Replace generic 'base64 encoding' terminology with the specific RFCs they match.

Remove duplicate documentation for two variants of Base64EscapeInternal().

Clarify role of base64 char array input (controls web-safe or not).

PiperOrigin-RevId: 500867221
Change-Id: Ie316a7ddd60794e041c5b9b39e9ab5b66ed565a6

absl/strings/internal/escaping.h

@@ -25,19 +25,17 @@ namespace strings_internal {
 
 
 ABSL_CONST_INIT extern const char kBase64Chars[];
 ABSL_CONST_INIT extern const char kBase64Chars[];
 
 
-// Calculates how long a string will be when it is base64 encoded given its
-// length and whether or not the result should be padded.
+// Calculates the length of a Base64 encoding (RFC 4648) of a string of length
+// `input_len`, with or without padding per `do_padding`. Note that 'web-safe'
+// encoding (section 5 of the RFC) does not change this length.
 size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding);
 size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding);
 
 
-// Base64-encodes `src` using the alphabet provided in `base64` and writes the
-// result to `dest`. If `do_padding` is true, `dest` is padded with '=' chars
-// until its length is a multiple of 3. Returns the length of `dest`.
+// Base64-encodes `src` using the alphabet provided in `base64` (which
+// determines whether to do web-safe encoding or not) and writes the result to
+// `dest`. If `do_padding` is true, `dest` is padded with '=' chars until its
+// length is a multiple of 3. Returns the length of `dest`.
 size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
 size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
                             size_t szdest, const char* base64, bool do_padding);
                             size_t szdest, const char* base64, bool do_padding);
-
-// Base64-encodes `src` using the alphabet provided in `base64` and writes the
-// result to `dest`. If `do_padding` is true, `dest` is padded with '=' chars
-// until its length is a multiple of 3.
 template <typename String>
 template <typename String>
 void Base64EscapeInternal(const unsigned char* src, size_t szsrc, String* dest,
 void Base64EscapeInternal(const unsigned char* src, size_t szsrc, String* dest,
                           bool do_padding, const char* base64_chars) {
                           bool do_padding, const char* base64_chars) {