Add base64_encode(), base64_decode()

1 files changed, 211 insertions, 0 deletions

diff --git a/butl/base64.cxx b/butl/base64.cxx
new file mode 100644
index 0000000..2939b46
--- /dev/null
+++ b/butl/base64.cxx
@@ -0,0 +1,211 @@
+// file      : butl/base64.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <butl/base64>
+
+#include <cstddef>   // size_t
+#include <istream>
+#include <ostream>
+#include <iterator>  // {istreambuf, ostreambuf, back_insert}_iterator
+#include <stdexcept> // invalid_argument
+
+using namespace std;
+
+namespace butl
+{
+  static const char* codes =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+  // base64-encode the data in the iterator range [i, e). Write the encoded
+  // data starting at the iterator position o.
+  //
+  template <typename I, typename O>
+  static void
+  base64_encode (I& i, const I& e, O& o)
+  {
+    const size_t un (65); // Non-existing index of the codes string.
+    for (size_t n (0); i != e; ++n)
+    {
+      if (n && n % 19 == 0)
+        *o++ = '\n'; // Split into lines, like the base64 utility does.
+
+      char c (*i++);
+      size_t i1 ((c >> 2) & 0x3F);
+      size_t i2 ((c << 4) & 0x30);
+
+      size_t i3 (un);
+      if (i != e)
+      {
+        c = *i++;
+        i2 |= (c >> 4) & 0xF;
+        i3 = (c << 2) & 0x3C;
+      }
+
+      size_t i4 (un);
+      if (i != e)
+      {
+        c = *i++;
+        i3 |= (c >> 6) & 0x3;
+        i4 = c & 0x3F;
+      }
+
+      *o++ = codes[i1];
+      *o++ = codes[i2];
+      *o++ = i3 == un ? '=' : codes[i3];
+      *o++ = i4 == un ? '=' : codes[i4];
+    }
+  }
+
+  static char
+  index (char c)
+  {
+    switch (c)
+    {
+    case '/': return 63;
+    case '+': return 62;
+    default:
+      {
+        if (c >= 'A' && c <= 'Z')
+          return c - 'A';
+        else if (c >= 'a' && c <= 'z')
+          return c - 'a' + 26;
+        else if (c >= '0' && c <= '9')
+          return c - '0' + 52;
+        else
+          throw invalid_argument ("invalid input");
+      }
+    }
+  }
+
+  // base64-decode the data in the iterator range [i, e). Write the decoded
+  // data starting at the iterator position o. Throw invalid_argument if the
+  // input data is invalid.
+  //
+  template <typename I, typename O>
+  static void
+  base64_decode (I& i, const I& e, O& o)
+  {
+    auto bad = []() {throw invalid_argument ("invalid input");};
+
+    auto next = [&i, &e, &bad]() -> char
+    {
+      if (i == e)
+        bad ();
+      return *i++;
+    };
+
+    while (i != e)
+    {
+      char c (next ());
+      if (c == '\n') // @@ Should we check for '\r' as well ?
+        continue;
+
+      char i1 = index (c);
+      char i2 = index (next ());
+      *o++ = (i1 << 2) | (i2 >> 4);
+
+      c = next ();
+      if (c == '=')
+      {
+        if (next () != '=' || i != e)
+          bad ();
+      }
+      else
+      {
+        char i3 = index (c);
+        *o++ = (i2 << 4) | (i3 >> 2);
+
+        c = next ();
+        if (c == '=')
+        {
+          if (i != e)
+            bad ();
+        }
+        else
+          *o++ = (i3 << 6) | index (c);
+      }
+    }
+  }
+
+  string
+  base64_encode (istream& is)
+  {
+    if (!is.good ())
+      throw invalid_argument ("bad stream");
+
+    string r;
+    istreambuf_iterator<char> i (is);
+    back_insert_iterator<string> o (r);
+
+    base64_encode (i, istreambuf_iterator<char> (), o);
+    is.setstate (istream::eofbit);
+    return r;
+  }
+
+  void
+  base64_encode (ostream& os, istream& is)
+  {
+    if (!os.good () || !is.good ())
+      throw invalid_argument ("bad stream");
+
+    istreambuf_iterator<char> i (is);
+    ostreambuf_iterator<char> o (os);
+    base64_encode (i, istreambuf_iterator<char> (), o);
+
+    if (o.failed ())
+      os.setstate (istream::badbit);
+
+    is.setstate (istream::eofbit);
+  }
+
+  std::string
+  base64_encode (const std::vector<char>& v)
+  {
+    string r;
+    back_insert_iterator<string> o (r);
+    auto i (v.begin ());
+    base64_encode (i, v.end (), o);
+    return r;
+  }
+
+  void
+  base64_decode (ostream& os, istream& is)
+  {
+    if (!os.good () || !is.good ())
+      throw invalid_argument ("bad stream");
+
+    istreambuf_iterator<char> i (is);
+    ostreambuf_iterator<char> o (os);
+    base64_decode (i, istreambuf_iterator<char> (), o);
+
+    if (o.failed ())
+      os.setstate (istream::badbit);
+
+    is.setstate (istream::eofbit);
+  }
+
+  void
+  base64_decode (ostream& os, const string& s)
+  {
+    if (!os.good ())
+      throw invalid_argument ("bad stream");
+
+    ostreambuf_iterator<char> o (os);
+    auto i (s.cbegin ());
+    base64_decode (i, s.cend (), o);
+
+    if (o.failed ())
+      os.setstate (istream::badbit);
+  }
+
+  vector<char>
+  base64_decode (const string& s)
+  {
+    vector<char> r;
+    back_insert_iterator<vector<char>> o (r);
+    auto i (s.cbegin ());
+    base64_decode (i, s.cend (), o);
+    return r;
+  }
+}