Revert "Remove functions which return strings"

We need these functions for the logging_enabled branch.

This reverts commit acae4e8438.

include/olm/crypto.hh

@@ -17,6 +17,7 @@
 
 #include <cstdint>
 #include <cstddef>
+#include <string>
 
 namespace olm {
 
@@ -26,6 +27,7 @@ static const std::size_t IV_LENGTH = 16;
 
 struct Curve25519PublicKey {
     std::uint8_t public_key[KEY_LENGTH];
+    std::string to_string() const;
 };
 
 

include/olm/memory.hh

@@ -87,4 +87,23 @@ std::uint8_t * store_array(
     return destination + sizeof(T);
 }
 
+/** convert an array of bytes to a string representation */
+template<typename T>
+std::string bytes_to_string(T start, T end) {
+    std::ostringstream ss;
+    ss << std::hex << std::setfill('0');
+    while (start != end) {
+        ss << std::setw(2) << static_cast<int>(*start++);
+        if (start != end) {
+            ss << ":";
+        }
+    }
+    return ss.str();
+}
+
+template<typename T>
+std::string bytes_to_string(T start, size_t len) {
+    return bytes_to_string(start, start+len);
+}
+
 } // namespace olm

src/crypto.cpp

@@ -101,6 +101,11 @@ inline static void hmac_sha256_final(
 
 } // namespace
 
+std::string olm::Curve25519PublicKey::to_string() const {
+    return olm::bytes_to_string(std::begin(public_key),
+                                std::end(public_key));
+};
+
 void olm::curve25519_generate_key(
     std::uint8_t const * random_32_bytes,
     olm::Curve25519KeyPair & key_pair