Add botan_hash_copy_state FFI function.

4 files changed, 38 insertions, 0 deletions

diff --git a/doc/manual/ffi.rst b/doc/manual/ffi.rst
index 24b2aaa38..89e075885 100644
--- a/doc/manual/ffi.rst
+++ b/doc/manual/ffi.rst
@@ -149,6 +149,10 @@ Hash Functions
 
    Destroy the object created by :cpp:func:`botan_hash_init`.
 
+.. cpp:function:: int botan_hash_copy_state(botan_hash_t* dest, const botan_hash_t source)
+
+   Copies the state of the hash object to a new hash object.
+
 .. cpp:function:: int botan_hash_clear(botan_hash_t hash)
 
    Reset the state of this object back to clean, as if no input has
diff --git a/src/lib/ffi/ffi.cpp b/src/lib/ffi/ffi.cpp
index 3686c26f1..7e96e5514 100644
--- a/src/lib/ffi/ffi.cpp
+++ b/src/lib/ffi/ffi.cpp
@@ -852,6 +852,12 @@ int botan_hash_final(botan_hash_t hash, uint8_t out[])
    return BOTAN_FFI_DO(Botan::HashFunction, hash, h, { h.final(out); });
    }
 
+int botan_hash_copy_state(botan_hash_t* dest, const botan_hash_t source)
+   {
+   return BOTAN_FFI_DO(Botan::HashFunction, source, src, {
+      *dest = new botan_hash_struct(src.copy_state().release()); });
+   }
+
 int botan_mac_init(botan_mac_t* mac, const char* mac_name, uint32_t flags)
    {
    try
diff --git a/src/lib/ffi/ffi.h b/src/lib/ffi/ffi.h
index 4953bce06..5ce86a9b0 100644
--- a/src/lib/ffi/ffi.h
+++ b/src/lib/ffi/ffi.h
@@ -225,6 +225,14 @@ typedef struct botan_hash_struct* botan_hash_t;
 BOTAN_DLL int botan_hash_init(botan_hash_t* hash, const char* hash_name, uint32_t flags);
 
 /**
+* Copy the state of a hash function object
+* @param dest destination hash object
+* @param source source hash object
+* @return 0 on success, a negative value on failure
+*/
+BOTAN_DLL int botan_hash_copy_state(botan_hash_t *dest, const botan_hash_t source);
+
+/**
 * Writes the output length of the hash function to *output_length
 * @param hash hash object
 * @param output_length output buffer to hold the hash function output length
diff --git a/src/tests/test_ffi.cpp b/src/tests/test_ffi.cpp
index 624b01032..cf97dd947 100644
--- a/src/tests/test_ffi.cpp
+++ b/src/tests/test_ffi.cpp
@@ -131,6 +131,26 @@ class FFI_Unit_Tests : public Test
                   result.test_eq("SHA-256 output", outbuf, "B5D4045C3F466FA91FE2CC6ABE79232A1A57CDF104F7A26E716E0A1E2789DF78");
                   }
 
+               // Test botan_hash_copy_state
+               const char *msg = "message digest";
+               const char *expected = "F7846F55CF23E14EEBEAB5B4E1550CAD5B509E3348FBC4EFA3A1413D393CB650";
+               TEST_FFI_OK(botan_hash_clear, (hash));
+               TEST_FFI_OK(botan_hash_update, (hash, reinterpret_cast<const uint8_t*>(&msg[0]), 1));
+               botan_hash_t fork;
+               if (TEST_FFI_OK(botan_hash_copy_state, (&fork, hash)))
+                  {
+                  TEST_FFI_OK(botan_hash_update, (fork, reinterpret_cast<const uint8_t*>(&msg[1]), std::strlen(msg) - 2));
+
+                  TEST_FFI_OK(botan_hash_update, (hash, reinterpret_cast<const uint8_t*>(&msg[1]), std::strlen(msg) - 1));
+                  TEST_FFI_OK(botan_hash_final, (hash, outbuf.data()));
+                  result.test_eq("hashing split", outbuf, expected);
+
+                  TEST_FFI_OK(botan_hash_update, (fork, reinterpret_cast<const uint8_t*>(&msg[std::strlen(msg)-1]), 1));
+                  TEST_FFI_OK(botan_hash_final, (fork, outbuf.data()));
+                  result.test_eq("hashing split", outbuf, expected);
+
+                  TEST_FFI_OK(botan_hash_destroy, (fork));
+                  }
                }
 
             TEST_FFI_OK(botan_hash_destroy, (hash));