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 = write(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                 if (errno == EAGAIN || errno == EINTR)
  31                         continue;
  32                 die("write error (%s)", strerror(errno));
  33         }
  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 = read(fd, buffer + n, size - n);
  72                 if (ret < 0) {
  73                         if (errno == EINTR || errno == EAGAIN)
  74                                 continue;
  75                         die("read error (%s)", strerror(errno));
  76                 }
  77                 if (!ret)
  78                         die("unexpected EOF");
  79                 n += ret;
  80         }
  81 }
  82
  83 int packet_read_line(int fd, char *buffer, unsigned size)
  84 {
  85         int n;
  86         unsigned len;
  87         char linelen[4];
  88
  89         safe_read(fd, linelen, 4);
  90
  91         len = 0;
  92         for (n = 0; n < 4; n++) {
  93                 unsigned char c = linelen[n];
  94                 len <<= 4;
  95                 if (c >= '0' && c <= '9') {
  96                         len += c - '0';
  97                         continue;
  98                 }
  99                 if (c >= 'a' && c <= 'f') {
 100                         len += c - 'a' + 10;
 101                         continue;
 102                 }
 103                 if (c >= 'A' && c <= 'F') {
 104                         len += c - 'A' + 10;
 105                         continue;
 106                 }
 107                 die("protocol error: bad line length character");
 108         }
 109         if (!len)
 110                 return 0;
 111         len -= 4;
 112         if (len >= size)
 113                 die("protocol error: bad line length %d", len);
 114         safe_read(fd, buffer, len);
 115         buffer[len] = 0;
 116         return len;
 117 }