refactor fonthost_tables into wrapper (fonthost) and impl (fontstream)

git-svn-id: http://skia.googlecode.com/svn/trunk@7958 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 169 insertions, 0 deletions

diff --git a/src/core/SkFontStream.cpp b/src/core/SkFontStream.cpp
new file mode 100644
index 0000000000..0b37fb1c53
--- /dev/null
+++ b/src/core/SkFontStream.cpp
@@ -0,0 +1,169 @@
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkEndian.h"
+#include "SkFontStream.h"
+#include "SkStream.h"
+
+struct SkSFNTHeader {
+    uint32_t    fVersion;
+    uint16_t    fNumTables;
+    uint16_t    fSearchRange;
+    uint16_t    fEntrySelector;
+    uint16_t    fRangeShift;
+};
+
+struct SkTTCFHeader {
+    uint32_t    fTag;
+    uint32_t    fVersion;
+    uint32_t    fNumOffsets;
+    uint32_t    fOffset0;   // the first of N (fNumOffsets)
+};
+
+union SkSharedTTHeader {
+    SkSFNTHeader    fSingle;
+    SkTTCFHeader    fCollection;
+};
+
+struct SkSFNTDirEntry {
+    uint32_t    fTag;
+    uint32_t    fChecksum;
+    uint32_t    fOffset;
+    uint32_t    fLength;
+};
+
+/** Return the number of tables, or if this is a TTC (collection), return the
+    number of tables in the first element of the collection. In either case,
+    if offsetToDir is not-null, set it to the offset to the beginning of the
+    table headers (SkSFNTDirEntry), relative to the start of the stream.
+
+    On an error, return 0 for number of tables, and ignore offsetToDir
+ */
+static int count_tables(SkStream* stream, size_t* offsetToDir = NULL) {
+    SkSharedTTHeader shared;
+    if (stream->read(&shared, sizeof(shared)) != sizeof(shared)) {
+        return 0;
+    }
+
+    // by default, SkSFNTHeader is at the start of the stream
+    size_t offset = 0;
+
+    // if we're really a collection, the first 4-bytes will be 'ttcf'
+    uint32_t tag = SkEndian_SwapBE32(shared.fCollection.fTag);
+    if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
+        if (shared.fCollection.fNumOffsets == 0) {
+            return 0;
+        }
+        // this is the offset to the first local SkSFNTHeader
+        offset = SkEndian_SwapBE32(shared.fCollection.fOffset0);
+        stream->rewind();
+        if (stream->skip(offset) != offset) {
+            return 0;
+        }
+        if (stream->read(&shared, sizeof(shared)) != sizeof(shared)) {
+            return 0;
+        }
+    }
+
+    if (offsetToDir) {
+        // add the size of the header, so we will point to the DirEntries
+        *offsetToDir = offset + sizeof(SkSFNTHeader);
+    }
+    return SkEndian_SwapBE16(shared.fSingle.fNumTables);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+struct SfntHeader {
+    SfntHeader() : fCount(0), fDir(NULL) {}
+    ~SfntHeader() { sk_free(fDir); }
+
+    /** If it returns true, then fCount and fDir are properly initialized.
+        Note: fDir will point to the raw array of SkSFNTDirEntry values,
+        meaning they will still be in the file's native endianness (BE).
+
+        fDir will be automatically freed when this object is destroyed
+     */
+    bool init(SkStream* stream) {
+        size_t offsetToDir;
+        fCount = count_tables(stream, &offsetToDir);
+        if (0 == fCount) {
+            return false;
+        }
+
+        stream->rewind();
+        if (stream->skip(offsetToDir) != offsetToDir) {
+            return false;
+        }
+
+        size_t size = fCount * sizeof(SkSFNTDirEntry);
+        fDir = reinterpret_cast<SkSFNTDirEntry*>(sk_malloc_throw(size));
+        return stream->read(fDir, size) == size;
+    }
+
+    int             fCount;
+    SkSFNTDirEntry* fDir;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+int SkFontStream::GetTableTags(SkStream* stream, SkFontTableTag tags[]) {
+    SfntHeader  header;
+    if (!header.init(stream)) {
+        return 0;
+    }
+
+    if (tags) {
+        for (int i = 0; i < header.fCount; i++) {
+            tags[i] = SkEndian_SwapBE32(header.fDir[i].fTag);
+        }
+    }
+    return header.fCount;
+}
+
+size_t SkFontStream::GetTableData(SkStream* stream, SkFontTableTag tag,
+                                  size_t offset, size_t length, void* data) {
+    SfntHeader  header;
+    if (!header.init(stream)) {
+        return 0;
+    }
+
+    for (int i = 0; i < header.fCount; i++) {
+        if (SkEndian_SwapBE32(header.fDir[i].fTag) == tag) {
+            size_t realOffset = SkEndian_SwapBE32(header.fDir[i].fOffset);
+            size_t realLength = SkEndian_SwapBE32(header.fDir[i].fLength);
+            // now sanity check the caller's offset/length
+            if (offset >= realLength) {
+                return 0;
+            }
+            // if the caller is trusting the length from the file, then a
+            // hostile file might choose a value which would overflow offset +
+            // length.
+            if (offset + length < offset) {
+                return 0;
+            }
+            if (length > realLength - offset) {
+                length = realLength - offset;
+            }
+            if (data) {
+                // skip the stream to the part of the table we want to copy from
+                stream->rewind();
+                size_t bytesToSkip = realOffset + offset;
+                if (stream->skip(bytesToSkip) != bytesToSkip) {
+                    return 0;
+                }
+                if (stream->read(data, length) != length) {
+                    return 0;
+                }
+            }
+            return length;
+        }
+    }
+    return 0;
+}
+
+