dyaml/source/dyaml/reader.d

//          Copyright Ferdinand Majerech 2011-2014.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)

module dyaml.reader;


import core.stdc.stdlib;
import core.stdc.string;
import core.thread;

import std.algorithm;
import std.array;
import std.conv;
import std.exception;
import std.stdio;
import std.string;
import std.system;
import std.utf;

import tinyendian;

import dyaml.fastcharsearch;
import dyaml.encoding;
import dyaml.exception;
import dyaml.streamcompat;



package:

//XXX VIM STUFF:
//XXX THE f/t COLORING PLUGIN, AND TRY TO REMOVE THE f/t AUTOREPEAT PLUGIN
// (AND MAYBE DO THE REPEAT WITH ALT-T/ALT-F
//XXX DDOC snippets such as $D, $BIGOH, anything else
//    OR MAYBE JUST $ - EXPANDING TO $(${1} ${2})
//    WHERE DEFAULT ${1} IS 'D' AND SPECIAL SNIPPETS FOR SPECIFIC DDOC MACROS
//    (E.G. XREF HAS 2 ARGS)
// XXX DON'T FORGET TO COMMIT DSNIPS CHANGES
// XXX SNIPPETS: WHY CAN'T WE USE NEW IN NEW? FIX!
// XXX ALSO WRITELN VISUAL! (print whatever we have selected)
// XXX AND ``fun`` VISUAL TOO!
// XXX snippet to print variable along its name AND
// OR MULTIPLE VARS - USE std.format!




///Exception thrown at Reader errors.
class ReaderException : YAMLException
{
    this(string msg, string file = __FILE__, int line = __LINE__)
        @safe pure nothrow
    {
        super("Reader error: " ~ msg, file, line);
    }
}

/// Lazily reads and decodes data from a buffer, only storing as much as needed at any
/// moment.
///
/// Adds a '\0' to the end of the data.
final class Reader
{
    private:
        // Buffer of currently loaded characters.
        dchar[] buffer_ = null;
        // Current position within buffer. Only data after this position can be read.
        uint bufferOffset_ = 0;
        // Index of the current character in the buffer.
        size_t charIndex_ = 0;
        // Current line in file.
        uint line_;
        // Current column in file.
        uint column_;

        // Original Unicode encoding of the data.
        Encoding encoding_;

        version(unittest)
        {
            // Endianness of the input before it was converted (for testing)
            Endian endian_;
        }

    public:
        import std.stream;
        /// Construct a Reader.
        ///
        /// Params:  stream = Input stream. Must be readable and seekable.
        ///
        /// Throws:  ReaderException if the stream is invalid, on a UTF decoding error
        ///          or if there are nonprintable unicode characters illegal in YAML.
        this(Stream stream) @trusted //!nothrow
        {
            auto streamBytes = streamToBytesGC(stream);
            auto endianResult = fixUTFByteOrder(streamBytes);
            if(endianResult.bytesStripped > 0)
            {
                throw new ReaderException("Size of UTF-16 or UTF-32 input not aligned "
                                          "to 2 or 4 bytes, respectively");
            }

            version(unittest) { endian_ = endianResult.endian; }
            encoding_ = endianResult.encoding;

            auto decodeResult = decodeUTF(endianResult.array, endianResult.encoding);

            const msg = decodeResult.errorMessage;
            if(msg !is null)
            {
                throw new ReaderException("UTF decoding error: " ~ msg);
            }

            buffer_ = decodeResult.decoded;
            // The part of buffer_ excluding trailing zeroes.
            auto noZeros = buffer_;
            while(!noZeros.empty && noZeros.back == '\0') { noZeros.popBack(); }
            enforce(printable(noZeros[]),
                    new ReaderException("Special unicode characters are not allowed"));
        }

