lib: read & validate the magic number from the picked source file before executing the import

examples/llama.android/app/src/main/java/com/example/llama/data/repo/ModelRepository.kt

@@ -2,6 +2,7 @@ package com.example.llama.data.repo
 
 import android.content.Context
 import android.llama.cpp.gguf.GgufMetadataReader
+import android.llama.cpp.gguf.InvalidFileFormatException
 import android.net.Uri
 import android.os.StatFs
 import android.util.Log
@@ -171,9 +172,15 @@ class ModelRepositoryImpl @Inject constructor(
             throw IllegalStateException("Another import is already in progress!")
         }
 
+        // Check file info
         val fileInfo = localFileDataSource.getFileInfo(uri)
         val fileSize = size ?: fileInfo?.size ?: throw FileNotFoundException("File size N/A")
         val fileName = name ?: fileInfo?.name ?: throw FileNotFoundException("File name N/A")
+        if (!ggufMetadataReader.ensureSourceFileFormat(context, uri)) {
+            throw InvalidFileFormatException()
+        }
+
+        // Check for enough storage
         if (!hasEnoughSpaceForImport(fileSize)) {
             throw InsufficientStorageException(
                 "Not enough storage space! " +
@@ -182,7 +189,6 @@ class ModelRepositoryImpl @Inject constructor(
             )
         }
         val modelFile = File(modelsDir, fileName)
-
         importJob = coroutineContext[Job]
         currentModelFile = modelFile
 

examples/llama.android/app/src/main/java/com/example/llama/viewmodel/ModelsManagementViewModel.kt

@@ -6,6 +6,7 @@ import android.content.Context
 import android.content.Context.RECEIVER_EXPORTED
 import android.content.Intent
 import android.content.IntentFilter
+import android.llama.cpp.gguf.InvalidFileFormatException
 import android.net.Uri
 import android.util.Log
 import androidx.lifecycle.ViewModel
@@ -208,13 +209,18 @@ class ModelsManagementViewModel @Inject constructor(
                 _managementState.value = Importation.Importing(progress, fileName, fileSize)
             }
             _managementState.value = Importation.Success(model)
+        } catch (_: InvalidFileFormatException) {
+            _managementState.value = Importation.Error(
+                message = "Not a valid GGUF model!",
+            )
         } catch (e: InsufficientStorageException) {
             _managementState.value = Importation.Error(
-                message = e.message ?: "Insufficient storage space to import $uri",
+                message = e.message ?: "Insufficient storage space to import $fileName",
             )
         } catch (e: Exception) {
+            Log.e(TAG, "Unknown exception importing $fileName", e)
             _managementState.value = Importation.Error(
-                message = e.message ?: "Unknown error importing $uri",
+                message = e.message ?: "Unknown error importing $fileName",
             )
         }
     }
@@ -376,6 +382,7 @@ sealed class ModelManagementState {
         data class Confirming(val uri: Uri, val fileName: String, val fileSize: Long) : Importation()
         data class Importing(val progress: Float = 0f, val fileName: String, val fileSize: Long, val isCancelling: Boolean = false) : Importation()
         data class Success(val model: ModelInfo) : Importation()
+        // TODO-han.yin: Add an optional explanation URL for more info!
         data class Error(val message: String) : Importation()
     }
 

examples/llama.android/llama/src/main/java/android/llama/cpp/gguf/GgufMetadataReader.kt

@@ -1,6 +1,8 @@
 package android.llama.cpp.gguf
 
+import android.content.Context
 import android.llama.cpp.internal.gguf.GgufMetadataReaderImpl
+import android.net.Uri
 import java.io.IOException
 
