lib/core: fix Reader::read

[nit.git] / lib / core / stream.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# This file is free software, which comes along with NIT. This software is
# distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
# without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
# PARTICULAR PURPOSE. You can modify it is you want, provided this header
# is kept unaltered, and a notification of the changes is added.
# You are allowed to redistribute it and sell it, alone or is a part of
# another product.

# Input and output streams of characters
module stream

import error
intrude import bytes
import codecs

in "C" `{
        #include <unistd.h>
        #include <string.h>
        #include <signal.h>
`}

# Any kind of error that could be produced by an operation on Streams
class IOError
        super Error
end

# Any kind of stream to read/write/both to or from a source
abstract class Stream
        # Codec used to transform raw data to text
        #
        # Note: defaults to UTF-8
        var codec: Codec = utf8_codec is protected writable(set_codec)

        # Lookahead buffer for codecs
        #
        # Since some codecs are multibyte, a lookahead may be required
        # to store the next bytes and consume them only if a valid character
        # is read.
        protected var lookahead: CString is noinit

        # Capacity of the lookahead
        protected var lookahead_capacity = 0

        # Current occupation of the lookahead
        protected var lookahead_length = 0

        # Buffer for writing data to a stream
        protected var write_buffer: CString is noinit

        init do
                var lcap = codec.max_lookahead
                lookahead = new CString(lcap)
                write_buffer = new CString(lcap)
                lookahead_length = 0
                lookahead_capacity = lcap
        end

        # Change the codec for this stream.
        fun codec=(c: Codec) do
                if c.max_lookahead > lookahead_capacity then
                        var lcap = codec.max_lookahead
                        var lk = new CString(lcap)
                        var llen = lookahead_length
                        if llen > 0 then
                                lookahead.copy_to(lk, llen, 0, 0)
                        end
                        lookahead = lk
                        lookahead_capacity = lcap
                        write_buffer = new CString(lcap)
                end
                set_codec(c)
        end

        # Error produced by the file stream
        #
        #     var ifs = new FileReader.open("donotmakethisfile.binx")
        #     ifs.read_all
        #     ifs.close
        #     assert ifs.last_error != null
        var last_error: nullable IOError = null

        # close the stream
        fun close is abstract

        # Pre-work hook.
        #
        # Used to inform `self` that operations will start.
        # Specific streams can use this to prepare some resources.
        #
        # Is automatically invoked at the beginning of `with` structures.
        #
        # Do nothing by default.
        fun start do end

        # Post-work hook.
        #
        # Used to inform `self` that the operations are over.
        # Specific streams can use this to free some resources.
        #
        # Is automatically invoked at the end of `with` structures.
        #
        # call `close` by default.
        fun finish do close
end

# A `Stream` that can be read from
abstract class Reader
        super Stream

        # Read a byte directly from the underlying stream, without
        # considering any eventual buffer
        protected fun raw_read_byte: Int is abstract

        # Read at most `max` bytes from the underlying stream into `buf`,
        # without considering any eventual buffer
        #
        # Returns how many bytes were read
        protected fun raw_read_bytes(buf: CString, max: Int): Int do
                var rd = 0
                for i in [0 .. max[ do
                        var b = raw_read_byte
                        if b < 0 then break
                        buf[i] = b.to_b
                        rd += 1
                end
                return rd
        end

        # Reads a character. Returns `null` on EOF or timeout
        fun read_char: nullable Char is abstract

        # Reads a byte. Returns a negative value on error
        fun read_byte: Int do
                var llen = lookahead_length
                if llen == 0 then return raw_read_byte
                var lk = lookahead
                var b = lk[0].to_i
                if llen == 1 then
                        lookahead_length = 0
                else
                        lk.lshift(1, llen - 1, 1)
                        lookahead_length -= 1
                end
                return b
        end

