1 files changed, 199 insertions, 0 deletions
diff --git a/src/s6-portable-utils/s6-tail.c b/src/s6-portable-utils/s6-tail.c
new file mode 100644
index 0000000..a3091cd
--- /dev/null
+++ b/src/s6-portable-utils/s6-tail.c
@@ -0,0 +1,199 @@
+/* ISC license. */
+
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <errno.h>
+#include <skalibs/sgetopt.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/types.h>
+#include <skalibs/buffer.h>
+#include <skalibs/strerr.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/skamisc.h>
+#include <skalibs/siovec.h>
+
+#define USAGE "s6-tail [ -c chars | -n lines | -1..9 ] [ file ]"
+
+typedef int tail_func (int, size_t) ;
+typedef tail_func *tail_func_ref ;
+
+static int tail_pluslines (int fd, size_t n)
+{
+  if (n) n-- ;
+  {
+    char buf[BUFFER_INSIZE] ;
+    buffer b = BUFFER_INIT(&buffer_read, fd, buf, BUFFER_INSIZE) ;
+    size_t count = 0 ;
+    while (count < n)
+    {
+      ssize_t r = buffer_fill(&b) ;
+      if (r <= 0) return !r ;
+      while (!buffer_isempty(&b) && (count < n))
+      {
+        struct iovec v[2] ;
+        size_t i ;
+        buffer_rpeek(&b, v) ;
+        i = siovec_bytechr(v, 2, '\n') ;
+        if (i < buffer_len(&b))
+        {
+          count++ ; i++ ;
+        }
+        buffer_rseek(&b, i) ;
+      }
+    }
+    b.op = &buffer_write ;
+    b.fd = 1 ;
+    if (!buffer_flush(&b)) return 0 ;
+  }
+  return (fd_cat(fd, 1) >= 0) ;
+}
+
+static int tail_pluschars (int fd, size_t n)
+{
+  if (n-- > 1)
+  {
+    int nil = open_write("/dev/null") ;
+    if (nil < 0) return 0 ;
+    if (!fd_catn(fd, nil, n))
+    {
+      fd_close(nil) ;
+      return 0 ;
+    }
+    fd_close(nil) ;
+  }
+  return (fd_cat(fd, 1) >= 0) ;
+}
+
+static int tail_minuslines (int fd, size_t n)
+{
+  char buf[BUFFER_INSIZE] ;
+  buffer b = BUFFER_INIT(&buffer_read, fd, buf, BUFFER_INSIZE) ;
+  size_t head = 0, tail = 0 ;
+  stralloc tab[n+1] ;
+  for (; head <= n ; head++) tab[head] = stralloc_zero ;
+  head = 0 ;
+  for (;;)
+  {
+    int r ;
+    r = skagetln(&b, tab + tail, '\n') ;
+    if (!r) break ;
+    if (r < 0)
+    {
+      if (errno == EPIPE) break ;
+      else goto err ;
+    }
+    tail = (tail + 1) % (n+1) ;
+    if (tail == head)
+    {
+      tab[head].len = 0 ;
+      head = (head + 1) % (n+1) ;
+    }
+  }
+  buffer_init(&b, &buffer_write, 1, buf, BUFFER_INSIZE) ;
+  for (; head != tail ; head = (head + 1) % (n+1))
+  {
+    if (buffer_put(&b, tab[head].s, tab[head].len) < tab[head].len)
+      goto err ;
+  }
+  for (head = 0 ; head <= n ; head++) stralloc_free(tab + head) ;
+  return buffer_flush(&b) ;
+ err:
+  for (head = 0 ; head <= n ; head++) stralloc_free(tab + head) ;
+  return 0 ;
+}
+
+static int tail_minuschars (int fd, size_t n)
+{
+  char buf[BUFFER_INSIZE + n] ;
+  buffer b = BUFFER_INIT(&buffer_read, fd, buf, BUFFER_INSIZE + n) ;
+  for (;;)
+  {
+    ssize_t r = buffer_fill(&b) ;
+    if (!r) break ;
+    if (r < 0) return 0 ;
+    buffer_rseek(&b, buffer_len(&b)) ;
+    buffer_unget(&b, n) ;
+  }
+  b.op = &buffer_write ;
+  b.fd = 1 ;
+  return buffer_flush(&b) ;
+}
+
+int main (int argc, char const *const *argv)
+{
+  tail_func_ref f = &tail_minuslines ;
+  unsigned int n = 10 ;
+  int gotit = 0 ;
+  PROG = "s6-tail" ;
+  {
+    subgetopt l = SUBGETOPT_ZERO ;
+    for (;;)
+    {
+      int opt = subgetopt_r(argc, argv, "123456789n:c:", &l) ;
+      if (opt == -1) break ;
+      switch (opt)
+      {
+        case '1' :
+        case '2' :
+        case '3' :
+        case '4' :
+        case '5' :
+        case '6' :
+        case '7' :
+        case '8' :
+        case '9' :
+        {
+          if (gotit) strerr_dieusage(100, USAGE) ;
+          gotit = 1 ;
+          f = &tail_minuslines ;
+          n = opt - '0' ;
+          break ;
+        }
+        case 'n':
+        {
+          if (gotit) strerr_dieusage(100, USAGE) ;
+          gotit = 1 ;
+          f = &tail_minuslines ;
+          if (*l.arg == '-') l.arg++ ;
+          else if (*l.arg == '+')
+          {
+            f = &tail_pluslines ;
+            l.arg++ ;
+          }
+          if (!uint0_scan(l.arg, &n)) strerr_dieusage(100, USAGE) ;
+          break ;
+        }
+        case 'c':
+        {
+          if (gotit) strerr_dieusage(100, USAGE) ;
+          gotit = 1 ;
+          f = &tail_minuschars ;
+          if (*l.arg == '-') l.arg++ ;
+          else if (*l.arg == '+')
+          {
+            f = &tail_pluschars ;
+            l.arg++ ;
+          }
+          if (!uint0_scan(l.arg, &n)) strerr_dieusage(100, USAGE) ;
+          break ;
+        }
+        default : strerr_dieusage(100, USAGE) ;
+      }
+    }
+    argc -= l.ind ; argv += l.ind ;
+  }
+  if (!argc)
+  {
+    if (!(*f)(0, n))
+      strerr_diefu1sys(111, "tail stdin") ;
+  }
+  else
+  {
+    int fd = open_readb(argv[0]) ;
+    if (fd == -1) strerr_diefu3sys(111, "open ", argv[0], " for reading") ;
+    if (!(*f)(fd, n))
+      strerr_diefu2sys(111, "tail ", argv[0]) ;
+    fd_close(fd) ;
+  }
+  return 0 ;
+}