\ Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
\
\ Permission is hereby granted, free of charge, to any person obtaining 
\ a copy of this software and associated documentation files (the
\ "Software"), to deal in the Software without restriction, including
\ without limitation the rights to use, copy, modify, merge, publish,
\ distribute, sublicense, and/or sell copies of the Software, and to
\ permit persons to whom the Software is furnished to do so, subject to
\ the following conditions:
\
\ The above copyright notice and this permission notice shall be 
\ included in all copies or substantial portions of the Software.
\
\ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
\ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
\ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
\ NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
\ BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
\ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
\ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
\ SOFTWARE.

preamble {

#include "inner.h"

#define CTX   ((br_x509_decoder_context *)(void *)((unsigned char *)t0ctx - offsetof(br_x509_decoder_context, cpu)))
#define CONTEXT_NAME   br_x509_decoder_context

/* see bearssl_x509.h */
void
br_x509_decoder_init(br_x509_decoder_context *ctx,
	void (*append_dn)(void *ctx, const void *buf, size_t len),
	void *append_dn_ctx,
	void (*append_in)(void *ctx, const void *buf, size_t len),
	void *append_in_ctx)
{
	memset(ctx, 0, sizeof *ctx);
	/* obsolete
	ctx->err = 0;
	ctx->hbuf = NULL;
	ctx->hlen = 0;
	*/
	ctx->append_dn = append_dn;
	ctx->append_dn_ctx = append_dn_ctx;
	ctx->append_in = append_in;
	ctx->append_in_ctx = append_in_ctx;
	ctx->cpu.dp = &ctx->dp_stack[0];
	ctx->cpu.rp = &ctx->rp_stack[0];
	br_x509_decoder_init_main(&ctx->cpu);
	br_x509_decoder_run(&ctx->cpu);
}

/* see bearssl_x509.h */
void
br_x509_decoder_push(br_x509_decoder_context *ctx,
	const void *data, size_t len)
{
	ctx->hbuf = data;
	ctx->hlen = len;
	br_x509_decoder_run(&ctx->cpu);
}

/* State machine should be squeezed for size, not performance critical */
#pragma GCC optimize ("Os")

}

addr: decoded
addr: notbefore_days
addr: notbefore_seconds
addr: notafter_days
addr: notafter_seconds
addr: isCA
addr: copy_dn
addr: copy_in
addr: signer_key_type
addr: signer_hash_id

cc: read8-low ( -- x ) {
	if (CTX->hlen == 0) {
		T0_PUSHi(-1);
	} else {
		unsigned char x = pgm_read_byte(CTX->hbuf ++);
		if (CTX->copy_dn && CTX->append_dn) {
			CTX->append_dn(CTX->append_dn_ctx, &x, 1);
		}
		if (CTX->copy_in && CTX->append_in) {
			CTX->append_in(CTX->append_in_ctx, &x, 1);
		}
		CTX->hlen --;
		T0_PUSH(x);
	}
}

cc: read-blob-inner ( addr len -- addr len ) {
	uint32_t len = T0_POP();
	uint32_t addr = T0_POP();
	size_t clen = CTX->hlen;
	if (clen > len) {
		clen = (size_t)len;
	}
	if (addr != 0) {
		memcpy_P((unsigned char *)CTX + addr, CTX->hbuf, clen);
	}
	if (CTX->copy_dn && CTX->append_dn) {
		CTX->append_dn(CTX->append_dn_ctx, CTX->hbuf, clen);
	}
	if (CTX->copy_in && CTX->append_in) {
		CTX->append_in(CTX->append_in_ctx, CTX->hbuf, clen);
	}
	CTX->hbuf += clen;
	CTX->hlen -= clen;
	T0_PUSH(addr + clen);
	T0_PUSH(len - clen);
}

\ Get the address and length for the pkey_data buffer.
: addr-len-pkey_data ( -- addr len )
	CX 0 8191 { offsetof(br_x509_decoder_context, pkey_data) }
	CX 0 8191 { BR_X509_BUFSIZE_KEY } ;

\ Copy the public key (RSA) to the permanent buffer.
cc: copy-rsa-pkey ( nlen elen -- ) {
	size_t elen = T0_POP();
	size_t nlen = T0_POP();
	CTX->pkey.key_type = BR_KEYTYPE_RSA;
	CTX->pkey.key.rsa.n = CTX->pkey_data;
	CTX->pkey.key.rsa.nlen = nlen;
	CTX->pkey.key.rsa.e = CTX->pkey_data + nlen;
	CTX->pkey.key.rsa.elen = elen;
}

\ Copy the public key (EC) to the permanent buffer.
cc: copy-ec-pkey ( curve qlen -- ) {
	size_t qlen = T0_POP();
	uint32_t curve = T0_POP();
	CTX->pkey.key_type = BR_KEYTYPE_EC;
	CTX->pkey.key.ec.curve = curve;
	CTX->pkey.key.ec.q = CTX->pkey_data;
	CTX->pkey.key.ec.qlen = qlen;
}

\ Extensions with specific processing.
OID: basicConstraints    2.5.29.19

\ Process a Basic Constraints extension. We want the "CA" flag only.
: process-basicConstraints ( lim -- lim )
	read-sequence-open
	read-tag-or-end dup 0x01 = if
		read-boolean 1 and addr-isCA set8
	else
		2drop
	then
	skip-close-elt
	;

\ Decode a certificate.
: main ( -- ! )