        /// Get character at specified index relative to current position.
        ///
        /// Params:  index = Index of the character to get relative to current position
        ///                  in the buffer.
        ///
        /// Returns: Character at specified position.
        ///
        // XXX removed; search for 'risky' to find why.
        // Throws:  ReaderException if trying to read past the end of the buffer.
        dchar peek(size_t index = 0) @safe pure nothrow const @nogc
        {
            if(buffer_.length <= bufferOffset_ + index)
            {
                // XXX This is risky; revert this and the 'risky' change in UTF decoder 
                // if any bugs are introduced. We rely on the assumption that Reader
                // only uses peek() to detect the of buffer. The test suite passes.
                // throw new ReaderException("Trying to read past the end of the buffer");
                return '\0';
            }

            return buffer_[bufferOffset_ + index];
        }

        /// Get specified number of characters starting at current position.
        ///
        /// Note: This gets only a "view" into the internal buffer,
        ///       which WILL get invalidated after other Reader calls.
        ///
        /// Params:  length = Number of characters to get. May reach past the end of the
        ///                   buffer; in that case the returned slice will be shorter.
        ///
        /// Returns: Characters starting at current position or an empty slice if out of bounds.
        const(dstring) prefix(size_t length) @safe pure nothrow const @nogc
        {
            return slice(0, length);
        }

        /// Get a slice view of the internal buffer.
        ///
        /// Note: This gets only a "view" into the internal buffer,
        ///       which WILL get invalidated after other Reader calls.
        ///
        /// Params:  start = Start of the slice relative to current position.
        ///          end   = End of the slice relative to current position. May reach
        ///                  past the end of the buffer; in that case the returned
        ///                  slice will be shorter.
        ///
        /// Returns: Slice into the internal buffer or an empty slice if out of bounds.
        const(dstring) slice(size_t start, size_t end) @trusted pure nothrow const @nogc
        {
            end += bufferOffset_;
            start += bufferOffset_;
            end = min(buffer_.length, end);

            return end > start ? cast(dstring)buffer_[start .. end] : "";
        }

        /// Get the next character, moving buffer position beyond it.
        ///
        /// Returns: Next character.
        ///
        /// Throws:  ReaderException if trying to read past the end of the buffer
        ///          or if invalid data is read.
        dchar get() @safe pure nothrow @nogc
        {
            const result = peek();
            forward();
            return result;
        }

        /// Get specified number of characters, moving buffer position beyond them.
        ///
        /// Params:  length = Number or characters to get.
        ///
        /// Returns: Characters starting at current position.
        dstring get(size_t length) @safe pure nothrow @nogc
        {
            auto result = prefix(length);
            forward(length);
            return result;
        }

        /// Move current position forward.
        ///
        /// Params:  length = Number of characters to move position forward.
        void forward(size_t length = 1) @safe pure nothrow @nogc
        {
            mixin FastCharSearch!"\n\u0085\u2028\u2029"d search;

            for(; length > 0; --length)
            {
                const c = buffer_[bufferOffset_];
                ++bufferOffset_;
                ++charIndex_;
                //New line.
                if(search.canFind(c) || (c == '\r' && buffer_[bufferOffset_] != '\n'))
                {
                    ++line_;
                    column_ = 0;
                }
                else if(c != '\uFEFF') { ++column_; }
            }
        }

        /// Get a string describing current buffer position, used for error messages.
        final Mark mark() @safe pure nothrow const @nogc { return Mark(line_, column_); }

        /// Get current line number.
        final uint line() @safe pure nothrow const @nogc { return line_; }

        /// Get current column number.
        final uint column() @safe pure nothrow const @nogc { return column_; }

        /// Get index of the current character in the buffer.
        final size_t charIndex() @safe pure nothrow const @nogc { return charIndex_; }

        /// Get encoding of the input buffer.
        final Encoding encoding() @safe pure nothrow const @nogc { return encoding_; }
}

private:

