tools/lib/subcmd/pager.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <sys/select.h>
   3 #include <stdlib.h>
   4 #include <stdio.h>
   5 #include <string.h>
   6 #include <signal.h>
   7 #include <sys/ioctl.h>
   8 #include "pager.h"
   9 #include "run-command.h"
  10 #include "sigchain.h"
  11 #include "subcmd-config.h"
  12
  13 /*
  14  * This is split up from the rest of git so that we can do
  15  * something different on Windows.
  16  */
  17
  18 static int spawned_pager;
  19 static int pager_columns;
  20
  21 void pager_init(const char *pager_env)
  22 {
  23         subcmd_config.pager_env = pager_env;
  24 }
  25
  26 static void pager_preexec(void)
  27 {
  28         /*
  29          * Work around bug in "less" by not starting it until we
  30          * have real input
  31          */
  32         fd_set in;
  33         fd_set exception;
  34
  35         FD_ZERO(&in);
  36         FD_ZERO(&exception);
  37         FD_SET(0, &in);
  38         FD_SET(0, &exception);
  39         select(1, &in, NULL, &exception, NULL);
  40
  41         setenv("LESS", "FRSX", 0);
  42 }
  43
  44 static const char *pager_argv[] = { "sh", "-c", NULL, NULL };
  45 static struct child_process pager_process;
  46
  47 static void wait_for_pager(void)
  48 {
  49         fflush(stdout);
  50         fflush(stderr);
  51         /* signal EOF to pager */
  52         close(1);
  53         close(2);
  54         finish_command(&pager_process);
  55 }
  56
  57 static void wait_for_pager_signal(int signo)
  58 {
  59         wait_for_pager();
  60         sigchain_pop(signo);
  61         raise(signo);
  62 }
  63
  64 void setup_pager(void)
  65 {
  66         const char *pager = getenv(subcmd_config.pager_env);
  67         struct winsize sz;
  68
  69         if (!isatty(1))
  70                 return;
  71         if (ioctl(1, TIOCGWINSZ, &sz) == 0)
  72                 pager_columns = sz.ws_col;
  73         if (!pager)
  74                 pager = getenv("PAGER");
  75         if (!(pager || access("/usr/bin/pager", X_OK)))
  76                 pager = "/usr/bin/pager";
  77         if (!(pager || access("/usr/bin/less", X_OK)))
  78                 pager = "/usr/bin/less";
  79         if (!pager)
  80                 pager = "cat";
  81         if (!*pager || !strcmp(pager, "cat"))
  82                 return;
  83
  84         spawned_pager = 1; /* means we are emitting to terminal */
  85
  86         /* spawn the pager */
  87         pager_argv[2] = pager;
  88         pager_process.argv = pager_argv;
  89         pager_process.in = -1;
  90         pager_process.preexec_cb = pager_preexec;
  91
  92         if (start_command(&pager_process))
  93                 return;
  94
  95         /* original process continues, but writes to the pipe */
  96         dup2(pager_process.in, 1);
  97         if (isatty(2))
  98                 dup2(pager_process.in, 2);
  99         close(pager_process.in);
 100
 101         /* this makes sure that the parent terminates after the pager */
 102         sigchain_push_common(wait_for_pager_signal);
 103         atexit(wait_for_pager);
 104 }
 105
 106 int pager_in_use(void)
 107 {
 108         return spawned_pager;
 109 }
 110
 111 int pager_get_columns(void)
 112 {
 113         char *s;
 114
 115         s = getenv("COLUMNS");
 116         if (s)
 117                 return atoi(s);
 118
 119         return (pager_columns ? pager_columns : 80) - 2;
 120 }