Better offline support in AWS implementation

s3buildcache/src/main/kotlin/androidx/build/gradle/s3buildcache/S3BuildCacheService.kt

@@ -69,6 +69,7 @@ class S3BuildCacheService(
     }
 
     override fun store(key: BuildCacheKey, writer: BuildCacheEntryWriter) {
+        if (writer.size == 0L) return // do not store empty entries into the cache
         logger.info("Storing ${key.blobKey()}")
         val cacheKey = key.blobKey()
         val output = ByteArrayOutputStream()

s3buildcache/src/main/kotlin/androidx/build/gradle/s3buildcache/S3StorageService.kt

@@ -100,9 +100,13 @@ class S3StorageService(
     }
 
     override fun validateConfiguration() {
-        val buckets = client.listBuckets().buckets()
-        if (buckets.none { bucket -> bucket.name() == bucketName }) {
-            throw Exception("Bucket $bucketName under project $region cannot be found or it is not accessible using the provided credentials")
+        try {
+            val buckets = client.listBuckets().buckets()
+            if (buckets.none { bucket -> bucket.name() == bucketName }) {
+                throw Exception("Bucket $bucketName under project $region cannot be found or is not accessible using the provided credentials")
+            }
+        } catch (e: Exception) {
+            logger.warn("Couldn't validate S3 client config: ${e.message}")
         }
     }
 
@@ -127,6 +131,7 @@ class S3StorageService(
             return try {
                 val inputStream = client.getObject(request)
                 val blob = inputStream.response() ?: return null
+                if (blob.contentLength() == 0L) return null // return empty entries as a cache miss
                 if (blob.contentLength() > sizeThreshold) {
                     val path = FileHandleInputStream.create()
                     val outputStream = path.outputStream()
@@ -162,7 +167,12 @@ class S3StorageService(
         }
 
         private fun delete(client: S3Client, request: DeleteObjectRequest): Boolean {
-            return client.deleteObject(request).deleteMarker()
+            return try {
+                client.deleteObject(request).deleteMarker()
+            } catch (e: Exception) {
+                logger.debug("Unable to delete $request", e)
+                false
+            }
         }
     }
 }