Thumbnails: pull full file + sips resize, max 3 concurrent ADB pulls
MediaStore content query is unreliable on Samsung. Switch to: 1. adb pull full file to tmp 2. sips --resampleWidth 240 to generate thumbnail 3. Cache in ~/.photophetch/thumbcache/<serial>/ 4. Semaphore(3) limits concurrent pulls — cells scrolled past are cancelled by Compose LaunchedEffect lifecycle automatically. First load per photo takes 2-3s. Subsequent views instant from cache.
This commit is contained in:
Kyle Bolen
@@ -1,5 +1,7 @@
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package com.bolenpad.photophetch.util
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import kotlinx.coroutines.sync.Semaphore
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import kotlinx.coroutines.sync.withPermit
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import org.slf4j.LoggerFactory
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import java.nio.file.Files
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import java.nio.file.Path
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@@ -8,28 +10,32 @@ import kotlin.io.path.createDirectories
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import kotlin.io.path.exists
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/**
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* Retrieves JPEG thumbnails from an Android device using the MediaStore
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* thumbnail database via `adb shell content query` + thumbnail URI pull.
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* Pulls and caches JPEG thumbnails from an Android device.
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*
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* Android pre-generates thumbnails at ~512px for every photo in the gallery.
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* These live in /sdcard/Android/data/com.android.providers.media/... or are
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* accessible via content://media/external/images/thumbnails.
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* Approach: pull the full file via `adb pull`, resize to 240px with macOS
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* `sips`, cache the thumbnail. Subsequent views are instant from cache.
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*
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* We use `adb shell content query` to find the thumbnail path for a given
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* media file, then `adb pull` to fetch just the thumbnail (~20-50KB vs 3-5MB
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* for the full file).
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* Concurrency: at most 3 simultaneous ADB pulls to avoid overwhelming the
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* connection. Cells that are scrolled past before their pull completes are
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* cancelled automatically by Compose's LaunchedEffect lifecycle.
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*
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* Cache location: ~/.photophetch/thumbcache/<serial>/<hash>.jpg
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* Cache: ~/.photophetch/thumbcache/<serial>/<hash>.jpg — persists across
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* sessions so re-opening the app is fast.
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*/
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object ThumbnailCache {
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private val log = LoggerFactory.getLogger(ThumbnailCache::class.java)
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private val cacheRoot: Path = Paths.get(System.getProperty("user.home"), ".photophetch", "thumbcache")
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private val tmpDir: Path = Paths.get(System.getProperty("java.io.tmpdir"), "photophetch-thumbs")
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// Max simultaneous ADB pulls
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private val semaphore = Semaphore(3)
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/**
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* Returns raw JPEG bytes for the thumbnail.
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* Returns null if unavailable (video, or MediaStore lookup failed).
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* Returns raw JPEG bytes for the thumbnail, pulling from device if not cached.
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* Suspend — respects coroutine cancellation (scrolling away cancels the pull).
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* Returns null for videos or on any error.
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*/
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fun get(
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suspend fun get(
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adbBin: String,
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serial: String,
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devicePath: String,
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@@ -40,70 +46,64 @@ object ThumbnailCache {
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val cacheDir = cacheRoot.resolve(serial)
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if (!cacheDir.exists()) cacheDir.createDirectories()
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if (!tmpDir.exists()) tmpDir.createDirectories()
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val cacheKey = (serial + devicePath).hashCode().toString(16)
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val cachePath = cacheDir.resolve("$cacheKey.jpg")
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// Return cached version immediately
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if (cachePath.exists() && cachePath.toFile().length() > 0) {
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return try { Files.readAllBytes(cachePath) } catch (_: Exception) { null }
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}
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// Acquire slot — waits if 3 pulls are already running
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return semaphore.withPermit {
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pullAndResize(adbBin, serial, devicePath, filename, ext, cachePath)
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}
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}
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private fun pullAndResize(
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adbBin: String,
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serial: String,
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devicePath: String,
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filename: String,
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ext: String,
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cachePath: Path,
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): ByteArray? {
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val tmpFile = tmpDir.resolve("${cachePath.fileName.toString().removeSuffix(".jpg")}.$ext")
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return try {
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// Step 1: Find the media _id for this file via MediaStore
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val mediaId = queryMediaId(adbBin, serial, devicePath) ?: return null
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// Step 2: Get the thumbnail path for this media_id
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val thumbPath = queryThumbnailPath(adbBin, serial, mediaId) ?: return null
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// Step 3: Pull just the thumbnail file (~20-50KB)
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val process = ProcessBuilder(adbBin, "-s", serial, "pull", thumbPath, cachePath.toString())
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// Pull full file
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val pull = ProcessBuilder(adbBin, "-s", serial, "pull", devicePath, tmpFile.toString())
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.redirectErrorStream(true)
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.start()
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process.inputStream.readBytes()
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process.waitFor()
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pull.inputStream.readBytes() // drain output
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pull.waitFor()
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if (!tmpFile.exists() || tmpFile.toFile().length() == 0L) return null
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// Resize to 240px wide thumbnail via sips (macOS built-in)
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val sips = ProcessBuilder(
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"sips",
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"--resampleWidth", "240",
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tmpFile.toString(),
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"--out", cachePath.toString()
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)
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.redirectErrorStream(true)
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.start()
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sips.inputStream.readBytes()
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sips.waitFor()
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if (cachePath.exists() && cachePath.toFile().length() > 0) {
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Files.readAllBytes(cachePath)
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} else null
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} catch (e: Exception) {
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log.debug("Thumbnail lookup failed for $filename: ${e.message}")
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log.debug("Thumbnail generation failed for $filename: ${e.message}")
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null
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} finally {
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tmpFile.toFile().delete()
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}
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}
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private fun queryMediaId(adbBin: String, serial: String, devicePath: String): String? {
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// Query MediaStore for the _id of the file at this path
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val output = runAdb(
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adbBin, serial,
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"shell", "content", "query",
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"--uri", "content://media/external/images/media",
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"--projection", "_id",
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"--where", "_data='$devicePath'"
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)
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// Output: "Row: 0 _id=12345"
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return Regex("_id=(\\d+)").find(output)?.groupValues?.getOrNull(1)
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}
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private fun queryThumbnailPath(adbBin: String, serial: String, mediaId: String): String? {
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val output = runAdb(
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adbBin, serial,
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"shell", "content", "query",
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"--uri", "content://media/external/images/thumbnails",
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"--projection", "_data",
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"--where", "image_id=$mediaId"
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)
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// Output: "Row: 0 _data=/sdcard/.thumbnails/12345.jpg"
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return Regex("_data=([^\\s]+)").find(output)?.groupValues?.getOrNull(1)
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}
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private fun runAdb(adbBin: String, serial: String, vararg args: String): String {
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val cmd = listOf(adbBin, "-s", serial) + args.toList()
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val process = ProcessBuilder(cmd).redirectErrorStream(true).start()
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val output = process.inputStream.bufferedReader().readText()
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process.waitFor()
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return output
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}
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fun clearForDevice(serial: String) {
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cacheRoot.resolve(serial).toFile().deleteRecursively()
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}
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