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_errno("write error");
  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 void packet_buf_flush(struct strbuf *buf)
  46 {
  47         strbuf_add(buf, "0000", 4);
  48 }
  49
  50 #define hex(a) (hexchar[(a) & 15])
  51 static char buffer[1000];
  52 static unsigned format_packet(const char *fmt, va_list args)
  53 {
  54         static char hexchar[] = "0123456789abcdef";
  55         unsigned n;
  56
  57         n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
  58         if (n >= sizeof(buffer)-4)
  59                 die("protocol error: impossibly long line");
  60         n += 4;
  61         buffer[0] = hex(n >> 12);
  62         buffer[1] = hex(n >> 8);
  63         buffer[2] = hex(n >> 4);
  64         buffer[3] = hex(n);
  65         return n;
  66 }
  67
  68 void packet_write(int fd, const char *fmt, ...)
  69 {
  70         va_list args;
  71         unsigned n;
  72
  73         va_start(args, fmt);
  74         n = format_packet(fmt, args);
  75         va_end(args);
  76         safe_write(fd, buffer, n);
  77 }
  78
  79 void packet_buf_write(struct strbuf *buf, const char *fmt, ...)
  80 {
  81         va_list args;
  82         unsigned n;
  83
  84         va_start(args, fmt);
  85         n = format_packet(fmt, args);
  86         va_end(args);
  87         strbuf_add(buf, buffer, n);
  88 }
  89
  90 static void safe_read(int fd, void *buffer, unsigned size)
  91 {
  92         ssize_t ret = read_in_full(fd, buffer, size);
  93         if (ret < 0)
  94                 die_errno("read error");
  95         else if (ret < size)
  96                 die("The remote end hung up unexpectedly");
  97 }
  98
  99 static int packet_length(const char *linelen)
 100 {
 101         int n;
 102         int len = 0;
 103
 104         for (n = 0; n < 4; n++) {
 105                 unsigned char c = linelen[n];
 106                 len <<= 4;
 107                 if (c >= '0' && c <= '9') {
 108                         len += c - '0';
 109                         continue;
 110                 }
 111                 if (c >= 'a' && c <= 'f') {
 112                         len += c - 'a' + 10;
 113                         continue;
 114                 }
 115                 if (c >= 'A' && c <= 'F') {
 116                         len += c - 'A' + 10;
 117                         continue;
 118                 }
 119                 return -1;
 120         }
 121         return len;
 122 }
 123
 124 int packet_read_line(int fd, char *buffer, unsigned size)
 125 {
 126         int len;
 127         char linelen[4];
 128
 129         safe_read(fd, linelen, 4);
 130         len = packet_length(linelen);
 131         if (len < 0)
 132                 die("protocol error: bad line length character: %.4s", linelen);
 133         if (!len)
 134                 return 0;
 135         len -= 4;
 136         if (len >= size)
 137                 die("protocol error: bad line length %d", len);
 138         safe_read(fd, buffer, len);
 139         buffer[len] = 0;
 140         return len;
 141 }
 142
 143 int packet_get_line(struct strbuf *out,
 144         char **src_buf, size_t *src_len)
 145 {
 146         int len;
 147
 148         if (*src_len < 4)
 149                 return -1;
 150         len = packet_length(*src_buf);
 151         if (len < 0)
 152                 return -1;
 153         if (!len) {
 154                 *src_buf += 4;
 155                 *src_len -= 4;
 156                 return 0;
 157         }
 158         if (*src_len < len)
 159                 return -2;
 160
 161         *src_buf += 4;
 162         *src_len -= 4;
 163         len -= 4;
 164
 165         strbuf_add(out, *src_buf, len);
 166         *src_buf += len;
 167         *src_len -= len;
 168         return len;
 169 }