Re: encode/decode support for base64url

Hi Florents,

On Jul 9, 2025, at 23:25, Florents Tselai <florents(dot)tselai(at)gmail(dot)com> wrote:

>> I reviewed and tested v4. To me it looks as good as it will get.
>> Personally I would change a few minor things here and there and
>> probably merge all three patches into a single commit. This however is
>> up to the committer to decide.
>
> Attaching a single-file patch

Somehow missed this thread previously. Had a quick look and had the same question Aleksander asked up-thread:

> Although it is a possible implementation, wouldn't it be better to
> parametrize pg_base64_encode instead of traversing the string twice?
> Same for pg_base64_decode. You can refactor pg_base64_encode and make
> it a wrapper for pg_base64_encode_impl if needed.

It looks as though there could be complements to _base64 and b64urllookup:

```patch
diff --git a/src/backend/utils/adt/encode.c b/src/backend/utils/adt/encode.c
@@ -273,6 +273,9 @@ hex_dec_len(const char *src, size_t srclen)
static const char _base64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

+static const char _base64url[] =
+"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
static const int8 b64lookup[128] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
@@ -284,6 +287,18 @@ static const int8 b64lookup[128] = {
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
};

+static const int8 b64urllookup[128] = {
+ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,
+ 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
+ -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
+ 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 62,
+ -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
+ 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
+};
+
+
static uint64
pg_base64_encode(const char *src, size_t len, char *dst)
{
```

And then add the implementation functions that take argument with the proper lookup tables.

Best,

David