Andrew's git - gitweb.git/blob

   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 */
  19ssize_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 */
  40void packet_flush(int fd)
  41{
  42        safe_write(fd, "0000", 4);
  43}
  44
  45#define hex(a) (hexchar[(a) & 15])
  46void 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
  66static 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
  80int 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}