        # Reads a String of at most `i` length
        fun read(i: Int): String do
                assert i >= 0
                var cs = new CString(i)
                var rd = read_bytes_to_cstring(cs, i)
                if rd < 0 then return ""
                return codec.decode_string(cs, rd)
        end

        # Reads up to `max` bytes from source
        fun read_bytes(max: Int): Bytes do
                assert max >= 0
                var cs = new CString(max)
                var rd = read_bytes_to_cstring(cs, max)
                return new Bytes(cs, rd, max)
        end

        # Reads up to `max` bytes from source and stores them in `bytes`
        fun read_bytes_to_cstring(bytes: CString, max: Int): Int do
                var llen = lookahead_length
                if llen == 0 then return raw_read_bytes(bytes, max)
                var rd = max.min(llen)
                var lk = lookahead
                lk.copy_to(bytes, rd, 0, 0)
                if rd < llen then
                        lk.lshift(rd, llen - rd, rd)
                        lookahead_length -= rd
                else
                        lookahead_length = 0
                end
                return rd + raw_read_bytes(bytes, max - rd)
        end

        # Read a string until the end of the line.
        #
        # The line terminator '\n' and '\r\n', if any, is removed in each line.
        #
        # ~~~
        # var txt = "Hello\n\nWorld\n"
        # var i = new StringReader(txt)
        # assert i.read_line == "Hello"
        # assert i.read_line == ""
        # assert i.read_line == "World"
        # assert i.eof
        # ~~~
        #
        # Only LINE FEED (`\n`), CARRIAGE RETURN & LINE FEED (`\r\n`), and
        # the end or file (EOF) is considered to delimit the end of lines.
        # CARRIAGE RETURN (`\r`) alone is not used for the end of line.
        #
        # ~~~
        # var txt2 = "Hello\r\n\n\rWorld"
        # var i2 = new StringReader(txt2)
        # assert i2.read_line == "Hello"
        # assert i2.read_line == ""
        # assert i2.read_line == "\rWorld"
        # assert i2.eof
        # ~~~
        #
        # NOTE: Use `append_line_to` if the line terminator needs to be preserved.
        fun read_line: String
        do
                if last_error != null then return ""
                if eof then return ""
                var s = new FlatBuffer
                append_line_to(s)
                return s.to_s.chomp
        end

        # Read all the lines until the eof.
        #
        # The line terminator '\n' and `\r\n` is removed in each line,
        #
        # ~~~
        # var txt = "Hello\n\nWorld\n"
        # var i = new StringReader(txt)
        # assert i.read_lines == ["Hello", "", "World"]
        # ~~~
        #
        # This method is more efficient that splitting
        # the result of `read_all`.
        #
        # NOTE: SEE `read_line` for details.
        fun read_lines: Array[String]
        do
                var res = new Array[String]
                while not eof do
                        res.add read_line
                end
                return res
        end

        # Return an iterator that read each line.
        #
        # The line terminator '\n' and `\r\n` is removed in each line,
        # The line are read with `read_line`. See this method for details.
        #
        # ~~~
        # var txt = "Hello\n\nWorld\n"
        # var i = new StringReader(txt)
        # assert i.each_line.to_a == ["Hello", "", "World"]
        # ~~~
        #
        # Unlike `read_lines` that read all lines at the call, `each_line` is lazy.
        # Therefore, the stream should no be closed until the end of the stream.
        #
        # ~~~
        # i = new StringReader(txt)
        # var el = i.each_line
        #
        # assert el.item == "Hello"
        # el.next
        # assert el.item == ""
        # el.next
        #
        # i.close
        #
        # assert not el.is_ok
        # # closed before "world" is read
        # ~~~
        fun each_line: LineIterator do return new LineIterator(self)

        # Read all the stream until the eof.
        #
        # The content of the file is returned as a String.
        #
        # ~~~
        # var txt = "Hello\n\nWorld\n"
        # var i = new StringReader(txt)
        # assert i.read_all == txt
        # ~~~
        fun read_all: String do
                var s = read_all_bytes
                var slen = s.length
                if slen == 0 then return ""
                return codec.decode_string(s.items, s.length)
        end

