Make base64 encoder incremental

As part of https://gerrit.openbmc.org/c/openbmc/bmcweb/+/67667, it would
be desirable if we could incrementally encode base64 in chunks.  Given
that base64 encoding requires encoding 3 characters to 4, there's a
possibility that a chunk might not be mod 3 length.

This commit moves the base64 encoder into a class that can run
incrementally.

Tested:  Unit tests pass.  More tests in next commit.

Change-Id: Ic7da3fd4db865c99fcbd96ae06fdecb87628f94c
Signed-off-by: Ed Tanous <ed@tanous.net>

1 files changed, 21 insertions, 0 deletions

diff --git a/test/http/utility_test.cpp b/test/http/utility_test.cpp
index 5f62d3f3d1..c0b6412af2 100644
--- a/test/http/utility_test.cpp
+++ b/test/http/utility_test.cpp
@@ -71,6 +71,27 @@ TEST(Utility, Base64EncodeString)
     EXPECT_EQ(encoded, "ZjAAIEJhcg==");
 }
 
+TEST(Utility, Base64Encoder)
+{
+    using namespace std::string_literals;
+    std::string data = "f0\0 Bar"s;
+    for (size_t chunkSize = 1; chunkSize < 6; chunkSize++)
+    {
+        std::string_view testString(data);
+        std::string out;
+        Base64Encoder encoder;
+        while (!testString.empty())
+        {
+            size_t thisChunk = std::min(testString.size(), chunkSize);
+            encoder.encode(testString.substr(0, thisChunk), out);
+            testString.remove_prefix(thisChunk);
+        }
+
+        encoder.finalize(out);
+        EXPECT_EQ(out, "ZjAAIEJhcg==");
+    }
+}
+
 TEST(Utility, Base64EncodeDecodeString)
 {
     using namespace std::string_literals;