Implement file(1).

Unlike the POSIX file(1), there's no magic file here, just hard-coded
common (non-obsolete) file formats. Personally most of my use of file(1)
is as a one-line readelf(1) summarizer, so although I assume a full POSIX
file(1) is out of scope (because just the database would likely be larger
than all the rest of toybox), a subset that only supports in-use file types
actually covers most of the use cases I encounter personally.

Also fix peek_be/peek_le.

lib/lib.c

@@ -508,18 +508,17 @@ int64_t peek_le(void *ptr, unsigned size)
  char *c = ptr;
  int i;
 
- for (i=0; i<size; i++) ret |= ((int64_t)c[i])<<i;
-
+ for (i=0; i<size; i++) ret |= ((int64_t)c[i])<<(i*8);
  return ret;
 }
 
 int64_t peek_be(void *ptr, unsigned size)
 {
  int64_t ret = 0;
  char *c = ptr;
+ int i;
 
- while (size--) ret = (ret<<8)|c[size];
-
+ for (i=0; i<size; i++) ret = (ret<<8)|(c[i]&0xff);
  return ret;
 }
 

toys/pending/file.c

@@ -0,0 +1,237 @@
+/* file.c - describe file type
+ *
+ * Copyright 2016 The Android Open Source Project
+ *
+ * See http:https://pubs.opengroup.org/onlinepubs/9699919799/utilities/file.html
+
+USE_FILE(NEWTOY(file, "<1", TOYFLAG_USR|TOYFLAG_BIN))
+
+config FILE
+ bool "file"
+ default n
+ help
+ usage: file [file...]
+
+ Examine the given files and describe their content types.
+*/
+
+#define FOR_file
+#include "toys.h"
+
+GLOBALS(
+ int max_name_len;
+)
+
+// TODO: all the ELF magic numbers are available in <elf.h> --- use that?
+
+static char *elf_arch(int e_machine)
+{
+ // TODO: include obsolete stuff we'll never see, like "PDP-10" and "VAX"?
+ switch (e_machine) {
+ case 3: return "Intel 80386";
+ case 8: return "MIPS";
+ case 40: return "ARM";
+ case 62: return "x86-64";
+ case 183: return "ARM aarch64";
+ default: return NULL;
+ }
+}
+
+static int64_t elf_int(int endian, char *data, int bytes)
+{
+ if (endian == 1) return peek_le(data, bytes);
+ return peek_be(data, bytes);
+}
+
+static void do_elf_file()
+{
+ int elf_endian = toybuf[5];
+ int e_type, e_machine;
+
+ xprintf("ELF");
+
+ // "64-bit"
+ if (toybuf[4] == 1) xprintf(" 32-bit");
+ else if (toybuf[4] == 2) xprintf(" 64-bit");
+ else xprintf(" (invalid class %d)", toybuf[4]);
+
+ // "LSB"
+ if (elf_endian == 1) xprintf(" LSB");
+ else if (elf_endian == 2) xprintf(" MSB");
+ else xprintf("(invalid endian %d) ", elf_endian);
+
+ if (elf_endian == 1 || elf_endian == 2) {
+ char *arch;
+
+ // ", executable"
+ e_type = elf_int(elf_endian, &toybuf[0x10], 2);
+ if (e_type == 1) xprintf(" relocatable");
+ else if (e_type == 2) xprintf(" executable");
+ else if (e_type == 3) xprintf(" shared object");
+ else if (e_type == 4) xprintf(" core dump");
+ else xprintf(" (invalid type %d)", e_type);
+
+ // ", x86-64"
+ e_machine = elf_int(elf_endian, &toybuf[0x12], 2);
+ arch = elf_arch(e_machine);
+ if (arch) xprintf(", %s", arch);
+ else xprintf(", (unknown arch %d)", e_machine);
+ }
+
+ // "version 1"
+ xprintf(", version %d", toybuf[6]);
+
+ // " (SYSV)"
+ // TODO: will we ever meet any of the others in practice?
+ if (toybuf[7] == 0) xprintf(" (SYSV)");
+ else xprintf(" (OS %d)", toybuf[7]);
+
+ // TODO: we'd need to actually parse the ELF file to report the rest...
+ // ", dynamically linked"
+ // " (uses shared libs)"
+ // ", for GNU/Linux 2.6.24"
+ // ", BuildID[sha1]=SHA"
+ // ", stripped"
+
+ xputs("");
+}
+
+// https://www.w3.org/TR/PNG/#6Colour-values
+static char *png_color_type(int color_type)
+{
+ switch (color_type) {