        # Read all the stream until the eof.
        #
        # The content of the file is returned verbatim.
        fun read_all_bytes: Bytes
        do
                if last_error != null then return new Bytes.empty
                var s = new Bytes.empty
                var buf = new CString(4096)
                while not eof do
                        var rd = read_bytes_to_cstring(buf, 4096)
                        s.append_ns(buf, rd)
                end
                return s
        end

        # Read a string until the end of the line and append it to `s`.
        #
        # Unlike `read_line` and other related methods,
        # the line terminator '\n', if any, is preserved in each line.
        # Use the method `Text::chomp` to safely remove it.
        #
        # ~~~
        # var txt = "Hello\n\nWorld\n"
        # var i = new StringReader(txt)
        # var b = new FlatBuffer
        # i.append_line_to(b)
        # assert b == "Hello\n"
        # i.append_line_to(b)
        # assert b == "Hello\n\n"
        # i.append_line_to(b)
        # assert b == txt
        # assert i.eof
        # ~~~
        #
        # If `\n` is not present at the end of the result, it means that
        # a non-eol terminated last line was returned.
        #
        # ~~~
        # var i2 = new StringReader("hello")
        # assert not i2.eof
        # var b2 = new FlatBuffer
        # i2.append_line_to(b2)
        # assert b2 == "hello"
        # assert i2.eof
        # ~~~
        #
        # NOTE: The single character LINE FEED (`\n`) delimits the end of lines.
        # Therefore CARRIAGE RETURN & LINE FEED (`\r\n`) is also recognized.
        fun append_line_to(s: Buffer)
        do
                if last_error != null then return
                loop
                        var x = read_char
                        if x == null then
                                if eof then return
                        else
                                s.chars.push(x)
                                if x == '\n' then return
                        end
                end
        end

        # Is there something to read.
        # This function returns 'false' if there is something to read.
        fun eof: Bool is abstract

        # Read the next sequence of non whitespace characters.
        #
        # Leading whitespace characters are skipped.
        # The first whitespace character that follows the result is consumed.
        #
        # An empty string is returned if the end of the file or an error is encounter.
        #
        # ~~~
        # var w = new StringReader(" Hello, \n\t World!")
        # assert w.read_word == "Hello,"
        # assert w.read_char == '\n'
        # assert w.read_word == "World!"
        # assert w.read_word == ""
        # ~~~
        #
        # `Char::is_whitespace` determines what is a whitespace.
        fun read_word: String
        do
                var buf = new FlatBuffer
                var c = read_nonwhitespace
                if c != null then
                        buf.add(c)
                        while not eof do
                                c = read_char
                                if c == null then break
                                if c.is_whitespace then break
                                buf.add(c)
                        end
                end
                var res = buf.to_s
                return res
        end

        # Skip whitespace characters (if any) then return the following non-whitespace character.
        #
        # Returns the code point of the character.
        # Returns `null` on end of file or error.
        #
        # In fact, this method works like `read_char` except it skips whitespace.
        #
        # ~~~
        # var w = new StringReader(" \nab\tc")
        # assert w.read_nonwhitespace == 'a'
        # assert w.read_nonwhitespace == 'b'
        # assert w.read_nonwhitespace == 'c'
        # assert w.read_nonwhitespace == null
        # ~~~
        #
        # `Char::is_whitespace` determines what is a whitespace.
        fun read_nonwhitespace: nullable Char
        do
                var c: nullable Char = null
                while not eof do
                        c = read_char
                        if c == null or not c.is_whitespace then break
                end
                return c
        end
end

# Iterator returned by `Reader::each_line`.
# See the aforementioned method for details.
class LineIterator
        super Iterator[String]

