asFilename readStream.
 s next.
 => character

aStream next: count => String

aStream.next( count ) [JS]

returns the next count characters (as a string) or bytes in binary mode

Example:

 s := 'data.txt' asFilename readStream.
 s next:5.
 => string-of-5-chars

Binary Bytes

aStream nextByte => Integer | nil

returns the next byte (as an integer in [0..255]), independent of the current text/binary read mode

aStream nextBytes: count => ByteArray

returns the next count bytes (as a byte array), independent of the text/binary read mode

aStream nextBytes: count into: aByteArray startingAt: index1Based => count

reads the next count bytes into the given byteArray starting at index in the byteArray. Returns the number of bytes read (which might be less than count, if the End-Of-File is reached). Will report an error, if the given buffer is too small.

Reading Words, Lines, etc.

aCharacterStream nextAlphaNumericWord => String | nil

aCharacterStream nextLine => String | nil

returns the next word (up to non-letterOrDigit) or line (up to the line end) as a string. The stream must be in text mode.

aStream upTo: element => String | ByteArray

returns characters (in text mode) or bytes (in binary mode) up to element as either a string or byte array. The element itself will be read, but not be part of the returned collection (i.e. it is skipped over). This is useful e.g. to read characters up to a semicolon.

aStream upToAny: collectionOfElements => String | ByteArray

similar, but looks for multiple such separators. This is useful e.g. to read characters up to a either a semicolon or a comma (as in CSV files).

aStream upToAnyForWhich: aBlock => String | ByteArray

similar, but a test-block (aka lambda function) is given, which checks for the limiting element.

aStream upToSeparator => String

returns all characters (in text mode) up to the next separator (space, tab or newline). The stream is left positioned before the separator (i.e. the next read will return the separator character).
Same as "aStream upToAnyForWhich: #isSeparator".

aStream upToEnd => String | ByteArray

returns all characters (in text mode) or bytes (in binary mode) up to the end of the stream as either a string or byte array.

Numbers

Number readFrom: aStringOrStream => Number

reads the string representation of a number.
E.g. Number readFrom:'123.456' => 123.456 (a float)
and: Number readFrom:'123456' => 123456 (an integer)

Integer readFrom: aStringOrStream => Number

reads the string representation of an integer.
E.g. Number readFrom:'123.456' => 123 (an integer)

C-Style Reading

formatString scanf: aStringOrStream => collection

reads according to format; returns a collection of matches. The argument can be string or stream.
For details see "Scanf Format Specifier" in the Number API page.
Eg.
'%d %x %s %s' scanf: '1234 ffee hello world'
=> #(1234 65518 'hello' 'world') (actually an OrderedCollection is returned)

aStream scanf: formatString => collection

same as above, but implemented by the stream

Binary Data Reading

The following functions read sequences of binary bytes - not human readable characters/digits.

aStream nextByte => Integer

aStream nextSignedByte => Integer

reads the next byte from the stream as an 8 bit unsigned / signed integer.

aStream nextInt16MSB: msbBoolean => Integer

aStream nextSignedInt16MSB: msbBoolean => Integer

reads the next 2 bytes from the stream as a 16 bit unsigned / signed integer.

aStream nextInt32MSB: msbBoolean => Integer

aStream nextSignedInt32MSB: msbBoolean => Integer

reads the next 4 bytes from the stream as a 32 bit unsigned or signed integer. The byte order is specified by msbBoolean as most-significant-first if true or least-significant-first if false.

aStream nextInt64MSB: msbBoolean => Integer

aStream nextSignedInt64MSB: msbBoolean => Integer

reads the next 8 bytes from the stream as a 64 bit unsigned / signed integer.

aStream nextIEEESingleMSB: msbBoolean => Float32

aStream nextIEEEDoubleMSB: msbBoolean => Float64

reads the next 4 bytes (8 bytes) from the stream as a 32 bit IEEE single (64 bit double) precision float.

Positioning

aStream position: pos => Stream

positions the stream; pos is 0-based (i.e. 0 is the very beginning). Some streams are not positionable and will report an error (e.g. PipeStream, Socket). If the stream is a byte- or character stream, the position is measured in bytes, If the stream is an internal (object-) stream, it is measured in number of objects.

aStream position => Integer

returns the position of the stream; pos is 0-based (i.e. 0 is the very beginning). Not all streams have a concept of a position (e.g. PipeStream, Socket do not)

aStream setToEnd => void

position the stream to the end. Usually used when appending to an existing file.

aStream reset => void

position the stream to the beginning.

aStream skip: count => Stream

positions the stream count elements further (i.e. reads but ignores count elements)

Writing

aStream nextPut: someElement

aStream.nextPut( someElement ) [JS]

