1 files changed, 159 insertions, 0 deletions
diff --git a/libbutl/sha256.hxx b/libbutl/sha256.hxx
new file mode 100644
index 0000000..566068f
--- /dev/null
+++ b/libbutl/sha256.hxx
@@ -0,0 +1,159 @@
+// file      : libbutl/sha256.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#pragma once
+
+#include <string>
+#include <iosfwd>      // istream
+#include <cstddef>     // size_t
+#include <cstdint>
+#include <cstring>     // strlen(), memcpy()
+#include <type_traits> // enable_if, is_integral
+
+#include <libbutl/export.hxx>
+
+namespace butl
+{
+  // SHA256 checksum calculator.
+  //
+  // For a single chunk of data a sum can be obtained in one line, for
+  // example:
+  //
+  // cerr << sha256 ("123").string () << endl;
+  //
+  class LIBBUTL_SYMEXPORT sha256
+  {
+  public:
+    sha256 () {reset ();}
+
+    // Append binary data.
+    //
+    void
+    append (const void*, std::size_t);
+
+    sha256 (const void* b, std::size_t n): sha256 () {append (b, n);}
+
+    // Append string.
+    //
+    // Note that the hash includes the '\0' terminator. Failed that, a call
+    // with an empty string will be indistinguishable from no call at all.
+    //
+    void
+    append (const std::string& s) {append (s.c_str (), s.size () + 1);}
+
+    void
+    append (const char* s) {append (s, std::strlen (s) + 1);}
+
+    explicit
+    sha256 (const std::string& s): sha256 () {append (s);}
+
+    explicit
+    sha256 (const char* s): sha256 () {append (s);}
+
+    // Append an integral type with a fast path optimization (see
+    // SHA256_Update() for details).
+    //
+    void
+    append (char c)
+    {
+      std::uint32_t r ((ctx_.count >> 3) & 0x3f);
+
+      if (1 < 64 - r)
+      {
+        ctx_.buf[r] = static_cast<std::uint8_t> (c);
+        ctx_.count += 8;
+      }
+      else
+        append (&c, 1);
+    }
+
+    template <typename T>
+    typename std::enable_if<std::is_integral<T>::value>::type
+    append (T x)
+    {
+      const std::size_t len (sizeof (x));
+      std::uint32_t r ((ctx_.count >> 3) & 0x3f);
+
+      if (len < 64 - r)
+      {
+        std::memcpy (&ctx_.buf[r], &x, sizeof (x));
+        ctx_.count += len << 3;
+      }
+      else
+        append (&x, len);
+    }
+
+    // Append stream.
+    //
+    // Note that currently the stream is expected to be bufstreambuf-based
+    // (e.g., ifdstream).
+    //
+    void
+    append (std::istream&);
+
+    explicit
+    sha256 (std::istream& i): sha256 () {append (i);}
+
+    // Check if any data has been hashed.
+    //
+    bool
+    empty () const {return empty_;}
+
+    // Reset to the default-constructed state.
+    //
+    void
+    reset ();
+
+    // Extract result.
+    //
+    // It can be obtained as either a 32-byte binary digest or as a 64-
+    // character hex-encoded C-string.
+    //
+    using digest_type = std::uint8_t[32];
+
+    const digest_type&
+    binary () const;
+
+    const char*
+    string () const;
+
+    std::string
+    abbreviated_string (std::size_t n) const
+    {
+      return std::string (string (), n < 64 ? n : 64);
+    }
+
+  private:
+    struct context // Note: identical to SHA256_CTX.
+    {
+      std::uint32_t state[8];
+      std::uint64_t count;
+      std::uint8_t buf[64];
+    };
+
+    union
+    {
+      mutable context ctx_;
+      mutable char buf_[sizeof (context)]; // Also used to store string rep.
+    };
+
+    mutable digest_type bin_;
+    mutable bool done_;
+    bool empty_;
+  };
+
+  // Convert a SHA256 string representation (64 hex digits) to the fingerprint
+  // canonical representation (32 colon-separated upper case hex digit pairs,
+  // like 01:AB:CD:...). Throw invalid_argument if the argument is not a valid
+  // SHA256 string.
+  //
+  LIBBUTL_SYMEXPORT std::string
+  sha256_to_fingerprint (const std::string&);
+
+  // Convert a fingerprint (32 colon-separated hex digit pairs) to the possibly
+  // abbreviated SHA256 string representation (up to 64 lower case hex digits).
+  // Throw invalid_argument if the first argument is not a valid fingerprint.
+  //
+  LIBBUTL_SYMEXPORT std::string
+  fingerprint_to_sha256 (const std::string&, std::size_t = 64);
+}