        # The original stream
        var stream: Reader

        redef fun is_ok
        do
                var res = not stream.eof
                if not res and close_on_finish then stream.close
                return res
        end

        redef fun item
        do
                var line = self.line
                if line == null then
                        line = stream.read_line
                end
                self.line = line
                return line
        end

        # The last line read (cache)
        private var line: nullable String = null

        redef fun next
        do
                # force the read
                if line == null then item
                # drop the line
                line = null
        end

        # Close the stream when the stream is at the EOF.
        #
        # Default is false.
        var close_on_finish = false is writable

        redef fun finish
        do
                if close_on_finish then stream.close
        end
end

# `Reader` capable of declaring if readable without blocking
abstract class PollableReader
        super Reader

        # Is there something to read? (without blocking)
        fun poll_in: Bool is abstract

end

# A `Stream` that can be written to
abstract class Writer
        super Stream

        # Write bytes from `s`
        fun write_bytes(s: Bytes) do write_bytes_from_cstring(s.items, s.length)

        # Write `len` bytes from `ns`
        fun write_bytes_from_cstring(ns: CString, len: Int) is abstract

        # Write a string
        fun write(s: Text) is abstract

        # Write a single byte
        fun write_byte(value: Byte) is abstract

        # Write a single char
        fun write_char(c: Char) do
                var ln = codec.add_char_to(c, write_buffer)
                write_bytes_from_cstring(write_buffer, ln)
        end

        # Can the stream be used to write
        fun is_writable: Bool is abstract
end

# Things that can be efficienlty written to a `Writer`
#
# The point of this interface is to allow the instance to be efficiently
# written into a `Writer`.
#
# Ready-to-save documents usually provide this interface.
interface Writable
        # Write itself to a `stream`
        # The specific logic it let to the concrete subclasses
        fun write_to(stream: Writer) is abstract

        # Like `write_to` but return a new String (may be quite large)
        #
        # This funtionality is anectodical, since the point
        # of streamable object to to be efficienlty written to a
        # stream without having to allocate and concatenate strings
        fun write_to_string: String
        do
                var stream = new StringWriter
                write_to(stream)
                return stream.to_s
        end
end

redef class Bytes
        super Writable
        redef fun write_to(s) do s.write_bytes(self)

        redef fun write_to_string do return to_s
end

redef class Text
        super Writable
        redef fun write_to(stream) do stream.write(self)
end

# Input streams with a buffered input for efficiency purposes
abstract class BufferedReader
        super Reader
        redef fun read_char
        do
                if last_error != null then return null
                if eof then
                        last_error = new IOError("Stream has reached eof")
                        return null
                end
                # TODO: Fix when supporting UTF-8
                var c = _buffer[_buffer_pos].to_i.code_point
                _buffer_pos += 1
                return c
        end

        redef fun read_byte
        do
                if last_error != null then return -1
                if eof then
                        last_error = new IOError("Stream has reached eof")
                        return -1
                end
                var c = _buffer[_buffer_pos]
                _buffer_pos += 1
                return c.to_i
        end

        # Resets the internal buffer
        fun buffer_reset do
                _buffer_length = 0
                _buffer_pos = 0
        end

        # Peeks up to `n` bytes in the buffer
        #
        # The operation does not consume the buffer
        #
        # ~~~nitish
        # var x = new FileReader.open("File.txt")
        # assert x.peek(5) == x.read(5)
        # ~~~
        fun peek(i: Int): Bytes do
                if eof then return new Bytes.empty
                var remsp = _buffer_length - _buffer_pos
                if i <= remsp then
                        var bf = new Bytes.with_capacity(i)
                        bf.append_ns_from(_buffer, i, _buffer_pos)
                        return bf
                end
                var bf = new Bytes.with_capacity(i)
                bf.append_ns_from(_buffer, remsp, _buffer_pos)
                _buffer_pos = _buffer_length
                read_intern(i - bf.length, bf)
                remsp = _buffer_length - _buffer_pos
                var full_len = bf.length + remsp
                if full_len > _buffer_capacity then
                        var c = _buffer_capacity
                        while c < full_len do c = c * 2 + 2
                        _buffer_capacity = c
                end
                var nns = new CString(_buffer_capacity)
                bf.items.copy_to(nns, bf.length, 0, 0)
                _buffer.copy_to(nns, remsp, _buffer_pos, bf.length)
                _buffer = nns
                _buffer_pos = 0
                _buffer_length = full_len
                return bf
        end

