1 files changed, 127 insertions, 0 deletions
diff --git a/src/rexmpp_base64.c b/src/rexmpp_base64.c
new file mode 100644
index 0000000..28afc7b
--- /dev/null
+++ b/src/rexmpp_base64.c
@@ -0,0 +1,127 @@
+/**
+   @file rexmpp_base64.c
+   @brief Base64 implementation
+   @author defanor <defanor@uberspace.net>
+   @date 2021
+   @copyright MIT license.
+
+   Implements RFC 4648.
+*/
+
+#include <stdlib.h>
+#include <stddef.h>
+
+#include "rexmpp_base64.h"
+
+
+char map_range (char x, char from_start, char from_end, char to_start, char otherwise) {
+  if (x >= from_start && x <= from_end) {
+    return (to_start + x - from_start);
+  } else {
+    return otherwise;
+  }
+}
+
+char to_b64 (char x) {
+  return map_range(x, 0, 25, 'A',
+                   map_range(x, 26, 51, 'a',
+                             map_range(x, 52, 61, '0',
+                                       map_range(x, 62, 62, '+',
+                                                 map_range(x, 63, 63, '/',
+                                                           '=')))));
+}
+
+char from_b64 (char x) {
+  return map_range(x, 'A', 'Z', 0,
+                   map_range(x, 'a', 'z', 26,
+                             map_range(x, '0', '9', 52,
+                                       map_range(x, '+', '+', 62,
+                                                 map_range(x, '/', '/', 63,
+                                                           64)))));
+}
+
+
+int rexmpp_base64_to (const char *in, size_t in_len, char **out, size_t *out_len) {
+  if (in_len == 0) {
+    return -1;
+  }
+  if (in == NULL) {
+    return -1;
+  }
+  *out_len = (in_len + 2) / 3 * 4;
+  char *res = malloc(*out_len + 1);
+  if (res == NULL) {
+    return -1;
+  }
+  res[*out_len] = '\0';
+  *out = res;
+  while (res < *out + *out_len) {
+    char a = in[0];
+    char b = in_len > 1 ? in[1] : 0;
+    char c = in_len > 2 ? in[2] : 0;
+    res[0] = to_b64((a & 0xFC) >> 2);
+    res[1] = to_b64(((a & 0x03) << 4) | ((b & 0xF0) >> 4));
+    res[2] = in_len > 1 ? to_b64((((b & 0x0F) << 2) | ((c & 0xC0) >> 6))) : '=';
+    res[3] = in_len > 2 ? to_b64((c & 0x3F)) : '=';
+    in_len -= 3;
+    in += 3;
+    res += 4;
+  }
+  return 0;
+}
+
+int rexmpp_base64_from (const char *in, size_t in_len, char **out, size_t *out_len) {
+  if (in_len == 0) {
+    return -1;
+  }
+  if (in == NULL) {
+    return -1;
+  }
+  if (in_len % 4) {
+    return -1;
+  }
+  *out_len = in_len / 4 * 3;
+  char *res = malloc(*out_len);
+  if (res == NULL) {
+    return -1;
+  }
+  *out = res;
+  while (res < *out + *out_len) {
+    char a = from_b64(in[0]);
+    char b = from_b64(in[1]);
+    char c = in[2] == '=' ? 0 : from_b64(in[2]);
+    char d = in[3] == '=' ? 0 : from_b64(in[3]);
+    if ((a | b | c | d) & 0xC0) {
+      free(*out);
+      *out = NULL;
+      *out_len = 0;
+      return -1;
+    }
+    res[0] = (a << 2) | ((b & 0x30) >> 4);
+    res[1] = ((b & 0x0F) << 4) | ((c & 0x3C) >> 2);
+    res[2] = ((c & 0x03) << 6) | d;
+
+    if (in[2] == '=') {
+      if (in[3] != '=') {
+        free(*out);
+        *out = NULL;
+        *out_len = 0;
+        return -1;
+      }
+      *out_len = *out_len - 1;
+    }
+    if (in[3] == '=') {
+      if (res + 3 < *out + *out_len) {
+        free(*out);
+        *out = NULL;
+        *out_len = 0;
+        return -1;
+      }
+      *out_len = *out_len - 1;
+    }
+
+    in += 4;
+    res += 3;
+  }
+  return 0;
+}