	\ Initialise state flags.
	0 addr-decoded set8
	0 addr-copy_dn set8
	0 addr-copy_in set8

	\ An arbitrary limit for the total certificate size.
	0xFFFFFF

	\ Open the outer SEQUENCE.
	read-sequence-open

	\ TBS
	read-sequence-open

	\ First element may be an explicit version. We accept only
	\ versions 0 to 2 (certificates v1 to v3).
	read-tag dup 0x20 = if
		drop check-constructed read-length-open-elt
		read-tag
		0x02 check-tag-primitive
		read-small-int-value
		2 > if ERR_X509_UNSUPPORTED fail then
		close-elt
		read-tag
	then

	\ Serial number. We just check that the tag is correct.
	0x02 check-tag-primitive read-length-skip

	\ Signature algorithm.
	read-sequence-open skip-close-elt

	\ Issuer name.
	1 addr-copy_in set8
	read-sequence-open skip-close-elt
	0 addr-copy_in set8

	\ Validity dates.
	read-sequence-open
	read-date addr-notbefore_seconds set32 addr-notbefore_days set32
	read-date addr-notafter_seconds set32 addr-notafter_days set32
	close-elt

	\ Subject name.
	1 addr-copy_dn set8
	read-sequence-open skip-close-elt
	0 addr-copy_dn set8

	\ Public Key.
	read-sequence-open
	\ Algorithm Identifier. Right now we are only interested in the
	\ OID, since we only support RSA keys.
	\ TODO: support EC keys
	read-sequence-open
	read-OID ifnot ERR_X509_UNSUPPORTED fail then
	choice
		\ RSA public key.
		rsaEncryption eqOID uf
			skip-close-elt
			\ Public key itself: the BIT STRING contains bytes
			\ (no partial byte) and these bytes encode the
			\ actual value.
			read-bits-open
				\ RSA public key is a SEQUENCE of two
				\ INTEGER. We get both INTEGER values into
				\ the pkey_data[] buffer, if they fit.
				read-sequence-open
				addr-len-pkey_data
				read-integer { nlen }
				addr-len-pkey_data swap nlen + swap nlen -
				read-integer { elen }
				close-elt
			close-elt
			nlen elen copy-rsa-pkey
		enduf

		\ EC public key.
		id-ecPublicKey eqOID uf
			\ We support only named curves, for which the
			\ "parameters" field in the AlgorithmIdentifier
			\ field should be an OID.
			read-curve-ID { curve }
			close-elt
			read-bits-open
			dup { qlen }
			dup addr-len-pkey_data rot < if
				ERR_X509_LIMIT_EXCEEDED fail
			then
			read-blob
			curve qlen copy-ec-pkey
		enduf
		ERR_X509_UNSUPPORTED fail
	endchoice
	close-elt

	\ This flag will be set to true if the Basic Constraints extension
	\ is encountered.
	0 addr-isCA set8

	\ Skip issuerUniqueID and subjectUniqueID, and process extensions
	\ if present. Extensions are an explicit context tag of value 3
	\ around a SEQUENCE OF extensions. Each extension is a SEQUENCE
	\ with an OID, an optional boolean, and a value; the value is
	\ an OCTET STRING.
	read-tag-or-end
	0x21 iftag-skip
	0x22 iftag-skip
	dup 0x23 = if
		drop
		check-constructed read-length-open-elt
		read-sequence-open
		begin dup while
			read-sequence-open
			read-OID drop
			read-tag dup 0x01 = if
				read-boolean drop
				read-tag
			then
			0x04 check-tag-primitive read-length-open-elt
			choice
				\ Extensions with specific processing.
				basicConstraints eqOID uf
					process-basicConstraints
				enduf
				skip-remaining
			endchoice
			close-elt
			close-elt
		repeat
		close-elt
		close-elt
	else
		-1 = ifnot ERR_X509_UNEXPECTED fail then
		drop
	then

	close-elt

	\ signature algorithm
	read-sequence-open
	read-OID if
		choice
			sha1WithRSAEncryption    eqOID uf 2 KEYTYPE_RSA enduf
			sha224WithRSAEncryption  eqOID uf 3 KEYTYPE_RSA enduf
			sha256WithRSAEncryption  eqOID uf 4 KEYTYPE_RSA enduf
			sha384WithRSAEncryption  eqOID uf 5 KEYTYPE_RSA enduf
			sha512WithRSAEncryption  eqOID uf 6 KEYTYPE_RSA enduf

			ecdsa-with-SHA1          eqOID uf 2 KEYTYPE_EC enduf
			ecdsa-with-SHA224        eqOID uf 3 KEYTYPE_EC enduf
			ecdsa-with-SHA256        eqOID uf 4 KEYTYPE_EC enduf
			ecdsa-with-SHA384        eqOID uf 5 KEYTYPE_EC enduf
			ecdsa-with-SHA512        eqOID uf 6 KEYTYPE_EC enduf

			0 0
		endchoice
	else
		0 0
	then
	addr-signer_key_type set8
	addr-signer_hash_id set8
	skip-close-elt
	\ read-sequence-open skip-close-elt

	\ signature value
	read-bits-open skip-close-elt

	\ Close the outer SEQUENCE.
	close-elt
	drop

	\ Mark the decoding as successful.
	1 addr-decoded set8

	\ Read one byte, then fail: if the read succeeds, then there is
	\ some trailing byte.
	read8-nc ERR_X509_EXTRA_ELEMENT fail
	;