        redef fun read_bytes_to_cstring(buf, i)
        do
                if last_error != null then return 0
                var bbf = new Bytes(buf, 0, i)
                return read_intern(i, bbf)
        end

        # Fills `buf` with at most `i` bytes read from `self`
        private fun read_intern(i: Int, buf: Bytes): Int do
                if eof then return 0
                var p = _buffer_pos
                var bufsp = _buffer_length - p
                if bufsp >= i then
                        _buffer_pos += i
                        buf.append_ns_from(_buffer, i, p)
                        return i
                end
                _buffer_pos = _buffer_length
                var readln = _buffer_length - p
                buf.append_ns_from(_buffer, readln, p)
                var rd = read_intern(i - readln, buf)
                return rd + readln
        end

        redef fun read_all_bytes
        do
                if last_error != null then return new Bytes.empty
                var s = new Bytes.with_capacity(10)
                var b = _buffer
                while not eof do
                        var j = _buffer_pos
                        var k = _buffer_length
                        var rd_sz = k - j
                        s.append_ns_from(b, rd_sz, j)
                        _buffer_pos = k
                        fill_buffer
                end
                return s
        end

        redef fun append_line_to(s)
        do
                var lb = new Bytes.with_capacity(10)
                loop
                        # First phase: look for a '\n'
                        var i = _buffer_pos
                        while i < _buffer_length and _buffer[i] != 0xAu8 do
                                i += 1
                        end

                        var eol
                        if i < _buffer_length then
                                assert _buffer[i] == 0xAu8
                                i += 1
                                eol = true
                        else
                                eol = false
                        end

                        # if there is something to append
                        if i > _buffer_pos then
                                # Copy from the buffer to the string
                                var j = _buffer_pos
                                while j < i do
                                        lb.add(_buffer[j])
                                        j += 1
                                end
                                _buffer_pos = i
                        else
                                assert end_reached
                                s.append lb.to_s
                                return
                        end

                        if eol then
                                # so \n is found
                                s.append lb.to_s
                                return
                        else
                                # so \n is not found
                                if end_reached then
                                        s.append lb.to_s
                                        return
                                end
                                fill_buffer
                        end
                end
        end

        redef fun eof
        do
                if _buffer_pos < _buffer_length then return false
                if end_reached then return true
                fill_buffer
                return _buffer_pos >= _buffer_length and end_reached
        end

        # The buffer
        private var buffer: CString = new CString(0)

        # The current position in the buffer
        private var buffer_pos = 0

        # Length of the current buffer (i.e. nuber of bytes in the buffer)
        private var buffer_length = 0

        # Capacity of the buffer
        private var buffer_capacity = 0

        # Fill the buffer
        protected fun fill_buffer is abstract

        # Has the last fill_buffer reached the end
        protected fun end_reached: Bool is abstract

        # Allocate a `_buffer` for a given `capacity`.
        protected fun prepare_buffer(capacity: Int)
        do
                _buffer = new CString(capacity)
                _buffer_pos = 0 # need to read
                _buffer_length = 0
                _buffer_capacity = capacity
        end
end

