Added a self-contained module to handle endianness fixing.

source/dyaml/tinyendian.d

@@ -0,0 +1,172 @@
+//          Copyright Ferdinand Majerech 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 tinyendian;
+
+
+import core.stdc.string;
+
+import std.algorithm;
+import std.system;
+import std.utf;
+
+// TODO tinyendian should be its own DUB package
+
+/// Unicode UTF encodings.
+enum UTFEncoding : ubyte
+{
+    UTF_8,
+    UTF_16,
+    UTF_32
+}
+
+@system pure nothrow @nogc:
+
+/// Swap byte order of items in an array in place.
+///
+/// Params:
+///
+/// T     = Item type. Must be either 2 or 4 bytes long.
+/// array = Buffer with values to fix byte order of.
+void swapByteOrder(T)(T[] array)
+    if([2, 4].canFind(T.sizeof))
+{
+    import core.bitop;
+    // Swap the byte order of all read characters.
+    foreach(ref item; array)
+    {
+        static if(T.sizeof == 2)
+        {
+            swap(*cast(ubyte*)&item, *(cast(ubyte*)&item + 1));
+        }
+        else static if(T.sizeof == 4)
+        {
+            item = bswap(cast(uint)item);
+        }
+        else static assert(false, "Unsupported T: " ~ T.stringof);
+    }
+}
+
+/// Convert byte order of an array encoded in UTF(8/16/32) to system endianness in
+/// place.
+///
+/// Uses the UTF byte-order-mark (BOM) to determine UTF encoding. If there is no BOM
+/// at the beginning of array, UTF-8 is assumed (this is compatible with ASCII). The
+/// BOM, if any, will be removed from the buffer.
+///
+/// If the encoding is determined to be UTF-16 or UTF-32 and there aren't enough bytes
+/// for the last code unit (i.e. if array.length is odd for UTF-16 or not divisible by
+/// 4 for UTF-32), the extra bytes (1 for UTF-16, 1-3 for UTF-32) are stripped.
+///
+/// Note that this function does $(B not) check if the array is a valid UTF string. It
+/// only works with the BOM and 1,2 or 4-byte items.
+///
+/// Params:
+///
+/// array = The array with UTF-data.
+///
+/// Returns:
+///
+/// A struct with the following members:
+///
+/// $(D ubyte[] array)            A slice of the input array containing data in correct
+///                               byte order, without BOM and in case of UTF-16/UTF-32,
+///                               without stripped bytes, if any.
+/// $(D UTFEncoding encoding)     Encoding of the result (UTF-8, UTF-16 or UTF-32)
+/// $(D std.system.Endian endian) Endianness of the original array.
+/// $(D uint bytesStripped)       Number of bytes stripped from a UTF-16/UTF-32 array,
+///                               if any. This is non-zero only if array.length was not
+///                               divisible by 2 or 4 for UTF-16 and UTF-32,
+///                               respectively.
+///
+/// Complexity: (BIGOH array.length)
+auto fixUTFByteOrder(ubyte[] array)
+{
+    // Enumerates UTF BOMs, matching indices to byteOrderMarks/bomEndian.
+    enum BOM: ubyte
+    {
+        UTF_8     = 0,
+        UTF_16_LE = 1,
+        UTF_16_BE = 2,
+        UTF_32_LE = 3,
+        UTF_32_BE = 4,
+        None      = ubyte.max
+    }
+
+    // From std.stream
+    static immutable ubyte[][5] byteOrderMarks = [ [0xEF, 0xBB, 0xBF],
+                                                   [0xFF, 0xFE],
+                                                   [0xFE, 0xFF],
+                                                   [0xFF, 0xFE, 0x00, 0x00],
+                                                   [0x00, 0x00, 0xFE, 0xFF] ];
+
+    // From std.stream
+    static immutable Endian[5] bomEndian = [ std.system.endian,
+                                             Endian.littleEndian,
+                                             Endian.bigEndian,
+                                             Endian.littleEndian, 
+                                             Endian.bigEndian ];
+
+    // Documented in function ddoc.
+    struct Result
+    {
+        ubyte[] array;
+        UTFEncoding encoding;
+        Endian endian;
+        uint bytesStripped = 0;
+    }
+    Result result;
+
+    // Detect BOM, if any, in the bytes we've read. -1 means no BOM.
+    // Need the last match: First 2 bytes of UTF-32LE BOM match the UTF-16LE BOM. If we
+    // used the first match, UTF-16LE would be detected when we have a UTF-32LE BOM.
+    BOM bomId = BOM.None;
+    foreach(i, bom; byteOrderMarks) if(array.startsWith(bom))
+    {
+        bomId = cast(BOM)i;
+    }
+
+    result.endian = (bomId != BOM.None) ? bomEndian[bomId] : Endian.init;
+
+    // Start of UTF data (after BOM, if any)
+    size_t start = 0;
+    // If we've read more than just the BOM, put the rest into the array.
+    with(BOM) final switch(bomId)
+    {
+        case None: result.encoding = UTFEncoding.UTF_8; break;
+        case UTF_8:
+            start = 3;
+            result.encoding = UTFEncoding.UTF_8;
+            break;
+        case UTF_16_LE, UTF_16_BE:
+            result.bytesStripped = array.length % 2;
+            start = 2;
+            result.encoding = UTFEncoding.UTF_16;
+            break;
+        case UTF_32_LE, UTF_32_BE:
+            result.bytesStripped = array.length % 4;
+            start = 4;
+            result.encoding = UTFEncoding.UTF_32;
+            break;
+    }
+
+    array = array[0 .. $ - result.bytesStripped];
+    // If there's a BOM, we need to move data back to ensure it starts at array[0]
+    if(start != 0)
+    {
+        core.stdc.string.memmove(array.ptr, array.ptr + start, array.length - start);
+        array = array[0 .. $ - start];
+    }
+
+    // We enforce above that array.length is divisible by 2/4 for UTF-16/32
+    if(std.system.endian != result.endian)
+    {
+        if(result.encoding == UTFEncoding.UTF_16)      { swapByteOrder(cast(wchar[])array); }
+        else if(result.encoding == UTFEncoding.UTF_32) { swapByteOrder(cast(dchar[])array); }
+    }
+
+    result.array = array;
+    return result;
+}