releasetools: Add unittest for common.GetSparseImage().

Add construct_sparse_image() to test_utils.py, which is a util function
to create sparse images. The new tests also partially cover the recent
changes that add 'incomplete' and 'uses_shard_blocks' tags.

Test: python -m unittest test_common
Change-Id: Ia15f5c4ad12423691216ebbad2c28f95c8427d7e

tools/releasetools/test_utils.py

@@ -18,7 +18,11 @@
 Utils for running unittests.
 """
 
+import os
 import os.path
+import struct
+
+import common
 
 
 def get_testdata_dir():
@@ -26,3 +30,67 @@ def get_testdata_dir():
   # The script dir is the one we want, which could be different from pwd.
   current_dir = os.path.dirname(os.path.realpath(__file__))
   return os.path.join(current_dir, 'testdata')
+
+
+def construct_sparse_image(chunks):
+  """Returns a sparse image file constructed from the given chunks.
+
+  From system/core/libsparse/sparse_format.h.
+  typedef struct sparse_header {
+    __le32 magic;  // 0xed26ff3a
+    __le16 major_version;  // (0x1) - reject images with higher major versions
+    __le16 minor_version;  // (0x0) - allow images with higer minor versions
+    __le16 file_hdr_sz;  // 28 bytes for first revision of the file format
+    __le16 chunk_hdr_sz;  // 12 bytes for first revision of the file format
+    __le32 blk_sz;  // block size in bytes, must be a multiple of 4 (4096)
+    __le32 total_blks;  // total blocks in the non-sparse output image
+    __le32 total_chunks;  // total chunks in the sparse input image
+    __le32 image_checksum;  // CRC32 checksum of the original data, counting
+                            // "don't care" as 0. Standard 802.3 polynomial,
+                            // use a Public Domain table implementation
+  } sparse_header_t;
+
+  typedef struct chunk_header {
+    __le16 chunk_type;  // 0xCAC1 -> raw; 0xCAC2 -> fill;
+                        // 0xCAC3 -> don't care
+    __le16 reserved1;
+    __le32 chunk_sz;  // in blocks in output image
+    __le32 total_sz;  // in bytes of chunk input file including chunk header
+                      // and data
+  } chunk_header_t;
+
+  Args:
+    chunks: A list of chunks to be written. Each entry should be a tuple of
+        (chunk_type, block_number).
+
+  Returns:
+    Filename of the created sparse image.
+  """
+  SPARSE_HEADER_MAGIC = 0xED26FF3A
+  SPARSE_HEADER_FORMAT = "<I4H4I"
+  CHUNK_HEADER_FORMAT = "<2H2I"
+
+  sparse_image = common.MakeTempFile(prefix='sparse-', suffix='.img')
+  with open(sparse_image, 'wb') as fp:
+    fp.write(struct.pack(
+        SPARSE_HEADER_FORMAT, SPARSE_HEADER_MAGIC, 1, 0, 28, 12, 4096,
+        sum(chunk[1] for chunk in chunks),
+        len(chunks), 0))
+
+    for chunk in chunks:
+      data_size = 0
+      if chunk[0] == 0xCAC1:
+        data_size = 4096 * chunk[1]
+      elif chunk[0] == 0xCAC2:
+        data_size = 4
+      elif chunk[0] == 0xCAC3:
+        pass
+      else:
+        assert False, "Unsupported chunk type: {}".format(chunk[0])
+
+      fp.write(struct.pack(
+          CHUNK_HEADER_FORMAT, chunk[0], 0, chunk[1], data_size + 12))
+      if data_size != 0:
+        fp.write(os.urandom(data_size))
+
+  return sparse_image