# A `Stream` that can be written to and read from
abstract class Duplex
        super Reader
        super Writer
end

# Write to `bytes` in memory
#
# ~~~
# var writer = new BytesWriter
#
# writer.write "Strings "
# writer.write_char '&'
# writer.write_byte 0x20u8
# writer.write_bytes "bytes".to_bytes
#
# assert writer.to_s == "\\x53\\x74\\x72\\x69\\x6E\\x67\\x73\\x20\\x26\\x20\\x62\\x79\\x74\\x65\\x73"
# assert writer.bytes.to_s == "Strings & bytes"
# ~~~
#
# As with any binary data, UTF-8 code points encoded on two bytes or more
# can be constructed byte by byte.
#
# ~~~
# writer = new BytesWriter
#
# # Write just the character first half
# writer.write_byte 0xC2u8
# assert writer.to_s == "\\xC2"
# assert writer.bytes.to_s == "�"
#
# # Complete the character
# writer.write_byte 0xA2u8
# assert writer.to_s == "\\xC2\\xA2"
# assert writer.bytes.to_s == "¢"
# ~~~
class BytesWriter
        super Writer

        # Written memory
        var bytes = new Bytes.empty

        redef fun to_s do return bytes.chexdigest

        redef fun write(str)
        do
                if closed then return
                str.append_to_bytes bytes
        end

        redef fun write_char(c)
        do
                if closed then return
                bytes.add_char c
        end

        redef fun write_byte(value)
        do
                if closed then return
                bytes.add value
        end

        redef fun write_bytes_from_cstring(ns, len) do
                if closed then return
                bytes.append_ns(ns, len)
        end

        # Is the stream closed?
        protected var closed = false

        redef fun close do closed = true
        redef fun is_writable do return not closed
end

# `Stream` writing to a `String`
#
# This class has the same behavior as `BytesWriter`
# except for `to_s` which decodes `bytes` to a string.
#
# ~~~
# var writer = new StringWriter
#
# writer.write "Strings "
# writer.write_char '&'
# writer.write_byte 0x20u8
# writer.write_bytes "bytes".to_bytes
#
# assert writer.to_s == "Strings & bytes"
# ~~~
class StringWriter
        super BytesWriter

        redef fun to_s do return bytes.to_s
end

# Read from `bytes` in memory
#
# ~~~
# var reader = new BytesReader(b"a…b")
# assert reader.read_char == 'a'
# assert reader.read_byte == 0xE2 # 1st byte of '…'
# assert reader.read_byte == 0x80 # 2nd byte of '…'
# assert reader.read_char == '�' # Reads the last byte as an invalid char
# assert reader.read_all_bytes == b"b"
# ~~~
class BytesReader
        super Reader

        # Source data to read
        var bytes: Bytes

        # The current position in `bytes`
        private var cursor = 0

        redef fun read_char
        do
                if cursor >= bytes.length then return null

                var len = bytes.items.length_of_char_at(cursor)
                var char = bytes.items.char_at(cursor)
                cursor += len
                return char
        end

        redef fun read_byte
        do
                if cursor >= bytes.length then return -1

                var c = bytes[cursor]
                cursor += 1
                return c.to_i
        end

        redef fun close do bytes = new Bytes.empty

        redef fun read_all_bytes
        do
                var res = bytes.slice_from(cursor)
                cursor = bytes.length
                return res
        end

        redef fun raw_read_bytes(ns, max) do
                if cursor >= bytes.length then return 0

                var copy = max.min(bytes.length - cursor)
                bytes.items.copy_to(ns, copy, cursor, 0)
                cursor += copy
                return copy
        end

        redef fun eof do return cursor >= bytes.length
end

# `Stream` reading from a `String` source
#
# This class has the same behavior as `BytesReader`
# except for its constructor accepting a `String`.
#
# ~~~
# var reader = new StringReader("a…b")
# assert reader.read_char == 'a'
# assert reader.read_byte == 0xE2 # 1st byte of '…'
# assert reader.read_byte == 0x80 # 2nd byte of '…'
# assert reader.read_char == '�' # Reads the last byte as an invalid char
# assert reader.read_all == "b"
# ~~~
class StringReader
        super BytesReader

        autoinit source

        # Source data to read
        var source: String

        init do bytes = source.to_bytes

        redef fun close
        do
                source = ""
                super
        end
end