6 #include "bytesource.h"
8 #define MARKER_CHAR 0xff
9 #define STUFF_MARKER 0x00
11 void init_byte_source(struct byte_source* source, raw_input_func_t* input_func, void* userdata)
13 // TODO: should this size be a different constant?
14 memset(source, 0, sizeof(*source));
15 source->bytes = (uint8_t*)malloc(BYTESOURCE_CHUNK_SIZE);
16 source->input_func = input_func;
17 source->userdata = userdata;
20 uint8_t byte_source_read_marker(struct byte_source* src)
22 // Refill until we have at least two bytes or EOF.
23 while (src->bytes_available < 2) {
24 const unsigned bytes_to_read = 2 - src->bytes_available;
25 const ssize_t bytes_read =
26 (*src->input_func)(src->userdata,
27 src->bytes + src->bytes_available,
29 assert(bytes_read >= -1);
30 assert(bytes_read <= (ssize_t)bytes_to_read);
32 if (bytes_read == -1 || bytes_read == 0) {
36 src->bytes_available += bytes_read;
39 assert(src->bytes_available >= 2);
40 if (src->bytes[0] != MARKER_CHAR || src->bytes[1] == STUFF_MARKER) {
44 uint8_t ret = src->bytes[1];
45 memmove(src->bytes, src->bytes + 2, src->bytes_available - 2);
46 src->bytes_available -= 2;
51 ssize_t byte_source_input_func(void* source, uint8_t* buf, size_t len)
53 struct byte_source* src = (struct byte_source*)source;
55 // If there's no data in the buffer (or only a partial marker), we have
56 // to read in more from our upstream src.
57 while (src->bytes_available == 0 ||
58 (src->bytes_available == 1 && src->bytes[0] == MARKER_CHAR)) {
59 const unsigned space_left = BYTESOURCE_CHUNK_SIZE - src->bytes_available;
60 const unsigned missing_data = len - src->bytes_available;
61 const size_t bytes_to_read = (missing_data > space_left ? space_left : missing_data);
62 assert(bytes_to_read <= BYTESOURCE_CHUNK_SIZE);
63 const ssize_t bytes_read =
64 (*src->input_func)(src->userdata,
65 src->bytes + src->bytes_available,
67 assert(bytes_read >= -1);
68 assert(bytes_read <= (ssize_t)bytes_to_read);
70 if (bytes_read == -1) {
72 } else if (bytes_read == 0) {
73 if (src->bytes_available == 1) {
74 // EOF in the middle of a marker => read error
77 assert(src->bytes_available == 0);
82 src->bytes_available += bytes_read;
85 // Now unstuff as much as we can. First of all, if there's a 0xFF at the
86 // end of the buffer, we don't include it this time; the unstuff function
87 // will only give us an error since it can't decide if it's a marker or
89 unsigned bytes_to_unstuff = src->bytes_available;
90 bool end_marker = false;
91 assert(bytes_to_unstuff > 0);
92 if (src->bytes[bytes_to_unstuff - 1] == 0xff) {
97 // Fast path: No markers in the data, we don't have more data than we
98 // need. We can basically just return it.
99 if (bytes_to_unstuff <= len) {
100 int unstuffed_bytes = (*unstuff_choice)(buf, src->bytes, bytes_to_unstuff);
101 assert(unstuffed_bytes != 0);
102 if (unstuffed_bytes > 0) {
103 // Fast path: No markers in the data. We can basically just
106 src->bytes_available = 1;
107 src->bytes[0] = 0xff;
109 src->bytes_available = 0;
111 return unstuffed_bytes;
115 // Slow path: There was a marker in the data. Unstuff manually until
116 // we hit the marker, then return that.
118 unsigned bytes_written = 0;
119 for (bytes_read = 0; bytes_read < bytes_to_unstuff && bytes_written < len; ++bytes_read) {
120 if (src->bytes[bytes_read] != MARKER_CHAR) {
121 buf[bytes_written++] = src->bytes[bytes_read];
125 assert(bytes_read < src->bytes_available);
126 if (src->bytes[bytes_read + 1] == STUFF_MARKER) {
127 src->bytes[bytes_written++] = MARKER_CHAR;
129 // Skip the stuff byte.
132 // OK, this is our marker.
137 memmove(src->bytes, src->bytes + bytes_read, src->bytes_available - bytes_read);
138 src->bytes_available -= bytes_read;
139 return bytes_written;