// Decode an UTF-8/16/32 buffer to UTF-32 (for UTF-32 this does nothing).
//
// Params:
//
// input    = The UTF-8/16/32 buffer to decode.
// encoding = Encoding of input.
// 
// Returns:
//
// A struct with the following members:
//
// $(D string errorMessage) In case of a decoding error, the error message is stored
//                          here. If there was no error, errorMessage is NULL. Always
//                          check this first before using the other members.
// $(D dchar[] decoded)     A GC-allocated buffer with decoded UTF-32 characters.
// $(D size_t maxChars)     XXX reserved for future
auto decodeUTF(ubyte[] input, UTFEncoding encoding) @safe pure nothrow
{
    // Documented in function ddoc.
    struct Result
    {
        string errorMessage;

        dchar[] decoded;
    }

    Result result;

    final switch(encoding)
    {
        case UTFEncoding.UTF_8:  result.maxChars = input.length;     break;
        case UTFEncoding.UTF_16: result.maxChars = input.length / 2; break;
        case UTFEncoding.UTF_32: result.maxChars = input.length / 2; break;
    }

    // Decode input_ if it's encoded as UTF-8 or UTF-16.
    //
    // Params:
    //
    // buffer = The input buffer to decode.
    // result = A Result struct to put decoded result and any error messages to.
    //
    // On error, result.errorMessage will be set.
    static void decode(C)(C[] input, ref Result result) @safe pure nothrow
    {
        // End of part of input that contains complete characters that can be decoded.
        const size_t end = endOfLastUTFSequence(input);
        // If end is 0, there are no full chars.
        // This can happen at the end of file if there is an incomplete UTF sequence.
        if(end < input.length)
        {
            result.errorMessage = "Invalid UTF character at the end of input";
            return;
        }

        const srclength = input.length;
        try for(size_t srcpos = 0; srcpos < srclength;)
        {
            const c = input[srcpos];
            if(c < 0x80)
            {
                result.decoded ~= c;
                ++srcpos;
            }
            else
            {
                result.decoded ~= std.utf.decode(input, srcpos);
            }
        }
        catch(UTFException e)
        {
            result.errorMessage = e.msg;
            return;
        }
        catch(Exception e)
        {
            assert(false, "Unexpected exception in decode(): " ~ e.msg);
        }
    }

    final switch(encoding)
    {
        case UTFEncoding.UTF_8:  decode(cast(char[])input, result); break;
        case UTFEncoding.UTF_16:
            assert(input.length % 2 == 0, "UTF-16 buffer size must be even");
            decode(cast(wchar[])input, result);
            break;
        case UTFEncoding.UTF_32:
            assert(input.length % 4 == 0,
                    "UTF-32 buffer size must be a multiple of 4");
            // No need to decode anything
            result.decoded = cast(dchar[])input;
            break;
    }

    if(result.errorMessage !is null) { return result; }

    // XXX This is risky. We rely on the assumption that the scanner only uses 
    // peek() to detect the end of the buffer. Should this cause any bugs,
    // revert.
    //
    // The buffer must be zero terminated for scanner to detect its end.
    // if(result.decoded.empty || result.decoded.back() != '\0')
    // {
    //     result.decoded ~= cast(dchar)'\0';
    // }

    return result;
}


/// Determine if all characters in an array are printable.
///
/// Params:  chars = Characters to check.
///
/// Returns: True if all the characters are printable, false otherwise.
bool printable(const dchar[] chars) @safe pure nothrow @nogc
{
    foreach(c; chars)
    {
        if(!((c == 0x09 || c == 0x0A || c == 0x0D || c == 0x85) ||
             (c >= 0x20 && c <= 0x7E) ||
             (c >= 0xA0 && c <= '\uD7FF') ||
             (c >= '\uE000' && c <= '\uFFFD')))
        {
            return false;
        }
    }
    return true;
}

