+ Initially, CTX must have been initialized via base64_decode_ctx_init.
+ Subsequent calls to this function must reuse whatever state is recorded
+ in that buffer. It is necessary for when a quadruple of base64 input
+ bytes spans two input buffers.
+
+ If CTX is NULL then newlines are treated as garbage and the input
+ buffer is processed as a unit. */
+
+bool
+base64_decode_ctx (struct base64_decode_context *ctx,
+ const char *restrict in, size_t inlen,
+ char *restrict out, size_t *outlen)
+{
+ size_t outleft = *outlen;
+ bool ignore_newlines = ctx != NULL;
+ bool flush_ctx = false;
+ unsigned int ctx_i = 0;
+
+ if (ignore_newlines)
+ {
+ ctx_i = ctx->i;
+ flush_ctx = inlen == 0;
+ }
+
+
+ while (true)
+ {
+ size_t outleft_save = outleft;
+ if (ctx_i == 0 && !flush_ctx)
+ {
+ while (true)
+ {
+ /* Save a copy of outleft, in case we need to re-parse this
+ block of four bytes. */
+ outleft_save = outleft;
+ if (!decode_4 (in, inlen, &out, &outleft))
+ break;
+
+ in += 4;
+ inlen -= 4;
+ }
+ }
+
+ if (inlen == 0 && !flush_ctx)
+ break;
+
+ /* Handle the common case of 72-byte wrapped lines.
+ This also handles any other multiple-of-4-byte wrapping. */
+ if (inlen && *in == '\n' && ignore_newlines)
+ {
+ ++in;
+ --inlen;
+ continue;
+ }
+
+ /* Restore OUT and OUTLEFT. */
+ out -= outleft_save - outleft;
+ outleft = outleft_save;
+
+ {
+ char const *in_end = in + inlen;
+ char const *non_nl;
+
+ if (ignore_newlines)
+ non_nl = get_4 (ctx, &in, in_end, &inlen);
+ else
+ non_nl = in; /* Might have nl in this case. */
+
+ /* If the input is empty or consists solely of newlines (0 non-newlines),
+ then we're done. Likewise if there are fewer than 4 bytes when not
+ flushing context and not treating newlines as garbage. */
+ if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
+ {
+ inlen = 0;
+ break;
+ }
+ if (!decode_4 (non_nl, inlen, &out, &outleft))
+ break;
+
+ inlen = in_end - in;
+ }
+ }
+
+ *outlen -= outleft;
+
+ return inlen == 0;