Support automatic SVG detection using the source contents. (#654)

coil-svg/README.md

@@ -16,4 +16,4 @@ val imageLoader = ImageLoader.Builder(context)
     .build()
 ```
 
-The `ImageLoader` will automatically detect and decode any SVGs if the request's MIME type is `image/svg+xml`. The MIME type is inferred using the HTTP `content-type` header, a URI's suffix, or a file's extension. If you need to force a specific request to use the `SvgDecoder`, you can [set the `Fetcher` explicitly](../api/coil-base/coil.request/-image-request/-builder/fetcher/) for the request.
+The `ImageLoader` will automatically detect and decode any SVGs. Coil detects SVGs by looking for the `<svg ` marker in the first 1 KB of the file, which should cover most cases. If the SVG is not automatically detected, you can [set the `Decoder` explicitly](../api/coil-base/coil.request/-image-request/-builder/decoder/) to `SvgDecoder` for the request.

coil-svg/src/androidTest/java/coil/decode/SvgDecoderTest.kt

@@ -13,6 +13,7 @@ import okio.buffer
 import okio.source
 import org.junit.Before
 import org.junit.Test
+import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 class SvgDecoderTest {
@@ -28,6 +29,30 @@ class SvgDecoderTest {
         decoder = SvgDecoder(context)
     }
 
+    @Test
+    fun handlesMimeType() {
+        var source = context.assets.open("coil_logo.svg").source().buffer()
+        assertTrue(decoder.handles(source, "image/svg+xml"))
+
+        source = context.assets.open("coil_logo_250.png").source().buffer()
+        assertFalse(decoder.handles(source, "image/png"))
+    }
+
+    @Test
+    fun handlesSource() {
+        var source = context.assets.open("coil_logo.svg").source().buffer()
+        assertTrue(decoder.handles(source, null))
+
+        source = context.assets.open("coil_logo_250.png").source().buffer()
+        assertFalse(decoder.handles(source, null))
+
+        source = context.assets.open("instacart_logo.svg").source().buffer()
+        assertTrue(decoder.handles(source, null))
+
+        source = context.assets.open("instacart_logo_326.png").source().buffer()
+        assertFalse(decoder.handles(source, null))
+    }
+
     @Test
     fun basic() {
         val source = context.assets.open("coil_logo.svg").source().buffer()

coil-svg/src/main/java/coil/decode/SvgDecoder.kt

@@ -11,16 +11,25 @@ import coil.bitmap.BitmapPool
 import coil.size.OriginalSize
 import coil.size.PixelSize
 import coil.size.Size
+import coil.util.indexOf
 import com.caverock.androidsvg.SVG
 import okio.BufferedSource
+import okio.ByteString.Companion.encodeUtf8
 import okio.buffer
 
 /**
  * A [Decoder] that uses [AndroidSVG](https://bigbadaboom.github.io/androidsvg/) to decode SVG files.
  */
 class SvgDecoder(private val context: Context) : Decoder {
 
-    override fun handles(source: BufferedSource, mimeType: String?) = mimeType == MIME_TYPE_SVG
+    override fun handles(source: BufferedSource, mimeType: String?): Boolean {
+        return mimeType == MIME_TYPE_SVG || containsSvgTag(source)
+    }
+
+    private fun containsSvgTag(source: BufferedSource): Boolean {
+        return source.rangeEquals(0, LEFT_ANGLE_BRACKET) &&
+            source.indexOf(SVG_TAG, 0, SVG_TAG_SEARCH_THRESHOLD_BYTES) != -1L
+    }
 
     override suspend fun decode(
         pool: BitmapPool,
@@ -87,5 +96,8 @@ class SvgDecoder(private val context: Context) : Decoder {
     private companion object {
         private const val MIME_TYPE_SVG = "image/svg+xml"
         private const val DEFAULT_SIZE = 512
+        private const val SVG_TAG_SEARCH_THRESHOLD_BYTES = 1024L
+        private val SVG_TAG = "<svg ".encodeUtf8()
+        private val LEFT_ANGLE_BRACKET = "<".encodeUtf8()
     }
 }

coil-svg/src/main/java/coil/util/Extensions.kt

@@ -0,0 +1,21 @@
+@file:JvmName("-SvgExtensions")
+
+package coil.util
+
+import okio.BufferedSource
+import okio.ByteString
+
+internal fun BufferedSource.indexOf(bytes: ByteString, fromIndex: Long, toIndex: Long): Long {
+    require(bytes.size > 0) { "bytes is empty" }
+
+    val firstByte = bytes[0]
+    var currentIndex = fromIndex
+    while (currentIndex < toIndex) {
+        currentIndex = indexOf(firstByte, currentIndex)
+        if (currentIndex == -1L || rangeEquals(currentIndex, bytes)) {
+            return currentIndex
+        }
+        currentIndex++
+    }
+    return -1
+}