// Determine the end of last UTF-8 or UTF-16 sequence in a raw buffer.
size_t endOfLastUTFSequence(C)(const C[] buffer)
    @safe pure nothrow @nogc
{
    // UTF-8 codepoint strides (0xFF are codepoints that can't start a sequence).
    static immutable ubyte[256] utf8Stride =
    [
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
        2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
        2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
        3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
        4,4,4,4,4,4,4,4,5,5,5,5,6,6,0xFF,0xFF,
    ];

    static if(is(C == char))
    {
        for(long end = buffer.length - 1; end >= 0; --end)
        {
            const stride = utf8Stride[buffer[cast(size_t)end]];
            if(stride != 0xFF)
            {
                // If stride goes beyond end of the buffer, return end.
                // Otherwise the last sequence ends at buffer.length, so we can
                // return that. (Unless there is an invalid code point, which is
                // caught at decoding)
                return (stride > buffer.length - end) ? cast(size_t)end : buffer.length;
            }
        }
        return 0;
    }
    else static if(is(C == wchar))
    {
        // TODO this is O(N), which is slow. Find out if we can somehow go
        // from the end backwards with UTF-16.
        size_t end = 0;
        while(end < buffer.length)
        {
            const s = stride(buffer, end);
            if(s + end > buffer.length) { break; }
            end += s;
        }
        return end;
    }
}

// Unittests.

import std.stream;
void testEndian(R)()
{
    writeln(typeid(R).toString() ~ ": endian unittest");
    void endian_test(ubyte[] data, Encoding encoding_expected, Endian endian_expected)
    {
        auto reader = new R(new MemoryStream(data));
        assert(reader.encoding == encoding_expected);
        assert(reader.endian_ == endian_expected);
    }
    ubyte[] little_endian_utf_16 = [0xFF, 0xFE, 0x7A, 0x00];
    ubyte[] big_endian_utf_16 = [0xFE, 0xFF, 0x00, 0x7A];
    endian_test(little_endian_utf_16, Encoding.UTF_16, Endian.littleEndian);
    endian_test(big_endian_utf_16, Encoding.UTF_16, Endian.bigEndian);
}

void testPeekPrefixForward(R)()
{
    writeln(typeid(R).toString() ~ ": peek/prefix/forward unittest");
    ubyte[] data = ByteOrderMarks[BOM.UTF8] ~ cast(ubyte[])"data";
    auto reader = new R(new MemoryStream(data));
    assert(reader.peek() == 'd');
    assert(reader.peek(1) == 'a');
    assert(reader.peek(2) == 't');
    assert(reader.peek(3) == 'a');
    assert(reader.peek(4) == '\0');
    assert(reader.prefix(4) == "data");
    // assert(reader.prefix(6) == "data\0");
    reader.forward(2);
    assert(reader.peek(1) == 'a');
    // assert(collectException(reader.peek(3)));
}

void testUTF(R)()
{
    writeln(typeid(R).toString() ~ ": UTF formats unittest");
    dchar[] data = cast(dchar[])"data";
    void utf_test(T)(T[] data, BOM bom)
    {
        ubyte[] bytes = ByteOrderMarks[bom] ~
                        (cast(ubyte*)data.ptr)[0 .. data.length * T.sizeof];
        auto reader = new R(new MemoryStream(bytes));
        assert(reader.peek() == 'd');
        assert(reader.peek(1) == 'a');
        assert(reader.peek(2) == 't');
        assert(reader.peek(3) == 'a');
    }
    utf_test!char(to!(char[])(data), BOM.UTF8);
    utf_test!wchar(to!(wchar[])(data), endian == Endian.bigEndian ? BOM.UTF16BE : BOM.UTF16LE);
    utf_test(data, endian == Endian.bigEndian ? BOM.UTF32BE : BOM.UTF32LE);
}

void test1Byte(R)()
{
    writeln(typeid(R).toString() ~ ": 1 byte file unittest");
    ubyte[] data = [97];

    auto reader = new R(new MemoryStream(data));
    assert(reader.peek() == 'a');
    assert(reader.peek(1) == '\0');
    // assert(collectException(reader.peek(2)));
}

unittest
{
    testEndian!Reader();
    testPeekPrefixForward!Reader();
    testUTF!Reader();
    test1Byte!Reader();
}