Andrew's git - gitweb.git/blob

bb3bab05cd203e114b24b778cb5f55218abdec95
   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 */
  19static 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 */
  38void packet_flush(int fd)
  39{
  40        safe_write(fd, "0000", 4);
  41}
  42
  43#define hex(a) (hexchar[(a) & 15])
  44void 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
  64static 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
  78int 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}