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 ssize_t safe_write(int fd, const void *buf, ssize_t n)
  20 {
  21         ssize_t nn = n;
  22         while (n) {
  23                 int ret = xwrite(fd, buf, n);
  24                 if (ret > 0) {
  25                         buf = (char *) buf + ret;
  26                         n -= ret;
  27                         continue;
  28                 }
  29                 if (!ret)
  30                         die("write error (disk full?)");
  31                 die("write error (%s)", strerror(errno));
  32         }
  33         return nn;
  34 }
  35
  36 /*
  37  * If we buffered things up above (we don't, but we should),
  38  * we'd flush it here
  39  */
  40 void packet_flush(int fd)
  41 {
  42         safe_write(fd, "0000", 4);
  43 }
  44
  45 #define hex(a) (hexchar[(a) & 15])
  46 void packet_write(int fd, const char *fmt, ...)
  47 {
  48         static char buffer[1000];
  49         static char hexchar[] = "0123456789abcdef";
  50         va_list args;
  51         unsigned n;
  52
  53         va_start(args, fmt);
  54         n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
  55         va_end(args);
  56         if (n >= sizeof(buffer)-4)
  57                 die("protocol error: impossibly long line");
  58         n += 4;
  59         buffer[0] = hex(n >> 12);
  60         buffer[1] = hex(n >> 8);
  61         buffer[2] = hex(n >> 4);
  62         buffer[3] = hex(n);
  63         safe_write(fd, buffer, n);
  64 }
  65
  66 static void safe_read(int fd, void *buffer, unsigned size)
  67 {
  68         int n = 0;
  69
  70         while (n < size) {
  71                 int ret = xread(fd, (char *) buffer + n, size - n);
  72                 if (ret < 0)
  73                         die("read error (%s)", strerror(errno));
  74                 if (!ret)
  75                         die("unexpected EOF");
  76                 n += ret;
  77         }
  78 }
  79
  80 int packet_read_line(int fd, char *buffer, unsigned size)
  81 {
  82         int n;
  83         unsigned len;
  84         char linelen[4];
  85
  86         safe_read(fd, linelen, 4);
  87
  88         len = 0;
  89         for (n = 0; n < 4; n++) {
  90                 unsigned char c = linelen[n];
  91                 len <<= 4;
  92                 if (c >= '0' && c <= '9') {
  93                         len += c - '0';
  94                         continue;
  95                 }
  96                 if (c >= 'a' && c <= 'f') {
  97                         len += c - 'a' + 10;
  98                         continue;
  99                 }
 100                 if (c >= 'A' && c <= 'F') {
 101                         len += c - 'A' + 10;
 102                         continue;
 103                 }
 104                 die("protocol error: bad line length character");
 105         }
 106         if (!len)
 107                 return 0;
 108         len -= 4;
 109         if (len >= size)
 110                 die("protocol error: bad line length %d", len);
 111         safe_read(fd, buffer, len);
 112         buffer[len] = 0;
 113         return len;
 114 }