pkt-line.c

   1 #include "cache.h"
   2 #include "pkt-line.h"
   3
   4 /*
   5  * Write a packetized stream, where each line is preceded by
   6  * its length (including the header) as a 4-byte hex number.
   7  * A length of 'zero' means end of stream (and a length of 1-3
   8  * would be an error).
   9  *
  10  * This is all pretty stupid, but we use this packetized line
  11  * format to make a streaming format possible without ever
  12  * over-running the read buffers. That way we'll never read
  13  * into what might be the pack data (which should go to another
  14  * process entirely).
  15  *
  16  * The writing side could use stdio, but since the reading
  17  * side can't, we stay with pure read/write interfaces.
  18  */
  19 static void safe_write(int fd, const void *buf, unsigned n)
  20 {
  21         while (n) {
  22                 int ret = xwrite(fd, buf, n);
  23                 if (ret > 0) {
  24                         buf += ret;
  25                         n -= ret;
  26                         continue;
  27                 }
  28                 if (!ret)
  29                         die("write error (disk full?)");
  30                 die("write error (%s)", strerror(errno));
  31         }
  32 }
  33
  34 /*
  35  * If we buffered things up above (we don't, but we should),
  36  * we'd flush it here
  37  */
  38 void packet_flush(int fd)
  39 {
  40         safe_write(fd, "0000", 4);
  41 }
  42
  43 #define hex(a) (hexchar[(a) & 15])
  44 void packet_write(int fd, const char *fmt, ...)
  45 {
  46         static char buffer[1000];
  47         static char hexchar[] = "0123456789abcdef";
  48         va_list args;
  49         unsigned n;
  50
  51         va_start(args, fmt);
  52         n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
  53         va_end(args);
  54         if (n >= sizeof(buffer)-4)
  55                 die("protocol error: impossibly long line");
  56         n += 4;
  57         buffer[0] = hex(n >> 12);
  58         buffer[1] = hex(n >> 8);
  59         buffer[2] = hex(n >> 4);
  60         buffer[3] = hex(n);
  61         safe_write(fd, buffer, n);
  62 }
  63
  64 static void safe_read(int fd, void *buffer, unsigned size)
  65 {
  66         int n = 0;
  67
  68         while (n < size) {
  69                 int ret = xread(fd, buffer + n, size - n);
  70                 if (ret < 0)
  71                         die("read error (%s)", strerror(errno));
  72                 if (!ret)
  73                         die("unexpected EOF");
  74                 n += ret;
  75         }
  76 }
  77
  78 int packet_read_line(int fd, char *buffer, unsigned size)
  79 {
  80         int n;
  81         unsigned len;
  82         char linelen[4];
  83
  84         safe_read(fd, linelen, 4);
  85
  86         len = 0;
  87         for (n = 0; n < 4; n++) {
  88                 unsigned char c = linelen[n];
  89                 len <<= 4;
  90                 if (c >= '0' && c <= '9') {
  91                         len += c - '0';
  92                         continue;
  93                 }
  94                 if (c >= 'a' && c <= 'f') {
  95                         len += c - 'a' + 10;
  96                         continue;
  97                 }
  98                 if (c >= 'A' && c <= 'F') {
  99                         len += c - 'A' + 10;
 100                         continue;
 101                 }
 102                 die("protocol error: bad line length character");
 103         }
 104         if (!len)
 105                 return 0;
 106         len -= 4;
 107         if (len >= size)
 108                 die("protocol error: bad line length %d", len);
 109         safe_read(fd, buffer, len);
 110         buffer[len] = 0;
 111         return len;
 112 }