+ case 0: return "grayscale";
+ case 2: return "color RGB";
+ case 3: return "indexed color";
+ case 4: return "grayscale with alpha";
+ case 6: return "color RGBA";
+ default: return "unknown";
+ }
+}
+
+static void do_png_file()
+{
+ // PNG is big-endian: https://www.w3.org/TR/PNG/#7Integers-and-byte-order
+ int chunk_length = peek_be(&toybuf[8], 4);
+
+ xprintf("PNG image data");
+
+ // The IHDR chunk comes first.
+ // https://www.w3.org/TR/PNG/#11IHDR
+ if (chunk_length == 13 && memcmp(&toybuf[12], "IHDR", 4) == 0) {
+ int width = peek_be(&toybuf[16], 4);
+ int height = peek_be(&toybuf[20], 4);
+ int bits = toybuf[24] & 0xff;
+ int type = toybuf[25] & 0xff;
+ int interlaced = toybuf[28] & 0xff;
+
+ xprintf(", %d x %d, %d-bit/%s, %s", width, height, bits,
+ png_color_type(type),
+ interlaced ? "interlaced" : "non-interlaced");
+ }
+
+ xputs("");
+}
+
+static void do_gif_file()
+{
+ // https://www.w3.org/Graphics/GIF/spec-gif89a.txt
+ int width = peek_le(&toybuf[6], 2);
+ int height = peek_le(&toybuf[8], 2);
+
+ xprintf("GIF image data, %d x %d\n", width, height);
+}
+
+static void do_jpeg_file()
+{
+ // TODO: parsing JPEG for width/height is harder than GIF or PNG.
+ xprintf("JPEG image data\n");
+}
+
+static void do_java_class_file()
+{
+ // https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html
+ int minor = peek_be(&toybuf[4], 2);
+ int major = peek_be(&toybuf[6], 2);
+
+ xprintf("Java class file, version %d.%d\n", major, minor);
+}
+
+static void do_regular_file(int fd, char *name)
+{
+ int len = read(fd, toybuf, sizeof(toybuf));
+
+ if (len<0) perror_msg("cannot open");
+
+ if (len>20 && memcmp(toybuf, "\177ELF", 4) == 0) {
+ do_elf_file(len);
+ } else if (len>28 && memcmp(toybuf, "\x89PNG\x0d\x0a\x1a\x0a", 8) == 0) {
+ do_png_file();
+ } else if (len>16 && (memcmp(toybuf, "GIF87a", 6) == 0 ||
+ memcmp(toybuf, "GIF89a", 6) == 0)) {
+ do_gif_file();
+ } else if (len>32 && memcmp(toybuf, "\xff\xd8", 2) == 0) {
+ do_jpeg_file();
+ } else if (len>8 && memcmp(toybuf, "\xca\xfe\xba\xbe", 4) == 0) {
+ do_java_class_file();
+
+ // TODO: cpio archive.
+ // TODO: tar archive.
+ // TODO: zip/jar/apk archive.
+ } else {
+ char *what = "ASCII text";
+ int i;
+
+ // TODO: report which interpreter?
+ if (strncmp(toybuf, "#!", 2) == 0) what = "commands text";
+
+ // TODO: try UTF-8 too before falling back to "data".
+ for (i = 0; i < len; ++i) {
+ if (!(isprint(toybuf[i]) || isspace(toybuf[i]))) {
+ what = "data";
+ break;
+ }
+ }
+ xputs(what);
+ }
+}
+
+static void do_file(int fd, char *name)
+{
+ struct stat sb;
+ char *what = "unknown";
+
+ xprintf("%s: %*s", name, (int)(TT.max_name_len - strlen(name)), "");
+
+ if (!fstat(fd, &sb)) what = "cannot open";
+ if (S_ISREG(sb.st_mode)) {
+ if (sb.st_size == 0) what = "empty";
+ else {
+ do_regular_file(fd, name);
+ return;
+ }
+ } else if (S_ISBLK(sb.st_mode)) what = "block special";
+ else if (S_ISCHR(sb.st_mode)) what = "character special";
+ else if (S_ISDIR(sb.st_mode)) what = "directory";
+ else if (S_ISFIFO(sb.st_mode)) what = "fifo";
+ else if (S_ISSOCK(sb.st_mode)) what = "socket";
+ else if (S_ISLNK(sb.st_mode)) what = "symbolic link";
+ xputs(what);
+}
+
+static void init_max_name_len()
+{
+ char **name;
+ int name_len;
+
+ for (name = toys.optargs; *name; ++name) {
+ name_len = strlen(*name);
+ if (name_len > TT.max_name_len) TT.max_name_len = name_len;
+ }
+}
+
+void file_main(void)
+{
+ init_max_name_len();
+ loopfiles(toys.optargs, do_file);
+}