 /**
@@ -8,13 +10,23 @@ import java.io.IOException
  * Use `GgufMetadataReader.create()` to get an instance.
  */
 interface GgufMetadataReader {
+    /**
+     * Reads the magic number from the specified file path.
+     *
+     * @param context Context for obtaining ContentResolver
+     * @param uri Uri to the GGUF file provided by ContentProvider
+     * @return true if file is valid GGUF, otherwise false
+     * @throws InvalidFileFormatException if file format is invalid
+     */
+    suspend fun ensureSourceFileFormat(context: Context, uri: Uri): Boolean
+
     /**
      * Reads and parses GGUF metadata from the specified file path.
      *
      * @param path The absolute path to the GGUF file
      * @return Structured metadata extracted from the file
-     * @throws IOException if file cannot be read
+     * @throws IOException if file is damaged or cannot be read
-     * @throws IllegalArgumentException if file format is invalid
+     * @throws InvalidFileFormatException if file format is invalid
      */
     suspend fun readStructuredMetadata(path: String): GgufMetadata
 
@@ -50,3 +62,5 @@ interface GgufMetadataReader {
         )
     }
 }
+
+class InvalidFileFormatException : IOException()

examples/llama.android/llama/src/main/java/android/llama/cpp/internal/gguf/GgufMetadataReaderImpl.kt

@@ -1,7 +1,10 @@
 package android.llama.cpp.internal.gguf
 
+import android.content.Context
 import android.llama.cpp.gguf.GgufMetadata
 import android.llama.cpp.gguf.GgufMetadataReader
+import android.llama.cpp.gguf.InvalidFileFormatException
+import android.net.Uri
 import java.io.File
 import java.io.IOException
 import java.io.InputStream
@@ -25,7 +28,7 @@ internal class GgufMetadataReaderImpl(
         UINT32(4), INT32(5), FLOAT32(6), BOOL(7),
         STRING(8), ARRAY(9), UINT64(10), INT64(11), FLOAT64(12);
         companion object {
-            private val codeMap = values().associateBy(MetadataType::code)
+            private val codeMap = entries.associateBy(MetadataType::code)
             fun fromCode(code: Int): MetadataType = codeMap[code]
                 ?: throw IOException("Unknown metadata value type code: $code")
         }
@@ -65,6 +68,23 @@ internal class GgufMetadataReaderImpl(
         is MetadataValue.ArrayVal  -> elements.map { it.toPrimitive() }
     }
 
+    /**
+     * Reads the magic number from the specified file path.
+     *
+     * @param context Context for obtaining ContentResolver
+     * @param uri Uri to the GGUF file provided by ContentProvider
+     * @return true if file is valid GGUF, otherwise false
+     */
+    override suspend fun ensureSourceFileFormat(context: Context, uri: Uri): Boolean =
+        context.contentResolver.openInputStream(uri)?.buffered()?.use { ensureMagic(it) } == true
+
+    /** Reads the 4‑byte magic; throws if magic ≠ "GGUF". */
+    private fun ensureMagic(input: InputStream): Boolean {
+        val magic = ByteArray(4)
+        if (input.read(magic) != 4) throw IOException("Not a valid file!")
+        return magic.contentEquals(byteArrayOf(0x47, 0x47, 0x55, 0x46)) // "GGUF"
+    }
+
     /**
      * High‑level entry point: parses a `.gguf` file on disk and returns the fully
      * populated [GgufMetadata] tree.
@@ -104,10 +124,7 @@ internal class GgufMetadataReaderImpl(
 
     /** Reads the 4‑byte magic + 4‑byte version; throws if magic ≠ "GGUF". */
     private fun ensureMagicAndVersion(input: InputStream): GgufMetadata.GgufVersion {
-        val magic = ByteArray(4)
+        if (!ensureMagic(input)) throw InvalidFileFormatException()
-        if (input.read(magic) != 4) throw IOException("File too short (no magic)")
-        if (!magic.contentEquals(byteArrayOf(0x47, 0x47, 0x55, 0x46)))  // "GGUF"
-            throw IOException("Not a GGUF file (bad magic)")
         return GgufMetadata.GgufVersion.fromCode(readLEUInt32(input))
     }