rework std.base64 api

* rename decode to decodeExactUnsafe.
* add decodeExact, which checks for invalid chars and padding.
* add decodeWithIgnore, which also allows ignoring chars.
* alphabets are supplied to the decoders with their
  char-to-index mapping already built, which enables it to be
  done at comptime.
* all decode/encode apis except decodeWithIgnore require dest
  to be the exactly correct length. This is calculated by a
  calc function corresponding to each api. These apis no longer
  return the dest parameter.
* for decodeWithIgnore, an exact size cannot be known a priori.
  Instead, a calc function gives an upperbound, and a runtime
  error is returned in case of overflow. decodeWithIgnore
  returns the number of bytes written to dest.

closes #611

1 files changed, 3 insertions, 3 deletions

diff --git a/std/os/index.zig b/std/os/index.zig
index 34de6f3bbf..872564224c 100644
--- a/std/os/index.zig
+++ b/std/os/index.zig
@@ -622,7 +622,7 @@ pub fn symLinkPosix(allocator: &Allocator, existing_path: []const u8, new_path:
 }
 
 // here we replace the standard +/ with -_ so that it can be used in a file name
-const b64_fs_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
+const b64_fs_alphabet_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
 
 pub fn atomicSymLink(allocator: &Allocator, existing_path: []const u8, new_path: []const u8) -> %void {
     if (symLink(allocator, existing_path, new_path)) {
@@ -639,7 +639,7 @@ pub fn atomicSymLink(allocator: &Allocator, existing_path: []const u8, new_path:
     mem.copy(u8, tmp_path[0..], new_path);
     while (true) {
         %return getRandomBytes(rand_buf[0..]);
-        _ = base64.encodeWithAlphabet(tmp_path[new_path.len..], rand_buf, b64_fs_alphabet);
+        base64.encode(tmp_path[new_path.len..], rand_buf, b64_fs_alphabet_chars, base64.standard_pad_char);
         if (symLink(allocator, existing_path, tmp_path)) {
             return rename(allocator, tmp_path, new_path);
         } else |err| {
@@ -721,7 +721,7 @@ pub fn copyFileMode(allocator: &Allocator, source_path: []const u8, dest_path: [
     defer allocator.free(tmp_path);
     mem.copy(u8, tmp_path[0..], dest_path);
     %return getRandomBytes(rand_buf[0..]);
-    _ = base64.encodeWithAlphabet(tmp_path[dest_path.len..], rand_buf, b64_fs_alphabet);
+    base64.encode(tmp_path[dest_path.len..], rand_buf, b64_fs_alphabet_chars, base64.standard_pad_char);
 
     var out_file = %return io.File.openWriteMode(tmp_path, mode, allocator);
     defer out_file.close();