Appends (writes) an element to the stream. For the special but most common case of a string- or file stream, the written element should be a character object.

aStream nextPutByte: anInteger

Appends (writes) a single byte. This is only allowed for string streams.

aStream cr

Appends (writes) a newline character (line-end character). Notice: although this function is named "cr", it actually writes a newline character (LF), which is the standard line-end convention used on Unix systems. The name "cr" is used for history reasons and for compatibility with other Smalltalk systems.
For external streams, the end of line character can be changed to one of CR, LF, CRLF or EOT.

aStream return

Appends (writes) a return character. Use this, if you explicitly want a CR to be written.

aStream crlf

Appends (writes) a cr-lf sequence. This is needed e.g. when generating HTTP headers or when talking to other internet socket connections.

aStream tab

Appends (writes) a tabulator character

aStream nextPutAll: aCollectionOfElements

aStream.nextPutAll( aCollectionOfElements ) [JS]

writes all elements from the argument to the stream. The collection's elements must be compatible with the streams element types. For string streams, this will usually be a string.

Example (writes a file):

 s := 'data.txt' asFilename writeStream.
 s nextPut: $a.
 s nextPut: $b.
 s nextPutByte: 0x0A.
 s nextPutAll: '123'. 
 s close.
 => file now contains 'ab<nl>123'

Example (writes a string):

 s := ' ' writeStream.  // or: WriteStream on:String new.
 s nextPut: $a.
 s nextPut: $b.
 s cr.
 s nextPutAll: '123'. 
 s contents.
 => 'ab<nl>123'

Example (writes an array):

 s := #() writeStream.   
 s nextPut: 1.
 s nextPut: 'two'.
 s nextPut: 3.14159.
 s nextPutAll: #(11 22 true false). 
 s contents
 => #( 1 'two' 3.14159 11 22 true false)

aStream nextPutLine: aString

aStream.nextPutLine( aString ) [JS]

writes aString followed by a line end (which is a newline-character by default, but can be changed for external streams)

Binary Data Writing

These functions write binary data - not human readable strings (digits).

aStream nextPutInt32: anInteger MSB: msbBoolean

writes anInteger as a 32 bit binary integer (4 bytes). The byte order is specified by msbBoolean as most-significant-first if true or least-significant-first if false.

aStream nextPutInt16: anInteger MSB: msbBoolean

writes anInteger as a 16 bit binary integer (2 bytes).

aStream nextPutInt64: anInteger MSB: msbBoolean

writes anInteger as a 64 bit binary integer (8 bytes).

aStream nextPutIEEESingle: aFloat MSB: msbBoolean

aStream nextPutIEEEDouble: aFloat MSB: msbBoolean

writes aFloat as a 32 bit (64 bit) binary IEEE single (double) precision float (4/8 bytes).

C-Style Writing

aStream printf: formatString withAll: argsCollection

prints according to format which is a C-printf style format specification.
For details see "Printf Format Specifier" in the Number API page.
E.g.
  Transcript
    printf: '%d %x foo %s %s'
    withAll: { 1234 . 1234 . 'hello' . 'world'}
will generate "1234 4d2 foo hello world".

aStream printf: formatString with: arg

shortcut for above if only one argument needs to be passed.

aStream printf: formatString with: arg1 with: arg2

shortcut for above if two arguments need to be passed.

Finish Writing

When done with writing, external streams should be closed with:

aStream flush => void

for write streams: flushes any buffered data. The stream remains open and more data can be written, but everything written before is given to the operating system to write it to disk or send it to a receiver. Notice: it is not guaranteed that the data is really on the disk/transmitted after a flush: if a machine crashes (looses power) immediately after the flush, the data may still be in another (operating system) buffer and not physically written. On some operating systems, you can ensure that by sending syncFileSystem to the stream after the flush.

aStream close => void

closes the stream; for file streams, any buffered output is now written. For sockets and pipes, the connection is shut down. If you forget to close an external stream, the data might be held in a buffer for an arbitrary time. If the garbage collector detects that an open stream is no longer references, it will close the stream (finalization). However, this may not happen for a long time, if enough memory is available or the system is otherwise idle.

When done with writing to an internal stream, its contents can be retrieved with:

aStream contents => Collection

retrieves the elements written so far. For a string stream, that is the characters written so far as a string; for binary streams, that is the bytes written so far as a byte array; for other streams, that will be an Array containing the written objects.

External Streams

By default, external streams (i.e. FileStream, PipeStream, Socket, etc.) are in text mode. Reading will return characters or strings. The stream can be put into binary mode to get byte-sized integers or byte arrays. In addition, the end-of-line mode can be configured to one of CR, LF, CRLF or EOT.

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