libbrillo: Blob combining utility

Add a function that concatenates given Blob's.

This provides analogous functionality of SecureBlob::Combine()
to Blob.

BUG=chromium:728047
TEST=new unit test (BlobTest.CombineBlobs)

Change-Id: I33218bd81a49a265d021e7afdcf438b7fc70921d
Reviewed-on: https://chromium-review.googlesource.com/1089338
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>

3 files changed, 30 insertions, 0 deletions

diff --git a/brillo/secure_blob.cc b/brillo/secure_blob.cc
index 70c6f6e..4294b14 100644
--- a/brillo/secure_blob.cc
+++ b/brillo/secure_blob.cc
@@ -18,6 +18,17 @@ Blob BlobFromString(const std::string& bytes) {
   return Blob(bytes.begin(), bytes.end());
 }
 
+Blob CombineBlobs(const std::initializer_list<Blob>& blobs) {
+  size_t total_size = 0;
+  for (const auto& blob : blobs)
+    total_size += blob.size();
+  Blob concatenation;
+  concatenation.reserve(total_size);
+  for (const auto& blob : blobs)
+    concatenation.insert(concatenation.end(), blob.begin(), blob.end());
+  return concatenation;
+}
+
 SecureBlob::SecureBlob(const Blob& blob)
     : SecureBlob(blob.begin(), blob.end()) {}
 
diff --git a/brillo/secure_blob.h b/brillo/secure_blob.h
index 41a5cc6..d2fe9c7 100644
--- a/brillo/secure_blob.h
+++ b/brillo/secure_blob.h
@@ -5,6 +5,7 @@
 #ifndef LIBBRILLO_BRILLO_SECURE_BLOB_H_
 #define LIBBRILLO_BRILLO_SECURE_BLOB_H_
 
+#include <initializer_list>
 #include <string>
 #include <vector>
 
@@ -20,6 +21,9 @@ using Blob = std::vector<uint8_t>;
 BRILLO_EXPORT std::string BlobToString(const Blob& blob);
 BRILLO_EXPORT Blob BlobFromString(const std::string& bytes);
 
+// Returns a concatenation of given Blobs.
+BRILLO_EXPORT Blob CombineBlobs(const std::initializer_list<Blob>& blobs);
+
 // SecureBlob erases the contents on destruction.  It does not guarantee erasure
 // on resize, assign, etc.
 class BRILLO_EXPORT SecureBlob : public Blob {
diff --git a/brillo/secure_blob_unittest.cc b/brillo/secure_blob_unittest.cc
index b1c2d94..9fcba85 100644
--- a/brillo/secure_blob_unittest.cc
+++ b/brillo/secure_blob_unittest.cc
@@ -30,6 +30,21 @@ TEST(BlobTest, StringConversions) {
   EXPECT_EQ(blob, obtained_blob);
 }
 
+// Tests CombineBlobs().
+TEST(BlobTest, CombineBlobs) {
+  const Blob kEmpty;
+  const Blob kBlob1 = {1};
+  const Blob kBlob2 = {2};
+  const Blob kBlob3 = {3};
+  const Blob kBlob12 = {1, 2};
+  const Blob kBlob123 = {1, 2, 3};
+  EXPECT_EQ(kBlob123, CombineBlobs({kBlob12, kBlob3}));
+  EXPECT_EQ(kBlob123, CombineBlobs({kBlob1, kBlob2, kBlob3}));
+  EXPECT_EQ(kBlob12, CombineBlobs({kBlob12}));
+  EXPECT_EQ(kBlob12, CombineBlobs({kEmpty, kBlob1, kEmpty, kBlob2, kEmpty}));
+  EXPECT_EQ(kEmpty, CombineBlobs({}));
+}
+
 class SecureBlobTest : public ::testing::Test {
  public:
   SecureBlobTest() {}