Add SvgDecoder class.

app/src/main/java/chat/rocket/android/app/utils/SvgDecoder.kt

+package chat.rocket.android.app.utils
+
+import android.graphics.Rect
+import android.graphics.drawable.Drawable
+import android.graphics.drawable.PictureDrawable
+import android.support.annotation.Nullable
+import com.caverock.androidsvg.SVG
+import com.caverock.androidsvg.SVGParseException
+import com.facebook.imageformat.ImageFormat
+import com.facebook.imageformat.ImageFormatCheckerUtils
+import com.facebook.imagepipeline.common.ImageDecodeOptions
+import com.facebook.imagepipeline.decoder.ImageDecoder
+import com.facebook.imagepipeline.drawable.DrawableFactory
+import com.facebook.imagepipeline.image.CloseableImage
+import com.facebook.imagepipeline.image.EncodedImage
+import com.facebook.imagepipeline.image.QualityInfo
+
+/**
+ * SVG example that defines all classes required to decode and render SVG images.
+ *
+ * @see {https://github.com/facebook/fresco/blob/master/samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/imageformat/svg/SvgDecoderExample.java}
+ */
+object SvgDecoder {
+    val svgFormat = ImageFormat("SVG_FORMAT", "svg")
+    // We do not include the closing ">" since there can be additional information.
+    private val headerTag = "<?xml"
+    private val possibleHeaderTags = arrayOf(ImageFormatCheckerUtils.asciiBytes("<svg"))
+
+    /**
+     * Custom SVG format checker that verifies that the header of the file corresponds to our [SvgDecoder.headerTag] or [SvgDecoder.possibleHeaderTags].
+     */
+    class SvgFormatChecker : ImageFormat.FormatChecker {
+        private val header = ImageFormatCheckerUtils.asciiBytes(headerTag)
+
+        override fun getHeaderSize(): Int {
+            return header.size
+        }
+
+        @Nullable override fun determineFormat(headerBytes: ByteArray, headerSize: Int): ImageFormat? {
+            if (headerSize > getHeaderSize()) {
+                if (ImageFormatCheckerUtils.startsWithPattern(headerBytes, header)) {
+                    return svgFormat
+                }
+
+                if (possibleHeaderTags.any { ImageFormatCheckerUtils.startsWithPattern(headerBytes, it) && ImageFormatCheckerUtils.indexOfPattern(headerBytes, headerBytes.size, header, header.size) > -1 }) {
+                    return svgFormat
+                }
+            }
+            return null
+        }
+    }
+
+    /**
+     * Custom closeable SVG image that holds a single SVG.
+     */
+    class CloseableSvgImage(val svg: SVG) : CloseableImage() {
+        private var isClose = false
+
+        override fun close() {
+            isClose = true
+        }
+
+        override fun getSizeInBytes(): Int = 0
+
+        override fun isClosed(): Boolean = isClose
+
+        override fun getWidth(): Int = 0
+
+        override fun getHeight(): Int = 0
+    }
+
+    /**
+     * Decodes a [SvgDecoder.svgFormat] image.
+     */
+    class Decoder : ImageDecoder {
+
+        @Nullable override fun decode(encodedImage: EncodedImage, length: Int, qualityInfo: QualityInfo, options: ImageDecodeOptions): CloseableImage? {
+            try {
+                val svg = SVG.getFromInputStream(encodedImage.inputStream)
+                return CloseableSvgImage(svg)
+            } catch (e: SVGParseException) {
+                e.printStackTrace()
+            }
+            // Return nothing if an error occurred
+            return null
+        }
+    }
+
+    /**
+     * SVG drawable factory that creates [PictureDrawable]s for SVG images.
+     */
+    class SvgDrawableFactory : DrawableFactory {
+
+        override fun supportsImageType(image: CloseableImage): Boolean {
+            return image is CloseableSvgImage
+        }
+
+        @Nullable override fun createDrawable(image: CloseableImage): Drawable? {
+            return SvgPictureDrawable((image as CloseableSvgImage).svg)
+        }
+    }
+
+    class SvgPictureDrawable(private val svg: SVG) : PictureDrawable(null) {
+
+        override fun onBoundsChange(bounds: Rect) {
+            super.onBoundsChange(bounds)
+            picture = svg.renderToPicture(bounds.width(), bounds.height())
+        }
+    }
+}
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